Initial

30 files changed, 19588 insertions, 0 deletions

diff --git a/src/os/darwin_usb.c b/src/os/darwin_usb.c
new file mode 100644
index 0000000..903422c
--- /dev/null
+++ b/src/os/darwin_usb.c
@@ -0,0 +1,2611 @@
+/* -*- Mode: C; indent-tabs-mode:nil -*- */
+/*
+ * darwin backend for libusb 1.0
+ * Copyright © 2008-2021 Nathan Hjelm <hjelmn@cs.unm.edu>
+ * Copyright © 2019-2021 Google LLC. All rights reserved.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+#include <assert.h>
+#include <time.h>
+#include <ctype.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/sysctl.h>
+
+#include <mach/clock.h>
+#include <mach/clock_types.h>
+#include <mach/mach_host.h>
+#include <mach/mach_port.h>
+
+/* Suppress warnings about the use of the deprecated objc_registerThreadWithCollector
+ * function. Its use is also conditionalized to only older deployment targets. */
+#define OBJC_SILENCE_GC_DEPRECATIONS 1
+
+/* Default timeout to 10s for reenumerate. This is needed because USBDeviceReEnumerate
+ * does not return error status on macOS. */
+#define DARWIN_REENUMERATE_TIMEOUT_US 10000000
+
+#include <AvailabilityMacros.h>
+#if MAC_OS_X_VERSION_MIN_REQUIRED >= 1060 && MAC_OS_X_VERSION_MIN_REQUIRED < 101200
+  #include <objc/objc-auto.h>
+#endif
+
+#include "darwin_usb.h"
+
+static int init_count = 0;
+
+/* Both kIOMasterPortDefault or kIOMainPortDefault are synonyms for 0. */
+static const mach_port_t darwin_default_master_port = 0;
+
+/* async event thread */
+static pthread_mutex_t libusb_darwin_at_mutex = PTHREAD_MUTEX_INITIALIZER;
+static pthread_cond_t  libusb_darwin_at_cond = PTHREAD_COND_INITIALIZER;
+
+#if !defined(HAVE_CLOCK_GETTIME)
+static clock_serv_t clock_realtime;
+static clock_serv_t clock_monotonic;
+#endif
+
+#define LIBUSB_DARWIN_STARTUP_FAILURE ((CFRunLoopRef) -1)
+
+static CFRunLoopRef libusb_darwin_acfl = NULL; /* event cf loop */
+static CFRunLoopSourceRef libusb_darwin_acfls = NULL; /* shutdown signal for event cf loop */
+
+static usbi_mutex_t darwin_cached_devices_lock = PTHREAD_MUTEX_INITIALIZER;
+static struct list_head darwin_cached_devices;
+static const char *darwin_device_class = "IOUSBDevice";
+
+#define DARWIN_CACHED_DEVICE(a) (((struct darwin_device_priv *)usbi_get_device_priv((a)))->dev)
+
+/* async event thread */
+static pthread_t libusb_darwin_at;
+
+static int darwin_get_config_descriptor(struct libusb_device *dev, uint8_t config_index, void *buffer, size_t len);
+static int darwin_claim_interface(struct libusb_device_handle *dev_handle, uint8_t iface);
+static int darwin_release_interface(struct libusb_device_handle *dev_handle, uint8_t iface);
+static int darwin_reenumerate_device(struct libusb_device_handle *dev_handle, bool capture);
+static int darwin_clear_halt(struct libusb_device_handle *dev_handle, unsigned char endpoint);
+static int darwin_reset_device(struct libusb_device_handle *dev_handle);
+static void darwin_async_io_callback (void *refcon, IOReturn result, void *arg0);
+
+static enum libusb_error darwin_scan_devices(struct libusb_context *ctx);
+static enum libusb_error process_new_device (struct libusb_context *ctx, struct darwin_cached_device *cached_device,
+                                             UInt64 old_session_id);
+
+static enum libusb_error darwin_get_cached_device(struct libusb_context *ctx, io_service_t service, struct darwin_cached_device **cached_out,
+                                                  UInt64 *old_session_id);
+
+#if defined(ENABLE_LOGGING)
+static const char *darwin_error_str (IOReturn result) {
+  static char string_buffer[50];
+  switch (result) {
+  case kIOReturnSuccess:
+    return "no error";
+  case kIOReturnNotOpen:
+    return "device not opened for exclusive access";
+  case kIOReturnNoDevice:
+    return "no connection to an IOService";
+  case kIOUSBNoAsyncPortErr:
+    return "no async port has been opened for interface";
+  case kIOReturnExclusiveAccess:
+    return "another process has device opened for exclusive access";
+  case kIOUSBPipeStalled:
+#if defined(kUSBHostReturnPipeStalled)
+  case kUSBHostReturnPipeStalled:
+#endif
+    return "pipe is stalled";
+  case kIOReturnError:
+    return "could not establish a connection to the Darwin kernel";
+  case kIOUSBTransactionTimeout:
+    return "transaction timed out";
+  case kIOReturnBadArgument:
+    return "invalid argument";
+  case kIOReturnAborted:
+    return "transaction aborted";
+  case kIOReturnNotResponding:
+    return "device not responding";
+  case kIOReturnOverrun:
+    return "data overrun";
+  case kIOReturnCannotWire:
+    return "physical memory can not be wired down";
+  case kIOReturnNoResources:
+    return "out of resources";
+  case kIOUSBHighSpeedSplitError:
+    return "high speed split error";
+  case kIOUSBUnknownPipeErr:
+    return "pipe ref not recognized";
+  default:
+    snprintf(string_buffer, sizeof(string_buffer), "unknown error (0x%x)", result);
+    return string_buffer;
+  }
+}
+#endif
+
+static enum libusb_error darwin_to_libusb (IOReturn result) {
+  switch (result) {
+  case kIOReturnUnderrun:
+  case kIOReturnSuccess:
+    return LIBUSB_SUCCESS;
+  case kIOReturnNotOpen:
+  case kIOReturnNoDevice:
+    return LIBUSB_ERROR_NO_DEVICE;
+  case kIOReturnExclusiveAccess:
+    return LIBUSB_ERROR_ACCESS;
+  case kIOUSBPipeStalled:
+#if defined(kUSBHostReturnPipeStalled)
+  case kUSBHostReturnPipeStalled:
+#endif
+    return LIBUSB_ERROR_PIPE;
+  case kIOReturnBadArgument:
+    return LIBUSB_ERROR_INVALID_PARAM;
+  case kIOUSBTransactionTimeout:
+    return LIBUSB_ERROR_TIMEOUT;
+  case kIOUSBUnknownPipeErr:
+    return LIBUSB_ERROR_NOT_FOUND;
+  case kIOReturnNotResponding:
+  case kIOReturnAborted:
+  case kIOReturnError:
+  case kIOUSBNoAsyncPortErr:
+  default:
+    return LIBUSB_ERROR_OTHER;
+  }
+}
+
+/* this function must be called with the darwin_cached_devices_lock held */
+static void darwin_deref_cached_device(struct darwin_cached_device *cached_dev) {
+  cached_dev->refcount--;
+  /* free the device and remove it from the cache */
+  if (0 == cached_dev->refcount) {
+    list_del(&cached_dev->list);
+
+    if (cached_dev->device) {
+      (*(cached_dev->device))->Release(cached_dev->device);
+      cached_dev->device = NULL;
+    }
+    IOObjectRelease (cached_dev->service);
+    free (cached_dev);
+  }
+}
+
+static void darwin_ref_cached_device(struct darwin_cached_device *cached_dev) {
+  cached_dev->refcount++;
+}
+
+static int ep_to_pipeRef(struct libusb_device_handle *dev_handle, uint8_t ep, uint8_t *pipep, uint8_t *ifcp, struct darwin_interface **interface_out) {
+  struct darwin_device_handle_priv *priv = usbi_get_device_handle_priv(dev_handle);
+
+  /* current interface */
+  struct darwin_interface *cInterface;
+
+  uint8_t i, iface;
+
+  struct libusb_context *ctx = HANDLE_CTX(dev_handle);
+
+  usbi_dbg (ctx, "converting ep address 0x%02x to pipeRef and interface", ep);
+
+  for (iface = 0 ; iface < USB_MAXINTERFACES ; iface++) {
+    cInterface = &priv->interfaces[iface];
+
+    if (dev_handle->claimed_interfaces & (1U << iface)) {
+      for (i = 0 ; i < cInterface->num_endpoints ; i++) {
+        if (cInterface->endpoint_addrs[i] == ep) {
+          *pipep = i + 1;
+
+          if (ifcp)
+            *ifcp = iface;
+
+          if (interface_out)
+            *interface_out = cInterface;
+
+          usbi_dbg (ctx, "pipe %d on interface %d matches", *pipep, iface);
+          return LIBUSB_SUCCESS;
+        }
+      }
+    }
+  }
+
+  /* No pipe found with the correct endpoint address */
+  usbi_warn (HANDLE_CTX(dev_handle), "no pipeRef found with endpoint address 0x%02x.", ep);
+
+  return LIBUSB_ERROR_NOT_FOUND;
+}
+
+static IOReturn usb_setup_device_iterator (io_iterator_t *deviceIterator, UInt32 location) {
+  CFMutableDictionaryRef matchingDict = IOServiceMatching(darwin_device_class);
+
+  if (!matchingDict)
+    return kIOReturnError;
+
+  if (location) {
+    CFMutableDictionaryRef propertyMatchDict = CFDictionaryCreateMutable(kCFAllocatorDefault, 0,
+                                                                         &kCFTypeDictionaryKeyCallBacks,
+                                                                         &kCFTypeDictionaryValueCallBacks);
+
+    /* there are no unsigned CFNumber types so treat the value as signed. the OS seems to do this
+         internally (CFNumberType of locationID is kCFNumberSInt32Type) */
+    CFTypeRef locationCF = CFNumberCreate (NULL, kCFNumberSInt32Type, &location);
+
+    if (propertyMatchDict && locationCF) {
+      CFDictionarySetValue (propertyMatchDict, CFSTR(kUSBDevicePropertyLocationID), locationCF);
+      CFDictionarySetValue (matchingDict, CFSTR(kIOPropertyMatchKey), propertyMatchDict);
+    }
+    /* else we can still proceed as long as the caller accounts for the possibility of other devices in the iterator */
+
+    /* release our references as per the Create Rule */
+    if (propertyMatchDict)
+      CFRelease (propertyMatchDict);
+    if (locationCF)
+      CFRelease (locationCF);
+  }
+
+  return IOServiceGetMatchingServices(darwin_default_master_port, matchingDict, deviceIterator);
+}
+
+/* Returns 1 on success, 0 on failure. */
+static bool get_ioregistry_value_number (io_service_t service, CFStringRef property, CFNumberType type, void *p) {
+  CFTypeRef cfNumber = IORegistryEntryCreateCFProperty (service, property, kCFAllocatorDefault, 0);
+  Boolean success = 0;
+
+  if (cfNumber) {
+    if (CFGetTypeID(cfNumber) == CFNumberGetTypeID()) {
+      success = CFNumberGetValue(cfNumber, type, p);
+    }
+
+    CFRelease (cfNumber);
+  }
+
+  return (success != 0);
+}
+
+/* Returns 1 on success, 0 on failure. */
+static bool get_ioregistry_value_data (io_service_t service, CFStringRef property, ssize_t size, void *p) {
+  CFTypeRef cfData = IORegistryEntryCreateCFProperty (service, property, kCFAllocatorDefault, 0);
+  bool success = false;
+
+  if (cfData) {
+    if (CFGetTypeID (cfData) == CFDataGetTypeID ()) {
+      CFIndex length = CFDataGetLength (cfData);
+      if (length < size) {
+        size = length;
+      }
+
+      CFDataGetBytes (cfData, CFRangeMake(0, size), p);
+      success = true;
+    }
+
+    CFRelease (cfData);
+  }
+
+  return success;
+}
+
+static usb_device_t **darwin_device_from_service (struct libusb_context *ctx, io_service_t service)
+{
+  io_cf_plugin_ref_t *plugInInterface = NULL;
+  usb_device_t **device;
+  IOReturn kresult;
+  SInt32 score;
+  const int max_retries = 5;
+
+  /* The IOCreatePlugInInterfaceForService function might consistently return
+     an "out of resources" error with certain USB devices the first time we run 
+     it. The reason is still unclear, but retrying fixes the problem */
+  for (int count = 0; count < max_retries; count++) {
+    kresult = IOCreatePlugInInterfaceForService(service, kIOUSBDeviceUserClientTypeID,
+                                                kIOCFPlugInInterfaceID, &plugInInterface,
+                                                &score);
+    if (kIOReturnSuccess == kresult && plugInInterface) {
+      break;
+    }
+
+    usbi_dbg (ctx, "set up plugin for service retry: %s", darwin_error_str (kresult));
+
+    /* sleep for a little while before trying again */
+    nanosleep(&(struct timespec){.tv_sec = 0, .tv_nsec = 1000}, NULL);
+  }
+
+  if (kIOReturnSuccess != kresult || !plugInInterface) {
+    usbi_dbg (ctx, "could not set up plugin for service: %s", darwin_error_str (kresult));
+    return NULL;
+  }
+
+  (void)(*plugInInterface)->QueryInterface(plugInInterface, CFUUIDGetUUIDBytes(DeviceInterfaceID),
+                                           (LPVOID)&device);
+  /* Use release instead of IODestroyPlugInInterface to avoid stopping IOServices associated with this device */
+  (*plugInInterface)->Release (plugInInterface);
+
+  return device;
+}
+
+static void darwin_devices_attached (void *ptr, io_iterator_t add_devices) {
+  UNUSED(ptr);
+  struct darwin_cached_device *cached_device;
+  UInt64 old_session_id;
+  struct libusb_context *ctx;
+  io_service_t service;
+  int ret;
+
+  usbi_mutex_lock(&active_contexts_lock);
+
+  while ((service = IOIteratorNext(add_devices))) {
+    ret = darwin_get_cached_device (NULL, service, &cached_device, &old_session_id);
+    if (ret < 0 || !cached_device->can_enumerate) {
+      continue;
+    }
+
+    /* add this device to each active context's device list */
+    for_each_context(ctx) {
+      process_new_device (ctx, cached_device, old_session_id);
+    }
+
+    if (cached_device->in_reenumerate) {
+      usbi_dbg (NULL, "cached device in reset state. reset complete...");
+      cached_device->in_reenumerate = false;
+    }
+
+    IOObjectRelease(service);
+  }
+
+  usbi_mutex_unlock(&active_contexts_lock);
+}
+
+static void darwin_devices_detached (void *ptr, io_iterator_t rem_devices) {
+  UNUSED(ptr);
+  struct libusb_device *dev = NULL;
+  struct libusb_context *ctx;
+  struct darwin_cached_device *old_device;
+
+  io_service_t device;
+  UInt64 session, locationID;
+  int ret;
+
+  usbi_mutex_lock(&active_contexts_lock);
+
+  while ((device = IOIteratorNext (rem_devices)) != 0) {
+    bool is_reenumerating = false;
+
+    /* get the location from the i/o registry */
+    ret = get_ioregistry_value_number (device, CFSTR("sessionID"), kCFNumberSInt64Type, &session);
+    (void) get_ioregistry_value_number (device, CFSTR("locationID"), kCFNumberSInt32Type, &locationID);
+    IOObjectRelease (device);
+    if (!ret)
+      continue;
+
+    /* we need to match darwin_ref_cached_device call made in darwin_get_cached_device function
+       otherwise no cached device will ever get freed */
+    usbi_mutex_lock(&darwin_cached_devices_lock);
+    list_for_each_entry(old_device, &darwin_cached_devices, list, struct darwin_cached_device) {
+      if (old_device->session == session) {
+        if (old_device->in_reenumerate) {
+          /* device is re-enumerating. do not dereference the device at this time. libusb_reset_device()
+           * will deref if needed. */
+          usbi_dbg (NULL, "detected device detached due to re-enumeration. sessionID: 0x%" PRIx64 ", locationID: 0x%" PRIx64,
+                    session, locationID);
+
+          /* the device object is no longer usable so go ahead and release it */
+          if (old_device->device) {
+            (*(old_device->device))->Release(old_device->device);
+            old_device->device = NULL;
+          }
+
+          is_reenumerating = true;
+        } else {
+          darwin_deref_cached_device (old_device);
+        }
+
+        break;
+      }
+    }
+
+    usbi_mutex_unlock(&darwin_cached_devices_lock);
+    if (is_reenumerating) {
+      continue;
+    }
+
+    for_each_context(ctx) {
+      usbi_dbg (ctx, "notifying context %p of device disconnect", ctx);
+
+      dev = usbi_get_device_by_session_id(ctx, (unsigned long) session);
+      if (dev) {
+        /* signal the core that this device has been disconnected. the core will tear down this device
+           when the reference count reaches 0 */
+        usbi_disconnect_device(dev);
+        libusb_unref_device(dev);
+      }
+    }
+  }
+
+  usbi_mutex_unlock(&active_contexts_lock);
+}
+
+static void darwin_hotplug_poll (void)
+{
+  /* not sure if 1 ms will be too long/short but it should work ok */
+  mach_timespec_t timeout = {.tv_sec = 0, .tv_nsec = 1000000ul};
+
+  /* since a kernel thread may notify the IOIterators used for
+   * hotplug notification we can't just clear the iterators.
+   * instead just wait until all IOService providers are quiet */
+  (void) IOKitWaitQuiet (darwin_default_master_port, &timeout);
+}
+
+static void darwin_clear_iterator (io_iterator_t iter) {
+  io_service_t device;
+
+  while ((device = IOIteratorNext (iter)) != 0)
+    IOObjectRelease (device);
+}
+
+static void darwin_fail_startup(void) {
+  pthread_mutex_lock (&libusb_darwin_at_mutex);
+  libusb_darwin_acfl = LIBUSB_DARWIN_STARTUP_FAILURE;
+  pthread_cond_signal (&libusb_darwin_at_cond);
+  pthread_mutex_unlock (&libusb_darwin_at_mutex);
+  pthread_exit (NULL);
+}
+
+static void *darwin_event_thread_main (void *arg0) {
+  IOReturn kresult;
+  struct libusb_context *ctx = (struct libusb_context *)arg0;
+  CFRunLoopRef runloop;
+  CFRunLoopSourceRef libusb_shutdown_cfsource;
+  CFRunLoopSourceContext libusb_shutdown_cfsourcectx;
+
+#if MAC_OS_X_VERSION_MIN_REQUIRED >= 1060
+  /* Set this thread's name, so it can be seen in the debugger
+     and crash reports. */
+  pthread_setname_np ("org.libusb.device-hotplug");
+#endif
+
+#if MAC_OS_X_VERSION_MIN_REQUIRED >= 1060 && MAC_OS_X_VERSION_MIN_REQUIRED < 101200
+  /* Tell the Objective-C garbage collector about this thread.
+     This is required because, unlike NSThreads, pthreads are
+     not automatically registered. Although we don't use
+     Objective-C, we use CoreFoundation, which does.
+     Garbage collection support was entirely removed in 10.12,
+     so don't bother there. */
+  objc_registerThreadWithCollector();
+#endif
+
+  /* hotplug (device arrival/removal) sources */
+  CFRunLoopSourceRef     libusb_notification_cfsource;
+  io_notification_port_t libusb_notification_port;
+  io_iterator_t          libusb_rem_device_iterator;
+  io_iterator_t          libusb_add_device_iterator;
+
+  usbi_dbg (ctx, "creating hotplug event source");
+
+  runloop = CFRunLoopGetCurrent ();
+  CFRetain (runloop);
+
+  /* add the shutdown cfsource to the run loop */
+  memset(&libusb_shutdown_cfsourcectx, 0, sizeof(libusb_shutdown_cfsourcectx));
+  libusb_shutdown_cfsourcectx.info = runloop;
+  libusb_shutdown_cfsourcectx.perform = (void (*)(void *))CFRunLoopStop;
+  libusb_shutdown_cfsource = CFRunLoopSourceCreate(NULL, 0, &libusb_shutdown_cfsourcectx);
+  CFRunLoopAddSource(runloop, libusb_shutdown_cfsource, kCFRunLoopDefaultMode);
+
+  /* add the notification port to the run loop */
+  libusb_notification_port     = IONotificationPortCreate (darwin_default_master_port);
+  libusb_notification_cfsource = IONotificationPortGetRunLoopSource (libusb_notification_port);
+  CFRunLoopAddSource(runloop, libusb_notification_cfsource, kCFRunLoopDefaultMode);
+
+  /* create notifications for removed devices */
+  kresult = IOServiceAddMatchingNotification (libusb_notification_port, kIOTerminatedNotification,
+                                              IOServiceMatching(darwin_device_class),
+                                              darwin_devices_detached,
+                                              ctx, &libusb_rem_device_iterator);
+
+  if (kresult != kIOReturnSuccess) {
+    usbi_err (ctx, "could not add hotplug event source: %s", darwin_error_str (kresult));
+    CFRelease (libusb_shutdown_cfsource);
+    CFRelease (runloop);
+    darwin_fail_startup ();
+  }
+
+  /* create notifications for attached devices */
+  kresult = IOServiceAddMatchingNotification(libusb_notification_port, kIOFirstMatchNotification,
+                                              IOServiceMatching(darwin_device_class),
+                                              darwin_devices_attached,
+                                              ctx, &libusb_add_device_iterator);
+
+  if (kresult != kIOReturnSuccess) {
+    usbi_err (ctx, "could not add hotplug event source: %s", darwin_error_str (kresult));
+    CFRelease (libusb_shutdown_cfsource);
+    CFRelease (runloop);
+    darwin_fail_startup ();
+  }
+
+  /* arm notifiers */
+  darwin_clear_iterator (libusb_rem_device_iterator);
+  darwin_clear_iterator (libusb_add_device_iterator);
+
+  usbi_dbg (ctx, "darwin event thread ready to receive events");
+
+  /* signal the main thread that the hotplug runloop has been created. */
+  pthread_mutex_lock (&libusb_darwin_at_mutex);
+  libusb_darwin_acfl = runloop;
+  libusb_darwin_acfls = libusb_shutdown_cfsource;
+  pthread_cond_signal (&libusb_darwin_at_cond);
+  pthread_mutex_unlock (&libusb_darwin_at_mutex);
+
+  /* run the runloop */
+  CFRunLoopRun();
+
+  usbi_dbg (ctx, "darwin event thread exiting");
+
+  /* signal the main thread that the hotplug runloop has finished. */
+  pthread_mutex_lock (&libusb_darwin_at_mutex);
+  libusb_darwin_acfls = NULL;
+  libusb_darwin_acfl = NULL;
+  pthread_cond_signal (&libusb_darwin_at_cond);
+  pthread_mutex_unlock (&libusb_darwin_at_mutex);
+
+  /* remove the notification cfsource */
+  CFRunLoopRemoveSource(runloop, libusb_notification_cfsource, kCFRunLoopDefaultMode);
+
+  /* remove the shutdown cfsource */
+  CFRunLoopRemoveSource(runloop, libusb_shutdown_cfsource, kCFRunLoopDefaultMode);
+
+  /* delete notification port */
+  IONotificationPortDestroy (libusb_notification_port);
+
+  /* delete iterators */
+  IOObjectRelease (libusb_rem_device_iterator);
+  IOObjectRelease (libusb_add_device_iterator);
+
+  CFRelease (libusb_shutdown_cfsource);
+  CFRelease (runloop);
+
+  pthread_exit (NULL);
+}
+
+/* cleanup function to destroy cached devices */
+static void darwin_cleanup_devices(void) {
+  struct darwin_cached_device *dev, *next;
+
+  list_for_each_entry_safe(dev, next, &darwin_cached_devices, list, struct darwin_cached_device) {
+    darwin_deref_cached_device(dev);
+  }
+}
+
+static int darwin_init(struct libusb_context *ctx) {
+  bool first_init;
+  int rc;
+
+  first_init = (1 == ++init_count);
+
+  do {
+    if (first_init) {
+      if (NULL == darwin_cached_devices.next) {
+        list_init (&darwin_cached_devices);
+      }
+      assert(list_empty(&darwin_cached_devices));
+#if !defined(HAVE_CLOCK_GETTIME)
+      /* create the clocks that will be used if clock_gettime() is not available */
+      host_name_port_t host_self;
+
+      host_self = mach_host_self();
+      host_get_clock_service(host_self, CALENDAR_CLOCK, &clock_realtime);
+      host_get_clock_service(host_self, SYSTEM_CLOCK, &clock_monotonic);
+      mach_port_deallocate(mach_task_self(), host_self);
+#endif
+    }
+
+    rc = darwin_scan_devices (ctx);
+    if (LIBUSB_SUCCESS != rc)
+      break;
+
+    if (first_init) {
+      rc = pthread_create (&libusb_darwin_at, NULL, darwin_event_thread_main, ctx);
+      if (0 != rc) {
+        usbi_err (ctx, "could not create event thread, error %d", rc);
+        rc = LIBUSB_ERROR_OTHER;
+        break;
+      }
+
+      pthread_mutex_lock (&libusb_darwin_at_mutex);
+      while (!libusb_darwin_acfl)
+        pthread_cond_wait (&libusb_darwin_at_cond, &libusb_darwin_at_mutex);
+      if (libusb_darwin_acfl == LIBUSB_DARWIN_STARTUP_FAILURE) {
+        libusb_darwin_acfl = NULL;
+        rc = LIBUSB_ERROR_OTHER;
+      }
+      pthread_mutex_unlock (&libusb_darwin_at_mutex);
+
+      if (0 != rc)
+        pthread_join (libusb_darwin_at, NULL);
+    }
+  } while (0);
+
+  if (LIBUSB_SUCCESS != rc) {
+    if (first_init) {
+      darwin_cleanup_devices ();
+#if !defined(HAVE_CLOCK_GETTIME)
+      mach_port_deallocate(mach_task_self(), clock_realtime);
+      mach_port_deallocate(mach_task_self(), clock_monotonic);
+#endif
+    }
+    --init_count;
+  }
+
+  return rc;
+}
+
+static void darwin_exit (struct libusb_context *ctx) {
+  UNUSED(ctx);
+
+  if (0 == --init_count) {
+    /* stop the event runloop and wait for the thread to terminate. */
+    pthread_mutex_lock (&libusb_darwin_at_mutex);
+    CFRunLoopSourceSignal (libusb_darwin_acfls);
+    CFRunLoopWakeUp (libusb_darwin_acfl);
+    while (libusb_darwin_acfl)
+      pthread_cond_wait (&libusb_darwin_at_cond, &libusb_darwin_at_mutex);
+    pthread_mutex_unlock (&libusb_darwin_at_mutex);
+    pthread_join (libusb_darwin_at, NULL);
+
+    darwin_cleanup_devices ();
+
+#if !defined(HAVE_CLOCK_GETTIME)
+    mach_port_deallocate(mach_task_self(), clock_realtime);
+    mach_port_deallocate(mach_task_self(), clock_monotonic);
+#endif
+  }
+}
+
+static int get_configuration_index (struct libusb_device *dev, UInt8 config_value) {
+  struct darwin_cached_device *priv = DARWIN_CACHED_DEVICE(dev);
+  UInt8 i, numConfig;
+  IOUSBConfigurationDescriptorPtr desc;
+  IOReturn kresult;
+
+  /* is there a simpler way to determine the index? */
+  kresult = (*(priv->device))->GetNumberOfConfigurations (priv->device, &numConfig);
+  if (kresult != kIOReturnSuccess)
+    return darwin_to_libusb (kresult);
+
+  for (i = 0 ; i < numConfig ; i++) {
+    (*(priv->device))->GetConfigurationDescriptorPtr (priv->device, i, &desc);
+
+    if (desc->bConfigurationValue == config_value)
+      return i;
+  }
+
+  /* configuration not found */
+  return LIBUSB_ERROR_NOT_FOUND;
+}
+
+static int darwin_get_active_config_descriptor(struct libusb_device *dev, void *buffer, size_t len) {
+  struct darwin_cached_device *priv = DARWIN_CACHED_DEVICE(dev);
+  int config_index;
+
+  if (0 == priv->active_config)
+    return LIBUSB_ERROR_NOT_FOUND;
+
+  config_index = get_configuration_index (dev, priv->active_config);
+  if (config_index < 0)
+    return config_index;
+
+  assert(config_index >= 0 && config_index <= UINT8_MAX);
+  return darwin_get_config_descriptor (dev, (UInt8)config_index, buffer, len);
+}
+
+static int darwin_get_config_descriptor(struct libusb_device *dev, uint8_t config_index, void *buffer, size_t len) {
+  struct darwin_cached_device *priv = DARWIN_CACHED_DEVICE(dev);
+  IOUSBConfigurationDescriptorPtr desc;
+  IOReturn kresult;
+  int ret;
+
+  if (!priv || !priv->device)
+    return LIBUSB_ERROR_OTHER;
+
+  kresult = (*priv->device)->GetConfigurationDescriptorPtr (priv->device, config_index, &desc);
+  if (kresult == kIOReturnSuccess) {
+    /* copy descriptor */
+    if (libusb_le16_to_cpu(desc->wTotalLength) < len)
+      len = libusb_le16_to_cpu(desc->wTotalLength);
+
+    memmove (buffer, desc, len);
+  }
+
+  ret = darwin_to_libusb (kresult);
+  if (ret != LIBUSB_SUCCESS)
+    return ret;
+
+  return (int) len;
+}
+
+/* check whether the os has configured the device */
+static enum libusb_error darwin_check_configuration (struct libusb_context *ctx, struct darwin_cached_device *dev) {
+  usb_device_t **darwin_device = dev->device;
+
+  IOUSBConfigurationDescriptorPtr configDesc;
+  IOUSBFindInterfaceRequest request;
+  IOReturn                  kresult;
+  io_iterator_t             interface_iterator;
+  io_service_t              firstInterface;
+
+  if (dev->dev_descriptor.bNumConfigurations < 1) {
+    usbi_err (ctx, "device has no configurations");
+    return LIBUSB_ERROR_OTHER; /* no configurations at this speed so we can't use it */
+  }
+
+  /* checking the configuration of a root hub simulation takes ~1 s in 10.11. the device is
+     not usable anyway */
+  if (0x05ac == libusb_le16_to_cpu (dev->dev_descriptor.idVendor) &&
+      0x8005 == libusb_le16_to_cpu (dev->dev_descriptor.idProduct)) {
+    usbi_dbg (ctx, "ignoring configuration on root hub simulation");
+    dev->active_config = 0;
+    return LIBUSB_SUCCESS;
+  }
+
+  /* find the first configuration */
+  kresult = (*darwin_device)->GetConfigurationDescriptorPtr (darwin_device, 0, &configDesc);
+  dev->first_config = (kIOReturnSuccess == kresult) ? configDesc->bConfigurationValue : 1;
+
+  /* check if the device is already configured. there is probably a better way than iterating over the
+     to accomplish this (the trick is we need to avoid a call to GetConfigurations since buggy devices
+     might lock up on the device request) */
+
+  /* Setup the Interface Request */
+  request.bInterfaceClass    = kIOUSBFindInterfaceDontCare;
+  request.bInterfaceSubClass = kIOUSBFindInterfaceDontCare;
+  request.bInterfaceProtocol = kIOUSBFindInterfaceDontCare;
+  request.bAlternateSetting  = kIOUSBFindInterfaceDontCare;
+
+  kresult = (*(darwin_device))->CreateInterfaceIterator(darwin_device, &request, &interface_iterator);
+  if (kresult != kIOReturnSuccess)
+    return darwin_to_libusb (kresult);
+
+  /* iterate once */
+  firstInterface = IOIteratorNext(interface_iterator);
+
+  /* done with the interface iterator */
+  IOObjectRelease(interface_iterator);
+
+  if (firstInterface) {
+    IOObjectRelease (firstInterface);
+
+    /* device is configured */
+    if (dev->dev_descriptor.bNumConfigurations == 1)
+      /* to avoid problems with some devices get the configurations value from the configuration descriptor */
+      dev->active_config = dev->first_config;
+    else
+      /* devices with more than one configuration should work with GetConfiguration */
+      (*darwin_device)->GetConfiguration (darwin_device, &dev->active_config);
+  } else
+    /* not configured */
+    dev->active_config = 0;
+
+  usbi_dbg (ctx, "active config: %u, first config: %u", dev->active_config, dev->first_config);
+
+  return LIBUSB_SUCCESS;
+}
+
+static IOReturn darwin_request_descriptor (usb_device_t **device, UInt8 desc, UInt8 desc_index, void *buffer, size_t buffer_size) {
+  IOUSBDevRequestTO req;
+
+  assert(buffer_size <= UINT16_MAX);
+
+  memset (buffer, 0, buffer_size);
+
+  /* Set up request for descriptor/ */
+  req.bmRequestType = USBmakebmRequestType(kUSBIn, kUSBStandard, kUSBDevice);
+  req.bRequest      = kUSBRqGetDescriptor;
+  req.wValue        = (UInt16)(desc << 8);
+  req.wIndex        = desc_index;
+  req.wLength       = (UInt16)buffer_size;
+  req.pData         = buffer;
+  req.noDataTimeout = 20;
+  req.completionTimeout = 100;
+
+  return (*device)->DeviceRequestTO (device, &req);
+}
+
+static enum libusb_error darwin_cache_device_descriptor (struct libusb_context *ctx, struct darwin_cached_device *dev) {
+  usb_device_t **device = dev->device;
+  int retries = 1;
+  long delay = 30000; // microseconds
+  int unsuspended = 0, try_unsuspend = 1, try_reconfigure = 1;
+  int is_open = 0;
+  IOReturn ret = 0, ret2;
+  UInt8 bDeviceClass;
+  UInt16 idProduct, idVendor;
+
+  dev->can_enumerate = 0;
+
+  (*device)->GetDeviceClass (device, &bDeviceClass);
+  (*device)->GetDeviceProduct (device, &idProduct);
+  (*device)->GetDeviceVendor (device, &idVendor);
+
+  /* According to Apple's documentation the device must be open for DeviceRequest but we may not be able to open some
+   * devices and Apple's USB Prober doesn't bother to open the device before issuing a descriptor request.  Still,
+   * to follow the spec as closely as possible, try opening the device */
+  is_open = ((*device)->USBDeviceOpenSeize(device) == kIOReturnSuccess);
+
+  do {
+    /**** retrieve device descriptor ****/
+    ret = darwin_request_descriptor (device, kUSBDeviceDesc, 0, &dev->dev_descriptor, sizeof(dev->dev_descriptor));
+
+    if (kIOReturnOverrun == ret && kUSBDeviceDesc == dev->dev_descriptor.bDescriptorType)
+      /* received an overrun error but we still received a device descriptor */
+      ret = kIOReturnSuccess;
+
+    if (kIOUSBVendorIDAppleComputer == idVendor) {
+      /* NTH: don't bother retrying or unsuspending Apple devices */
+      break;
+    }
+
+    if (kIOReturnSuccess == ret && (0 == dev->dev_descriptor.bNumConfigurations ||
+                                    0 == dev->dev_descriptor.bcdUSB)) {
+      /* work around for incorrectly configured devices */
+      if (try_reconfigure && is_open) {
+        usbi_dbg(ctx, "descriptor appears to be invalid. resetting configuration before trying again...");
+
+        /* set the first configuration */
+        (*device)->SetConfiguration(device, 1);
+
+        /* don't try to reconfigure again */
+        try_reconfigure = 0;
+      }
+
+      ret = kIOUSBPipeStalled;
+    }
+
+    if (kIOReturnSuccess != ret && is_open && try_unsuspend) {
+      /* device may be suspended. unsuspend it and try again */
+#if DeviceVersion >= 320
+      UInt32 info = 0;
+
+      /* IOUSBFamily 320+ provides a way to detect device suspension but earlier versions do not */
+      (void)(*device)->GetUSBDeviceInformation (device, &info);
+
+      /* note that the device was suspended */
+      if (info & (1U << kUSBInformationDeviceIsSuspendedBit) || 0 == info)
+        try_unsuspend = 1;
+#endif
+
+      if (try_unsuspend) {
+        /* try to unsuspend the device */
+        ret2 = (*device)->USBDeviceSuspend (device, 0);
+        if (kIOReturnSuccess != ret2) {
+          /* prevent log spew from poorly behaving devices.  this indicates the
+             os actually had trouble communicating with the device */
+          usbi_dbg(ctx, "could not retrieve device descriptor. failed to unsuspend: %s",darwin_error_str(ret2));
+        } else
+          unsuspended = 1;
+
+        try_unsuspend = 0;
+      }
+    }
+
+    if (kIOReturnSuccess != ret) {
+      usbi_dbg(ctx, "kernel responded with code: 0x%08x. sleeping for %ld ms before trying again", ret, delay/1000);
+      /* sleep for a little while before trying again */
+      nanosleep(&(struct timespec){delay / 1000000, (delay * 1000) % 1000000000}, NULL);
+    }
+  } while (kIOReturnSuccess != ret && retries--);
+
+  if (unsuspended)
+    /* resuspend the device */
+    (void)(*device)->USBDeviceSuspend (device, 1);
+
+  if (is_open)
+    (void) (*device)->USBDeviceClose (device);
+
+  if (ret != kIOReturnSuccess) {
+    /* a debug message was already printed out for this error */
+    if (LIBUSB_CLASS_HUB == bDeviceClass)
+      usbi_dbg (ctx, "could not retrieve device descriptor %.4x:%.4x: %s (%x). skipping device",
+                idVendor, idProduct, darwin_error_str (ret), ret);
+    else
+      usbi_warn (ctx, "could not retrieve device descriptor %.4x:%.4x: %s (%x). skipping device",
+                 idVendor, idProduct, darwin_error_str (ret), ret);
+    return darwin_to_libusb (ret);
+  }
+
+  /* catch buggy hubs (which appear to be virtual). Apple's own USB prober has problems with these devices. */
+  if (libusb_le16_to_cpu (dev->dev_descriptor.idProduct) != idProduct) {
+    /* not a valid device */
+    usbi_warn (NULL, "idProduct from iokit (%04x) does not match idProduct in descriptor (%04x). skipping device",
+               idProduct, libusb_le16_to_cpu (dev->dev_descriptor.idProduct));
+    return LIBUSB_ERROR_NO_DEVICE;
+  }
+
+  usbi_dbg (ctx, "cached device descriptor:");
+  usbi_dbg (ctx, "  bDescriptorType:    0x%02x", dev->dev_descriptor.bDescriptorType);
+  usbi_dbg (ctx, "  bcdUSB:             0x%04x", libusb_le16_to_cpu (dev->dev_descriptor.bcdUSB));
+  usbi_dbg (ctx, "  bDeviceClass:       0x%02x", dev->dev_descriptor.bDeviceClass);
+  usbi_dbg (ctx, "  bDeviceSubClass:    0x%02x", dev->dev_descriptor.bDeviceSubClass);
+  usbi_dbg (ctx, "  bDeviceProtocol:    0x%02x", dev->dev_descriptor.bDeviceProtocol);
+  usbi_dbg (ctx, "  bMaxPacketSize0:    0x%02x", dev->dev_descriptor.bMaxPacketSize0);
+  usbi_dbg (ctx, "  idVendor:           0x%04x", libusb_le16_to_cpu (dev->dev_descriptor.idVendor));
+  usbi_dbg (ctx, "  idProduct:          0x%04x", libusb_le16_to_cpu (dev->dev_descriptor.idProduct));
+  usbi_dbg (ctx, "  bcdDevice:          0x%04x", libusb_le16_to_cpu (dev->dev_descriptor.bcdDevice));
+  usbi_dbg (ctx, "  iManufacturer:      0x%02x", dev->dev_descriptor.iManufacturer);
+  usbi_dbg (ctx, "  iProduct:           0x%02x", dev->dev_descriptor.iProduct);
+  usbi_dbg (ctx, "  iSerialNumber:      0x%02x", dev->dev_descriptor.iSerialNumber);
+  usbi_dbg (ctx, "  bNumConfigurations: 0x%02x", dev->dev_descriptor.bNumConfigurations);
+
+  dev->can_enumerate = 1;
+
+  return LIBUSB_SUCCESS;
+}
+
+/* Returns 1 on success, 0 on failure. */
+static bool get_device_port (io_service_t service, UInt8 *port) {
+  IOReturn kresult;
+  io_service_t parent;
+  bool ret = false;
+
+  if (get_ioregistry_value_number (service, CFSTR("PortNum"), kCFNumberSInt8Type, port)) {
+    return true;
+  }
+
+  kresult = IORegistryEntryGetParentEntry (service, kIOServicePlane, &parent);
+  if (kIOReturnSuccess == kresult) {
+    ret = get_ioregistry_value_data (parent, CFSTR("port"), 1, port);
+    IOObjectRelease (parent);
+  }
+
+  return ret;
+}
+
+/* Returns 1 on success, 0 on failure. */
+static bool get_device_parent_sessionID(io_service_t service, UInt64 *parent_sessionID) {
+  IOReturn kresult;
+  io_service_t parent;
+
+  /* Walk up the tree in the IOService plane until we find a parent that has a sessionID */
+  parent = service;
+  while((kresult = IORegistryEntryGetParentEntry (parent, kIOUSBPlane, &parent)) == kIOReturnSuccess) {
+    if (get_ioregistry_value_number (parent, CFSTR("sessionID"), kCFNumberSInt64Type, parent_sessionID)) {
+        /* Success */
+        return true;
+    }
+  }
+
+  /* We ran out of parents */
+  return false;
+}
+
+static enum libusb_error darwin_get_cached_device(struct libusb_context *ctx, io_service_t service, struct darwin_cached_device **cached_out,
+                                                  UInt64 *old_session_id) {
+  struct darwin_cached_device *new_device;
+  UInt64 sessionID = 0, parent_sessionID = 0;
+  UInt32 locationID = 0;
+  enum libusb_error ret = LIBUSB_SUCCESS;
+  usb_device_t **device;
+  UInt8 port = 0;
+
+  /* assuming sessionID != 0 normally (never seen it be 0) */
+  *old_session_id = 0;
+  *cached_out = NULL;
+
+  /* get some info from the io registry */
+  (void) get_ioregistry_value_number (service, CFSTR("sessionID"), kCFNumberSInt64Type, &sessionID);
+  (void) get_ioregistry_value_number (service, CFSTR("locationID"), kCFNumberSInt32Type, &locationID);
+  if (!get_device_port (service, &port)) {
+    usbi_dbg(ctx, "could not get connected port number");
+  }
+
+  usbi_dbg(ctx, "finding cached device for sessionID 0x%" PRIx64, sessionID);
+
+  if (get_device_parent_sessionID(service, &parent_sessionID)) {
+    usbi_dbg(ctx, "parent sessionID: 0x%" PRIx64, parent_sessionID);
+  }
+
+  usbi_mutex_lock(&darwin_cached_devices_lock);
+  do {
+    list_for_each_entry(new_device, &darwin_cached_devices, list, struct darwin_cached_device) {
+      usbi_dbg(ctx, "matching sessionID/locationID 0x%" PRIx64 "/0x%x against cached device with sessionID/locationID 0x%" PRIx64 "/0x%x",
+               sessionID, locationID, new_device->session, new_device->location);
+      if (new_device->location == locationID && new_device->in_reenumerate) {
+        usbi_dbg (ctx, "found cached device with matching location that is being re-enumerated");
+        *old_session_id = new_device->session;
+        break;
+      }
+
+      if (new_device->session == sessionID) {
+        usbi_dbg(ctx, "using cached device for device");
+        *cached_out = new_device;
+        break;
+      }
+    }
+
+    if (*cached_out)
+      break;
+
+    usbi_dbg(ctx, "caching new device with sessionID 0x%" PRIx64, sessionID);
+
+    device = darwin_device_from_service (ctx, service);
+    if (!device) {
+      ret = LIBUSB_ERROR_NO_DEVICE;
+      break;
+    }
+
+    if (!(*old_session_id)) {
+      new_device = calloc (1, sizeof (*new_device));
+      if (!new_device) {
+        ret = LIBUSB_ERROR_NO_MEM;
+        break;
+      }
+
+      /* add this device to the cached device list */
+      list_add(&new_device->list, &darwin_cached_devices);
+
+      (*device)->GetDeviceAddress (device, (USBDeviceAddress *)&new_device->address);
+
+      /* keep a reference to this device */
+      darwin_ref_cached_device(new_device);
+
+      (*device)->GetLocationID (device, &new_device->location);
+      new_device->port = port;
+      new_device->parent_session = parent_sessionID;
+    } else {
+      /* release the ref to old device's service */
+      IOObjectRelease (new_device->service);
+    }
+
+    /* keep track of devices regardless of if we successfully enumerate them to
+       prevent them from being enumerated multiple times */
+    *cached_out = new_device;
+
+    new_device->session = sessionID;
+    new_device->device = device;
+    new_device->service = service;
+
+    /* retain the service */
+    IOObjectRetain (service);
+
+    /* cache the device descriptor */
+    ret = darwin_cache_device_descriptor(ctx, new_device);
+    if (ret)
+      break;
+
+    if (new_device->can_enumerate) {
+      snprintf(new_device->sys_path, 20, "%03i-%04x-%04x-%02x-%02x", new_device->address,
+               libusb_le16_to_cpu (new_device->dev_descriptor.idVendor),
+               libusb_le16_to_cpu (new_device->dev_descriptor.idProduct),
+               new_device->dev_descriptor.bDeviceClass, new_device->dev_descriptor.bDeviceSubClass);
+    }
+  } while (0);
+
+  usbi_mutex_unlock(&darwin_cached_devices_lock);
+
+  return ret;
+}
+
+static enum libusb_error process_new_device (struct libusb_context *ctx, struct darwin_cached_device *cached_device,
+                                             UInt64 old_session_id) {
+  struct darwin_device_priv *priv;
+  struct libusb_device *dev = NULL;
+  UInt8 devSpeed;
+  enum libusb_error ret = LIBUSB_SUCCESS;
+
+  do {
+    /* check current active configuration (and cache the first configuration value--
+       which may be used by claim_interface) */
+    ret = darwin_check_configuration (ctx, cached_device);
+    if (ret)
+      break;
+
+    if (0 != old_session_id) {
+      usbi_dbg (ctx, "re-using existing device from context %p for with session 0x%" PRIx64 " new session 0x%" PRIx64,
+                ctx, old_session_id, cached_device->session);
+      /* save the libusb device before the session id is updated */
+      dev = usbi_get_device_by_session_id (ctx, (unsigned long) old_session_id);
+    }
+
+    if (!dev) {
+      usbi_dbg (ctx, "allocating new device in context %p for with session 0x%" PRIx64,
+                ctx, cached_device->session);
+
+      dev = usbi_alloc_device(ctx, (unsigned long) cached_device->session);
+      if (!dev) {
+        return LIBUSB_ERROR_NO_MEM;
+      }
+
+      priv = usbi_get_device_priv(dev);
+
+      priv->dev = cached_device;
+      darwin_ref_cached_device (priv->dev);
+      dev->port_number    = cached_device->port;
+      /* the location ID encodes the path to the device. the top byte of the location ID contains the bus number
+         (numbered from 0). the remaining bytes can be used to construct the device tree for that bus. */
+      dev->bus_number     = cached_device->location >> 24;
+      assert(cached_device->address <= UINT8_MAX);
+      dev->device_address = (uint8_t)cached_device->address;
+    } else {
+      priv = usbi_get_device_priv(dev);
+    }
+
+    static_assert(sizeof(dev->device_descriptor) == sizeof(cached_device->dev_descriptor),
+                  "mismatch between libusb and IOKit device descriptor sizes");
+    memcpy(&dev->device_descriptor, &cached_device->dev_descriptor, LIBUSB_DT_DEVICE_SIZE);
+    usbi_localize_device_descriptor(&dev->device_descriptor);
+    dev->session_data = cached_device->session;
+
+    if (NULL != dev->parent_dev) {
+      libusb_unref_device(dev->parent_dev);
+      dev->parent_dev = NULL;
+    }
+
+    if (cached_device->parent_session > 0) {
+      dev->parent_dev = usbi_get_device_by_session_id (ctx, (unsigned long) cached_device->parent_session);
+    }
+
+    (*(priv->dev->device))->GetDeviceSpeed (priv->dev->device, &devSpeed);
+
+    switch (devSpeed) {
+    case kUSBDeviceSpeedLow: dev->speed = LIBUSB_SPEED_LOW; break;
+    case kUSBDeviceSpeedFull: dev->speed = LIBUSB_SPEED_FULL; break;
+    case kUSBDeviceSpeedHigh: dev->speed = LIBUSB_SPEED_HIGH; break;
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= 1080
+    case kUSBDeviceSpeedSuper: dev->speed = LIBUSB_SPEED_SUPER; break;
+#endif
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= 101200
+    case kUSBDeviceSpeedSuperPlus: dev->speed = LIBUSB_SPEED_SUPER_PLUS; break;
+#endif
+    default:
+      usbi_warn (ctx, "Got unknown device speed %d", devSpeed);
+    }
+
+    ret = usbi_sanitize_device (dev);
+    if (ret < 0)
+      break;
+
+    usbi_dbg (ctx, "found device with address %d port = %d parent = %p at %p", dev->device_address,
+              dev->port_number, (void *) dev->parent_dev, priv->dev->sys_path);
+
+  } while (0);
+
+  if (!cached_device->in_reenumerate && 0 == ret) {
+    usbi_connect_device (dev);
+  } else {
+    libusb_unref_device (dev);
+  }
+
+  return ret;
+}
+
+static enum libusb_error darwin_scan_devices(struct libusb_context *ctx) {
+  struct darwin_cached_device *cached_device;
+  UInt64 old_session_id;
+  io_iterator_t deviceIterator;
+  io_service_t service;
+  IOReturn kresult;
+  int ret;
+
+  kresult = usb_setup_device_iterator (&deviceIterator, 0);
+  if (kresult != kIOReturnSuccess)
+    return darwin_to_libusb (kresult);
+
+  while ((service = IOIteratorNext (deviceIterator))) {
+    ret = darwin_get_cached_device (ctx, service, &cached_device, &old_session_id);
+    if (ret < 0 || !cached_device->can_enumerate) {
+      continue;
+    }
+
+    (void) process_new_device (ctx, cached_device, old_session_id);
+
+    IOObjectRelease(service);
+  }
+
+  IOObjectRelease(deviceIterator);
+
+  return LIBUSB_SUCCESS;
+}
+
+static int darwin_open (struct libusb_device_handle *dev_handle) {
+  struct darwin_device_handle_priv *priv = usbi_get_device_handle_priv(dev_handle);
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(dev_handle->dev);
+  IOReturn kresult;
+
+  if (0 == dpriv->open_count) {
+    /* try to open the device */
+    kresult = (*(dpriv->device))->USBDeviceOpenSeize (dpriv->device);
+    if (kresult != kIOReturnSuccess) {
+      usbi_warn (HANDLE_CTX (dev_handle), "USBDeviceOpen: %s", darwin_error_str(kresult));
+
+      if (kIOReturnExclusiveAccess != kresult) {
+        return darwin_to_libusb (kresult);
+      }
+
+      /* it is possible to perform some actions on a device that is not open so do not return an error */
+      priv->is_open = false;
+    } else {
+      priv->is_open = true;
+    }
+
+    /* create async event source */
+    kresult = (*(dpriv->device))->CreateDeviceAsyncEventSource (dpriv->device, &priv->cfSource);
+    if (kresult != kIOReturnSuccess) {
+      usbi_err (HANDLE_CTX (dev_handle), "CreateDeviceAsyncEventSource: %s", darwin_error_str(kresult));
+
+      if (priv->is_open) {
+        (*(dpriv->device))->USBDeviceClose (dpriv->device);
+      }
+
+      priv->is_open = false;
+
+      return darwin_to_libusb (kresult);
+    }
+
+    CFRetain (libusb_darwin_acfl);
+
+    /* add the cfSource to the async run loop */
+    CFRunLoopAddSource(libusb_darwin_acfl, priv->cfSource, kCFRunLoopCommonModes);
+  }
+
+  /* device opened successfully */
+  dpriv->open_count++;
+
+  usbi_dbg (HANDLE_CTX(dev_handle), "device open for access");
+
+  return 0;
+}
+
+static void darwin_close (struct libusb_device_handle *dev_handle) {
+  struct darwin_device_handle_priv *priv = usbi_get_device_handle_priv(dev_handle);
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(dev_handle->dev);
+  IOReturn kresult;
+  int i;
+
+  if (dpriv->open_count == 0) {
+    /* something is probably very wrong if this is the case */
+    usbi_err (HANDLE_CTX (dev_handle), "Close called on a device that was not open!");
+    return;
+  }
+
+  dpriv->open_count--;
+  if (NULL == dpriv->device) {
+    usbi_warn (HANDLE_CTX (dev_handle), "darwin_close device missing IOService");
+    return;
+  }
+
+  /* make sure all interfaces are released */
+  for (i = 0 ; i < USB_MAXINTERFACES ; i++)
+    if (dev_handle->claimed_interfaces & (1U << i))
+      libusb_release_interface (dev_handle, i);
+
+  if (0 == dpriv->open_count) {
+    /* delete the device's async event source */
+    if (priv->cfSource) {
+      CFRunLoopRemoveSource (libusb_darwin_acfl, priv->cfSource, kCFRunLoopDefaultMode);
+      CFRelease (priv->cfSource);
+      priv->cfSource = NULL;
+      CFRelease (libusb_darwin_acfl);
+    }
+
+    if (priv->is_open) {
+      /* close the device */
+      kresult = (*(dpriv->device))->USBDeviceClose(dpriv->device);
+      if (kresult != kIOReturnSuccess) {
+        /* Log the fact that we had a problem closing the file, however failing a
+         * close isn't really an error, so return success anyway */
+        usbi_warn (HANDLE_CTX (dev_handle), "USBDeviceClose: %s", darwin_error_str(kresult));
+      }
+    }
+  }
+}
+
+static int darwin_get_configuration(struct libusb_device_handle *dev_handle, uint8_t *config) {
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(dev_handle->dev);
+
+  *config = dpriv->active_config;
+
+  return LIBUSB_SUCCESS;
+}
+
+static enum libusb_error darwin_set_configuration(struct libusb_device_handle *dev_handle, int config) {
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(dev_handle->dev);
+  IOReturn kresult;
+  uint8_t i;
+
+  if (config == -1)
+    config = 0;
+
+  /* Setting configuration will invalidate the interface, so we need
+     to reclaim it. First, dispose of existing interfaces, if any. */
+  for (i = 0 ; i < USB_MAXINTERFACES ; i++)
+    if (dev_handle->claimed_interfaces & (1U << i))
+      darwin_release_interface (dev_handle, i);
+
+  kresult = (*(dpriv->device))->SetConfiguration (dpriv->device, (UInt8)config);
+  if (kresult != kIOReturnSuccess)
+    return darwin_to_libusb (kresult);
+
+  /* Reclaim any interfaces. */
+  for (i = 0 ; i < USB_MAXINTERFACES ; i++)
+    if (dev_handle->claimed_interfaces & (1U << i))
+      darwin_claim_interface (dev_handle, i);
+
+  dpriv->active_config = (UInt8)config;
+
+  return LIBUSB_SUCCESS;
+}
+
+static IOReturn darwin_get_interface (usb_device_t **darwin_device, uint8_t ifc, io_service_t *usbInterfacep) {
+  IOUSBFindInterfaceRequest request;
+  IOReturn                  kresult;
+  io_iterator_t             interface_iterator;
+  UInt8                     bInterfaceNumber;
+  bool                      ret;
+
+  *usbInterfacep = IO_OBJECT_NULL;
+
+  /* Setup the Interface Request */
+  request.bInterfaceClass    = kIOUSBFindInterfaceDontCare;
+  request.bInterfaceSubClass = kIOUSBFindInterfaceDontCare;
+  request.bInterfaceProtocol = kIOUSBFindInterfaceDontCare;
+  request.bAlternateSetting  = kIOUSBFindInterfaceDontCare;
+
+  kresult = (*(darwin_device))->CreateInterfaceIterator(darwin_device, &request, &interface_iterator);
+  if (kresult != kIOReturnSuccess)
+    return kresult;
+
+  while ((*usbInterfacep = IOIteratorNext(interface_iterator))) {
+    /* find the interface number */
+    ret = get_ioregistry_value_number (*usbInterfacep, CFSTR("bInterfaceNumber"), kCFNumberSInt8Type,
+                                       &bInterfaceNumber);
+
+    if (ret && bInterfaceNumber == ifc) {
+      break;
+    }
+
+    (void) IOObjectRelease (*usbInterfacep);
+  }
+
+  /* done with the interface iterator */
+  IOObjectRelease(interface_iterator);
+
+  return kIOReturnSuccess;
+}
+
+static enum libusb_error get_endpoints (struct libusb_device_handle *dev_handle, uint8_t iface) {
+  struct darwin_device_handle_priv *priv = usbi_get_device_handle_priv(dev_handle);
+
+  /* current interface */
+  struct darwin_interface *cInterface = &priv->interfaces[iface];
+
+  IOReturn kresult;
+
+  UInt8 numep, direction, number;
+  UInt8 dont_care1, dont_care3;
+  UInt16 dont_care2;
+  int rc;
+  struct libusb_context *ctx = HANDLE_CTX (dev_handle);
+
+
+  usbi_dbg (ctx, "building table of endpoints.");
+
+  /* retrieve the total number of endpoints on this interface */
+  kresult = (*(cInterface->interface))->GetNumEndpoints(cInterface->interface, &numep);
+  if (kresult != kIOReturnSuccess) {
+    usbi_err (ctx, "can't get number of endpoints for interface: %s", darwin_error_str(kresult));
+    return darwin_to_libusb (kresult);
+  }
+
+  /* iterate through pipe references */
+  for (UInt8 i = 1 ; i <= numep ; i++) {
+    kresult = (*(cInterface->interface))->GetPipeProperties(cInterface->interface, i, &direction, &number, &dont_care1,
+                                                            &dont_care2, &dont_care3);
+
+    if (kresult != kIOReturnSuccess) {
+      /* probably a buggy device. try to get the endpoint address from the descriptors */
+      struct libusb_config_descriptor *config;
+      const struct libusb_endpoint_descriptor *endpoint_desc;
+      UInt8 alt_setting;
+
+      kresult = (*(cInterface->interface))->GetAlternateSetting (cInterface->interface, &alt_setting);
+      if (kresult != kIOReturnSuccess) {
+        usbi_err (HANDLE_CTX (dev_handle), "can't get alternate setting for interface");
+        return darwin_to_libusb (kresult);
+      }
+
+      rc = libusb_get_active_config_descriptor (dev_handle->dev, &config);
+      if (LIBUSB_SUCCESS != rc) {
+        return rc;
+      }
+
+      endpoint_desc = config->interface[iface].altsetting[alt_setting].endpoint + i - 1;
+
+      cInterface->endpoint_addrs[i - 1] = endpoint_desc->bEndpointAddress;
+    } else {
+      cInterface->endpoint_addrs[i - 1] = (UInt8)(((kUSBIn == direction) << kUSBRqDirnShift) | (number & LIBUSB_ENDPOINT_ADDRESS_MASK));
+    }
+
+    usbi_dbg (ctx, "interface: %i pipe %i: dir: %i number: %i", iface, i, cInterface->endpoint_addrs[i - 1] >> kUSBRqDirnShift,
+              cInterface->endpoint_addrs[i - 1] & LIBUSB_ENDPOINT_ADDRESS_MASK);
+  }
+
+  cInterface->num_endpoints = numep;
+
+  return LIBUSB_SUCCESS;
+}
+
+static int darwin_claim_interface(struct libusb_device_handle *dev_handle, uint8_t iface) {
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(dev_handle->dev);
+  struct darwin_device_handle_priv *priv = usbi_get_device_handle_priv(dev_handle);
+  io_service_t          usbInterface = IO_OBJECT_NULL;
+  IOReturn              kresult;
+  enum libusb_error     ret;
+  IOCFPlugInInterface **plugInInterface = NULL;
+  SInt32                score;
+
+  /* current interface */
+  struct darwin_interface *cInterface = &priv->interfaces[iface];
+
+  struct libusb_context *ctx = HANDLE_CTX (dev_handle);
+
+  kresult = darwin_get_interface (dpriv->device, iface, &usbInterface);
+  if (kresult != kIOReturnSuccess)
+    return darwin_to_libusb (kresult);
+
+  /* make sure we have an interface */
+  if (!usbInterface && dpriv->first_config != 0) {
+    usbi_info (ctx, "no interface found; setting configuration: %d", dpriv->first_config);
+
+    /* set the configuration */
+    ret = darwin_set_configuration (dev_handle, (int) dpriv->first_config);
+    if (ret != LIBUSB_SUCCESS) {
+      usbi_err (ctx, "could not set configuration");
+      return ret;
+    }
+
+    kresult = darwin_get_interface (dpriv->device, iface, &usbInterface);
+    if (kresult != kIOReturnSuccess) {
+      usbi_err (ctx, "darwin_get_interface: %s", darwin_error_str(kresult));
+      return darwin_to_libusb (kresult);
+    }
+  }
+
+  if (!usbInterface) {
+    usbi_info (ctx, "interface not found");
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  /* get an interface to the device's interface */
+  kresult = IOCreatePlugInInterfaceForService (usbInterface, kIOUSBInterfaceUserClientTypeID,
+                                               kIOCFPlugInInterfaceID, &plugInInterface, &score);
+
+  /* ignore release error */
+  (void)IOObjectRelease (usbInterface);
+
+  if (kresult != kIOReturnSuccess) {
+    usbi_err (ctx, "IOCreatePlugInInterfaceForService: %s", darwin_error_str(kresult));
+    return darwin_to_libusb (kresult);
+  }
+
+  if (!plugInInterface) {
+    usbi_err (ctx, "plugin interface not found");
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  /* Do the actual claim */
+  kresult = (*plugInInterface)->QueryInterface(plugInInterface,
+                                               CFUUIDGetUUIDBytes(InterfaceInterfaceID),
+                                               (LPVOID)&cInterface->interface);
+  /* We no longer need the intermediate plug-in */
+  /* Use release instead of IODestroyPlugInInterface to avoid stopping IOServices associated with this device */
+  (*plugInInterface)->Release (plugInInterface);
+  if (kresult != kIOReturnSuccess || !cInterface->interface) {
+    usbi_err (ctx, "QueryInterface: %s", darwin_error_str(kresult));
+    return darwin_to_libusb (kresult);
+  }
+
+  /* claim the interface */
+  kresult = (*(cInterface->interface))->USBInterfaceOpen(cInterface->interface);
+  if (kresult != kIOReturnSuccess) {
+    usbi_info (ctx, "USBInterfaceOpen: %s", darwin_error_str(kresult));
+    return darwin_to_libusb (kresult);
+  }
+
+  /* update list of endpoints */
+  ret = get_endpoints (dev_handle, iface);
+  if (ret) {
+    /* this should not happen */
+    darwin_release_interface (dev_handle, iface);
+    usbi_err (ctx, "could not build endpoint table");
+    return ret;
+  }
+
+  cInterface->cfSource = NULL;
+
+  /* create async event source */
+  kresult = (*(cInterface->interface))->CreateInterfaceAsyncEventSource (cInterface->interface, &cInterface->cfSource);
+  if (kresult != kIOReturnSuccess) {
+    usbi_err (ctx, "could not create async event source");
+
+    /* can't continue without an async event source */
+    (void)darwin_release_interface (dev_handle, iface);
+
+    return darwin_to_libusb (kresult);
+  }
+
+  /* add the cfSource to the async thread's run loop */
+  CFRunLoopAddSource(libusb_darwin_acfl, cInterface->cfSource, kCFRunLoopDefaultMode);
+
+  usbi_dbg (ctx, "interface opened");
+
+  return LIBUSB_SUCCESS;
+}
+
+static int darwin_release_interface(struct libusb_device_handle *dev_handle, uint8_t iface) {
+  struct darwin_device_handle_priv *priv = usbi_get_device_handle_priv(dev_handle);
+  IOReturn kresult;
+
+  /* current interface */
+  struct darwin_interface *cInterface = &priv->interfaces[iface];
+
+  /* Check to see if an interface is open */
+  if (!cInterface->interface)
+    return LIBUSB_SUCCESS;
+
+  /* clean up endpoint data */
+  cInterface->num_endpoints = 0;
+
+  /* delete the interface's async event source */
+  if (cInterface->cfSource) {
+    CFRunLoopRemoveSource (libusb_darwin_acfl, cInterface->cfSource, kCFRunLoopDefaultMode);
+    CFRelease (cInterface->cfSource);
+    cInterface->cfSource = NULL;
+  }
+
+  kresult = (*(cInterface->interface))->USBInterfaceClose(cInterface->interface);
+  if (kresult != kIOReturnSuccess)
+    usbi_warn (HANDLE_CTX (dev_handle), "USBInterfaceClose: %s", darwin_error_str(kresult));
+
+  kresult = (*(cInterface->interface))->Release(cInterface->interface);
+  if (kresult != kIOReturnSuccess)
+    usbi_warn (HANDLE_CTX (dev_handle), "Release: %s", darwin_error_str(kresult));
+
+  cInterface->interface = (usb_interface_t **) IO_OBJECT_NULL;
+
+  return darwin_to_libusb (kresult);
+}
+
+static int check_alt_setting_and_clear_halt(struct libusb_device_handle *dev_handle, uint8_t altsetting, struct darwin_interface *cInterface) {
+  enum libusb_error ret;
+  IOReturn kresult;
+  uint8_t current_alt_setting;
+
+  kresult = (*(cInterface->interface))->GetAlternateSetting (cInterface->interface, &current_alt_setting);
+  if (kresult == kIOReturnSuccess && altsetting != current_alt_setting) {
+    return LIBUSB_ERROR_PIPE;
+  }
+
+  for (int i = 0 ; i < cInterface->num_endpoints ; i++) {
+    ret = darwin_clear_halt(dev_handle, cInterface->endpoint_addrs[i]);
+    if (LIBUSB_SUCCESS != ret) {
+      usbi_warn(HANDLE_CTX (dev_handle), "error clearing pipe halt for endpoint %d", i);
+      if (LIBUSB_ERROR_NOT_FOUND == ret) {
+        /* may need to re-open the interface */
+        return ret;
+      }
+    }
+  }
+
+  return LIBUSB_SUCCESS;
+}
+
+static int darwin_set_interface_altsetting(struct libusb_device_handle *dev_handle, uint8_t iface, uint8_t altsetting) {
+  struct darwin_device_handle_priv *priv = usbi_get_device_handle_priv(dev_handle);
+  IOReturn kresult;
+  enum libusb_error ret;
+
+  /* current interface */
+  struct darwin_interface *cInterface = &priv->interfaces[iface];
+
+  if (!cInterface->interface)
+    return LIBUSB_ERROR_NO_DEVICE;
+
+  kresult = (*(cInterface->interface))->SetAlternateInterface (cInterface->interface, altsetting);
+  if (kresult == kIOReturnSuccess) {
+    /* update the list of endpoints */
+    ret = get_endpoints (dev_handle, iface);
+    if (ret) {
+      /* this should not happen */
+      darwin_release_interface (dev_handle, iface);
+      usbi_err (HANDLE_CTX (dev_handle), "could not build endpoint table");
+    }
+    return ret;
+  }
+
+  usbi_warn (HANDLE_CTX (dev_handle), "SetAlternateInterface: %s", darwin_error_str(kresult));
+
+  ret = darwin_to_libusb(kresult);
+  if (ret != LIBUSB_ERROR_PIPE) {
+    return ret;
+  }
+
+  /* If a device only supports a default setting for the specified interface, then a STALL
+     (kIOUSBPipeStalled) may be returned. Ref: USB 2.0 specs 9.4.10.
+     Mimic the behaviour in e.g. the Linux kernel: in such case, reset all endpoints
+     of the interface (as would have been done per 9.1.1.5) and return success. */
+
+  ret = check_alt_setting_and_clear_halt(dev_handle, altsetting, cInterface);
+  if (LIBUSB_ERROR_NOT_FOUND == ret) {
+    /* For some reason we need to reclaim the interface after the pipe error with some versions of macOS */
+    ret = darwin_claim_interface (dev_handle, iface);
+    if (LIBUSB_SUCCESS != ret) {
+      darwin_release_interface (dev_handle, iface);
+      usbi_err (HANDLE_CTX (dev_handle), "could not reclaim interface: %s", darwin_error_str(kresult));
+    }
+    ret = check_alt_setting_and_clear_halt(dev_handle, altsetting, cInterface);
+  }
+
+  return ret;
+}
+
+static int darwin_clear_halt(struct libusb_device_handle *dev_handle, unsigned char endpoint) {
+  /* current interface */
+  struct darwin_interface *cInterface;
+  IOReturn kresult;
+  uint8_t pipeRef;
+
+  /* determine the interface/endpoint to use */
+  if (ep_to_pipeRef (dev_handle, endpoint, &pipeRef, NULL, &cInterface) != 0) {
+    usbi_err (HANDLE_CTX (dev_handle), "endpoint not found on any open interface");
+
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  /* newer versions of darwin support clearing additional bits on the device's endpoint */
+  kresult = (*(cInterface->interface))->ClearPipeStallBothEnds(cInterface->interface, pipeRef);
+  if (kresult != kIOReturnSuccess)
+    usbi_warn (HANDLE_CTX (dev_handle), "ClearPipeStall: %s", darwin_error_str (kresult));
+
+  return darwin_to_libusb (kresult);
+}
+
+static int darwin_restore_state (struct libusb_device_handle *dev_handle, int8_t active_config,
+                                 unsigned long claimed_interfaces) {
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(dev_handle->dev);
+  struct darwin_device_handle_priv *priv = usbi_get_device_handle_priv(dev_handle);
+  int open_count = dpriv->open_count;
+  int ret;
+
+  struct libusb_context *ctx = HANDLE_CTX (dev_handle);
+
+  /* clear claimed interfaces temporarily */
+  dev_handle->claimed_interfaces = 0;
+
+  /* close and re-open the device */
+  priv->is_open = false;
+  dpriv->open_count = 1;
+
+  /* clean up open interfaces */
+  (void) darwin_close (dev_handle);
+
+  /* re-open the device */
+  ret = darwin_open (dev_handle);
+  dpriv->open_count = open_count;
+  if (LIBUSB_SUCCESS != ret) {
+    /* could not restore configuration */
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  if (dpriv->active_config != active_config) {
+    usbi_dbg (ctx, "darwin/restore_state: restoring configuration %d...", active_config);
+
+    ret = darwin_set_configuration (dev_handle, active_config);
+    if (LIBUSB_SUCCESS != ret) {
+      usbi_dbg (ctx, "darwin/restore_state: could not restore configuration");
+      return LIBUSB_ERROR_NOT_FOUND;
+    }
+  }
+
+  usbi_dbg (ctx, "darwin/restore_state: reclaiming interfaces");
+
+  if (claimed_interfaces) {
+    for (uint8_t iface = 0 ; iface < USB_MAXINTERFACES ; ++iface) {
+      if (!(claimed_interfaces & (1U << iface))) {
+        continue;
+      }
+
+      usbi_dbg (ctx, "darwin/restore_state: re-claiming interface %u", iface);
+
+      ret = darwin_claim_interface (dev_handle, iface);
+      if (LIBUSB_SUCCESS != ret) {
+        usbi_dbg (ctx, "darwin/restore_state: could not claim interface %u", iface);
+        return LIBUSB_ERROR_NOT_FOUND;
+      }
+
+      dev_handle->claimed_interfaces |= 1U << iface;
+    }
+  }
+
+  usbi_dbg (ctx, "darwin/restore_state: device state restored");
+
+  return LIBUSB_SUCCESS;
+}
+
+static int darwin_reenumerate_device (struct libusb_device_handle *dev_handle, bool capture) {
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(dev_handle->dev);
+  unsigned long claimed_interfaces = dev_handle->claimed_interfaces;
+  int8_t active_config = dpriv->active_config;
+  UInt32 options = 0;
+  IOUSBDeviceDescriptor descriptor;
+  IOUSBConfigurationDescriptorPtr cached_configuration;
+  IOUSBConfigurationDescriptor *cached_configurations;
+  IOReturn kresult;
+  UInt8 i;
+
+  struct libusb_context *ctx = HANDLE_CTX (dev_handle);
+
+  if (dpriv->in_reenumerate) {
+    /* ack, two (or more) threads are trying to reset the device! abort! */
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  dpriv->in_reenumerate = true;
+
+  /* store copies of descriptors so they can be compared after the reset */
+  memcpy (&descriptor, &dpriv->dev_descriptor, sizeof (descriptor));
+  cached_configurations = alloca (sizeof (*cached_configurations) * descriptor.bNumConfigurations);
+
+  for (i = 0 ; i < descriptor.bNumConfigurations ; ++i) {
+    (*(dpriv->device))->GetConfigurationDescriptorPtr (dpriv->device, i, &cached_configuration);
+    memcpy (cached_configurations + i, cached_configuration, sizeof (cached_configurations[i]));
+  }
+
+  /* if we need to release capture */
+  if (HAS_CAPTURE_DEVICE()) {
+    if (capture) {
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= 101000
+      options |= kUSBReEnumerateCaptureDeviceMask;
+#endif
+    }
+  } else {
+    capture = false;
+  }
+
+  /* from macOS 10.11 ResetDevice no longer does anything so just use USBDeviceReEnumerate */
+  kresult = (*(dpriv->device))->USBDeviceReEnumerate (dpriv->device, options);
+  if (kresult != kIOReturnSuccess) {
+    usbi_err (ctx, "USBDeviceReEnumerate: %s", darwin_error_str (kresult));
+    dpriv->in_reenumerate = false;
+    return darwin_to_libusb (kresult);
+  }
+
+  /* capture mode does not re-enumerate but it does require re-open */
+  if (capture) {
+    usbi_dbg (ctx, "darwin/reenumerate_device: restoring state...");
+    dpriv->in_reenumerate = false;
+    return darwin_restore_state (dev_handle, active_config, claimed_interfaces);
+  }
+
+  usbi_dbg (ctx, "darwin/reenumerate_device: waiting for re-enumeration to complete...");
+
+  struct timespec start;
+  clock_gettime(CLOCK_MONOTONIC, &start);
+
+  while (dpriv->in_reenumerate) {
+    struct timespec delay = {.tv_sec = 0, .tv_nsec = 1000};
+    nanosleep (&delay, NULL);
+
+    struct timespec now;
+    clock_gettime(CLOCK_MONOTONIC, &now);
+    UInt32 elapsed = (now.tv_sec - start.tv_sec) * 1000000 + (now.tv_nsec - start.tv_nsec) / 1000;
+
+    if (elapsed >= DARWIN_REENUMERATE_TIMEOUT_US) {
+      usbi_err (ctx, "darwin/reenumerate_device: timeout waiting for reenumerate");
+      dpriv->in_reenumerate = false;
+      return LIBUSB_ERROR_TIMEOUT;
+    }
+  }
+
+  /* compare descriptors */
+  usbi_dbg (ctx, "darwin/reenumerate_device: checking whether descriptors changed");
+
+  if (memcmp (&descriptor, &dpriv->dev_descriptor, sizeof (descriptor))) {
+    /* device descriptor changed. need to return not found. */
+    usbi_dbg (ctx, "darwin/reenumerate_device: device descriptor changed");
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  for (i = 0 ; i < descriptor.bNumConfigurations ; ++i) {
+    (void) (*(dpriv->device))->GetConfigurationDescriptorPtr (dpriv->device, i, &cached_configuration);
+    if (memcmp (cached_configuration, cached_configurations + i, sizeof (cached_configurations[i]))) {
+      usbi_dbg (ctx, "darwin/reenumerate_device: configuration descriptor %d changed", i);
+      return LIBUSB_ERROR_NOT_FOUND;
+    }
+  }
+
+  usbi_dbg (ctx, "darwin/reenumerate_device: device reset complete. restoring state...");
+
+  return darwin_restore_state (dev_handle, active_config, claimed_interfaces);
+}
+
+static int darwin_reset_device (struct libusb_device_handle *dev_handle) {
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(dev_handle->dev);
+  IOReturn kresult;
+
+  if (dpriv->capture_count > 0) {
+    /* we have to use ResetDevice as USBDeviceReEnumerate() loses the authorization for capture */
+    kresult = (*(dpriv->device))->ResetDevice (dpriv->device);
+    return darwin_to_libusb (kresult);
+  } else {
+    return darwin_reenumerate_device (dev_handle, false);
+  }
+}
+
+static io_service_t usb_find_interface_matching_location (const io_name_t class_name, UInt8 interface_number, UInt32 location) {
+  CFMutableDictionaryRef matchingDict = IOServiceMatching (class_name);
+  CFMutableDictionaryRef propertyMatchDict = CFDictionaryCreateMutable (kCFAllocatorDefault, 0,
+                                                                        &kCFTypeDictionaryKeyCallBacks,
+                                                                        &kCFTypeDictionaryValueCallBacks);
+  CFTypeRef locationCF = CFNumberCreate (NULL, kCFNumberSInt32Type, &location);
+  CFTypeRef interfaceCF =  CFNumberCreate (NULL, kCFNumberSInt8Type, &interface_number);
+
+  CFDictionarySetValue (matchingDict, CFSTR(kIOPropertyMatchKey), propertyMatchDict);
+  CFDictionarySetValue (propertyMatchDict, CFSTR(kUSBDevicePropertyLocationID), locationCF);
+  CFDictionarySetValue (propertyMatchDict, CFSTR(kUSBHostMatchingPropertyInterfaceNumber), interfaceCF);
+
+  CFRelease (interfaceCF);
+  CFRelease (locationCF);
+  CFRelease (propertyMatchDict);
+
+  return IOServiceGetMatchingService (darwin_default_master_port, matchingDict);
+}
+
+static int darwin_kernel_driver_active(struct libusb_device_handle *dev_handle, uint8_t interface) {
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(dev_handle->dev);
+  io_service_t usb_interface, child = IO_OBJECT_NULL;
+
+  /* locate the IO registry entry for this interface */
+  usb_interface = usb_find_interface_matching_location (kIOUSBHostInterfaceClassName, interface, dpriv->location);
+  if (0 == usb_interface) {
+    /* check for the legacy class entry */
+    usb_interface = usb_find_interface_matching_location (kIOUSBInterfaceClassName, interface, dpriv->location);
+    if (0 == usb_interface) {
+      return LIBUSB_ERROR_NOT_FOUND;
+    }
+  }
+
+  /* if the IO object has a child entry in the IO Registry it has a kernel driver attached */
+  (void) IORegistryEntryGetChildEntry (usb_interface, kIOServicePlane, &child);
+  IOObjectRelease (usb_interface);
+  if (IO_OBJECT_NULL != child) {
+    IOObjectRelease (child);
+    return 1;
+  }
+
+  /* no driver */
+  return 0;
+}
+
+static void darwin_destroy_device(struct libusb_device *dev) {
+  struct darwin_device_priv *dpriv = usbi_get_device_priv(dev);
+
+  if (dpriv->dev) {
+    /* need to hold the lock in case this is the last reference to the device */
+    usbi_mutex_lock(&darwin_cached_devices_lock);
+    darwin_deref_cached_device (dpriv->dev);
+    dpriv->dev = NULL;
+    usbi_mutex_unlock(&darwin_cached_devices_lock);
+  }
+}
+
+static int submit_bulk_transfer(struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+  IOReturn               ret;
+  uint8_t                transferType;
+  uint8_t                pipeRef;
+  uint16_t               maxPacketSize;
+
+  struct darwin_interface *cInterface;
+#if InterfaceVersion >= 550
+  IOUSBEndpointProperties pipeProperties = {.bVersion = kUSBEndpointPropertiesVersion3};
+#else
+  /* None of the values below are used in libusb for bulk transfers */
+  uint8_t                 direction, number, interval;
+#endif
+
+  if (ep_to_pipeRef (transfer->dev_handle, transfer->endpoint, &pipeRef, NULL, &cInterface) != 0) {
+    usbi_err (TRANSFER_CTX (transfer), "endpoint not found on any open interface");
+
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+#if InterfaceVersion >= 550
+  ret = (*(cInterface->interface))->GetPipePropertiesV3 (cInterface->interface, pipeRef, &pipeProperties);
+
+  transferType = pipeProperties.bTransferType;
+  maxPacketSize = pipeProperties.wMaxPacketSize;
+#else
+  ret = (*(cInterface->interface))->GetPipeProperties (cInterface->interface, pipeRef, &direction, &number,
+                                                       &transferType, &maxPacketSize, &interval);
+#endif
+
+  if (ret) {
+    usbi_err (TRANSFER_CTX (transfer), "bulk transfer failed (dir = %s): %s (code = 0x%08x)", IS_XFERIN(transfer) ? "In" : "Out",
+              darwin_error_str(ret), ret);
+    return darwin_to_libusb (ret);
+  }
+
+  if (0 != (transfer->length % maxPacketSize)) {
+    /* do not need a zero packet */
+    transfer->flags &= ~LIBUSB_TRANSFER_ADD_ZERO_PACKET;
+  }
+
+  /* submit the request */
+  /* timeouts are unavailable on interrupt endpoints */
+  if (transferType == kUSBInterrupt) {
+    if (IS_XFERIN(transfer))
+      ret = (*(cInterface->interface))->ReadPipeAsync(cInterface->interface, pipeRef, transfer->buffer,
+                                                      (UInt32)transfer->length, darwin_async_io_callback, itransfer);
+    else
+      ret = (*(cInterface->interface))->WritePipeAsync(cInterface->interface, pipeRef, transfer->buffer,
+                                                       (UInt32)transfer->length, darwin_async_io_callback, itransfer);
+  } else {
+    itransfer->timeout_flags |= USBI_TRANSFER_OS_HANDLES_TIMEOUT;
+
+    if (IS_XFERIN(transfer))
+      ret = (*(cInterface->interface))->ReadPipeAsyncTO(cInterface->interface, pipeRef, transfer->buffer,
+                                                        (UInt32)transfer->length, transfer->timeout, transfer->timeout,
+                                                        darwin_async_io_callback, itransfer);
+    else
+      ret = (*(cInterface->interface))->WritePipeAsyncTO(cInterface->interface, pipeRef, transfer->buffer,
+                                                         (UInt32)transfer->length, transfer->timeout, transfer->timeout,
+                                                         darwin_async_io_callback, itransfer);
+  }
+
+  if (ret)
+    usbi_err (TRANSFER_CTX (transfer), "bulk transfer failed (dir = %s): %s (code = 0x%08x)", IS_XFERIN(transfer) ? "In" : "Out",
+               darwin_error_str(ret), ret);
+
+  return darwin_to_libusb (ret);
+}
+
+#if InterfaceVersion >= 550
+static int submit_stream_transfer(struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct darwin_interface *cInterface;
+  uint8_t pipeRef;
+  IOReturn ret;
+
+  if (ep_to_pipeRef (transfer->dev_handle, transfer->endpoint, &pipeRef, NULL, &cInterface) != 0) {
+    usbi_err (TRANSFER_CTX (transfer), "endpoint not found on any open interface");
+
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  itransfer->timeout_flags |= USBI_TRANSFER_OS_HANDLES_TIMEOUT;
+
+  if (IS_XFERIN(transfer))
+    ret = (*(cInterface->interface))->ReadStreamsPipeAsyncTO(cInterface->interface, pipeRef, itransfer->stream_id,
+                                                             transfer->buffer, (UInt32)transfer->length, transfer->timeout,
+                                                             transfer->timeout, darwin_async_io_callback, itransfer);
+  else
+    ret = (*(cInterface->interface))->WriteStreamsPipeAsyncTO(cInterface->interface, pipeRef, itransfer->stream_id,
+                                                              transfer->buffer, (UInt32)transfer->length, transfer->timeout,
+                                                              transfer->timeout, darwin_async_io_callback, itransfer);
+
+  if (ret)
+    usbi_err (TRANSFER_CTX (transfer), "bulk stream transfer failed (dir = %s): %s (code = 0x%08x)", IS_XFERIN(transfer) ? "In" : "Out",
+               darwin_error_str(ret), ret);
+
+  return darwin_to_libusb (ret);
+}
+#endif
+
+static int submit_iso_transfer(struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct darwin_transfer_priv *tpriv = usbi_get_transfer_priv(itransfer);
+
+  IOReturn kresult;
+  uint8_t direction, number, interval, pipeRef, transferType;
+  uint16_t maxPacketSize;
+  UInt64 frame;
+  AbsoluteTime atTime;
+  int i;
+
+  struct darwin_interface *cInterface;
+
+  /* construct an array of IOUSBIsocFrames, reuse the old one if the sizes are the same */
+  if (tpriv->num_iso_packets != transfer->num_iso_packets) {
+    free(tpriv->isoc_framelist);
+    tpriv->isoc_framelist = NULL;
+  }
+
+  if (!tpriv->isoc_framelist) {
+    tpriv->num_iso_packets = transfer->num_iso_packets;
+    tpriv->isoc_framelist = (IOUSBIsocFrame*) calloc ((size_t)transfer->num_iso_packets, sizeof(IOUSBIsocFrame));
+    if (!tpriv->isoc_framelist)
+      return LIBUSB_ERROR_NO_MEM;
+  }
+
+  /* copy the frame list from the libusb descriptor (the structures differ only is member order) */
+  for (i = 0 ; i < transfer->num_iso_packets ; i++) {
+    unsigned int length = transfer->iso_packet_desc[i].length;
+    assert(length <= UINT16_MAX);
+    tpriv->isoc_framelist[i].frReqCount = (UInt16)length;
+  }
+
+  /* determine the interface/endpoint to use */
+  if (ep_to_pipeRef (transfer->dev_handle, transfer->endpoint, &pipeRef, NULL, &cInterface) != 0) {
+    usbi_err (TRANSFER_CTX (transfer), "endpoint not found on any open interface");
+
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  /* determine the properties of this endpoint and the speed of the device */
+  (*(cInterface->interface))->GetPipeProperties (cInterface->interface, pipeRef, &direction, &number,
+                                                 &transferType, &maxPacketSize, &interval);
+
+  /* Last but not least we need the bus frame number */
+  kresult = (*(cInterface->interface))->GetBusFrameNumber(cInterface->interface, &frame, &atTime);
+  if (kresult != kIOReturnSuccess) {
+    usbi_err (TRANSFER_CTX (transfer), "failed to get bus frame number: %d", kresult);
+    free(tpriv->isoc_framelist);
+    tpriv->isoc_framelist = NULL;
+
+    return darwin_to_libusb (kresult);
+  }
+
+  (*(cInterface->interface))->GetPipeProperties (cInterface->interface, pipeRef, &direction, &number,
+                                                 &transferType, &maxPacketSize, &interval);
+
+  /* schedule for a frame a little in the future */
+  frame += 4;
+
+  if (cInterface->frames[transfer->endpoint] && frame < cInterface->frames[transfer->endpoint])
+    frame = cInterface->frames[transfer->endpoint];
+
+  /* submit the request */
+  if (IS_XFERIN(transfer))
+    kresult = (*(cInterface->interface))->ReadIsochPipeAsync(cInterface->interface, pipeRef, transfer->buffer, frame,
+                                                             (UInt32)transfer->num_iso_packets, tpriv->isoc_framelist, darwin_async_io_callback,
+                                                             itransfer);
+  else
+    kresult = (*(cInterface->interface))->WriteIsochPipeAsync(cInterface->interface, pipeRef, transfer->buffer, frame,
+                                                              (UInt32)transfer->num_iso_packets, tpriv->isoc_framelist, darwin_async_io_callback,
+                                                              itransfer);
+
+  if (LIBUSB_SPEED_FULL == transfer->dev_handle->dev->speed)
+    /* Full speed */
+    cInterface->frames[transfer->endpoint] = frame + (UInt32)transfer->num_iso_packets * (1U << (interval - 1));
+  else
+    /* High/super speed */
+    cInterface->frames[transfer->endpoint] = frame + (UInt32)transfer->num_iso_packets * (1U << (interval - 1)) / 8;
+
+  if (kresult != kIOReturnSuccess) {
+    usbi_err (TRANSFER_CTX (transfer), "isochronous transfer failed (dir: %s): %s", IS_XFERIN(transfer) ? "In" : "Out",
+               darwin_error_str(kresult));
+    free (tpriv->isoc_framelist);
+    tpriv->isoc_framelist = NULL;
+  }
+
+  return darwin_to_libusb (kresult);
+}
+
+static int submit_control_transfer(struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct libusb_control_setup *setup = (struct libusb_control_setup *) transfer->buffer;
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(transfer->dev_handle->dev);
+  struct darwin_transfer_priv *tpriv = usbi_get_transfer_priv(itransfer);
+
+  IOReturn               kresult;
+
+  memset(&tpriv->req, 0, sizeof(tpriv->req));
+
+  /* IOUSBDeviceInterface expects the request in cpu endianness */
+  tpriv->req.bmRequestType     = setup->bmRequestType;
+  tpriv->req.bRequest          = setup->bRequest;
+  /* these values should be in bus order from libusb_fill_control_setup */
+  tpriv->req.wValue            = OSSwapLittleToHostInt16 (setup->wValue);
+  tpriv->req.wIndex            = OSSwapLittleToHostInt16 (setup->wIndex);
+  tpriv->req.wLength           = OSSwapLittleToHostInt16 (setup->wLength);
+  /* data is stored after the libusb control block */
+  tpriv->req.pData             = transfer->buffer + LIBUSB_CONTROL_SETUP_SIZE;
+  tpriv->req.completionTimeout = transfer->timeout;
+  tpriv->req.noDataTimeout     = transfer->timeout;
+
+  itransfer->timeout_flags |= USBI_TRANSFER_OS_HANDLES_TIMEOUT;
+
+  /* all transfers in libusb-1.0 are async */
+
+  if (transfer->endpoint) {
+    struct darwin_interface *cInterface;
+    uint8_t                 pipeRef;
+
+    if (ep_to_pipeRef (transfer->dev_handle, transfer->endpoint, &pipeRef, NULL, &cInterface) != 0) {
+      usbi_err (TRANSFER_CTX (transfer), "endpoint not found on any open interface");
+
+      return LIBUSB_ERROR_NOT_FOUND;
+    }
+
+    kresult = (*(cInterface->interface))->ControlRequestAsyncTO (cInterface->interface, pipeRef, &(tpriv->req), darwin_async_io_callback, itransfer);
+  } else
+    /* control request on endpoint 0 */
+    kresult = (*(dpriv->device))->DeviceRequestAsyncTO(dpriv->device, &(tpriv->req), darwin_async_io_callback, itransfer);
+
+  if (kresult != kIOReturnSuccess)
+    usbi_err (TRANSFER_CTX (transfer), "control request failed: %s", darwin_error_str(kresult));
+
+  return darwin_to_libusb (kresult);
+}
+
+static int darwin_submit_transfer(struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+  switch (transfer->type) {
+  case LIBUSB_TRANSFER_TYPE_CONTROL:
+    return submit_control_transfer(itransfer);
+  case LIBUSB_TRANSFER_TYPE_BULK:
+  case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+    return submit_bulk_transfer(itransfer);
+  case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+    return submit_iso_transfer(itransfer);
+  case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
+#if InterfaceVersion >= 550
+    return submit_stream_transfer(itransfer);
+#else
+    usbi_err (TRANSFER_CTX(transfer), "IOUSBFamily version does not support bulk stream transfers");
+    return LIBUSB_ERROR_NOT_SUPPORTED;
+#endif
+  default:
+    usbi_err (TRANSFER_CTX(transfer), "unknown endpoint type %d", transfer->type);
+    return LIBUSB_ERROR_INVALID_PARAM;
+  }
+}
+
+static int cancel_control_transfer(struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(transfer->dev_handle->dev);
+  IOReturn kresult;
+
+  usbi_warn (ITRANSFER_CTX (itransfer), "aborting all transactions control pipe");
+
+  if (!dpriv->device)
+    return LIBUSB_ERROR_NO_DEVICE;
+
+  kresult = (*(dpriv->device))->USBDeviceAbortPipeZero (dpriv->device);
+
+  return darwin_to_libusb (kresult);
+}
+
+static int darwin_abort_transfers (struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(transfer->dev_handle->dev);
+  struct darwin_interface *cInterface;
+  uint8_t pipeRef, iface;
+  IOReturn kresult;
+
+  struct libusb_context *ctx = ITRANSFER_CTX (itransfer);
+
+  if (ep_to_pipeRef (transfer->dev_handle, transfer->endpoint, &pipeRef, &iface, &cInterface) != 0) {
+    usbi_err (ctx, "endpoint not found on any open interface");
+
+    return LIBUSB_ERROR_NOT_FOUND;
+  }
+
+  if (!dpriv->device)
+    return LIBUSB_ERROR_NO_DEVICE;
+
+  usbi_warn (ctx, "aborting all transactions on interface %d pipe %d", iface, pipeRef);
+
+  /* abort transactions */
+#if InterfaceVersion >= 550
+  if (LIBUSB_TRANSFER_TYPE_BULK_STREAM == transfer->type)
+    (*(cInterface->interface))->AbortStreamsPipe (cInterface->interface, pipeRef, itransfer->stream_id);
+  else
+#endif
+    (*(cInterface->interface))->AbortPipe (cInterface->interface, pipeRef);
+
+  usbi_dbg (ctx, "calling clear pipe stall to clear the data toggle bit");
+
+  /* newer versions of darwin support clearing additional bits on the device's endpoint */
+  kresult = (*(cInterface->interface))->ClearPipeStallBothEnds(cInterface->interface, pipeRef);
+
+  return darwin_to_libusb (kresult);
+}
+
+static int darwin_cancel_transfer(struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+  switch (transfer->type) {
+  case LIBUSB_TRANSFER_TYPE_CONTROL:
+    return cancel_control_transfer(itransfer);
+  case LIBUSB_TRANSFER_TYPE_BULK:
+  case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+  case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+    return darwin_abort_transfers (itransfer);
+  default:
+    usbi_err (TRANSFER_CTX(transfer), "unknown endpoint type %d", transfer->type);
+    return LIBUSB_ERROR_INVALID_PARAM;
+  }
+}
+
+static void darwin_async_io_callback (void *refcon, IOReturn result, void *arg0) {
+  struct usbi_transfer *itransfer = (struct usbi_transfer *)refcon;
+  struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct darwin_transfer_priv *tpriv = usbi_get_transfer_priv(itransfer);
+
+  usbi_dbg (TRANSFER_CTX(transfer), "an async io operation has completed");
+
+  /* if requested write a zero packet */
+  if (kIOReturnSuccess == result && IS_XFEROUT(transfer) && transfer->flags & LIBUSB_TRANSFER_ADD_ZERO_PACKET) {
+    struct darwin_interface *cInterface;
+    uint8_t pipeRef;
+
+    (void) ep_to_pipeRef (transfer->dev_handle, transfer->endpoint, &pipeRef, NULL, &cInterface);
+
+    (*(cInterface->interface))->WritePipe (cInterface->interface, pipeRef, transfer->buffer, 0);
+  }
+
+  tpriv->result = result;
+  tpriv->size = (UInt32) (uintptr_t) arg0;
+
+  /* signal the core that this transfer is complete */
+  usbi_signal_transfer_completion(itransfer);
+}
+
+static enum libusb_transfer_status darwin_transfer_status (struct usbi_transfer *itransfer, IOReturn result) {
+  if (itransfer->timeout_flags & USBI_TRANSFER_TIMED_OUT)
+    result = kIOUSBTransactionTimeout;
+
+  struct libusb_context *ctx = ITRANSFER_CTX (itransfer);
+
+  switch (result) {
+  case kIOReturnUnderrun:
+  case kIOReturnSuccess:
+    return LIBUSB_TRANSFER_COMPLETED;
+  case kIOReturnAborted:
+    return LIBUSB_TRANSFER_CANCELLED;
+  case kIOUSBPipeStalled:
+    usbi_dbg (ctx, "transfer error: pipe is stalled");
+    return LIBUSB_TRANSFER_STALL;
+  case kIOReturnOverrun:
+    usbi_warn (ctx, "transfer error: data overrun");
+    return LIBUSB_TRANSFER_OVERFLOW;
+  case kIOUSBTransactionTimeout:
+    usbi_warn (ctx, "transfer error: timed out");
+    itransfer->timeout_flags |= USBI_TRANSFER_TIMED_OUT;
+    return LIBUSB_TRANSFER_TIMED_OUT;
+  default:
+    usbi_warn (ctx, "transfer error: %s (value = 0x%08x)", darwin_error_str (result), result);
+    return LIBUSB_TRANSFER_ERROR;
+  }
+}
+
+static int darwin_handle_transfer_completion (struct usbi_transfer *itransfer) {
+  struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+  struct darwin_transfer_priv *tpriv = usbi_get_transfer_priv(itransfer);
+  const unsigned char max_transfer_type = LIBUSB_TRANSFER_TYPE_BULK_STREAM;
+  const char *transfer_types[] = {"control", "isoc", "bulk", "interrupt", "bulk-stream", NULL};
+  bool is_isoc = LIBUSB_TRANSFER_TYPE_ISOCHRONOUS == transfer->type;
+  struct libusb_context *ctx = ITRANSFER_CTX (itransfer);
+
+  if (transfer->type > max_transfer_type) {
+    usbi_err (ctx, "unknown endpoint type %d", transfer->type);
+    return LIBUSB_ERROR_INVALID_PARAM;
+  }
+
+  if (NULL == tpriv) {
+    usbi_err (ctx, "malformed request is missing transfer priv");
+    return LIBUSB_ERROR_INVALID_PARAM;
+  }
+
+  usbi_dbg (ctx, "handling transfer completion type %s with kernel status %d", transfer_types[transfer->type], tpriv->result);
+
+  if (kIOReturnSuccess == tpriv->result || kIOReturnUnderrun == tpriv->result || kIOUSBTransactionTimeout == tpriv->result) {
+    if (is_isoc && tpriv->isoc_framelist) {
+      /* copy isochronous results back */
+
+      for (int i = 0; i < transfer->num_iso_packets ; i++) {
+        struct libusb_iso_packet_descriptor *lib_desc = &transfer->iso_packet_desc[i];
+        lib_desc->status = darwin_transfer_status (itransfer, tpriv->isoc_framelist[i].frStatus);
+        lib_desc->actual_length = tpriv->isoc_framelist[i].frActCount;
+      }
+    } else if (!is_isoc) {
+      itransfer->transferred += tpriv->size;
+    }
+  }
+
+  /* it is ok to handle cancelled transfers without calling usbi_handle_transfer_cancellation (we catch timeout transfers) */
+  return usbi_handle_transfer_completion (itransfer, darwin_transfer_status (itransfer, tpriv->result));
+}
+
+#if !defined(HAVE_CLOCK_GETTIME)
+void usbi_get_monotonic_time(struct timespec *tp) {
+  mach_timespec_t sys_time;
+
+  /* use system boot time as reference for the monotonic clock */
+  clock_get_time (clock_monotonic, &sys_time);
+
+  tp->tv_sec  = sys_time.tv_sec;
+  tp->tv_nsec = sys_time.tv_nsec;
+}
+
+void usbi_get_real_time(struct timespec *tp) {
+  mach_timespec_t sys_time;
+
+  /* CLOCK_REALTIME represents time since the epoch */
+  clock_get_time (clock_realtime, &sys_time);
+
+  tp->tv_sec  = sys_time.tv_sec;
+  tp->tv_nsec = sys_time.tv_nsec;
+}
+#endif
+
+#if InterfaceVersion >= 550
+static int darwin_alloc_streams (struct libusb_device_handle *dev_handle, uint32_t num_streams, unsigned char *endpoints,
+                                 int num_endpoints) {
+  struct darwin_interface *cInterface;
+  UInt32 supportsStreams;
+  uint8_t pipeRef;
+  int rc, i;
+
+  /* find the minimum number of supported streams on the endpoint list */
+  for (i = 0 ; i < num_endpoints ; ++i) {
+    if (0 != (rc = ep_to_pipeRef (dev_handle, endpoints[i], &pipeRef, NULL, &cInterface))) {
+      return rc;
+    }
+
+    (*(cInterface->interface))->SupportsStreams (cInterface->interface, pipeRef, &supportsStreams);
+    if (num_streams > supportsStreams)
+      num_streams = supportsStreams;
+  }
+
+  /* it is an error if any endpoint in endpoints does not support streams */
+  if (0 == num_streams)
+    return LIBUSB_ERROR_INVALID_PARAM;
+
+  /* create the streams */
+  for (i = 0 ; i < num_endpoints ; ++i) {
+    (void) ep_to_pipeRef (dev_handle, endpoints[i], &pipeRef, NULL, &cInterface);
+
+    rc = (*(cInterface->interface))->CreateStreams (cInterface->interface, pipeRef, num_streams);
+    if (kIOReturnSuccess != rc)
+      return darwin_to_libusb(rc);
+  }
+
+  assert(num_streams <= INT_MAX);
+  return (int)num_streams;
+}
+
+static int darwin_free_streams (struct libusb_device_handle *dev_handle, unsigned char *endpoints, int num_endpoints) {
+  struct darwin_interface *cInterface;
+  UInt32 supportsStreams;
+  uint8_t pipeRef;
+  int rc;
+
+  for (int i = 0 ; i < num_endpoints ; ++i) {
+    if (0 != (rc = ep_to_pipeRef (dev_handle, endpoints[i], &pipeRef, NULL, &cInterface)))
+      return rc;
+
+    (*(cInterface->interface))->SupportsStreams (cInterface->interface, pipeRef, &supportsStreams);
+    if (0 == supportsStreams)
+      return LIBUSB_ERROR_INVALID_PARAM;
+
+    rc = (*(cInterface->interface))->CreateStreams (cInterface->interface, pipeRef, 0);
+    if (kIOReturnSuccess != rc)
+      return darwin_to_libusb(rc);
+  }
+
+  return LIBUSB_SUCCESS;
+}
+#endif
+
+#if InterfaceVersion >= 700
+
+/* macOS APIs for getting entitlement values */
+
+#if TARGET_OS_OSX
+#include <Security/Security.h>
+#else
+typedef struct __SecTask *SecTaskRef;
+extern SecTaskRef SecTaskCreateFromSelf(CFAllocatorRef allocator);
+extern CFTypeRef SecTaskCopyValueForEntitlement(SecTaskRef task, CFStringRef entitlement, CFErrorRef *error);
+#endif
+
+static bool darwin_has_capture_entitlements (void) {
+  SecTaskRef task;
+  CFTypeRef value;
+  bool entitled;
+
+  task = SecTaskCreateFromSelf (kCFAllocatorDefault);
+  if (task == NULL) {
+    return false;
+  }
+  value = SecTaskCopyValueForEntitlement(task, CFSTR("com.apple.vm.device-access"), NULL);
+  CFRelease (task);
+  entitled = value && (CFGetTypeID (value) == CFBooleanGetTypeID ()) && CFBooleanGetValue (value);
+  if (value) {
+    CFRelease (value);
+  }
+  return entitled;
+}
+
+static int darwin_reload_device (struct libusb_device_handle *dev_handle) {
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(dev_handle->dev);
+  enum libusb_error err;
+
+  usbi_mutex_lock(&darwin_cached_devices_lock);
+  (*(dpriv->device))->Release(dpriv->device);
+  dpriv->device = darwin_device_from_service (HANDLE_CTX (dev_handle), dpriv->service);
+  if (!dpriv->device) {
+    err = LIBUSB_ERROR_NO_DEVICE;
+  } else {
+    err = LIBUSB_SUCCESS;
+  }
+  usbi_mutex_unlock(&darwin_cached_devices_lock);
+
+  return err;
+}
+
+/* On macOS, we capture an entire device at once, not individual interfaces. */
+
+static int darwin_detach_kernel_driver (struct libusb_device_handle *dev_handle, uint8_t interface) {
+  UNUSED(interface);
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(dev_handle->dev);
+  IOReturn kresult;
+  enum libusb_error err;
+  struct libusb_context *ctx = HANDLE_CTX (dev_handle);
+
+  if (HAS_CAPTURE_DEVICE()) {
+  } else {
+    return LIBUSB_ERROR_NOT_SUPPORTED;
+  }
+
+  if (dpriv->capture_count == 0) {
+    usbi_dbg (ctx, "attempting to detach kernel driver from device");
+
+    if (darwin_has_capture_entitlements ()) {
+      /* request authorization */
+      kresult = IOServiceAuthorize (dpriv->service, kIOServiceInteractionAllowed);
+      if (kresult != kIOReturnSuccess) {
+        usbi_warn (ctx, "IOServiceAuthorize: %s", darwin_error_str(kresult));
+        return darwin_to_libusb (kresult);
+      }
+
+      /* we need start() to be called again for authorization status to refresh */
+      err = darwin_reload_device (dev_handle);
+      if (err != LIBUSB_SUCCESS) {
+        return err;
+      }
+    } else {
+      usbi_info (ctx, "no capture entitlements. may not be able to detach the kernel driver for this device");
+      if (0 != geteuid()) {
+        usbi_warn (ctx, "USB device capture requires either an entitlement (com.apple.vm.device-access) or root privilege");
+        return LIBUSB_ERROR_ACCESS;
+      }
+    }
+
+    /* reset device to release existing drivers */
+    err = darwin_reenumerate_device (dev_handle, true);
+    if (err != LIBUSB_SUCCESS) {
+      return err;
+    }
+  }
+  dpriv->capture_count++;
+  return LIBUSB_SUCCESS;
+}
+
+
+static int darwin_attach_kernel_driver (struct libusb_device_handle *dev_handle, uint8_t interface) {
+  UNUSED(interface);
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(dev_handle->dev);
+
+  if (HAS_CAPTURE_DEVICE()) {
+  } else {
+    return LIBUSB_ERROR_NOT_SUPPORTED;
+  }
+
+  dpriv->capture_count--;
+  if (dpriv->capture_count > 0) {
+    return LIBUSB_SUCCESS;
+  }
+
+  usbi_dbg (HANDLE_CTX (dev_handle), "reenumerating device for kernel driver attach");
+
+  /* reset device to attach kernel drivers */
+  return darwin_reenumerate_device (dev_handle, false);
+}
+
+static int darwin_capture_claim_interface(struct libusb_device_handle *dev_handle, uint8_t iface) {
+  enum libusb_error ret;
+  if (dev_handle->auto_detach_kernel_driver && darwin_kernel_driver_active(dev_handle, iface)) {
+    ret = darwin_detach_kernel_driver (dev_handle, iface);
+    if (ret != LIBUSB_SUCCESS) {
+      usbi_info (HANDLE_CTX (dev_handle), "failed to auto-detach the kernel driver for this device, ret=%d", ret);
+    }
+  }
+
+  return darwin_claim_interface (dev_handle, iface);
+}
+
+static int darwin_capture_release_interface(struct libusb_device_handle *dev_handle, uint8_t iface) {
+  enum libusb_error ret;
+  struct darwin_cached_device *dpriv = DARWIN_CACHED_DEVICE(dev_handle->dev);
+
+  ret = darwin_release_interface (dev_handle, iface);
+  if (ret != LIBUSB_SUCCESS) {
+    return ret;
+  }
+
+  if (dev_handle->auto_detach_kernel_driver && dpriv->capture_count > 0) {
+    ret = darwin_attach_kernel_driver (dev_handle, iface);
+    if (LIBUSB_SUCCESS != ret) {
+      usbi_info (HANDLE_CTX (dev_handle), "on attempt to reattach the kernel driver got ret=%d", ret);
+    }
+    /* ignore the error as the interface was successfully released */
+  }
+
+  return LIBUSB_SUCCESS;
+}
+
+#endif
+
+const struct usbi_os_backend usbi_backend = {
+        .name = "Darwin",
+        .caps = USBI_CAP_SUPPORTS_DETACH_KERNEL_DRIVER,
+        .init = darwin_init,
+        .exit = darwin_exit,
+        .get_active_config_descriptor = darwin_get_active_config_descriptor,
+        .get_config_descriptor = darwin_get_config_descriptor,
+        .hotplug_poll = darwin_hotplug_poll,
+
+        .open = darwin_open,
+        .close = darwin_close,
+        .get_configuration = darwin_get_configuration,
+        .set_configuration = darwin_set_configuration,
+
+        .set_interface_altsetting = darwin_set_interface_altsetting,
+        .clear_halt = darwin_clear_halt,
+        .reset_device = darwin_reset_device,
+
+#if InterfaceVersion >= 550
+        .alloc_streams = darwin_alloc_streams,
+        .free_streams = darwin_free_streams,
+#endif
+
+        .kernel_driver_active = darwin_kernel_driver_active,
+
+#if InterfaceVersion >= 700
+        .detach_kernel_driver = darwin_detach_kernel_driver,
+        .attach_kernel_driver = darwin_attach_kernel_driver,
+        .claim_interface = darwin_capture_claim_interface,
+        .release_interface = darwin_capture_release_interface,
+#else
+        .claim_interface = darwin_claim_interface,
+        .release_interface = darwin_release_interface,
+#endif
+
+        .destroy_device = darwin_destroy_device,
+
+        .submit_transfer = darwin_submit_transfer,
+        .cancel_transfer = darwin_cancel_transfer,
+
+        .handle_transfer_completion = darwin_handle_transfer_completion,
+
+        .device_priv_size = sizeof(struct darwin_device_priv),
+        .device_handle_priv_size = sizeof(struct darwin_device_handle_priv),
+        .transfer_priv_size = sizeof(struct darwin_transfer_priv),
+};
diff --git a/src/os/darwin_usb.h b/src/os/darwin_usb.h
new file mode 100644
index 0000000..7b72fff
--- /dev/null
+++ b/src/os/darwin_usb.h
@@ -0,0 +1,227 @@
+/*
+ * darwin backend for libusb 1.0
+ * Copyright © 2008-2019 Nathan Hjelm <hjelmn@users.sourceforge.net>
+ * Copyright © 2019      Google LLC. All rights reserved.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#if !defined(LIBUSB_DARWIN_H)
+#define LIBUSB_DARWIN_H
+
+#include <stdbool.h>
+
+#include "libusbi.h"
+
+#include <IOKit/IOTypes.h>
+#include <IOKit/IOCFBundle.h>
+#include <IOKit/usb/IOUSBLib.h>
+#include <IOKit/IOCFPlugIn.h>
+
+#if defined(HAVE_IOKIT_USB_IOUSBHOSTFAMILYDEFINITIONS_H)
+#include <IOKit/usb/IOUSBHostFamilyDefinitions.h>
+#endif
+
+/* IOUSBInterfaceInferface */
+
+/* New in OS 10.12.0. */
+#if defined (kIOUSBInterfaceInterfaceID800)
+
+#define usb_interface_t IOUSBInterfaceInterface800
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID800
+#define InterfaceVersion 800
+
+/* New in OS 10.10.0. */
+#elif defined (kIOUSBInterfaceInterfaceID700)
+
+#define usb_interface_t IOUSBInterfaceInterface700
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID700
+#define InterfaceVersion 700
+
+/* New in OS 10.9.0. */
+#elif defined (kIOUSBInterfaceInterfaceID650)
+
+#define usb_interface_t IOUSBInterfaceInterface650
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID650
+#define InterfaceVersion 650
+
+/* New in OS 10.8.2 but can't test deployment target to that granularity, so round up. */
+#elif defined (kIOUSBInterfaceInterfaceID550)
+
+#define usb_interface_t IOUSBInterfaceInterface550
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID550
+#define InterfaceVersion 550
+
+/* New in OS 10.7.3 but can't test deployment target to that granularity, so round up. */
+#elif defined (kIOUSBInterfaceInterfaceID500)
+
+#define usb_interface_t IOUSBInterfaceInterface500
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID500
+#define InterfaceVersion 500
+
+/* New in OS 10.5.0. */
+#elif defined (kIOUSBInterfaceInterfaceID300)
+
+#define usb_interface_t IOUSBInterfaceInterface300
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID300
+#define InterfaceVersion 300
+
+/* New in OS 10.4.5 (or 10.4.6?) but can't test deployment target to that granularity, so round up. */
+#elif defined (kIOUSBInterfaceInterfaceID245)
+
+#define usb_interface_t IOUSBInterfaceInterface245
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID245
+#define InterfaceVersion 245
+
+/* New in OS 10.4.0. */
+#elif defined (kIOUSBInterfaceInterfaceID220)
+
+#define usb_interface_t IOUSBInterfaceInterface220
+#define InterfaceInterfaceID kIOUSBInterfaceInterfaceID220
+#define InterfaceVersion 220
+
+#else
+
+#error "IOUSBFamily is too old. Please upgrade your SDK and/or deployment target"
+
+#endif
+
+/* IOUSBDeviceInterface */
+
+/* New in OS 10.9.0. */
+#if defined (kIOUSBDeviceInterfaceID650)
+
+#define usb_device_t    IOUSBDeviceInterface650
+#define DeviceInterfaceID kIOUSBDeviceInterfaceID650
+#define DeviceVersion 650
+
+/* New in OS 10.7.3 but can't test deployment target to that granularity, so round up. */
+#elif defined (kIOUSBDeviceInterfaceID500)
+
+#define usb_device_t    IOUSBDeviceInterface500
+#define DeviceInterfaceID kIOUSBDeviceInterfaceID500
+#define DeviceVersion 500
+
+/* New in OS 10.5.4 but can't test deployment target to that granularity, so round up. */
+#elif defined (kIOUSBDeviceInterfaceID320)
+
+#define usb_device_t    IOUSBDeviceInterface320
+#define DeviceInterfaceID kIOUSBDeviceInterfaceID320
+#define DeviceVersion 320
+
+/* New in OS 10.5.0. */
+#elif defined (kIOUSBDeviceInterfaceID300)
+
+#define usb_device_t    IOUSBDeviceInterface300
+#define DeviceInterfaceID kIOUSBDeviceInterfaceID300
+#define DeviceVersion 300
+
+/* New in OS 10.4.5 (or 10.4.6?) but can't test deployment target to that granularity, so round up. */
+#elif defined (kIOUSBDeviceInterfaceID245)
+
+#define usb_device_t    IOUSBDeviceInterface245
+#define DeviceInterfaceID kIOUSBDeviceInterfaceID245
+#define DeviceVersion 245
+
+/* New in OS 10.2.3 but can't test deployment target to that granularity, so round up. */
+#elif defined (kIOUSBDeviceInterfaceID197)
+
+#define usb_device_t    IOUSBDeviceInterface197
+#define DeviceInterfaceID kIOUSBDeviceInterfaceID197
+#define DeviceVersion 197
+
+#else
+
+#error "IOUSBFamily is too old. Please upgrade your SDK and/or deployment target"
+
+#endif
+
+#if !defined(kIOUSBHostInterfaceClassName)
+#define kIOUSBHostInterfaceClassName "IOUSBHostInterface"
+#endif
+
+#if !defined(kUSBHostMatchingPropertyInterfaceNumber)
+#define kUSBHostMatchingPropertyInterfaceNumber "bInterfaceNumber"
+#endif
+
+#if !defined(IO_OBJECT_NULL)
+#define IO_OBJECT_NULL ((io_object_t) 0)
+#endif
+
+/* Testing availability */
+#ifndef __has_builtin
+  #define __has_builtin(x) 0  // Compatibility with non-clang compilers.
+#endif
+#if __has_builtin(__builtin_available)
+  #define HAS_CAPTURE_DEVICE() __builtin_available(macOS 10.10, *)
+#else
+  #define HAS_CAPTURE_DEVICE() 0
+#endif
+
+typedef IOCFPlugInInterface *io_cf_plugin_ref_t;
+typedef IONotificationPortRef io_notification_port_t;
+
+/* private structures */
+struct darwin_cached_device {
+  struct list_head      list;
+  IOUSBDeviceDescriptor dev_descriptor;
+  UInt32                location;
+  UInt64                parent_session;
+  UInt64                session;
+  USBDeviceAddress      address;
+  char                  sys_path[21];
+  usb_device_t        **device;
+  io_service_t          service;
+  int                   open_count;
+  UInt8                 first_config, active_config, port;
+  int                   can_enumerate;
+  int                   refcount;
+  bool                  in_reenumerate;
+  int                   capture_count;
+};
+
+struct darwin_device_priv {
+  struct darwin_cached_device *dev;
+};
+
+struct darwin_device_handle_priv {
+  bool                 is_open;
+  CFRunLoopSourceRef   cfSource;
+
+  struct darwin_interface {
+    usb_interface_t    **interface;
+    uint8_t              num_endpoints;
+    CFRunLoopSourceRef   cfSource;
+    uint64_t             frames[256];
+    uint8_t              endpoint_addrs[USB_MAXENDPOINTS];
+  } interfaces[USB_MAXINTERFACES];
+};
+
+struct darwin_transfer_priv {
+  /* Isoc */
+  IOUSBIsocFrame *isoc_framelist;
+  int num_iso_packets;
+
+  /* Control */
+  IOUSBDevRequestTO req;
+
+  /* Bulk */
+
+  /* Completion status */
+  IOReturn result;
+  UInt32 size;
+};
+
+#endif
diff --git a/src/os/events_posix.c b/src/os/events_posix.c
new file mode 100644
index 0000000..715a2d5
--- /dev/null
+++ b/src/os/events_posix.c
@@ -0,0 +1,300 @@
+/*
+ * libusb event abstraction on POSIX platforms
+ *
+ * Copyright © 2020 Chris Dickens <christopher.a.dickens@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "libusbi.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#ifdef HAVE_EVENTFD
+#include <sys/eventfd.h>
+#endif
+#ifdef HAVE_TIMERFD
+#include <sys/timerfd.h>
+#endif
+#include <unistd.h>
+
+#ifdef HAVE_EVENTFD
+#define EVENT_READ_FD(e)	((e)->eventfd)
+#define EVENT_WRITE_FD(e)	((e)->eventfd)
+#else
+#define EVENT_READ_FD(e)	((e)->pipefd[0])
+#define EVENT_WRITE_FD(e)	((e)->pipefd[1])
+#endif
+
+#ifdef HAVE_NFDS_T
+typedef nfds_t usbi_nfds_t;
+#else
+typedef unsigned int usbi_nfds_t;
+#endif
+
+int usbi_create_event(usbi_event_t *event)
+{
+#ifdef HAVE_EVENTFD
+	event->eventfd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
+	if (event->eventfd == -1) {
+		usbi_err(NULL, "failed to create eventfd, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+#else
+#if defined(HAVE_PIPE2)
+	int ret = pipe2(event->pipefd, O_CLOEXEC);
+#else
+	int ret = pipe(event->pipefd);
+#endif
+
+	if (ret != 0) {
+		usbi_err(NULL, "failed to create pipe, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+#if !defined(HAVE_PIPE2) && defined(FD_CLOEXEC)
+	ret = fcntl(event->pipefd[0], F_GETFD);
+	if (ret == -1) {
+		usbi_err(NULL, "failed to get pipe fd flags, errno=%d", errno);
+		goto err_close_pipe;
+	}
+	ret = fcntl(event->pipefd[0], F_SETFD, ret | FD_CLOEXEC);
+	if (ret == -1) {
+		usbi_err(NULL, "failed to set pipe fd flags, errno=%d", errno);
+		goto err_close_pipe;
+	}
+
+	ret = fcntl(event->pipefd[1], F_GETFD);
+	if (ret == -1) {
+		usbi_err(NULL, "failed to get pipe fd flags, errno=%d", errno);
+		goto err_close_pipe;
+	}
+	ret = fcntl(event->pipefd[1], F_SETFD, ret | FD_CLOEXEC);
+	if (ret == -1) {
+		usbi_err(NULL, "failed to set pipe fd flags, errno=%d", errno);
+		goto err_close_pipe;
+	}
+#endif
+
+	ret = fcntl(event->pipefd[1], F_GETFL);
+	if (ret == -1) {
+		usbi_err(NULL, "failed to get pipe fd status flags, errno=%d", errno);
+		goto err_close_pipe;
+	}
+	ret = fcntl(event->pipefd[1], F_SETFL, ret | O_NONBLOCK);
+	if (ret == -1) {
+		usbi_err(NULL, "failed to set pipe fd status flags, errno=%d", errno);
+		goto err_close_pipe;
+	}
+
+	return 0;
+
+err_close_pipe:
+	close(event->pipefd[1]);
+	close(event->pipefd[0]);
+	return LIBUSB_ERROR_OTHER;
+#endif
+}
+
+void usbi_destroy_event(usbi_event_t *event)
+{
+#ifdef HAVE_EVENTFD
+	if (close(event->eventfd) == -1)
+		usbi_warn(NULL, "failed to close eventfd, errno=%d", errno);
+#else
+	if (close(event->pipefd[1]) == -1)
+		usbi_warn(NULL, "failed to close pipe write end, errno=%d", errno);
+	if (close(event->pipefd[0]) == -1)
+		usbi_warn(NULL, "failed to close pipe read end, errno=%d", errno);
+#endif
+}
+
+void usbi_signal_event(usbi_event_t *event)
+{
+	uint64_t dummy = 1;
+	ssize_t r;
+
+	r = write(EVENT_WRITE_FD(event), &dummy, sizeof(dummy));
+	if (r != sizeof(dummy))
+		usbi_warn(NULL, "event write failed");
+}
+
+void usbi_clear_event(usbi_event_t *event)
+{
+	uint64_t dummy;
+	ssize_t r;
+
+	r = read(EVENT_READ_FD(event), &dummy, sizeof(dummy));
+	if (r != sizeof(dummy))
+		usbi_warn(NULL, "event read failed");
+}
+
+#ifdef HAVE_TIMERFD
+int usbi_create_timer(usbi_timer_t *timer)
+{
+	timer->timerfd = timerfd_create(CLOCK_MONOTONIC, TFD_NONBLOCK | TFD_CLOEXEC);
+	if (timer->timerfd == -1) {
+		usbi_warn(NULL, "failed to create timerfd, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+void usbi_destroy_timer(usbi_timer_t *timer)
+{
+	if (close(timer->timerfd) == -1)
+		usbi_warn(NULL, "failed to close timerfd, errno=%d", errno);
+}
+
+int usbi_arm_timer(usbi_timer_t *timer, const struct timespec *timeout)
+{
+	const struct itimerspec it = { { 0, 0 }, { timeout->tv_sec, timeout->tv_nsec } };
+
+	if (timerfd_settime(timer->timerfd, TFD_TIMER_ABSTIME, &it, NULL) == -1) {
+		usbi_warn(NULL, "failed to arm timerfd, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+int usbi_disarm_timer(usbi_timer_t *timer)
+{
+	const struct itimerspec it = { { 0, 0 }, { 0, 0 } };
+
+	if (timerfd_settime(timer->timerfd, 0, &it, NULL) == -1) {
+		usbi_warn(NULL, "failed to disarm timerfd, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+#endif
+
+int usbi_alloc_event_data(struct libusb_context *ctx)
+{
+	struct usbi_event_source *ievent_source;
+	struct pollfd *fds;
+	size_t i = 0;
+
+	if (ctx->event_data) {
+		free(ctx->event_data);
+		ctx->event_data = NULL;
+	}
+
+	ctx->event_data_cnt = 0;
+	for_each_event_source(ctx, ievent_source)
+		ctx->event_data_cnt++;
+
+	fds = calloc(ctx->event_data_cnt, sizeof(*fds));
+	if (!fds)
+		return LIBUSB_ERROR_NO_MEM;
+
+	for_each_event_source(ctx, ievent_source) {
+		fds[i].fd = ievent_source->data.os_handle;
+		fds[i].events = ievent_source->data.poll_events;
+		i++;
+	}
+
+	ctx->event_data = fds;
+	return 0;
+}
+
+int usbi_wait_for_events(struct libusb_context *ctx,
+	struct usbi_reported_events *reported_events, int timeout_ms)
+{
+	struct pollfd *fds = ctx->event_data;
+	usbi_nfds_t nfds = (usbi_nfds_t)ctx->event_data_cnt;
+	int internal_fds, num_ready;
+
+	usbi_dbg(ctx, "poll() %u fds with timeout in %dms", (unsigned int)nfds, timeout_ms);
+	num_ready = poll(fds, nfds, timeout_ms);
+	usbi_dbg(ctx, "poll() returned %d", num_ready);
+	if (num_ready == 0) {
+		if (usbi_using_timer(ctx))
+			goto done;
+		return LIBUSB_ERROR_TIMEOUT;
+	} else if (num_ready == -1) {
+		if (errno == EINTR)
+			return LIBUSB_ERROR_INTERRUPTED;
+		usbi_err(ctx, "poll() failed, errno=%d", errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	/* fds[0] is always the internal signalling event */
+	if (fds[0].revents) {
+		reported_events->event_triggered = 1;
+		num_ready--;
+	} else {
+		reported_events->event_triggered = 0;
+	}
+
+#ifdef HAVE_OS_TIMER
+	/* on timer configurations, fds[1] is the timer */
+	if (usbi_using_timer(ctx) && fds[1].revents) {
+		reported_events->timer_triggered = 1;
+		num_ready--;
+	} else {
+		reported_events->timer_triggered = 0;
+	}
+#endif
+
+	if (!num_ready)
+		goto done;
+
+	/* the backend will never need to attempt to handle events on the
+	 * library's internal file descriptors, so we determine how many are
+	 * in use internally for this context and skip these when passing any
+	 * remaining pollfds to the backend. */
+	internal_fds = usbi_using_timer(ctx) ? 2 : 1;
+	fds += internal_fds;
+	nfds -= internal_fds;
+
+	usbi_mutex_lock(&ctx->event_data_lock);
+	if (ctx->event_flags & USBI_EVENT_EVENT_SOURCES_MODIFIED) {
+		struct usbi_event_source *ievent_source;
+
+		for_each_removed_event_source(ctx, ievent_source) {
+			usbi_nfds_t n;
+
+			for (n = 0; n < nfds; n++) {
+				if (ievent_source->data.os_handle != fds[n].fd)
+					continue;
+				if (!fds[n].revents)
+					continue;
+				/* pollfd was removed between the creation of the fds array and
+				 * here. remove triggered revent as it is no longer relevant. */
+				usbi_dbg(ctx, "fd %d was removed, ignoring raised events", fds[n].fd);
+				fds[n].revents = 0;
+				num_ready--;
+				break;
+			}
+		}
+	}
+	usbi_mutex_unlock(&ctx->event_data_lock);
+
+	if (num_ready) {
+		assert(num_ready > 0);
+		reported_events->event_data = fds;
+		reported_events->event_data_count = (unsigned int)nfds;
+	}
+
+done:
+	reported_events->num_ready = num_ready;
+	return LIBUSB_SUCCESS;
+}
diff --git a/src/os/events_posix.h b/src/os/events_posix.h
new file mode 100644
index 0000000..d81b5c4
--- /dev/null
+++ b/src/os/events_posix.h
@@ -0,0 +1,59 @@
+/*
+ * libusb event abstraction on POSIX platforms
+ *
+ * Copyright © 2020 Chris Dickens <christopher.a.dickens@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef LIBUSB_EVENTS_POSIX_H
+#define LIBUSB_EVENTS_POSIX_H
+
+#include <poll.h>
+
+typedef int usbi_os_handle_t;
+#define USBI_OS_HANDLE_FORMAT_STRING	"fd %d"
+
+#ifdef HAVE_EVENTFD
+typedef struct usbi_event {
+	int eventfd;
+} usbi_event_t;
+#define USBI_EVENT_OS_HANDLE(e)	((e)->eventfd)
+#define USBI_EVENT_POLL_EVENTS	POLLIN
+#define USBI_INVALID_EVENT	{ -1 }
+#else
+typedef struct usbi_event {
+	int pipefd[2];
+} usbi_event_t;
+#define USBI_EVENT_OS_HANDLE(e)	((e)->pipefd[0])
+#define USBI_EVENT_POLL_EVENTS	POLLIN
+#define USBI_INVALID_EVENT	{ { -1, -1 } }
+#endif
+
+#ifdef HAVE_TIMERFD
+#define HAVE_OS_TIMER 1
+typedef struct usbi_timer {
+	int timerfd;
+} usbi_timer_t;
+#define USBI_TIMER_OS_HANDLE(t)	((t)->timerfd)
+#define USBI_TIMER_POLL_EVENTS	POLLIN
+
+static inline int usbi_timer_valid(usbi_timer_t *timer)
+{
+	return timer->timerfd >= 0;
+}
+#endif
+
+#endif
diff --git a/src/os/events_windows.c b/src/os/events_windows.c
new file mode 100644
index 0000000..f22bebc
--- /dev/null
+++ b/src/os/events_windows.c
@@ -0,0 +1,214 @@
+/*
+ * libusb event abstraction on Microsoft Windows
+ *
+ * Copyright © 2020 Chris Dickens <christopher.a.dickens@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+
+#include "libusbi.h"
+#include "windows_common.h"
+
+int usbi_create_event(usbi_event_t *event)
+{
+	event->hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
+	if (event->hEvent == NULL) {
+		usbi_err(NULL, "CreateEvent failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+void usbi_destroy_event(usbi_event_t *event)
+{
+	if (!CloseHandle(event->hEvent))
+		usbi_warn(NULL, "CloseHandle failed: %s", windows_error_str(0));
+}
+
+void usbi_signal_event(usbi_event_t *event)
+{
+	if (!SetEvent(event->hEvent))
+		usbi_warn(NULL, "SetEvent failed: %s", windows_error_str(0));
+}
+
+void usbi_clear_event(usbi_event_t *event)
+{
+	if (!ResetEvent(event->hEvent))
+		usbi_warn(NULL, "ResetEvent failed: %s", windows_error_str(0));
+}
+
+#ifdef HAVE_OS_TIMER
+int usbi_create_timer(usbi_timer_t *timer)
+{
+	timer->hTimer = CreateWaitableTimer(NULL, TRUE, NULL);
+	if (timer->hTimer == NULL) {
+		usbi_warn(NULL, "CreateWaitableTimer failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+void usbi_destroy_timer(usbi_timer_t *timer)
+{
+	if (!CloseHandle(timer->hTimer))
+		usbi_warn(NULL, "CloseHandle failed: %s", windows_error_str(0));
+}
+
+int usbi_arm_timer(usbi_timer_t *timer, const struct timespec *timeout)
+{
+	struct timespec systime, remaining;
+	FILETIME filetime;
+	LARGE_INTEGER dueTime;
+
+	/* Transfer timeouts are based on the monotonic clock and the waitable
+	 * timers on the system clock. This requires a conversion between the
+	 * two, so we calculate the remaining time relative to the monotonic
+	 * clock and calculate an absolute system time for the timer expiration.
+	 * Note that if the timeout has already passed, the remaining time will
+	 * be negative and thus an absolute system time in the past will be set.
+	 * This works just as intended because the timer becomes signalled
+	 * immediately. */
+	usbi_get_monotonic_time(&systime);
+
+	TIMESPEC_SUB(timeout, &systime, &remaining);
+
+	GetSystemTimeAsFileTime(&filetime);
+	dueTime.LowPart = filetime.dwLowDateTime;
+	dueTime.HighPart = filetime.dwHighDateTime;
+	dueTime.QuadPart += (remaining.tv_sec * 10000000LL) + (remaining.tv_nsec / 100LL);
+
+	if (!SetWaitableTimer(timer->hTimer, &dueTime, 0, NULL, NULL, FALSE)) {
+		usbi_warn(NULL, "SetWaitableTimer failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+int usbi_disarm_timer(usbi_timer_t *timer)
+{
+	LARGE_INTEGER dueTime;
+
+	/* A manual-reset waitable timer will stay in the signalled state until
+	 * another call to SetWaitableTimer() is made. It is possible that the
+	 * timer has already expired by the time we come in to disarm it, so to
+	 * be entirely sure the timer is disarmed and not in the signalled state,
+	 * we will set it with an impossibly large expiration and immediately
+	 * cancel. */
+	dueTime.QuadPart = LLONG_MAX;
+	if (!SetWaitableTimer(timer->hTimer, &dueTime, 0, NULL, NULL, FALSE)) {
+		usbi_warn(NULL, "SetWaitableTimer failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	if (!CancelWaitableTimer(timer->hTimer)) {
+		usbi_warn(NULL, "SetWaitableTimer failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+#endif
+
+int usbi_alloc_event_data(struct libusb_context *ctx)
+{
+	struct usbi_event_source *ievent_source;
+	HANDLE *handles;
+	size_t i = 0;
+
+	/* Event sources are only added during usbi_io_init(). We should not
+	 * be running this function again if the event data has already been
+	 * allocated. */
+	if (ctx->event_data) {
+		usbi_warn(ctx, "program assertion failed - event data already allocated");
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	ctx->event_data_cnt = 0;
+	for_each_event_source(ctx, ievent_source)
+		ctx->event_data_cnt++;
+
+	/* We only expect up to two HANDLEs to wait on, one for the internal
+	 * signalling event and the other for the timer. */
+	if (ctx->event_data_cnt != 1 && ctx->event_data_cnt != 2) {
+		usbi_err(ctx, "program assertion failed - expected exactly 1 or 2 HANDLEs");
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	handles = calloc(ctx->event_data_cnt, sizeof(HANDLE));
+	if (!handles)
+		return LIBUSB_ERROR_NO_MEM;
+
+	for_each_event_source(ctx, ievent_source) {
+		handles[i] = ievent_source->data.os_handle;
+		i++;
+	}
+
+	ctx->event_data = handles;
+	return 0;
+}
+
+int usbi_wait_for_events(struct libusb_context *ctx,
+	struct usbi_reported_events *reported_events, int timeout_ms)
+{
+	HANDLE *handles = ctx->event_data;
+	DWORD num_handles = (DWORD)ctx->event_data_cnt;
+	DWORD result;
+
+	usbi_dbg(ctx, "WaitForMultipleObjects() for %lu HANDLEs with timeout in %dms", ULONG_CAST(num_handles), timeout_ms);
+	result = WaitForMultipleObjects(num_handles, handles, FALSE, (DWORD)timeout_ms);
+	usbi_dbg(ctx, "WaitForMultipleObjects() returned %lu", ULONG_CAST(result));
+	if (result == WAIT_TIMEOUT) {
+		if (usbi_using_timer(ctx))
+			goto done;
+		return LIBUSB_ERROR_TIMEOUT;
+	} else if (result == WAIT_FAILED) {
+		usbi_err(ctx, "WaitForMultipleObjects() failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_IO;
+	}
+
+	result -= WAIT_OBJECT_0;
+
+	/* handles[0] is always the internal signalling event */
+	if (result == 0)
+		reported_events->event_triggered = 1;
+	else
+		reported_events->event_triggered = 0;
+
+#ifdef HAVE_OS_TIMER
+	/* on timer configurations, handles[1] is the timer */
+	if (usbi_using_timer(ctx)) {
+		/* The WaitForMultipleObjects() function reports the index of
+		 * the first object that became signalled. If the internal
+		 * signalling event was reported, we need to also check and
+		 * report whether the timer is in the signalled state. */
+		if (result == 1 || WaitForSingleObject(handles[1], 0) == WAIT_OBJECT_0)
+			reported_events->timer_triggered = 1;
+		else
+			reported_events->timer_triggered = 0;
+	} else {
+		reported_events->timer_triggered = 0;
+	}
+#endif
+
+done:
+	/* no events are ever reported to the backend */
+	reported_events->num_ready = 0;
+	return LIBUSB_SUCCESS;
+}
diff --git a/src/os/events_windows.h b/src/os/events_windows.h
new file mode 100644
index 0000000..0c5e0b0
--- /dev/null
+++ b/src/os/events_windows.h
@@ -0,0 +1,46 @@
+/*
+ * libusb event abstraction on Microsoft Windows
+ *
+ * Copyright © 2020 Chris Dickens <christopher.a.dickens@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef LIBUSB_EVENTS_WINDOWS_H
+#define LIBUSB_EVENTS_WINDOWS_H
+
+typedef HANDLE usbi_os_handle_t;
+#define USBI_OS_HANDLE_FORMAT_STRING	"HANDLE %p"
+
+typedef struct usbi_event {
+	HANDLE hEvent;
+} usbi_event_t;
+#define USBI_EVENT_OS_HANDLE(e)	((e)->hEvent)
+#define USBI_EVENT_POLL_EVENTS	0
+#define USBI_INVALID_EVENT	{ INVALID_HANDLE_VALUE }
+
+#define HAVE_OS_TIMER 1
+typedef struct usbi_timer {
+	HANDLE hTimer;
+} usbi_timer_t;
+#define USBI_TIMER_OS_HANDLE(t)	((t)->hTimer)
+#define USBI_TIMER_POLL_EVENTS	0
+
+static inline int usbi_timer_valid(usbi_timer_t *timer)
+{
+	return timer->hTimer != NULL;
+}
+
+#endif
diff --git a/src/os/haiku_pollfs.cpp b/src/os/haiku_pollfs.cpp
new file mode 100644
index 0000000..b85edf7
--- /dev/null
+++ b/src/os/haiku_pollfs.cpp
@@ -0,0 +1,372 @@
+/*
+ * Copyright 2007-2008, Haiku Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ *
+ * Authors:
+ *		Michael Lotz <mmlr@mlotz.ch>
+ */
+
+#include "haiku_usb.h"
+#include <cstdio>
+#include <Directory.h>
+#include <Entry.h>
+#include <Looper.h>
+#include <Messenger.h>
+#include <Node.h>
+#include <NodeMonitor.h>
+#include <Path.h>
+#include <cstring>
+
+class WatchedEntry {
+public:
+			WatchedEntry(BMessenger *, entry_ref *);
+			~WatchedEntry();
+	bool		EntryCreated(entry_ref *ref);
+	bool		EntryRemoved(ino_t node);
+	bool		InitCheck();
+
+private:
+	BMessenger*	fMessenger;
+	node_ref	fNode;
+	bool		fIsDirectory;
+	USBDevice*	fDevice;
+	WatchedEntry*	fEntries;
+	WatchedEntry*	fLink;
+	bool		fInitCheck;
+};
+
+
+class RosterLooper : public BLooper {
+public:
+			RosterLooper(USBRoster *);
+	void		Stop();
+	virtual void	MessageReceived(BMessage *);
+	bool		InitCheck();
+
+private:
+	USBRoster*	fRoster;
+	WatchedEntry*	fRoot;
+	BMessenger*	fMessenger;
+	bool		fInitCheck;
+};
+
+
+WatchedEntry::WatchedEntry(BMessenger *messenger, entry_ref *ref)
+	:	fMessenger(messenger),
+		fIsDirectory(false),
+		fDevice(NULL),
+		fEntries(NULL),
+		fLink(NULL),
+		fInitCheck(false)
+{
+	BEntry entry(ref);
+	entry.GetNodeRef(&fNode);
+
+	BDirectory directory;
+	if (entry.IsDirectory() && directory.SetTo(ref) >= B_OK) {
+		fIsDirectory = true;
+
+		while (directory.GetNextEntry(&entry) >= B_OK) {
+			if (entry.GetRef(ref) < B_OK)
+				continue;
+
+			WatchedEntry *child = new(std::nothrow) WatchedEntry(fMessenger, ref);
+			if (child == NULL)
+				continue;
+			if (child->InitCheck() == false) {
+				delete child;
+				continue;
+			}
+
+			child->fLink = fEntries;
+			fEntries = child;
+		}
+
+		watch_node(&fNode, B_WATCH_DIRECTORY, *fMessenger);
+	}
+	else {
+		if (strncmp(ref->name, "raw", 3) == 0)
+			return;
+
+		BPath path, parent_path;
+		entry.GetPath(&path);
+		fDevice = new(std::nothrow) USBDevice(path.Path());
+		if (fDevice != NULL && fDevice->InitCheck() == true) {
+			// Add this new device to each active context's device list
+			struct libusb_context *ctx;
+			unsigned long session_id = (unsigned long)&fDevice;
+
+			usbi_mutex_lock(&active_contexts_lock);
+			for_each_context(ctx) {
+				struct libusb_device *dev = usbi_get_device_by_session_id(ctx, session_id);
+				if (dev) {
+					usbi_dbg(NULL, "using previously allocated device with location %lu", session_id);
+					libusb_unref_device(dev);
+					continue;
+				}
+				usbi_dbg(NULL, "allocating new device with location %lu", session_id);
+				dev = usbi_alloc_device(ctx, session_id);
+				if (!dev) {
+					usbi_dbg(NULL, "device allocation failed");
+					continue;
+				}
+				*((USBDevice **)usbi_get_device_priv(dev)) = fDevice;
+
+				// Calculate pseudo-device-address
+				int addr, tmp;
+				if (strcmp(path.Leaf(), "hub") == 0)
+					tmp = 100;	//Random Number
+				else
+					sscanf(path.Leaf(), "%d", &tmp);
+				addr = tmp + 1;
+				path.GetParent(&parent_path);
+				while (strcmp(parent_path.Leaf(), "usb") != 0) {
+					sscanf(parent_path.Leaf(), "%d", &tmp);
+					addr += tmp + 1;
+					parent_path.GetParent(&parent_path);
+				}
+				sscanf(path.Path(), "/dev/bus/usb/%hhu", &dev->bus_number);
+				dev->device_address = addr - (dev->bus_number + 1);
+
+				static_assert(sizeof(dev->device_descriptor) == sizeof(usb_device_descriptor),
+					      "mismatch between libusb and OS device descriptor sizes");
+				memcpy(&dev->device_descriptor, fDevice->Descriptor(), LIBUSB_DT_DEVICE_SIZE);
+				usbi_localize_device_descriptor(&dev->device_descriptor);
+
+				if (usbi_sanitize_device(dev) < 0) {
+					usbi_dbg(NULL, "device sanitization failed");
+					libusb_unref_device(dev);
+					continue;
+				}
+				usbi_connect_device(dev);
+			}
+			usbi_mutex_unlock(&active_contexts_lock);
+		}
+		else if (fDevice) {
+			delete fDevice;
+			fDevice = NULL;
+			return;
+		}
+	}
+	fInitCheck = true;
+}
+
+
+WatchedEntry::~WatchedEntry()
+{
+	if (fIsDirectory) {
+		watch_node(&fNode, B_STOP_WATCHING, *fMessenger);
+
+		WatchedEntry *child = fEntries;
+		while (child) {
+			WatchedEntry *next = child->fLink;
+			delete child;
+			child = next;
+		}
+	}
+
+	if (fDevice) {
+		// Remove this device from each active context's device list
+		struct libusb_context *ctx;
+		struct libusb_device *dev;
+		unsigned long session_id = (unsigned long)&fDevice;
+
+		usbi_mutex_lock(&active_contexts_lock);
+		for_each_context(ctx) {
+			dev = usbi_get_device_by_session_id(ctx, session_id);
+			if (dev != NULL) {
+				usbi_disconnect_device(dev);
+				libusb_unref_device(dev);
+			} else {
+				usbi_dbg(ctx, "device with location %lu not found", session_id);
+			}
+		}
+		usbi_mutex_static_unlock(&active_contexts_lock);
+		delete fDevice;
+	}
+}
+
+
+bool
+WatchedEntry::EntryCreated(entry_ref *ref)
+{
+	if (!fIsDirectory)
+		return false;
+
+	if (ref->directory != fNode.node) {
+		WatchedEntry *child = fEntries;
+		while (child) {
+			if (child->EntryCreated(ref))
+				return true;
+			child = child->fLink;
+		}
+		return false;
+	}
+
+	WatchedEntry *child = new(std::nothrow) WatchedEntry(fMessenger, ref);
+	if (child == NULL)
+		return false;
+	child->fLink = fEntries;
+	fEntries = child;
+	return true;
+}
+
+
+bool
+WatchedEntry::EntryRemoved(ino_t node)
+{
+	if (!fIsDirectory)
+		return false;
+
+	WatchedEntry *child = fEntries;
+	WatchedEntry *lastChild = NULL;
+	while (child) {
+		if (child->fNode.node == node) {
+			if (lastChild)
+				lastChild->fLink = child->fLink;
+			else
+				fEntries = child->fLink;
+			delete child;
+			return true;
+		}
+
+		if (child->EntryRemoved(node))
+			return true;
+
+		lastChild = child;
+		child = child->fLink;
+	}
+	return false;
+}
+
+
+bool
+WatchedEntry::InitCheck()
+{
+	return fInitCheck;
+}
+
+
+RosterLooper::RosterLooper(USBRoster *roster)
+	:	BLooper("LibusbRoster Looper"),
+		fRoster(roster),
+		fRoot(NULL),
+		fMessenger(NULL),
+		fInitCheck(false)
+{
+	BEntry entry("/dev/bus/usb");
+	if (!entry.Exists()) {
+		usbi_err(NULL, "usb_raw not published");
+		return;
+	}
+
+	Run();
+	fMessenger = new(std::nothrow) BMessenger(this);
+	if (fMessenger == NULL) {
+		usbi_err(NULL, "error creating BMessenger object");
+		return;
+	}
+
+	if (Lock()) {
+		entry_ref ref;
+		entry.GetRef(&ref);
+		fRoot = new(std::nothrow) WatchedEntry(fMessenger, &ref);
+		Unlock();
+		if (fRoot == NULL)
+			return;
+		if (fRoot->InitCheck() == false) {
+			delete fRoot;
+			fRoot = NULL;
+			return;
+		}
+	}
+	fInitCheck = true;
+}
+
+
+void
+RosterLooper::Stop()
+{
+	Lock();
+	delete fRoot;
+	delete fMessenger;
+	Quit();
+}
+
+
+void
+RosterLooper::MessageReceived(BMessage *message)
+{
+	int32 opcode;
+	if (message->FindInt32("opcode", &opcode) < B_OK)
+		return;
+
+	switch (opcode) {
+		case B_ENTRY_CREATED:
+		{
+			dev_t device;
+			ino_t directory;
+			const char *name;
+			if (message->FindInt32("device", &device) < B_OK ||
+				message->FindInt64("directory", &directory) < B_OK ||
+				message->FindString("name", &name) < B_OK)
+				break;
+
+			entry_ref ref(device, directory, name);
+			fRoot->EntryCreated(&ref);
+			break;
+		}
+		case B_ENTRY_REMOVED:
+		{
+			ino_t node;
+			if (message->FindInt64("node", &node) < B_OK)
+				break;
+			fRoot->EntryRemoved(node);
+			break;
+		}
+	}
+}
+
+
+bool
+RosterLooper::InitCheck()
+{
+	return fInitCheck;
+}
+
+
+USBRoster::USBRoster()
+	:	fLooper(NULL)
+{
+}
+
+
+USBRoster::~USBRoster()
+{
+	Stop();
+}
+
+
+int
+USBRoster::Start()
+{
+	if (fLooper == NULL) {
+		fLooper = new(std::nothrow) RosterLooper(this);
+		if (fLooper == NULL || ((RosterLooper *)fLooper)->InitCheck() == false) {
+			if (fLooper)
+				fLooper = NULL;
+			return LIBUSB_ERROR_OTHER;
+		}
+	}
+	return LIBUSB_SUCCESS;
+}
+
+
+void
+USBRoster::Stop()
+{
+	if (fLooper) {
+		((RosterLooper *)fLooper)->Stop();
+		fLooper = NULL;
+	}
+}
diff --git a/src/os/haiku_usb.h b/src/os/haiku_usb.h
new file mode 100644
index 0000000..2dd5177
--- /dev/null
+++ b/src/os/haiku_usb.h
@@ -0,0 +1,113 @@
+/*
+ * Haiku Backend for libusb
+ * Copyright © 2014 Akshay Jaggi <akshay1994.leo@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <List.h>
+#include <Locker.h>
+#include <Autolock.h>
+#include <USBKit.h>
+#include <map>
+#include "libusbi.h"
+#include "haiku_usb_raw.h"
+
+using namespace std;
+
+class USBDevice;
+class USBDeviceHandle;
+class USBTransfer;
+
+class USBDevice {
+public:
+						USBDevice(const char *);
+	virtual					~USBDevice();
+	const char*				Location() const;
+	uint8					CountConfigurations() const;
+	const usb_device_descriptor*		Descriptor() const;
+	const usb_configuration_descriptor*	ConfigurationDescriptor(uint8) const;
+	const usb_configuration_descriptor*	ActiveConfiguration() const;
+	uint8					EndpointToIndex(uint8) const;
+	uint8					EndpointToInterface(uint8) const;
+	int					ClaimInterface(uint8);
+	int					ReleaseInterface(uint8);
+	int					CheckInterfacesFree(uint8);
+	void					SetActiveConfiguration(uint8);
+	uint8					ActiveConfigurationIndex() const;
+	bool					InitCheck();
+private:
+	int					Initialise();
+	unsigned int				fClaimedInterfaces;	// Max Interfaces can be 32. Using a bitmask
+	usb_device_descriptor			fDeviceDescriptor;
+	unsigned char**				fConfigurationDescriptors;
+	uint8					fActiveConfiguration;
+	char*					fPath;
+	map<uint8,uint8>			fConfigToIndex;
+	map<uint8,uint8>*			fEndpointToIndex;
+	map<uint8,uint8>*			fEndpointToInterface;
+	bool					fInitCheck;
+};
+
+class USBDeviceHandle {
+public:
+				USBDeviceHandle(USBDevice *dev);
+	virtual			~USBDeviceHandle();
+	int			ClaimInterface(uint8);
+	int			ReleaseInterface(uint8);
+	int			SetConfiguration(uint8);
+	int			SetAltSetting(uint8, uint8);
+	int			ClearHalt(uint8);
+	status_t		SubmitTransfer(struct usbi_transfer *);
+	status_t		CancelTransfer(USBTransfer *);
+	bool			InitCheck();
+private:
+	int			fRawFD;
+	static status_t		TransfersThread(void *);
+	void			TransfersWorker();
+	USBDevice*		fUSBDevice;
+	unsigned int		fClaimedInterfaces;
+	BList			fTransfers;
+	BLocker			fTransfersLock;
+	sem_id			fTransfersSem;
+	thread_id		fTransfersThread;
+	bool			fInitCheck;
+};
+
+class USBTransfer {
+public:
+					USBTransfer(struct usbi_transfer *, USBDevice *);
+	virtual				~USBTransfer();
+	void				Do(int);
+	struct usbi_transfer*		UsbiTransfer();
+	void				SetCancelled();
+	bool				IsCancelled();
+private:
+	struct usbi_transfer*		fUsbiTransfer;
+	struct libusb_transfer*		fLibusbTransfer;
+	USBDevice*			fUSBDevice;
+	BLocker				fStatusLock;
+	bool				fCancelled;
+};
+
+class USBRoster {
+public:
+			USBRoster();
+	virtual		~USBRoster();
+	int		Start();
+	void		Stop();
+private:
+	void*		fLooper;
+};
diff --git a/src/os/haiku_usb_backend.cpp b/src/os/haiku_usb_backend.cpp
new file mode 100644
index 0000000..2fcefdd
--- /dev/null
+++ b/src/os/haiku_usb_backend.cpp
@@ -0,0 +1,532 @@
+/*
+ * Haiku Backend for libusb
+ * Copyright © 2014 Akshay Jaggi <akshay1994.leo@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+
+#include <unistd.h>
+#include <string.h>
+#include <stdlib.h>
+#include <new>
+#include <vector>
+
+#include "haiku_usb.h"
+
+static int _errno_to_libusb(int status)
+{
+	return status;
+}
+
+USBTransfer::USBTransfer(struct usbi_transfer *itransfer, USBDevice *device)
+{
+	fUsbiTransfer = itransfer;
+	fLibusbTransfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	fUSBDevice = device;
+	fCancelled = false;
+}
+
+USBTransfer::~USBTransfer()
+{
+}
+
+struct usbi_transfer *
+USBTransfer::UsbiTransfer()
+{
+	return fUsbiTransfer;
+}
+
+void
+USBTransfer::SetCancelled()
+{
+	fCancelled = true;
+}
+
+bool
+USBTransfer::IsCancelled()
+{
+	return fCancelled;
+}
+
+void
+USBTransfer::Do(int fRawFD)
+{
+	switch (fLibusbTransfer->type) {
+		case LIBUSB_TRANSFER_TYPE_CONTROL:
+		{
+			struct libusb_control_setup *setup = (struct libusb_control_setup *)fLibusbTransfer->buffer;
+			usb_raw_command command;
+			command.control.request_type = setup->bmRequestType;
+			command.control.request = setup->bRequest;
+			command.control.value = setup->wValue;
+			command.control.index = setup->wIndex;
+			command.control.length = setup->wLength;
+			command.control.data = fLibusbTransfer->buffer + LIBUSB_CONTROL_SETUP_SIZE;
+			if (fCancelled)
+				break;
+			if (ioctl(fRawFD, B_USB_RAW_COMMAND_CONTROL_TRANSFER, &command, sizeof(command)) ||
+					command.control.status != B_USB_RAW_STATUS_SUCCESS) {
+				fUsbiTransfer->transferred = -1;
+				usbi_err(TRANSFER_CTX(fLibusbTransfer), "failed control transfer");
+				break;
+			}
+			fUsbiTransfer->transferred = command.control.length;
+		}
+		break;
+		case LIBUSB_TRANSFER_TYPE_BULK:
+		case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		{
+			usb_raw_command command;
+			command.transfer.interface = fUSBDevice->EndpointToInterface(fLibusbTransfer->endpoint);
+			command.transfer.endpoint = fUSBDevice->EndpointToIndex(fLibusbTransfer->endpoint);
+			command.transfer.data = fLibusbTransfer->buffer;
+			command.transfer.length = fLibusbTransfer->length;
+			if (fCancelled)
+				break;
+			if (fLibusbTransfer->type == LIBUSB_TRANSFER_TYPE_BULK) {
+				if (ioctl(fRawFD, B_USB_RAW_COMMAND_BULK_TRANSFER, &command, sizeof(command)) ||
+						command.transfer.status != B_USB_RAW_STATUS_SUCCESS) {
+					fUsbiTransfer->transferred = -1;
+					usbi_err(TRANSFER_CTX(fLibusbTransfer), "failed bulk transfer");
+					break;
+				}
+			}
+			else {
+				if (ioctl(fRawFD, B_USB_RAW_COMMAND_INTERRUPT_TRANSFER, &command, sizeof(command)) ||
+						command.transfer.status != B_USB_RAW_STATUS_SUCCESS) {
+					fUsbiTransfer->transferred = -1;
+					usbi_err(TRANSFER_CTX(fLibusbTransfer), "failed interrupt transfer");
+					break;
+				}
+			}
+			fUsbiTransfer->transferred = command.transfer.length;
+		}
+		break;
+		// IsochronousTransfers not tested
+		case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		{
+			usb_raw_command command;
+			command.isochronous.interface = fUSBDevice->EndpointToInterface(fLibusbTransfer->endpoint);
+			command.isochronous.endpoint = fUSBDevice->EndpointToIndex(fLibusbTransfer->endpoint);
+			command.isochronous.data = fLibusbTransfer->buffer;
+			command.isochronous.length = fLibusbTransfer->length;
+			command.isochronous.packet_count = fLibusbTransfer->num_iso_packets;
+			int i;
+			usb_iso_packet_descriptor *packetDescriptors = new usb_iso_packet_descriptor[fLibusbTransfer->num_iso_packets];
+			for (i = 0; i < fLibusbTransfer->num_iso_packets; i++) {
+				if ((fLibusbTransfer->iso_packet_desc[i]).length > (unsigned int)INT16_MAX) {
+					fUsbiTransfer->transferred = -1;
+					usbi_err(TRANSFER_CTX(fLibusbTransfer), "failed isochronous transfer");
+					break;
+				}
+				packetDescriptors[i].request_length = (int16)(fLibusbTransfer->iso_packet_desc[i]).length;
+			}
+			if (i < fLibusbTransfer->num_iso_packets)
+				break;	// TODO Handle this error
+			command.isochronous.packet_descriptors = packetDescriptors;
+			if (fCancelled)
+				break;
+			if (ioctl(fRawFD, B_USB_RAW_COMMAND_ISOCHRONOUS_TRANSFER, &command, sizeof(command)) ||
+					command.isochronous.status != B_USB_RAW_STATUS_SUCCESS) {
+				fUsbiTransfer->transferred = -1;
+				usbi_err(TRANSFER_CTX(fLibusbTransfer), "failed isochronous transfer");
+				break;
+			}
+			for (i = 0; i < fLibusbTransfer->num_iso_packets; i++) {
+				(fLibusbTransfer->iso_packet_desc[i]).actual_length = packetDescriptors[i].actual_length;
+				switch (packetDescriptors[i].status) {
+					case B_OK:
+						(fLibusbTransfer->iso_packet_desc[i]).status = LIBUSB_TRANSFER_COMPLETED;
+						break;
+					default:
+						(fLibusbTransfer->iso_packet_desc[i]).status = LIBUSB_TRANSFER_ERROR;
+						break;
+				}
+			}
+			delete[] packetDescriptors;
+			// Do we put the length of transfer here, for isochronous transfers?
+			fUsbiTransfer->transferred = command.transfer.length;
+		}
+		break;
+		default:
+			usbi_err(TRANSFER_CTX(fLibusbTransfer), "Unknown type of transfer");
+	}
+}
+
+bool
+USBDeviceHandle::InitCheck()
+{
+	return fInitCheck;
+}
+
+status_t
+USBDeviceHandle::TransfersThread(void *self)
+{
+	USBDeviceHandle *handle = (USBDeviceHandle *)self;
+	handle->TransfersWorker();
+	return B_OK;
+}
+
+void
+USBDeviceHandle::TransfersWorker()
+{
+	while (true) {
+		status_t status = acquire_sem(fTransfersSem);
+		if (status == B_BAD_SEM_ID)
+			break;
+		if (status == B_INTERRUPTED)
+			continue;
+		fTransfersLock.Lock();
+		USBTransfer *fPendingTransfer = (USBTransfer *) fTransfers.RemoveItem((int32)0);
+		fTransfersLock.Unlock();
+		fPendingTransfer->Do(fRawFD);
+		usbi_signal_transfer_completion(fPendingTransfer->UsbiTransfer());
+	}
+}
+
+status_t
+USBDeviceHandle::SubmitTransfer(struct usbi_transfer *itransfer)
+{
+	USBTransfer *transfer = new USBTransfer(itransfer, fUSBDevice);
+	*((USBTransfer **)usbi_get_transfer_priv(itransfer)) = transfer;
+	BAutolock locker(fTransfersLock);
+	fTransfers.AddItem(transfer);
+	release_sem(fTransfersSem);
+	return LIBUSB_SUCCESS;
+}
+
+status_t
+USBDeviceHandle::CancelTransfer(USBTransfer *transfer)
+{
+	transfer->SetCancelled();
+	fTransfersLock.Lock();
+	bool removed = fTransfers.RemoveItem(transfer);
+	fTransfersLock.Unlock();
+	if (removed)
+		usbi_signal_transfer_completion(transfer->UsbiTransfer());
+	return LIBUSB_SUCCESS;
+}
+
+USBDeviceHandle::USBDeviceHandle(USBDevice *dev)
+	:
+	fUSBDevice(dev),
+	fClaimedInterfaces(0),
+	fTransfersThread(-1),
+	fInitCheck(false)
+{
+	fRawFD = open(dev->Location(), O_RDWR | O_CLOEXEC);
+	if (fRawFD < 0) {
+		usbi_err(NULL,"failed to open device");
+		return;
+	}
+	fTransfersSem = create_sem(0, "Transfers Queue Sem");
+	fTransfersThread = spawn_thread(TransfersThread, "Transfer Worker", B_NORMAL_PRIORITY, this);
+	resume_thread(fTransfersThread);
+	fInitCheck = true;
+}
+
+USBDeviceHandle::~USBDeviceHandle()
+{
+	if (fRawFD > 0)
+		close(fRawFD);
+	for (int i = 0; i < 32; i++) {
+		if (fClaimedInterfaces & (1U << i))
+			ReleaseInterface(i);
+	}
+	delete_sem(fTransfersSem);
+	if (fTransfersThread > 0)
+		wait_for_thread(fTransfersThread, NULL);
+}
+
+int
+USBDeviceHandle::ClaimInterface(uint8 inumber)
+{
+	int status = fUSBDevice->ClaimInterface(inumber);
+	if (status == LIBUSB_SUCCESS)
+		fClaimedInterfaces |= (1U << inumber);
+	return status;
+}
+
+int
+USBDeviceHandle::ReleaseInterface(uint8 inumber)
+{
+	fUSBDevice->ReleaseInterface(inumber);
+	fClaimedInterfaces &= ~(1U << inumber);
+	return LIBUSB_SUCCESS;
+}
+
+int
+USBDeviceHandle::SetConfiguration(uint8 config)
+{
+	int config_index = fUSBDevice->CheckInterfacesFree(config);
+	if (config_index == LIBUSB_ERROR_BUSY || config_index == LIBUSB_ERROR_NOT_FOUND)
+		return config_index;
+	usb_raw_command command;
+	command.config.config_index = config_index;
+	if (ioctl(fRawFD, B_USB_RAW_COMMAND_SET_CONFIGURATION, &command, sizeof(command)) ||
+			command.config.status != B_USB_RAW_STATUS_SUCCESS) {
+		return _errno_to_libusb(command.config.status);
+	}
+	fUSBDevice->SetActiveConfiguration((uint8)config_index);
+	return LIBUSB_SUCCESS;
+}
+
+int
+USBDeviceHandle::SetAltSetting(uint8 inumber, uint8 alt)
+{
+	usb_raw_command command;
+	command.alternate.config_index = fUSBDevice->ActiveConfigurationIndex();
+	command.alternate.interface_index = inumber;
+	if (ioctl(fRawFD, B_USB_RAW_COMMAND_GET_ACTIVE_ALT_INTERFACE_INDEX, &command, sizeof(command)) ||
+			command.alternate.status != B_USB_RAW_STATUS_SUCCESS) {
+		usbi_err(NULL, "Error retrieving active alternate interface");
+		return _errno_to_libusb(command.alternate.status);
+	}
+	if (command.alternate.alternate_info == (uint32)alt) {
+		usbi_dbg(NULL, "Setting alternate interface successful");
+		return LIBUSB_SUCCESS;
+	}
+	command.alternate.alternate_info = alt;
+	if (ioctl(fRawFD, B_USB_RAW_COMMAND_SET_ALT_INTERFACE, &command, sizeof(command)) ||
+			command.alternate.status != B_USB_RAW_STATUS_SUCCESS) { //IF IOCTL FAILS DEVICE DISCONNECTED PROBABLY
+		usbi_err(NULL, "Error setting alternate interface");
+		return _errno_to_libusb(command.alternate.status);
+	}
+	usbi_dbg(NULL, "Setting alternate interface successful");
+	return LIBUSB_SUCCESS;
+}
+
+int
+USBDeviceHandle::ClearHalt(uint8 endpoint)
+{
+	usb_raw_command command;
+	command.control.request_type = USB_REQTYPE_ENDPOINT_OUT;
+	command.control.request = USB_REQUEST_CLEAR_FEATURE;
+	command.control.value = USB_FEATURE_ENDPOINT_HALT;
+	command.control.index = endpoint;
+	command.control.length = 0;
+
+	if (ioctl(fRawFD, B_USB_RAW_COMMAND_CONTROL_TRANSFER, &command, sizeof(command)) ||
+			command.control.status != B_USB_RAW_STATUS_SUCCESS) {
+		return _errno_to_libusb(command.control.status);
+	}
+	return LIBUSB_SUCCESS;
+}
+
+
+USBDevice::USBDevice(const char *path)
+	:
+	fClaimedInterfaces(0),
+	fConfigurationDescriptors(NULL),
+	fActiveConfiguration(0),	//0?
+	fPath(NULL),
+	fEndpointToIndex(NULL),
+	fEndpointToInterface(NULL),
+	fInitCheck(false)
+{
+	fPath=strdup(path);
+	Initialise();
+}
+
+USBDevice::~USBDevice()
+{
+	free(fPath);
+	if (fConfigurationDescriptors) {
+		for (uint8 i = 0; i < fDeviceDescriptor.num_configurations; i++) {
+			if (fConfigurationDescriptors[i])
+				delete fConfigurationDescriptors[i];
+		}
+		delete[] fConfigurationDescriptors;
+	}
+	if (fEndpointToIndex)
+		delete[] fEndpointToIndex;
+	if (fEndpointToInterface)
+		delete[] fEndpointToInterface;
+}
+
+bool
+USBDevice::InitCheck()
+{
+	return fInitCheck;
+}
+
+const char *
+USBDevice::Location() const
+{
+	return fPath;
+}
+
+uint8
+USBDevice::CountConfigurations() const
+{
+	return fDeviceDescriptor.num_configurations;
+}
+
+const usb_device_descriptor *
+USBDevice::Descriptor() const
+{
+	return &fDeviceDescriptor;
+}
+
+const usb_configuration_descriptor *
+USBDevice::ConfigurationDescriptor(uint8 index) const
+{
+	if (index > CountConfigurations())
+		return NULL;
+	return (usb_configuration_descriptor *) fConfigurationDescriptors[index];
+}
+
+const usb_configuration_descriptor *
+USBDevice::ActiveConfiguration() const
+{
+	return (usb_configuration_descriptor *) fConfigurationDescriptors[fActiveConfiguration];
+}
+
+uint8
+USBDevice::ActiveConfigurationIndex() const
+{
+	return fActiveConfiguration;
+}
+
+int USBDevice::ClaimInterface(uint8 interface)
+{
+	if (interface > ActiveConfiguration()->number_interfaces)
+		return LIBUSB_ERROR_NOT_FOUND;
+	if (fClaimedInterfaces & (1U << interface))
+		return LIBUSB_ERROR_BUSY;
+	fClaimedInterfaces |= (1U << interface);
+	return LIBUSB_SUCCESS;
+}
+
+int USBDevice::ReleaseInterface(uint8 interface)
+{
+	fClaimedInterfaces &= ~(1U << interface);
+	return LIBUSB_SUCCESS;
+}
+
+int
+USBDevice::CheckInterfacesFree(uint8 config)
+{
+	if (fConfigToIndex.count(config) == 0)
+		return LIBUSB_ERROR_NOT_FOUND;
+	if (fClaimedInterfaces == 0)
+		return fConfigToIndex[config];
+	return LIBUSB_ERROR_BUSY;
+}
+
+void
+USBDevice::SetActiveConfiguration(uint8 config_index)
+{
+	fActiveConfiguration = config_index;
+}
+
+uint8
+USBDevice::EndpointToIndex(uint8 address) const
+{
+	return fEndpointToIndex[fActiveConfiguration][address];
+}
+
+uint8
+USBDevice::EndpointToInterface(uint8 address) const
+{
+	return fEndpointToInterface[fActiveConfiguration][address];
+}
+
+int
+USBDevice::Initialise()		//Do we need more error checking, etc? How to report?
+{
+	int fRawFD = open(fPath, O_RDWR | O_CLOEXEC);
+	if (fRawFD < 0)
+		return B_ERROR;
+	usb_raw_command command;
+	command.device.descriptor = &fDeviceDescriptor;
+	if (ioctl(fRawFD, B_USB_RAW_COMMAND_GET_DEVICE_DESCRIPTOR, &command, sizeof(command)) ||
+			command.device.status != B_USB_RAW_STATUS_SUCCESS) {
+		close(fRawFD);
+		return B_ERROR;
+	}
+
+	fConfigurationDescriptors = new(std::nothrow) unsigned char *[fDeviceDescriptor.num_configurations];
+	fEndpointToIndex = new(std::nothrow) map<uint8,uint8> [fDeviceDescriptor.num_configurations];
+	fEndpointToInterface = new(std::nothrow) map<uint8,uint8> [fDeviceDescriptor.num_configurations];
+	for (uint8 i = 0; i < fDeviceDescriptor.num_configurations; i++) {
+		usb_configuration_descriptor tmp_config;
+		command.config.descriptor = &tmp_config;
+		command.config.config_index = i;
+		if (ioctl(fRawFD, B_USB_RAW_COMMAND_GET_CONFIGURATION_DESCRIPTOR, &command, sizeof(command)) ||
+				command.config.status != B_USB_RAW_STATUS_SUCCESS) {
+			usbi_err(NULL, "failed retrieving configuration descriptor");
+			close(fRawFD);
+			return B_ERROR;
+		}
+		fConfigToIndex[tmp_config.configuration_value] = i;
+		fConfigurationDescriptors[i] = new(std::nothrow) unsigned char[tmp_config.total_length];
+
+		command.config_etc.descriptor = (usb_configuration_descriptor*)fConfigurationDescriptors[i];
+		command.config_etc.length = tmp_config.total_length;
+		command.config_etc.config_index = i;
+		if (ioctl(fRawFD, B_USB_RAW_COMMAND_GET_CONFIGURATION_DESCRIPTOR_ETC, &command, sizeof(command)) ||
+				command.config_etc.status != B_USB_RAW_STATUS_SUCCESS) {
+			usbi_err(NULL, "failed retrieving full configuration descriptor");
+			close(fRawFD);
+			return B_ERROR;
+		}
+
+		for (uint8 j = 0; j < tmp_config.number_interfaces; j++) {
+			command.alternate.config_index = i;
+			command.alternate.interface_index = j;
+			if (ioctl(fRawFD, B_USB_RAW_COMMAND_GET_ALT_INTERFACE_COUNT, &command, sizeof(command)) ||
+					command.config.status != B_USB_RAW_STATUS_SUCCESS) {
+				usbi_err(NULL, "failed retrieving number of alternate interfaces");
+				close(fRawFD);
+				return B_ERROR;
+			}
+			uint8 num_alternate = (uint8)command.alternate.alternate_info;
+			for (uint8 k = 0; k < num_alternate; k++) {
+				usb_interface_descriptor tmp_interface;
+				command.interface_etc.config_index = i;
+				command.interface_etc.interface_index = j;
+				command.interface_etc.alternate_index = k;
+				command.interface_etc.descriptor = &tmp_interface;
+				if (ioctl(fRawFD, B_USB_RAW_COMMAND_GET_INTERFACE_DESCRIPTOR_ETC, &command, sizeof(command)) ||
+						command.config.status != B_USB_RAW_STATUS_SUCCESS) {
+					usbi_err(NULL, "failed retrieving interface descriptor");
+					close(fRawFD);
+					return B_ERROR;
+				}
+				for (uint8 l = 0; l < tmp_interface.num_endpoints; l++) {
+					usb_endpoint_descriptor tmp_endpoint;
+					command.endpoint_etc.config_index = i;
+					command.endpoint_etc.interface_index = j;
+					command.endpoint_etc.alternate_index = k;
+					command.endpoint_etc.endpoint_index = l;
+					command.endpoint_etc.descriptor = &tmp_endpoint;
+					if (ioctl(fRawFD, B_USB_RAW_COMMAND_GET_ENDPOINT_DESCRIPTOR_ETC, &command, sizeof(command)) ||
+							command.config.status != B_USB_RAW_STATUS_SUCCESS) {
+						usbi_err(NULL, "failed retrieving endpoint descriptor");
+						close(fRawFD);
+						return B_ERROR;
+					}
+					fEndpointToIndex[i][tmp_endpoint.endpoint_address] = l;
+					fEndpointToInterface[i][tmp_endpoint.endpoint_address] = j;
+				}
+			}
+		}
+	}
+	close(fRawFD);
+	fInitCheck = true;
+	return B_OK;
+}
diff --git a/src/os/haiku_usb_raw.cpp b/src/os/haiku_usb_raw.cpp
new file mode 100644
index 0000000..bce706c
--- /dev/null
+++ b/src/os/haiku_usb_raw.cpp
@@ -0,0 +1,231 @@
+/*
+ * Haiku Backend for libusb
+ * Copyright © 2014 Akshay Jaggi <akshay1994.leo@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+
+#include <unistd.h>
+#include <string.h>
+#include <stdlib.h>
+#include <new>
+#include <vector>
+
+#include "haiku_usb.h"
+
+USBRoster gUsbRoster;
+int32 gInitCount = 0;
+
+static int haiku_get_config_descriptor(struct libusb_device *, uint8_t,
+    void *, size_t);
+
+static int
+haiku_init(struct libusb_context *ctx)
+{
+	UNUSED(ctx);
+	if (atomic_add(&gInitCount, 1) == 0)
+		return gUsbRoster.Start();
+	return LIBUSB_SUCCESS;
+}
+
+static void
+haiku_exit(struct libusb_context *ctx)
+{
+	UNUSED(ctx);
+	if (atomic_add(&gInitCount, -1) == 1)
+		gUsbRoster.Stop();
+}
+
+static int
+haiku_open(struct libusb_device_handle *dev_handle)
+{
+	USBDevice *dev = *((USBDevice **)usbi_get_device_priv(dev_handle->dev));
+	USBDeviceHandle *handle = new(std::nothrow) USBDeviceHandle(dev);
+	if (handle == NULL)
+		return LIBUSB_ERROR_NO_MEM;
+	if (handle->InitCheck() == false) {
+		delete handle;
+		return LIBUSB_ERROR_NO_DEVICE;
+	}
+	*((USBDeviceHandle **)usbi_get_device_handle_priv(dev_handle)) = handle;
+	return LIBUSB_SUCCESS;
+}
+
+static void
+haiku_close(struct libusb_device_handle *dev_handle)
+{
+	USBDeviceHandle **pHandle = (USBDeviceHandle **)usbi_get_device_handle_priv(dev_handle);
+	USBDeviceHandle *handle = *pHandle;
+	if (handle == NULL)
+		return;
+	delete handle;
+	*pHandle = NULL;
+}
+
+static int
+haiku_get_active_config_descriptor(struct libusb_device *device, void *buffer, size_t len)
+{
+	USBDevice *dev = *((USBDevice **)usbi_get_device_priv(device));
+	return haiku_get_config_descriptor(device, dev->ActiveConfigurationIndex(), buffer, len);
+}
+
+static int
+haiku_get_config_descriptor(struct libusb_device *device, uint8_t config_index, void *buffer, size_t len)
+{
+	USBDevice *dev = *((USBDevice **)usbi_get_device_priv(device));
+	const usb_configuration_descriptor *config = dev->ConfigurationDescriptor(config_index);
+	if (config == NULL) {
+		usbi_err(DEVICE_CTX(device), "failed getting configuration descriptor");
+		return LIBUSB_ERROR_IO;
+	}
+	if (len > config->total_length) {
+		len = config->total_length;
+	}
+	memcpy(buffer, config, len);
+	return len;
+}
+
+static int
+haiku_set_configuration(struct libusb_device_handle *dev_handle, int config)
+{
+	USBDeviceHandle *handle= *((USBDeviceHandle **)usbi_get_device_handle_priv(dev_handle));
+	if (config <= 0)
+		return LIBUSB_ERROR_NOT_SUPPORTED;	// cannot unconfigure
+	return handle->SetConfiguration((uint8)config);
+}
+
+static int
+haiku_claim_interface(struct libusb_device_handle *dev_handle, uint8_t interface_number)
+{
+	USBDeviceHandle *handle = *((USBDeviceHandle **)usbi_get_device_handle_priv(dev_handle));
+	return handle->ClaimInterface(interface_number);
+}
+
+static int
+haiku_set_altsetting(struct libusb_device_handle *dev_handle, uint8_t interface_number, uint8_t altsetting)
+{
+	USBDeviceHandle *handle = *((USBDeviceHandle **)usbi_get_device_handle_priv(dev_handle));
+	return handle->SetAltSetting(interface_number, altsetting);
+}
+
+static int
+haiku_clear_halt(struct libusb_device_handle *dev_handle, unsigned char endpoint)
+{
+	USBDeviceHandle *handle = *((USBDeviceHandle **)usbi_get_device_handle_priv(dev_handle));
+	return handle->ClearHalt(endpoint);
+}
+
+static int
+haiku_release_interface(struct libusb_device_handle *dev_handle, uint8_t interface_number)
+{
+	USBDeviceHandle *handle = *((USBDeviceHandle **)usbi_get_device_handle_priv(dev_handle));
+	haiku_set_altsetting(dev_handle, interface_number, 0);
+	return handle->ReleaseInterface(interface_number);
+}
+
+static int
+haiku_submit_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *fLibusbTransfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	USBDeviceHandle *fDeviceHandle = *((USBDeviceHandle **)usbi_get_device_handle_priv(fLibusbTransfer->dev_handle));
+	return fDeviceHandle->SubmitTransfer(itransfer);
+}
+
+static int
+haiku_cancel_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *fLibusbTransfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	USBDeviceHandle *fDeviceHandle = *((USBDeviceHandle **)usbi_get_device_handle_priv(fLibusbTransfer->dev_handle));
+	return fDeviceHandle->CancelTransfer(*((USBTransfer **)usbi_get_transfer_priv(itransfer)));
+}
+
+static int
+haiku_handle_transfer_completion(struct usbi_transfer *itransfer)
+{
+	USBTransfer **pTransfer = (USBTransfer **)usbi_get_transfer_priv(itransfer);
+	USBTransfer *transfer = *pTransfer;
+
+	usbi_mutex_lock(&itransfer->lock);
+	if (transfer->IsCancelled()) {
+		delete transfer;
+		*pTransfer = NULL;
+		usbi_mutex_unlock(&itransfer->lock);
+		if (itransfer->transferred < 0)
+			itransfer->transferred = 0;
+		return usbi_handle_transfer_cancellation(itransfer);
+	}
+	libusb_transfer_status status = LIBUSB_TRANSFER_COMPLETED;
+	if (itransfer->transferred < 0) {
+		usbi_err(ITRANSFER_CTX(itransfer), "error in transfer");
+		status = LIBUSB_TRANSFER_ERROR;
+		itransfer->transferred = 0;
+	}
+	delete transfer;
+	*pTransfer = NULL;
+	usbi_mutex_unlock(&itransfer->lock);
+	return usbi_handle_transfer_completion(itransfer, status);
+}
+
+const struct usbi_os_backend usbi_backend = {
+	/*.name =*/ "Haiku usbfs",
+	/*.caps =*/ 0,
+	/*.init =*/ haiku_init,
+	/*.exit =*/ haiku_exit,
+	/*.set_option =*/ NULL,
+	/*.get_device_list =*/ NULL,
+	/*.hotplug_poll =*/ NULL,
+	/*.wrap_sys_device =*/ NULL,
+	/*.open =*/ haiku_open,
+	/*.close =*/ haiku_close,
+
+	/*.get_active_config_descriptor =*/ haiku_get_active_config_descriptor,
+	/*.get_config_descriptor =*/ haiku_get_config_descriptor,
+	/*.get_config_descriptor_by_value =*/ NULL,
+
+	/*.get_configuration =*/ NULL,
+	/*.set_configuration =*/ haiku_set_configuration,
+
+	/*.claim_interface =*/ haiku_claim_interface,
+	/*.release_interface =*/ haiku_release_interface,
+	/*.set_interface_altsetting =*/ haiku_set_altsetting,
+
+	/*.clear_halt =*/ haiku_clear_halt,
+	/*.reset_device =*/ NULL,
+
+	/*.alloc_streams =*/ NULL,
+	/*.free_streams =*/ NULL,
+
+	/*.dev_mem_alloc =*/ NULL,
+	/*.dev_mem_free =*/ NULL,
+
+	/*.kernel_driver_active =*/ NULL,
+	/*.detach_kernel_driver =*/ NULL,
+	/*.attach_kernel_driver =*/ NULL,
+
+	/*.destroy_device =*/ NULL,
+
+	/*.submit_transfer =*/ haiku_submit_transfer,
+	/*.cancel_transfer =*/ haiku_cancel_transfer,
+	/*.clear_transfer_priv =*/ NULL,
+
+	/*.handle_events =*/ NULL,
+	/*.handle_transfer_completion =*/ haiku_handle_transfer_completion,
+
+	/*.context_priv_size =*/ 0,
+	/*.device_priv_size =*/ sizeof(USBDevice *),
+	/*.device_handle_priv_size =*/ sizeof(USBDeviceHandle *),
+	/*.transfer_priv_size =*/ sizeof(USBTransfer *),
+};
diff --git a/src/os/haiku_usb_raw.h b/src/os/haiku_usb_raw.h
new file mode 100644
index 0000000..d371f01
--- /dev/null
+++ b/src/os/haiku_usb_raw.h
@@ -0,0 +1,188 @@
+/*
+ * Copyright 2006-2008, Haiku Inc. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+
+#ifndef _USB_RAW_H_
+#define _USB_RAW_H_
+
+#include <USB3.h>
+
+#define B_USB_RAW_PROTOCOL_VERSION	0x0015
+#define B_USB_RAW_ACTIVE_ALTERNATE	0xffffffff
+
+typedef enum {
+	B_USB_RAW_COMMAND_GET_VERSION = 0x1000,
+
+	B_USB_RAW_COMMAND_GET_DEVICE_DESCRIPTOR = 0x2000,
+	B_USB_RAW_COMMAND_GET_CONFIGURATION_DESCRIPTOR,
+	B_USB_RAW_COMMAND_GET_INTERFACE_DESCRIPTOR,
+	B_USB_RAW_COMMAND_GET_ENDPOINT_DESCRIPTOR,
+	B_USB_RAW_COMMAND_GET_STRING_DESCRIPTOR,
+	B_USB_RAW_COMMAND_GET_GENERIC_DESCRIPTOR,
+	B_USB_RAW_COMMAND_GET_ALT_INTERFACE_COUNT,
+	B_USB_RAW_COMMAND_GET_ACTIVE_ALT_INTERFACE_INDEX,
+	B_USB_RAW_COMMAND_GET_INTERFACE_DESCRIPTOR_ETC,
+	B_USB_RAW_COMMAND_GET_ENDPOINT_DESCRIPTOR_ETC,
+	B_USB_RAW_COMMAND_GET_GENERIC_DESCRIPTOR_ETC,
+	B_USB_RAW_COMMAND_GET_CONFIGURATION_DESCRIPTOR_ETC,
+
+	B_USB_RAW_COMMAND_SET_CONFIGURATION = 0x3000,
+	B_USB_RAW_COMMAND_SET_FEATURE,
+	B_USB_RAW_COMMAND_CLEAR_FEATURE,
+	B_USB_RAW_COMMAND_GET_STATUS,
+	B_USB_RAW_COMMAND_GET_DESCRIPTOR,
+	B_USB_RAW_COMMAND_SET_ALT_INTERFACE,
+
+	B_USB_RAW_COMMAND_CONTROL_TRANSFER = 0x4000,
+	B_USB_RAW_COMMAND_INTERRUPT_TRANSFER,
+	B_USB_RAW_COMMAND_BULK_TRANSFER,
+	B_USB_RAW_COMMAND_ISOCHRONOUS_TRANSFER
+} usb_raw_command_id;
+
+
+typedef enum {
+	B_USB_RAW_STATUS_SUCCESS = 0,
+
+	B_USB_RAW_STATUS_FAILED,
+	B_USB_RAW_STATUS_ABORTED,
+	B_USB_RAW_STATUS_STALLED,
+	B_USB_RAW_STATUS_CRC_ERROR,
+	B_USB_RAW_STATUS_TIMEOUT,
+
+	B_USB_RAW_STATUS_INVALID_CONFIGURATION,
+	B_USB_RAW_STATUS_INVALID_INTERFACE,
+	B_USB_RAW_STATUS_INVALID_ENDPOINT,
+	B_USB_RAW_STATUS_INVALID_STRING,
+
+	B_USB_RAW_STATUS_NO_MEMORY
+} usb_raw_command_status;
+
+
+typedef union {
+	struct {
+		status_t status;
+	} version;
+
+	struct {
+		status_t status;
+		usb_device_descriptor *descriptor;
+	} device;
+
+	struct {
+		status_t status;
+		usb_configuration_descriptor *descriptor;
+		uint32 config_index;
+	} config;
+
+	struct {
+		status_t status;
+		usb_configuration_descriptor *descriptor;
+		uint32 config_index;
+		size_t length;
+	} config_etc;
+
+	struct {
+		status_t status;
+		uint32 alternate_info;
+		uint32 config_index;
+		uint32 interface_index;
+	} alternate;
+
+	struct {
+		status_t status;
+		usb_interface_descriptor *descriptor;
+		uint32 config_index;
+		uint32 interface_index;
+	} interface;
+
+	struct {
+		status_t status;
+		usb_interface_descriptor *descriptor;
+		uint32 config_index;
+		uint32 interface_index;
+		uint32 alternate_index;
+	} interface_etc;
+
+	struct {
+		status_t status;
+		usb_endpoint_descriptor *descriptor;
+		uint32 config_index;
+		uint32 interface_index;
+		uint32 endpoint_index;
+	} endpoint;
+
+	struct {
+		status_t status;
+		usb_endpoint_descriptor *descriptor;
+		uint32 config_index;
+		uint32 interface_index;
+		uint32 alternate_index;
+		uint32 endpoint_index;
+	} endpoint_etc;
+
+	struct {
+		status_t status;
+		usb_descriptor *descriptor;
+		uint32 config_index;
+		uint32 interface_index;
+		uint32 generic_index;
+		size_t length;
+	} generic;
+
+	struct {
+		status_t status;
+		usb_descriptor *descriptor;
+		uint32 config_index;
+		uint32 interface_index;
+		uint32 alternate_index;
+		uint32 generic_index;
+		size_t length;
+	} generic_etc;
+
+	struct {
+		status_t status;
+		usb_string_descriptor *descriptor;
+		uint32 string_index;
+		size_t length;
+	} string;
+
+	struct {
+		status_t status;
+		uint8 type;
+		uint8 index;
+		uint16 language_id;
+		void *data;
+		size_t length;
+	} descriptor;
+
+	struct {
+		status_t status;
+		uint8 request_type;
+		uint8 request;
+		uint16 value;
+		uint16 index;
+		uint16 length;
+		void *data;
+	} control;
+
+	struct {
+		status_t status;
+		uint32 interface;
+		uint32 endpoint;
+		void *data;
+		size_t length;
+	} transfer;
+
+	struct {
+		status_t status;
+		uint32 interface;
+		uint32 endpoint;
+		void *data;
+		size_t length;
+		usb_iso_packet_descriptor *packet_descriptors;
+		uint32 packet_count;
+	} isochronous;
+} usb_raw_command;
+
+#endif // _USB_RAW_H_
diff --git a/src/os/linux_netlink.c b/src/os/linux_netlink.c
new file mode 100644
index 0000000..899084f
--- /dev/null
+++ b/src/os/linux_netlink.c
@@ -0,0 +1,401 @@
+/* -*- Mode: C; c-basic-offset:8 ; indent-tabs-mode:t -*- */
+/*
+ * Linux usbfs backend for libusb
+ * Copyright (C) 2007-2009 Daniel Drake <dsd@gentoo.org>
+ * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ * Copyright (c) 2013 Nathan Hjelm <hjelmn@mac.com>
+ * Copyright (c) 2016 Chris Dickens <christopher.a.dickens@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "libusbi.h"
+#include "linux_usbfs.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <pthread.h>
+#include <string.h>
+#include <unistd.h>
+
+#ifdef HAVE_ASM_TYPES_H
+#include <asm/types.h>
+#endif
+#include <sys/socket.h>
+#include <linux/netlink.h>
+
+#define NL_GROUP_KERNEL 1
+
+#ifndef SOCK_CLOEXEC
+#define SOCK_CLOEXEC	0
+#endif
+
+#ifndef SOCK_NONBLOCK
+#define SOCK_NONBLOCK	0
+#endif
+
+static int linux_netlink_socket = -1;
+static usbi_event_t netlink_control_event = USBI_INVALID_EVENT;
+static pthread_t libusb_linux_event_thread;
+
+static void *linux_netlink_event_thread_main(void *arg);
+
+static int set_fd_cloexec_nb(int fd, int socktype)
+{
+	int flags;
+
+#if defined(FD_CLOEXEC)
+	/* Make sure the netlink socket file descriptor is marked as CLOEXEC */
+	if (!(socktype & SOCK_CLOEXEC)) {
+		flags = fcntl(fd, F_GETFD);
+		if (flags == -1) {
+			usbi_err(NULL, "failed to get netlink fd flags, errno=%d", errno);
+			return -1;
+		}
+
+		if (fcntl(fd, F_SETFD, flags | FD_CLOEXEC) == -1) {
+			usbi_err(NULL, "failed to set netlink fd flags, errno=%d", errno);
+			return -1;
+		}
+	}
+#endif
+
+	/* Make sure the netlink socket is non-blocking */
+	if (!(socktype & SOCK_NONBLOCK)) {
+		flags = fcntl(fd, F_GETFL);
+		if (flags == -1) {
+			usbi_err(NULL, "failed to get netlink fd status flags, errno=%d", errno);
+			return -1;
+		}
+
+		if (fcntl(fd, F_SETFL, flags | O_NONBLOCK) == -1) {
+			usbi_err(NULL, "failed to set netlink fd status flags, errno=%d", errno);
+			return -1;
+		}
+	}
+
+	return 0;
+}
+
+int linux_netlink_start_event_monitor(void)
+{
+	struct sockaddr_nl sa_nl = { .nl_family = AF_NETLINK, .nl_groups = NL_GROUP_KERNEL };
+	int socktype = SOCK_RAW | SOCK_NONBLOCK | SOCK_CLOEXEC;
+	int opt = 1;
+	int ret;
+
+	linux_netlink_socket = socket(PF_NETLINK, socktype, NETLINK_KOBJECT_UEVENT);
+	if (linux_netlink_socket == -1 && errno == EINVAL) {
+		usbi_dbg(NULL, "failed to create netlink socket of type %d, attempting SOCK_RAW", socktype);
+		socktype = SOCK_RAW;
+		linux_netlink_socket = socket(PF_NETLINK, socktype, NETLINK_KOBJECT_UEVENT);
+	}
+
+	if (linux_netlink_socket == -1) {
+		usbi_err(NULL, "failed to create netlink socket, errno=%d", errno);
+		goto err;
+	}
+
+	ret = set_fd_cloexec_nb(linux_netlink_socket, socktype);
+	if (ret == -1)
+		goto err_close_socket;
+
+	ret = bind(linux_netlink_socket, (struct sockaddr *)&sa_nl, sizeof(sa_nl));
+	if (ret == -1) {
+		usbi_err(NULL, "failed to bind netlink socket, errno=%d", errno);
+		goto err_close_socket;
+	}
+
+	ret = setsockopt(linux_netlink_socket, SOL_SOCKET, SO_PASSCRED, &opt, sizeof(opt));
+	if (ret == -1) {
+		usbi_err(NULL, "failed to set netlink socket SO_PASSCRED option, errno=%d", errno);
+		goto err_close_socket;
+	}
+
+	ret = usbi_create_event(&netlink_control_event);
+	if (ret) {
+		usbi_err(NULL, "failed to create netlink control event");
+		goto err_close_socket;
+	}
+
+	ret = pthread_create(&libusb_linux_event_thread, NULL, linux_netlink_event_thread_main, NULL);
+	if (ret != 0) {
+		usbi_err(NULL, "failed to create netlink event thread (%d)", ret);
+		goto err_destroy_event;
+	}
+
+	return LIBUSB_SUCCESS;
+
+err_destroy_event:
+	usbi_destroy_event(&netlink_control_event);
+	netlink_control_event = (usbi_event_t)USBI_INVALID_EVENT;
+err_close_socket:
+	close(linux_netlink_socket);
+	linux_netlink_socket = -1;
+err:
+	return LIBUSB_ERROR_OTHER;
+}
+
+int linux_netlink_stop_event_monitor(void)
+{
+	int ret;
+
+	assert(linux_netlink_socket != -1);
+
+	/* Signal the control event and wait for the thread to exit */
+	usbi_signal_event(&netlink_control_event);
+
+	ret = pthread_join(libusb_linux_event_thread, NULL);
+	if (ret)
+		usbi_warn(NULL, "failed to join netlink event thread (%d)", ret);
+
+	usbi_destroy_event(&netlink_control_event);
+	netlink_control_event = (usbi_event_t)USBI_INVALID_EVENT;
+
+	close(linux_netlink_socket);
+	linux_netlink_socket = -1;
+
+	return LIBUSB_SUCCESS;
+}
+
+static const char *netlink_message_parse(const char *buffer, size_t len, const char *key)
+{
+	const char *end = buffer + len;
+	size_t keylen = strlen(key);
+
+	while (buffer < end && *buffer) {
+		if (strncmp(buffer, key, keylen) == 0 && buffer[keylen] == '=')
+			return buffer + keylen + 1;
+		buffer += strlen(buffer) + 1;
+	}
+
+	return NULL;
+}
+
+/* parse parts of netlink message common to both libudev and the kernel */
+static int linux_netlink_parse(const char *buffer, size_t len, int *detached,
+	const char **sys_name, uint8_t *busnum, uint8_t *devaddr)
+{
+	const char *tmp, *slash;
+
+	errno = 0;
+
+	*sys_name = NULL;
+	*detached = 0;
+	*busnum   = 0;
+	*devaddr  = 0;
+
+	tmp = netlink_message_parse(buffer, len, "ACTION");
+	if (!tmp) {
+		return -1;
+	} else if (strcmp(tmp, "remove") == 0) {
+		*detached = 1;
+	} else if (strcmp(tmp, "add") != 0) {
+		usbi_dbg(NULL, "unknown device action %s", tmp);
+		return -1;
+	}
+
+	/* check that this is a usb message */
+	tmp = netlink_message_parse(buffer, len, "SUBSYSTEM");
+	if (!tmp || strcmp(tmp, "usb") != 0) {
+		/* not usb. ignore */
+		return -1;
+	}
+
+	/* check that this is an actual usb device */
+	tmp = netlink_message_parse(buffer, len, "DEVTYPE");
+	if (!tmp || strcmp(tmp, "usb_device") != 0) {
+		/* not usb. ignore */
+		return -1;
+	}
+
+	tmp = netlink_message_parse(buffer, len, "BUSNUM");
+	if (tmp) {
+		*busnum = (uint8_t)(strtoul(tmp, NULL, 10) & 0xff);
+		if (errno) {
+			errno = 0;
+			return -1;
+		}
+
+		tmp = netlink_message_parse(buffer, len, "DEVNUM");
+		if (NULL == tmp)
+			return -1;
+
+		*devaddr = (uint8_t)(strtoul(tmp, NULL, 10) & 0xff);
+		if (errno) {
+			errno = 0;
+			return -1;
+		}
+	} else {
+		/* no bus number. try "DEVICE" */
+		tmp = netlink_message_parse(buffer, len, "DEVICE");
+		if (!tmp) {
+			/* not usb. ignore */
+			return -1;
+		}
+
+		/* Parse a device path such as /dev/bus/usb/003/004 */
+		slash = strrchr(tmp, '/');
+		if (!slash)
+			return -1;
+
+		*busnum = (uint8_t)(strtoul(slash - 3, NULL, 10) & 0xff);
+		if (errno) {
+			errno = 0;
+			return -1;
+		}
+
+		*devaddr = (uint8_t)(strtoul(slash + 1, NULL, 10) & 0xff);
+		if (errno) {
+			errno = 0;
+			return -1;
+		}
+
+		return 0;
+	}
+
+	tmp = netlink_message_parse(buffer, len, "DEVPATH");
+	if (!tmp)
+		return -1;
+
+	slash = strrchr(tmp, '/');
+	if (slash)
+		*sys_name = slash + 1;
+
+	/* found a usb device */
+	return 0;
+}
+
+static int linux_netlink_read_message(void)
+{
+	char cred_buffer[CMSG_SPACE(sizeof(struct ucred))];
+	char msg_buffer[2048];
+	const char *sys_name = NULL;
+	uint8_t busnum, devaddr;
+	int detached, r;
+	ssize_t len;
+	struct cmsghdr *cmsg;
+	struct ucred *cred;
+	struct sockaddr_nl sa_nl;
+	struct iovec iov = { .iov_base = msg_buffer, .iov_len = sizeof(msg_buffer) };
+	struct msghdr msg = {
+		.msg_iov = &iov, .msg_iovlen = 1,
+		.msg_control = cred_buffer, .msg_controllen = sizeof(cred_buffer),
+		.msg_name = &sa_nl, .msg_namelen = sizeof(sa_nl)
+	};
+
+	/* read netlink message */
+	len = recvmsg(linux_netlink_socket, &msg, 0);
+	if (len == -1) {
+		if (errno != EAGAIN && errno != EINTR)
+			usbi_err(NULL, "error receiving message from netlink, errno=%d", errno);
+		return -1;
+	}
+
+	if (len < 32 || (msg.msg_flags & MSG_TRUNC)) {
+		usbi_err(NULL, "invalid netlink message length");
+		return -1;
+	}
+
+	if (sa_nl.nl_groups != NL_GROUP_KERNEL || sa_nl.nl_pid != 0) {
+		usbi_dbg(NULL, "ignoring netlink message from unknown group/PID (%u/%u)",
+			 (unsigned int)sa_nl.nl_groups, (unsigned int)sa_nl.nl_pid);
+		return -1;
+	}
+
+	cmsg = CMSG_FIRSTHDR(&msg);
+	if (!cmsg || cmsg->cmsg_type != SCM_CREDENTIALS) {
+		usbi_dbg(NULL, "ignoring netlink message with no sender credentials");
+		return -1;
+	}
+
+	cred = (struct ucred *)CMSG_DATA(cmsg);
+	if (cred->uid != 0) {
+		usbi_dbg(NULL, "ignoring netlink message with non-zero sender UID %u", (unsigned int)cred->uid);
+		return -1;
+	}
+
+	r = linux_netlink_parse(msg_buffer, (size_t)len, &detached, &sys_name, &busnum, &devaddr);
+	if (r)
+		return r;
+
+	usbi_dbg(NULL, "netlink hotplug found device busnum: %hhu, devaddr: %hhu, sys_name: %s, removed: %s",
+		 busnum, devaddr, sys_name, detached ? "yes" : "no");
+
+	/* signal device is available (or not) to all contexts */
+	if (detached)
+		linux_device_disconnected(busnum, devaddr);
+	else
+		linux_hotplug_enumerate(busnum, devaddr, sys_name);
+
+	return 0;
+}
+
+static void *linux_netlink_event_thread_main(void *arg)
+{
+	struct pollfd fds[] = {
+		{ .fd = USBI_EVENT_OS_HANDLE(&netlink_control_event),
+		  .events = USBI_EVENT_POLL_EVENTS },
+		{ .fd = linux_netlink_socket,
+		  .events = POLLIN },
+	};
+	int r;
+
+	UNUSED(arg);
+
+#if defined(HAVE_PTHREAD_SETNAME_NP)
+	r = pthread_setname_np(pthread_self(), "libusb_event");
+	if (r)
+		usbi_warn(NULL, "failed to set hotplug event thread name, error=%d", r);
+#endif
+
+	usbi_dbg(NULL, "netlink event thread entering");
+
+	while (1) {
+		r = poll(fds, 2, -1);
+		if (r == -1) {
+			/* check for temporary failure */
+			if (errno == EINTR)
+				continue;
+			usbi_err(NULL, "poll() failed, errno=%d", errno);
+			break;
+		}
+		if (fds[0].revents) {
+			/* activity on control event, exit */
+			break;
+		}
+		if (fds[1].revents) {
+			usbi_mutex_static_lock(&linux_hotplug_lock);
+			linux_netlink_read_message();
+			usbi_mutex_static_unlock(&linux_hotplug_lock);
+		}
+	}
+
+	usbi_dbg(NULL, "netlink event thread exiting");
+
+	return NULL;
+}
+
+void linux_netlink_hotplug_poll(void)
+{
+	int r;
+
+	usbi_mutex_static_lock(&linux_hotplug_lock);
+	do {
+		r = linux_netlink_read_message();
+	} while (r == 0);
+	usbi_mutex_static_unlock(&linux_hotplug_lock);
+}
diff --git a/src/os/linux_udev.c b/src/os/linux_udev.c
new file mode 100644
index 0000000..9ec9eb1
--- /dev/null
+++ b/src/os/linux_udev.c
@@ -0,0 +1,321 @@
+/* -*- Mode: C; c-basic-offset:8 ; indent-tabs-mode:t -*- */
+/*
+ * Linux usbfs backend for libusb
+ * Copyright (C) 2007-2009 Daniel Drake <dsd@gentoo.org>
+ * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ * Copyright (c) 2012-2013 Nathan Hjelm <hjelmn@mac.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "libusbi.h"
+#include "linux_usbfs.h"
+
+#include <errno.h>
+#include <fcntl.h>
+#include <libudev.h>
+#include <poll.h>
+#include <pthread.h>
+#include <string.h>
+#include <unistd.h>
+
+/* udev context */
+static struct udev *udev_ctx = NULL;
+static int udev_monitor_fd = -1;
+static usbi_event_t udev_control_event = USBI_INVALID_EVENT;
+static struct udev_monitor *udev_monitor = NULL;
+static pthread_t linux_event_thread;
+
+static void udev_hotplug_event(struct udev_device *udev_dev);
+static void *linux_udev_event_thread_main(void *arg);
+
+int linux_udev_start_event_monitor(void)
+{
+	int r;
+
+	assert(udev_ctx == NULL);
+	udev_ctx = udev_new();
+	if (!udev_ctx) {
+		usbi_err(NULL, "could not create udev context");
+		goto err;
+	}
+
+	udev_monitor = udev_monitor_new_from_netlink(udev_ctx, "udev");
+	if (!udev_monitor) {
+		usbi_err(NULL, "could not initialize udev monitor");
+		goto err_free_ctx;
+	}
+
+	r = udev_monitor_filter_add_match_subsystem_devtype(udev_monitor, "usb", "usb_device");
+	if (r) {
+		usbi_err(NULL, "could not initialize udev monitor filter for \"usb\" subsystem");
+		goto err_free_monitor;
+	}
+
+	if (udev_monitor_enable_receiving(udev_monitor)) {
+		usbi_err(NULL, "failed to enable the udev monitor");
+		goto err_free_monitor;
+	}
+
+	udev_monitor_fd = udev_monitor_get_fd(udev_monitor);
+
+#if defined(FD_CLOEXEC)
+	/* Make sure the udev file descriptor is marked as CLOEXEC */
+	r = fcntl(udev_monitor_fd, F_GETFD);
+	if (r == -1) {
+		usbi_err(NULL, "failed to get udev monitor fd flags, errno=%d", errno);
+		goto err_free_monitor;
+	}
+	if (!(r & FD_CLOEXEC)) {
+		if (fcntl(udev_monitor_fd, F_SETFD, r | FD_CLOEXEC) == -1) {
+			usbi_err(NULL, "failed to set udev monitor fd flags, errno=%d", errno);
+			goto err_free_monitor;
+		}
+	}
+#endif
+
+	/* Some older versions of udev are not non-blocking by default,
+	 * so make sure this is set */
+	r = fcntl(udev_monitor_fd, F_GETFL);
+	if (r == -1) {
+		usbi_err(NULL, "failed to get udev monitor fd status flags, errno=%d", errno);
+		goto err_free_monitor;
+	}
+	if (!(r & O_NONBLOCK)) {
+		if (fcntl(udev_monitor_fd, F_SETFL, r | O_NONBLOCK) == -1) {
+			usbi_err(NULL, "failed to set udev monitor fd status flags, errno=%d", errno);
+			goto err_free_monitor;
+		}
+	}
+
+	r = usbi_create_event(&udev_control_event);
+	if (r) {
+		usbi_err(NULL, "failed to create udev control event");
+		goto err_free_monitor;
+	}
+
+	r = pthread_create(&linux_event_thread, NULL, linux_udev_event_thread_main, NULL);
+	if (r) {
+		usbi_err(NULL, "failed to create hotplug event thread (%d)", r);
+		goto err_destroy_event;
+	}
+
+	return LIBUSB_SUCCESS;
+
+err_destroy_event:
+	usbi_destroy_event(&udev_control_event);
+	udev_control_event = (usbi_event_t)USBI_INVALID_EVENT;
+err_free_monitor:
+	udev_monitor_unref(udev_monitor);
+	udev_monitor = NULL;
+	udev_monitor_fd = -1;
+err_free_ctx:
+	udev_unref(udev_ctx);
+err:
+	udev_ctx = NULL;
+	return LIBUSB_ERROR_OTHER;
+}
+
+int linux_udev_stop_event_monitor(void)
+{
+	int r;
+
+	assert(udev_ctx != NULL);
+	assert(udev_monitor != NULL);
+	assert(udev_monitor_fd != -1);
+
+	/* Signal the control event and wait for the thread to exit */
+	usbi_signal_event(&udev_control_event);
+
+	r = pthread_join(linux_event_thread, NULL);
+	if (r)
+		usbi_warn(NULL, "failed to join hotplug event thread (%d)", r);
+
+	usbi_destroy_event(&udev_control_event);
+	udev_control_event = (usbi_event_t)USBI_INVALID_EVENT;
+
+	/* Release the udev monitor */
+	udev_monitor_unref(udev_monitor);
+	udev_monitor = NULL;
+	udev_monitor_fd = -1;
+
+	/* Clean up the udev context */
+	udev_unref(udev_ctx);
+	udev_ctx = NULL;
+
+	return LIBUSB_SUCCESS;
+}
+
+static void *linux_udev_event_thread_main(void *arg)
+{
+	struct pollfd fds[] = {
+		{ .fd = USBI_EVENT_OS_HANDLE(&udev_control_event),
+		  .events = USBI_EVENT_POLL_EVENTS },
+		{ .fd = udev_monitor_fd,
+		  .events = POLLIN },
+	};
+	struct udev_device *udev_dev;
+	int r;
+
+	UNUSED(arg);
+
+#if defined(HAVE_PTHREAD_SETNAME_NP)
+	r = pthread_setname_np(pthread_self(), "libusb_event");
+	if (r)
+		usbi_warn(NULL, "failed to set hotplug event thread name, error=%d", r);
+#endif
+
+	usbi_dbg(NULL, "udev event thread entering");
+
+	while (1) {
+		r = poll(fds, 2, -1);
+		if (r == -1) {
+			/* check for temporary failure */
+			if (errno == EINTR)
+				continue;
+			usbi_err(NULL, "poll() failed, errno=%d", errno);
+			break;
+		}
+		if (fds[0].revents) {
+			/* activity on control event, exit */
+			break;
+		}
+		if (fds[1].revents) {
+			usbi_mutex_static_lock(&linux_hotplug_lock);
+			udev_dev = udev_monitor_receive_device(udev_monitor);
+			if (udev_dev)
+				udev_hotplug_event(udev_dev);
+			usbi_mutex_static_unlock(&linux_hotplug_lock);
+		}
+	}
+
+	usbi_dbg(NULL, "udev event thread exiting");
+
+	return NULL;
+}
+
+static int udev_device_info(struct libusb_context *ctx, int detached,
+			    struct udev_device *udev_dev, uint8_t *busnum,
+			    uint8_t *devaddr, const char **sys_name) {
+	const char *dev_node;
+
+	dev_node = udev_device_get_devnode(udev_dev);
+	if (!dev_node) {
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	*sys_name = udev_device_get_sysname(udev_dev);
+	if (!*sys_name) {
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return linux_get_device_address(ctx, detached, busnum, devaddr,
+					dev_node, *sys_name, -1);
+}
+
+static void udev_hotplug_event(struct udev_device *udev_dev)
+{
+	const char *udev_action;
+	const char *sys_name = NULL;
+	uint8_t busnum = 0, devaddr = 0;
+	int detached;
+	int r;
+
+	do {
+		udev_action = udev_device_get_action(udev_dev);
+		if (!udev_action) {
+			break;
+		}
+
+		detached = !strncmp(udev_action, "remove", 6);
+
+		r = udev_device_info(NULL, detached, udev_dev, &busnum, &devaddr, &sys_name);
+		if (LIBUSB_SUCCESS != r) {
+			break;
+		}
+
+		usbi_dbg(NULL, "udev hotplug event. action: %s.", udev_action);
+
+		if (strncmp(udev_action, "add", 3) == 0) {
+			linux_hotplug_enumerate(busnum, devaddr, sys_name);
+		} else if (detached) {
+			linux_device_disconnected(busnum, devaddr);
+		} else if (strncmp(udev_action, "bind", 4) == 0) {
+			/* silently ignore "known unhandled" action */
+		} else {
+			usbi_err(NULL, "ignoring udev action %s", udev_action);
+		}
+	} while (0);
+
+	udev_device_unref(udev_dev);
+}
+
+int linux_udev_scan_devices(struct libusb_context *ctx)
+{
+	struct udev_enumerate *enumerator;
+	struct udev_list_entry *devices, *entry;
+	struct udev_device *udev_dev;
+	const char *sys_name;
+	int r;
+
+	assert(udev_ctx != NULL);
+
+	enumerator = udev_enumerate_new(udev_ctx);
+	if (NULL == enumerator) {
+		usbi_err(ctx, "error creating udev enumerator");
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	udev_enumerate_add_match_subsystem(enumerator, "usb");
+	udev_enumerate_add_match_property(enumerator, "DEVTYPE", "usb_device");
+	udev_enumerate_scan_devices(enumerator);
+	devices = udev_enumerate_get_list_entry(enumerator);
+
+	entry = NULL;
+	udev_list_entry_foreach(entry, devices) {
+		const char *path = udev_list_entry_get_name(entry);
+		uint8_t busnum = 0, devaddr = 0;
+
+		udev_dev = udev_device_new_from_syspath(udev_ctx, path);
+
+		r = udev_device_info(ctx, 0, udev_dev, &busnum, &devaddr, &sys_name);
+		if (r) {
+			udev_device_unref(udev_dev);
+			continue;
+		}
+
+		linux_enumerate_device(ctx, busnum, devaddr, sys_name);
+		udev_device_unref(udev_dev);
+	}
+
+	udev_enumerate_unref(enumerator);
+
+	return LIBUSB_SUCCESS;
+}
+
+void linux_udev_hotplug_poll(void)
+{
+	struct udev_device *udev_dev;
+
+	usbi_mutex_static_lock(&linux_hotplug_lock);
+	do {
+		udev_dev = udev_monitor_receive_device(udev_monitor);
+		if (udev_dev) {
+			usbi_dbg(NULL, "Handling hotplug event from hotplug_poll");
+			udev_hotplug_event(udev_dev);
+		}
+	} while (udev_dev);
+	usbi_mutex_static_unlock(&linux_hotplug_lock);
+}
diff --git a/src/os/linux_usbfs.c b/src/os/linux_usbfs.c
new file mode 100644
index 0000000..c300675
--- /dev/null
+++ b/src/os/linux_usbfs.c
@@ -0,0 +1,2807 @@
+/* -*- Mode: C; c-basic-offset:8 ; indent-tabs-mode:t -*- */
+/*
+ * Linux usbfs backend for libusb
+ * Copyright © 2007-2009 Daniel Drake <dsd@gentoo.org>
+ * Copyright © 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ * Copyright © 2013 Nathan Hjelm <hjelmn@mac.com>
+ * Copyright © 2012-2013 Hans de Goede <hdegoede@redhat.com>
+ * Copyright © 2020 Chris Dickens <christopher.a.dickens@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "libusbi.h"
+#include "linux_usbfs.h"
+
+#include <alloca.h>
+#include <ctype.h>
+#include <dirent.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/utsname.h>
+#include <sys/vfs.h>
+#include <unistd.h>
+
+/* sysfs vs usbfs:
+ * opening a usbfs node causes the device to be resumed, so we attempt to
+ * avoid this during enumeration.
+ *
+ * sysfs allows us to read the kernel's in-memory copies of device descriptors
+ * and so forth, avoiding the need to open the device:
+ *  - The binary "descriptors" file contains all config descriptors since
+ *    2.6.26, commit 217a9081d8e69026186067711131b77f0ce219ed
+ *  - The binary "descriptors" file was added in 2.6.23, commit
+ *    69d42a78f935d19384d1f6e4f94b65bb162b36df, but it only contains the
+ *    active config descriptors
+ *  - The "busnum" file was added in 2.6.22, commit
+ *    83f7d958eab2fbc6b159ee92bf1493924e1d0f72
+ *  - The "devnum" file has been present since pre-2.6.18
+ *  - the "bConfigurationValue" file has been present since pre-2.6.18
+ *
+ * If we have bConfigurationValue, busnum, and devnum, then we can determine
+ * the active configuration without having to open the usbfs node in RDWR mode.
+ * The busnum file is important as that is the only way we can relate sysfs
+ * devices to usbfs nodes.
+ *
+ * If we also have all descriptors, we can obtain the device descriptor and
+ * configuration without touching usbfs at all.
+ */
+
+/* endianness for multi-byte fields:
+ *
+ * Descriptors exposed by usbfs have the multi-byte fields in the device
+ * descriptor as host endian. Multi-byte fields in the other descriptors are
+ * bus-endian. The kernel documentation says otherwise, but it is wrong.
+ *
+ * In sysfs all descriptors are bus-endian.
+ */
+
+#define USBDEV_PATH		"/dev"
+#define USB_DEVTMPFS_PATH	"/dev/bus/usb"
+
+/* use usbdev*.* device names in /dev instead of the usbfs bus directories */
+static int usbdev_names = 0;
+
+/* Linux has changed the maximum length of an individual isochronous packet
+ * over time.  Initially this limit was 1,023 bytes, but Linux 2.6.18
+ * (commit 3612242e527eb47ee4756b5350f8bdf791aa5ede) increased this value to
+ * 8,192 bytes to support higher bandwidth devices.  Linux 3.10
+ * (commit e2e2f0ea1c935edcf53feb4c4c8fdb4f86d57dd9) further increased this
+ * value to 49,152 bytes to support super speed devices.  Linux 5.2
+ * (commit 8a1dbc8d91d3d1602282c7e6b4222c7759c916fa) even further increased
+ * this value to 98,304 bytes to support super speed plus devices.
+ */
+static unsigned int max_iso_packet_len = 0;
+
+/* is sysfs available (mounted) ? */
+static int sysfs_available = -1;
+
+/* how many times have we initted (and not exited) ? */
+static int init_count = 0;
+
+/* have no authority to operate usb device directly */
+static int no_enumeration = 0;
+
+/* Serialize scan-devices, event-thread, and poll */
+usbi_mutex_static_t linux_hotplug_lock = USBI_MUTEX_INITIALIZER;
+
+static int linux_scan_devices(struct libusb_context *ctx);
+static int detach_kernel_driver_and_claim(struct libusb_device_handle *, uint8_t);
+
+#if !defined(HAVE_LIBUDEV)
+static int linux_default_scan_devices(struct libusb_context *ctx);
+#endif
+
+struct kernel_version {
+	int major;
+	int minor;
+	int sublevel;
+};
+
+struct config_descriptor {
+	struct usbi_configuration_descriptor *desc;
+	size_t actual_len;
+};
+
+struct linux_device_priv {
+	char *sysfs_dir;
+	void *descriptors;
+	size_t descriptors_len;
+	struct config_descriptor *config_descriptors;
+	int active_config; /* cache val for !sysfs_available  */
+};
+
+struct linux_device_handle_priv {
+	int fd;
+	int fd_removed;
+	int fd_keep;
+	uint32_t caps;
+};
+
+enum reap_action {
+	NORMAL = 0,
+	/* submission failed after the first URB, so await cancellation/completion
+	 * of all the others */
+	SUBMIT_FAILED,
+
+	/* cancelled by user or timeout */
+	CANCELLED,
+
+	/* completed multi-URB transfer in non-final URB */
+	COMPLETED_EARLY,
+
+	/* one or more urbs encountered a low-level error */
+	ERROR,
+};
+
+struct linux_transfer_priv {
+	union {
+		struct usbfs_urb *urbs;
+		struct usbfs_urb **iso_urbs;
+	};
+
+	enum reap_action reap_action;
+	int num_urbs;
+	int num_retired;
+	enum libusb_transfer_status reap_status;
+
+	/* next iso packet in user-supplied transfer to be populated */
+	int iso_packet_offset;
+};
+
+static int dev_has_config0(struct libusb_device *dev)
+{
+	struct linux_device_priv *priv = usbi_get_device_priv(dev);
+	struct config_descriptor *config;
+	uint8_t idx;
+
+	for (idx = 0; idx < dev->device_descriptor.bNumConfigurations; idx++) {
+		config = &priv->config_descriptors[idx];
+		if (config->desc->bConfigurationValue == 0)
+			return 1;
+	}
+
+	return 0;
+}
+
+static int get_usbfs_fd(struct libusb_device *dev, mode_t mode, int silent)
+{
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	char path[24];
+	int fd;
+
+	if (usbdev_names)
+		sprintf(path, USBDEV_PATH "/usbdev%u.%u",
+			dev->bus_number, dev->device_address);
+	else
+		sprintf(path, USB_DEVTMPFS_PATH "/%03u/%03u",
+			dev->bus_number, dev->device_address);
+
+	fd = open(path, mode | O_CLOEXEC);
+	if (fd != -1)
+		return fd; /* Success */
+
+	if (errno == ENOENT) {
+		const long delay_ms = 10L;
+		const struct timespec delay_ts = { 0L, delay_ms * 1000L * 1000L };
+
+		if (!silent)
+			usbi_err(ctx, "File doesn't exist, wait %ld ms and try again", delay_ms);
+
+		/* Wait 10ms for USB device path creation.*/
+		nanosleep(&delay_ts, NULL);
+
+		fd = open(path, mode | O_CLOEXEC);
+		if (fd != -1)
+			return fd; /* Success */
+	}
+
+	if (!silent) {
+		usbi_err(ctx, "libusb couldn't open USB device %s, errno=%d", path, errno);
+		if (errno == EACCES && mode == O_RDWR)
+			usbi_err(ctx, "libusb requires write access to USB device nodes");
+	}
+
+	if (errno == EACCES)
+		return LIBUSB_ERROR_ACCESS;
+	if (errno == ENOENT)
+		return LIBUSB_ERROR_NO_DEVICE;
+	return LIBUSB_ERROR_IO;
+}
+
+/* check dirent for a /dev/usbdev%d.%d name
+ * optionally return bus/device on success */
+static int is_usbdev_entry(const char *name, uint8_t *bus_p, uint8_t *dev_p)
+{
+	int busnum, devnum;
+
+	if (sscanf(name, "usbdev%d.%d", &busnum, &devnum) != 2)
+		return 0;
+	if (busnum < 0 || busnum > UINT8_MAX || devnum < 0 || devnum > UINT8_MAX) {
+		usbi_dbg(NULL, "invalid usbdev format '%s'", name);
+		return 0;
+	}
+
+	usbi_dbg(NULL, "found: %s", name);
+	if (bus_p)
+		*bus_p = (uint8_t)busnum;
+	if (dev_p)
+		*dev_p = (uint8_t)devnum;
+	return 1;
+}
+
+static const char *find_usbfs_path(void)
+{
+	const char *path;
+	DIR *dir;
+	struct dirent *entry;
+
+	path = USB_DEVTMPFS_PATH;
+	dir = opendir(path);
+	if (dir) {
+		while ((entry = readdir(dir))) {
+			if (entry->d_name[0] == '.')
+				continue;
+
+			/* We assume if we find any files that it must be the right place */
+			break;
+		}
+
+		closedir(dir);
+
+		if (entry)
+			return path;
+	}
+
+	/* look for /dev/usbdev*.* if the normal place fails */
+	path = USBDEV_PATH;
+	dir = opendir(path);
+	if (dir) {
+		while ((entry = readdir(dir))) {
+			if (entry->d_name[0] == '.')
+				continue;
+
+			if (is_usbdev_entry(entry->d_name, NULL, NULL)) {
+				/* found one; that's enough */
+				break;
+			}
+		}
+
+		closedir(dir);
+
+		if (entry) {
+			usbdev_names = 1;
+			return path;
+		}
+	}
+
+/* On udev based systems without any usb-devices /dev/bus/usb will not
+ * exist. So if we've not found anything and we're using udev for hotplug
+ * simply assume /dev/bus/usb rather then making libusb_init fail.
+ * Make the same assumption for Android where SELinux policies might block us
+ * from reading /dev on newer devices. */
+#if defined(HAVE_LIBUDEV) || defined(__ANDROID__)
+	return USB_DEVTMPFS_PATH;
+#else
+	return NULL;
+#endif
+}
+
+static int get_kernel_version(struct libusb_context *ctx,
+	struct kernel_version *ver)
+{
+	struct utsname uts;
+	int atoms;
+
+	if (uname(&uts) < 0) {
+		usbi_err(ctx, "uname failed, errno=%d", errno);
+		return -1;
+	}
+
+	atoms = sscanf(uts.release, "%d.%d.%d", &ver->major, &ver->minor, &ver->sublevel);
+	if (atoms < 2) {
+		usbi_err(ctx, "failed to parse uname release '%s'", uts.release);
+		return -1;
+	}
+
+	if (atoms < 3)
+		ver->sublevel = -1;
+
+	usbi_dbg(ctx, "reported kernel version is %s", uts.release);
+
+	return 0;
+}
+
+static int kernel_version_ge(const struct kernel_version *ver,
+	int major, int minor, int sublevel)
+{
+	if (ver->major > major)
+		return 1;
+	else if (ver->major < major)
+		return 0;
+
+	/* kmajor == major */
+	if (ver->minor > minor)
+		return 1;
+	else if (ver->minor < minor)
+		return 0;
+
+	/* kminor == minor */
+	if (ver->sublevel == -1)
+		return sublevel == 0;
+
+	return ver->sublevel >= sublevel;
+}
+
+static int op_init(struct libusb_context *ctx)
+{
+	struct kernel_version kversion;
+	const char *usbfs_path;
+	int r;
+
+	if (get_kernel_version(ctx, &kversion) < 0)
+		return LIBUSB_ERROR_OTHER;
+
+	if (!kernel_version_ge(&kversion, 2, 6, 32)) {
+		usbi_err(ctx, "kernel version is too old (reported as %d.%d.%d)",
+			 kversion.major, kversion.minor,
+			 kversion.sublevel != -1 ? kversion.sublevel : 0);
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+	}
+
+	usbfs_path = find_usbfs_path();
+	if (!usbfs_path) {
+		usbi_err(ctx, "could not find usbfs");
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	usbi_dbg(ctx, "found usbfs at %s", usbfs_path);
+
+	if (!max_iso_packet_len) {
+		if (kernel_version_ge(&kversion, 5, 2, 0))
+			max_iso_packet_len = 98304;
+		else if (kernel_version_ge(&kversion, 3, 10, 0))
+			max_iso_packet_len = 49152;
+		else
+			max_iso_packet_len = 8192;
+	}
+
+	usbi_dbg(ctx, "max iso packet length is (likely) %u bytes", max_iso_packet_len);
+
+	if (sysfs_available == -1) {
+		struct statfs statfsbuf;
+
+		r = statfs(SYSFS_MOUNT_PATH, &statfsbuf);
+		if (r == 0 && statfsbuf.f_type == SYSFS_MAGIC) {
+			usbi_dbg(ctx, "sysfs is available");
+			sysfs_available = 1;
+		} else {
+			usbi_warn(ctx, "sysfs not mounted");
+			sysfs_available = 0;
+		}
+	}
+
+	if (no_enumeration) {
+		return LIBUSB_SUCCESS;
+	}
+
+	r = LIBUSB_SUCCESS;
+	if (init_count == 0) {
+		/* start up hotplug event handler */
+		r = linux_start_event_monitor();
+	}
+	if (r == LIBUSB_SUCCESS) {
+		r = linux_scan_devices(ctx);
+		if (r == LIBUSB_SUCCESS)
+			init_count++;
+		else if (init_count == 0)
+			linux_stop_event_monitor();
+	} else {
+		usbi_err(ctx, "error starting hotplug event monitor");
+	}
+
+	return r;
+}
+
+static void op_exit(struct libusb_context *ctx)
+{
+	UNUSED(ctx);
+
+	if (no_enumeration) {
+		return;
+	}
+
+	assert(init_count != 0);
+	if (!--init_count) {
+		/* tear down event handler */
+		linux_stop_event_monitor();
+	}
+}
+
+static int op_set_option(struct libusb_context *ctx, enum libusb_option option, va_list ap)
+{
+	UNUSED(ctx);
+	UNUSED(ap);
+
+	if (option == LIBUSB_OPTION_NO_DEVICE_DISCOVERY) {
+		usbi_dbg(ctx, "no enumeration will be performed");
+		no_enumeration = 1;
+		return LIBUSB_SUCCESS;
+	}
+
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static int linux_scan_devices(struct libusb_context *ctx)
+{
+	int ret;
+
+	usbi_mutex_static_lock(&linux_hotplug_lock);
+
+#if defined(HAVE_LIBUDEV)
+	ret = linux_udev_scan_devices(ctx);
+#else
+	ret = linux_default_scan_devices(ctx);
+#endif
+
+	usbi_mutex_static_unlock(&linux_hotplug_lock);
+
+	return ret;
+}
+
+static void op_hotplug_poll(void)
+{
+	linux_hotplug_poll();
+}
+
+static int open_sysfs_attr(struct libusb_context *ctx,
+	const char *sysfs_dir, const char *attr)
+{
+	char filename[256];
+	int fd;
+
+	snprintf(filename, sizeof(filename), SYSFS_DEVICE_PATH "/%s/%s", sysfs_dir, attr);
+	fd = open(filename, O_RDONLY | O_CLOEXEC);
+	if (fd < 0) {
+		if (errno == ENOENT) {
+			/* File doesn't exist. Assume the device has been
+			   disconnected (see trac ticket #70). */
+			return LIBUSB_ERROR_NO_DEVICE;
+		}
+		usbi_err(ctx, "open %s failed, errno=%d", filename, errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	return fd;
+}
+
+/* Note only suitable for attributes which always read >= 0, < 0 is error */
+static int read_sysfs_attr(struct libusb_context *ctx,
+	const char *sysfs_dir, const char *attr, int max_value, int *value_p)
+{
+	char buf[20], *endptr;
+	long value;
+	ssize_t r;
+	int fd;
+
+	fd = open_sysfs_attr(ctx, sysfs_dir, attr);
+	if (fd < 0)
+		return fd;
+
+	r = read(fd, buf, sizeof(buf) - 1);
+	if (r < 0) {
+		r = errno;
+		close(fd);
+		if (r == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+		usbi_err(ctx, "attribute %s read failed, errno=%zd", attr, r);
+		return LIBUSB_ERROR_IO;
+	}
+	close(fd);
+
+	if (r == 0) {
+		/* Certain attributes (e.g. bConfigurationValue) are not
+		 * populated if the device is not configured. */
+		*value_p = -1;
+		return 0;
+	}
+
+	/* The kernel does *not* NUL-terminate the string, but every attribute
+	 * should be terminated with a newline character. */
+	if (!isdigit(buf[0])) {
+		usbi_err(ctx, "attribute %s doesn't have numeric value?", attr);
+		return LIBUSB_ERROR_IO;
+	} else if (buf[r - 1] != '\n') {
+		usbi_warn(ctx, "attribute %s doesn't end with newline?", attr);
+	} else {
+		/* Remove the terminating newline character */
+		r--;
+	}
+	buf[r] = '\0';
+
+	errno = 0;
+	value = strtol(buf, &endptr, 10);
+	if (value < 0 || value > (long)max_value || errno) {
+		usbi_err(ctx, "attribute %s contains an invalid value: '%s'", attr, buf);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	} else if (*endptr != '\0') {
+		/* Consider the value to be valid if the remainder is a '.'
+		 * character followed by numbers.  This occurs, for example,
+		 * when reading the "speed" attribute for a low-speed device
+		 * (e.g. "1.5") */
+		if (*endptr == '.' && isdigit(*(endptr + 1))) {
+			endptr++;
+			while (isdigit(*endptr))
+				endptr++;
+		}
+		if (*endptr != '\0') {
+			usbi_err(ctx, "attribute %s contains an invalid value: '%s'", attr, buf);
+			return LIBUSB_ERROR_INVALID_PARAM;
+		}
+	}
+
+	*value_p = (int)value;
+	return 0;
+}
+
+static int sysfs_scan_device(struct libusb_context *ctx, const char *devname)
+{
+	uint8_t busnum, devaddr;
+	int ret;
+
+	ret = linux_get_device_address(ctx, 0, &busnum, &devaddr, NULL, devname, -1);
+	if (ret != LIBUSB_SUCCESS)
+		return ret;
+
+	return linux_enumerate_device(ctx, busnum, devaddr, devname);
+}
+
+/* read the bConfigurationValue for a device */
+static int sysfs_get_active_config(struct libusb_device *dev, int *config)
+{
+	struct linux_device_priv *priv = usbi_get_device_priv(dev);
+
+	return read_sysfs_attr(DEVICE_CTX(dev), priv->sysfs_dir, "bConfigurationValue",
+			UINT8_MAX, config);
+}
+
+int linux_get_device_address(struct libusb_context *ctx, int detached,
+	uint8_t *busnum, uint8_t *devaddr, const char *dev_node,
+	const char *sys_name, int fd)
+{
+	int sysfs_val;
+	int r;
+
+	usbi_dbg(ctx, "getting address for device: %s detached: %d", sys_name, detached);
+	/* can't use sysfs to read the bus and device number if the
+	 * device has been detached */
+	if (!sysfs_available || detached || !sys_name) {
+		if (!dev_node && fd >= 0) {
+			char *fd_path = alloca(PATH_MAX);
+			char proc_path[32];
+
+			/* try to retrieve the device node from fd */
+			sprintf(proc_path, "/proc/self/fd/%d", fd);
+			r = readlink(proc_path, fd_path, PATH_MAX - 1);
+			if (r > 0) {
+				fd_path[r] = '\0';
+				dev_node = fd_path;
+			}
+		}
+
+		if (!dev_node)
+			return LIBUSB_ERROR_OTHER;
+
+		/* will this work with all supported kernel versions? */
+		if (!strncmp(dev_node, "/dev/bus/usb", 12))
+			sscanf(dev_node, "/dev/bus/usb/%hhu/%hhu", busnum, devaddr);
+		else
+			return LIBUSB_ERROR_OTHER;
+
+		return LIBUSB_SUCCESS;
+	}
+
+	usbi_dbg(ctx, "scan %s", sys_name);
+
+	r = read_sysfs_attr(ctx, sys_name, "busnum", UINT8_MAX, &sysfs_val);
+	if (r < 0)
+		return r;
+	*busnum = (uint8_t)sysfs_val;
+
+	r = read_sysfs_attr(ctx, sys_name, "devnum", UINT8_MAX, &sysfs_val);
+	if (r < 0)
+		return r;
+	*devaddr = (uint8_t)sysfs_val;
+
+	usbi_dbg(ctx, "bus=%u dev=%u", *busnum, *devaddr);
+
+	return LIBUSB_SUCCESS;
+}
+
+/* Return offset of the next config descriptor */
+static int seek_to_next_config(struct libusb_context *ctx,
+	uint8_t *buffer, size_t len)
+{
+	struct usbi_descriptor_header *header;
+	int offset;
+
+	/* Start seeking past the config descriptor */
+	offset = LIBUSB_DT_CONFIG_SIZE;
+	buffer += LIBUSB_DT_CONFIG_SIZE;
+	len -= LIBUSB_DT_CONFIG_SIZE;
+
+	while (len > 0) {
+		if (len < 2) {
+			usbi_err(ctx, "short descriptor read %zu/2", len);
+			return LIBUSB_ERROR_IO;
+		}
+
+		header = (struct usbi_descriptor_header *)buffer;
+		if (header->bDescriptorType == LIBUSB_DT_CONFIG)
+			return offset;
+
+		if (len < header->bLength) {
+			usbi_err(ctx, "bLength overflow by %zu bytes",
+				 (size_t)header->bLength - len);
+			return LIBUSB_ERROR_IO;
+		}
+
+		offset += header->bLength;
+		buffer += header->bLength;
+		len -= header->bLength;
+	}
+
+	usbi_err(ctx, "config descriptor not found");
+	return LIBUSB_ERROR_IO;
+}
+
+static int parse_config_descriptors(struct libusb_device *dev)
+{
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	struct linux_device_priv *priv = usbi_get_device_priv(dev);
+	struct usbi_device_descriptor *device_desc;
+	uint8_t idx, num_configs;
+	uint8_t *buffer;
+	size_t remaining;
+
+	device_desc = priv->descriptors;
+	num_configs = device_desc->bNumConfigurations;
+
+	if (num_configs == 0)
+		return 0;	/* no configurations? */
+
+	priv->config_descriptors = malloc(num_configs * sizeof(priv->config_descriptors[0]));
+	if (!priv->config_descriptors)
+		return LIBUSB_ERROR_NO_MEM;
+
+	buffer = (uint8_t *)priv->descriptors + LIBUSB_DT_DEVICE_SIZE;
+	remaining = priv->descriptors_len - LIBUSB_DT_DEVICE_SIZE;
+
+	for (idx = 0; idx < num_configs; idx++) {
+		struct usbi_configuration_descriptor *config_desc;
+		uint16_t config_len;
+
+		if (remaining < LIBUSB_DT_CONFIG_SIZE) {
+			usbi_err(ctx, "short descriptor read %zu/%d",
+				 remaining, LIBUSB_DT_CONFIG_SIZE);
+			return LIBUSB_ERROR_IO;
+		}
+
+		config_desc = (struct usbi_configuration_descriptor *)buffer;
+		if (config_desc->bDescriptorType != LIBUSB_DT_CONFIG) {
+			usbi_err(ctx, "descriptor is not a config desc (type 0x%02x)",
+				 config_desc->bDescriptorType);
+			return LIBUSB_ERROR_IO;
+		} else if (config_desc->bLength < LIBUSB_DT_CONFIG_SIZE) {
+			usbi_err(ctx, "invalid descriptor bLength %u",
+				 config_desc->bLength);
+			return LIBUSB_ERROR_IO;
+		}
+
+		config_len = libusb_le16_to_cpu(config_desc->wTotalLength);
+		if (config_len < LIBUSB_DT_CONFIG_SIZE) {
+			usbi_err(ctx, "invalid wTotalLength %u", config_len);
+			return LIBUSB_ERROR_IO;
+		}
+
+		if (priv->sysfs_dir) {
+			/*
+			 * In sysfs wTotalLength is ignored, instead the kernel returns a
+			 * config descriptor with verified bLength fields, with descriptors
+			 * with an invalid bLength removed.
+			 */
+			uint16_t sysfs_config_len;
+			int offset;
+
+			if (num_configs > 1 && idx < num_configs - 1) {
+				offset = seek_to_next_config(ctx, buffer, remaining);
+				if (offset < 0)
+					return offset;
+				sysfs_config_len = (uint16_t)offset;
+			} else {
+				sysfs_config_len = (uint16_t)remaining;
+			}
+
+			if (config_len != sysfs_config_len) {
+				usbi_warn(ctx, "config length mismatch wTotalLength %u real %u",
+					  config_len, sysfs_config_len);
+				config_len = sysfs_config_len;
+			}
+		} else {
+			/*
+			 * In usbfs the config descriptors are wTotalLength bytes apart,
+			 * with any short reads from the device appearing as holes in the file.
+			 */
+			if (config_len > remaining) {
+				usbi_warn(ctx, "short descriptor read %zu/%u", remaining, config_len);
+				config_len = (uint16_t)remaining;
+			}
+		}
+
+		if (config_desc->bConfigurationValue == 0)
+			usbi_warn(ctx, "device has configuration 0");
+
+		priv->config_descriptors[idx].desc = config_desc;
+		priv->config_descriptors[idx].actual_len = config_len;
+
+		buffer += config_len;
+		remaining -= config_len;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int op_get_config_descriptor_by_value(struct libusb_device *dev,
+	uint8_t value, void **buffer)
+{
+	struct linux_device_priv *priv = usbi_get_device_priv(dev);
+	struct config_descriptor *config;
+	uint8_t idx;
+
+	for (idx = 0; idx < dev->device_descriptor.bNumConfigurations; idx++) {
+		config = &priv->config_descriptors[idx];
+		if (config->desc->bConfigurationValue == value) {
+			*buffer = config->desc;
+			return (int)config->actual_len;
+		}
+	}
+
+	return LIBUSB_ERROR_NOT_FOUND;
+}
+
+static int op_get_active_config_descriptor(struct libusb_device *dev,
+	void *buffer, size_t len)
+{
+	struct linux_device_priv *priv = usbi_get_device_priv(dev);
+	void *config_desc;
+	int active_config;
+	int r;
+
+	if (priv->sysfs_dir) {
+		r = sysfs_get_active_config(dev, &active_config);
+		if (r < 0)
+			return r;
+	} else {
+		/* Use cached bConfigurationValue */
+		active_config = priv->active_config;
+	}
+
+	if (active_config == -1) {
+		usbi_err(DEVICE_CTX(dev), "device unconfigured");
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	r = op_get_config_descriptor_by_value(dev, (uint8_t)active_config, &config_desc);
+	if (r < 0)
+		return r;
+
+	len = MIN(len, (size_t)r);
+	memcpy(buffer, config_desc, len);
+	return len;
+}
+
+static int op_get_config_descriptor(struct libusb_device *dev,
+	uint8_t config_index, void *buffer, size_t len)
+{
+	struct linux_device_priv *priv = usbi_get_device_priv(dev);
+	struct config_descriptor *config;
+
+	if (config_index >= dev->device_descriptor.bNumConfigurations)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	config = &priv->config_descriptors[config_index];
+	len = MIN(len, config->actual_len);
+	memcpy(buffer, config->desc, len);
+	return len;
+}
+
+/* send a control message to retrieve active configuration */
+static int usbfs_get_active_config(struct libusb_device *dev, int fd)
+{
+	struct linux_device_priv *priv = usbi_get_device_priv(dev);
+	uint8_t active_config = 0;
+	int r;
+
+	struct usbfs_ctrltransfer ctrl = {
+		.bmRequestType = LIBUSB_ENDPOINT_IN,
+		.bRequest = LIBUSB_REQUEST_GET_CONFIGURATION,
+		.wValue = 0,
+		.wIndex = 0,
+		.wLength = 1,
+		.timeout = 1000,
+		.data = &active_config
+	};
+
+	r = ioctl(fd, IOCTL_USBFS_CONTROL, &ctrl);
+	if (r < 0) {
+		if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		/* we hit this error path frequently with buggy devices :( */
+		usbi_warn(DEVICE_CTX(dev), "get configuration failed, errno=%d", errno);
+
+		/* assume the current configuration is the first one if we have
+		 * the configuration descriptors, otherwise treat the device
+		 * as unconfigured. */
+		if (priv->config_descriptors)
+			priv->active_config = (int)priv->config_descriptors[0].desc->bConfigurationValue;
+		else
+			priv->active_config = -1;
+	} else if (active_config == 0) {
+		if (dev_has_config0(dev)) {
+			/* some buggy devices have a configuration 0, but we're
+			 * reaching into the corner of a corner case here. */
+			priv->active_config = 0;
+		} else {
+			priv->active_config = -1;
+		}
+	} else {
+		priv->active_config = (int)active_config;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static enum libusb_speed usbfs_get_speed(struct libusb_context *ctx, int fd)
+{
+	int r;
+
+	r = ioctl(fd, IOCTL_USBFS_GET_SPEED, NULL);
+	switch (r) {
+	case USBFS_SPEED_UNKNOWN:	return LIBUSB_SPEED_UNKNOWN;
+	case USBFS_SPEED_LOW:		return LIBUSB_SPEED_LOW;
+	case USBFS_SPEED_FULL:		return LIBUSB_SPEED_FULL;
+	case USBFS_SPEED_HIGH:		return LIBUSB_SPEED_HIGH;
+	case USBFS_SPEED_WIRELESS:	return LIBUSB_SPEED_HIGH;
+	case USBFS_SPEED_SUPER:		return LIBUSB_SPEED_SUPER;
+	case USBFS_SPEED_SUPER_PLUS:	return LIBUSB_SPEED_SUPER_PLUS;
+	default:
+		usbi_warn(ctx, "Error getting device speed: %d", r);
+	}
+
+	return LIBUSB_SPEED_UNKNOWN;
+}
+
+static int initialize_device(struct libusb_device *dev, uint8_t busnum,
+	uint8_t devaddr, const char *sysfs_dir, int wrapped_fd)
+{
+	struct linux_device_priv *priv = usbi_get_device_priv(dev);
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	size_t alloc_len;
+	int fd, speed, r;
+	ssize_t nb;
+
+	dev->bus_number = busnum;
+	dev->device_address = devaddr;
+
+	if (sysfs_dir) {
+		priv->sysfs_dir = strdup(sysfs_dir);
+		if (!priv->sysfs_dir)
+			return LIBUSB_ERROR_NO_MEM;
+
+		/* Note speed can contain 1.5, in this case read_sysfs_attr()
+		   will stop parsing at the '.' and return 1 */
+		if (read_sysfs_attr(ctx, sysfs_dir, "speed", INT_MAX, &speed) == 0) {
+			switch (speed) {
+			case     1: dev->speed = LIBUSB_SPEED_LOW; break;
+			case    12: dev->speed = LIBUSB_SPEED_FULL; break;
+			case   480: dev->speed = LIBUSB_SPEED_HIGH; break;
+			case  5000: dev->speed = LIBUSB_SPEED_SUPER; break;
+			case 10000: dev->speed = LIBUSB_SPEED_SUPER_PLUS; break;
+			default:
+				usbi_warn(ctx, "unknown device speed: %d Mbps", speed);
+			}
+		}
+	} else if (wrapped_fd >= 0) {
+		dev->speed = usbfs_get_speed(ctx, wrapped_fd);
+	}
+
+	/* cache descriptors in memory */
+	if (sysfs_dir) {
+		fd = open_sysfs_attr(ctx, sysfs_dir, "descriptors");
+	} else if (wrapped_fd < 0) {
+		fd = get_usbfs_fd(dev, O_RDONLY, 0);
+	} else {
+		fd = wrapped_fd;
+		r = lseek(fd, 0, SEEK_SET);
+		if (r < 0) {
+			usbi_err(ctx, "lseek failed, errno=%d", errno);
+			return LIBUSB_ERROR_IO;
+		}
+	}
+	if (fd < 0)
+		return fd;
+
+	alloc_len = 0;
+	do {
+		const size_t desc_read_length = 256;
+		uint8_t *read_ptr;
+
+		alloc_len += desc_read_length;
+		priv->descriptors = usbi_reallocf(priv->descriptors, alloc_len);
+		if (!priv->descriptors) {
+			if (fd != wrapped_fd)
+				close(fd);
+			return LIBUSB_ERROR_NO_MEM;
+		}
+		read_ptr = (uint8_t *)priv->descriptors + priv->descriptors_len;
+		/* usbfs has holes in the file */
+		if (!sysfs_dir)
+			memset(read_ptr, 0, desc_read_length);
+		nb = read(fd, read_ptr, desc_read_length);
+		if (nb < 0) {
+			usbi_err(ctx, "read descriptor failed, errno=%d", errno);
+			if (fd != wrapped_fd)
+				close(fd);
+			return LIBUSB_ERROR_IO;
+		}
+		priv->descriptors_len += (size_t)nb;
+	} while (priv->descriptors_len == alloc_len);
+
+	if (fd != wrapped_fd)
+		close(fd);
+
+	if (priv->descriptors_len < LIBUSB_DT_DEVICE_SIZE) {
+		usbi_err(ctx, "short descriptor read (%zu)", priv->descriptors_len);
+		return LIBUSB_ERROR_IO;
+	}
+
+	r = parse_config_descriptors(dev);
+	if (r < 0)
+		return r;
+
+	memcpy(&dev->device_descriptor, priv->descriptors, LIBUSB_DT_DEVICE_SIZE);
+
+	if (sysfs_dir) {
+		/* sysfs descriptors are in bus-endian format */
+		usbi_localize_device_descriptor(&dev->device_descriptor);
+		return LIBUSB_SUCCESS;
+	}
+
+	/* cache active config */
+	if (wrapped_fd < 0)
+		fd = get_usbfs_fd(dev, O_RDWR, 1);
+	else
+		fd = wrapped_fd;
+	if (fd < 0) {
+		/* cannot send a control message to determine the active
+		 * config. just assume the first one is active. */
+		usbi_warn(ctx, "Missing rw usbfs access; cannot determine "
+			       "active configuration descriptor");
+		if (priv->config_descriptors)
+			priv->active_config = (int)priv->config_descriptors[0].desc->bConfigurationValue;
+		else
+			priv->active_config = -1; /* No config dt */
+
+		return LIBUSB_SUCCESS;
+	}
+
+	r = usbfs_get_active_config(dev, fd);
+	if (fd != wrapped_fd)
+		close(fd);
+
+	return r;
+}
+
+static int linux_get_parent_info(struct libusb_device *dev, const char *sysfs_dir)
+{
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	struct libusb_device *it;
+	char *parent_sysfs_dir, *tmp;
+	int ret, add_parent = 1;
+
+	/* XXX -- can we figure out the topology when using usbfs? */
+	if (!sysfs_dir || !strncmp(sysfs_dir, "usb", 3)) {
+		/* either using usbfs or finding the parent of a root hub */
+		return LIBUSB_SUCCESS;
+	}
+
+	parent_sysfs_dir = strdup(sysfs_dir);
+	if (!parent_sysfs_dir)
+		return LIBUSB_ERROR_NO_MEM;
+
+	if ((tmp = strrchr(parent_sysfs_dir, '.')) ||
+	    (tmp = strrchr(parent_sysfs_dir, '-'))) {
+	        dev->port_number = atoi(tmp + 1);
+		*tmp = '\0';
+	} else {
+		usbi_warn(ctx, "Can not parse sysfs_dir: %s, no parent info",
+			  parent_sysfs_dir);
+		free(parent_sysfs_dir);
+		return LIBUSB_SUCCESS;
+	}
+
+	/* is the parent a root hub? */
+	if (!strchr(parent_sysfs_dir, '-')) {
+		tmp = parent_sysfs_dir;
+		ret = asprintf(&parent_sysfs_dir, "usb%s", tmp);
+		free(tmp);
+		if (ret < 0)
+			return LIBUSB_ERROR_NO_MEM;
+	}
+
+retry:
+	/* find the parent in the context */
+	usbi_mutex_lock(&ctx->usb_devs_lock);
+	for_each_device(ctx, it) {
+		struct linux_device_priv *priv = usbi_get_device_priv(it);
+
+		if (priv->sysfs_dir) {
+			if (!strcmp(priv->sysfs_dir, parent_sysfs_dir)) {
+				dev->parent_dev = libusb_ref_device(it);
+				break;
+			}
+		}
+	}
+	usbi_mutex_unlock(&ctx->usb_devs_lock);
+
+	if (!dev->parent_dev && add_parent) {
+		usbi_dbg(ctx, "parent_dev %s not enumerated yet, enumerating now",
+			 parent_sysfs_dir);
+		sysfs_scan_device(ctx, parent_sysfs_dir);
+		add_parent = 0;
+		goto retry;
+	}
+
+	usbi_dbg(ctx, "dev %p (%s) has parent %p (%s) port %u", dev, sysfs_dir,
+		 dev->parent_dev, parent_sysfs_dir, dev->port_number);
+
+	free(parent_sysfs_dir);
+
+	return LIBUSB_SUCCESS;
+}
+
+int linux_enumerate_device(struct libusb_context *ctx,
+	uint8_t busnum, uint8_t devaddr, const char *sysfs_dir)
+{
+	unsigned long session_id;
+	struct libusb_device *dev;
+	int r;
+
+	/* FIXME: session ID is not guaranteed unique as addresses can wrap and
+	 * will be reused. instead we should add a simple sysfs attribute with
+	 * a session ID. */
+	session_id = busnum << 8 | devaddr;
+	usbi_dbg(ctx, "busnum %u devaddr %u session_id %lu", busnum, devaddr, session_id);
+
+	dev = usbi_get_device_by_session_id(ctx, session_id);
+	if (dev) {
+		/* device already exists in the context */
+		usbi_dbg(ctx, "session_id %lu already exists", session_id);
+		libusb_unref_device(dev);
+		return LIBUSB_SUCCESS;
+	}
+
+	usbi_dbg(ctx, "allocating new device for %u/%u (session %lu)",
+		 busnum, devaddr, session_id);
+	dev = usbi_alloc_device(ctx, session_id);
+	if (!dev)
+		return LIBUSB_ERROR_NO_MEM;
+
+	r = initialize_device(dev, busnum, devaddr, sysfs_dir, -1);
+	if (r < 0)
+		goto out;
+	r = usbi_sanitize_device(dev);
+	if (r < 0)
+		goto out;
+
+	r = linux_get_parent_info(dev, sysfs_dir);
+	if (r < 0)
+		goto out;
+out:
+	if (r < 0)
+		libusb_unref_device(dev);
+	else
+		usbi_connect_device(dev);
+
+	return r;
+}
+
+void linux_hotplug_enumerate(uint8_t busnum, uint8_t devaddr, const char *sys_name)
+{
+	struct libusb_context *ctx;
+
+	usbi_mutex_static_lock(&active_contexts_lock);
+	for_each_context(ctx) {
+		linux_enumerate_device(ctx, busnum, devaddr, sys_name);
+	}
+	usbi_mutex_static_unlock(&active_contexts_lock);
+}
+
+void linux_device_disconnected(uint8_t busnum, uint8_t devaddr)
+{
+	struct libusb_context *ctx;
+	struct libusb_device *dev;
+	unsigned long session_id = busnum << 8 | devaddr;
+
+	usbi_mutex_static_lock(&active_contexts_lock);
+	for_each_context(ctx) {
+		dev = usbi_get_device_by_session_id(ctx, session_id);
+		if (dev) {
+			usbi_disconnect_device(dev);
+			libusb_unref_device(dev);
+		} else {
+			usbi_dbg(ctx, "device not found for session %lx", session_id);
+		}
+	}
+	usbi_mutex_static_unlock(&active_contexts_lock);
+}
+
+#if !defined(HAVE_LIBUDEV)
+static int parse_u8(const char *str, uint8_t *val_p)
+{
+	char *endptr;
+	long num;
+
+	errno = 0;
+	num = strtol(str, &endptr, 10);
+	if (num < 0 || num > UINT8_MAX || errno)
+		return 0;
+	if (endptr == str || *endptr != '\0')
+		return 0;
+
+	*val_p = (uint8_t)num;
+	return 1;
+}
+
+/* open a bus directory and adds all discovered devices to the context */
+static int usbfs_scan_busdir(struct libusb_context *ctx, uint8_t busnum)
+{
+	DIR *dir;
+	char dirpath[20];
+	struct dirent *entry;
+	int r = LIBUSB_ERROR_IO;
+
+	sprintf(dirpath, USB_DEVTMPFS_PATH "/%03u", busnum);
+	usbi_dbg(ctx, "%s", dirpath);
+	dir = opendir(dirpath);
+	if (!dir) {
+		usbi_err(ctx, "opendir '%s' failed, errno=%d", dirpath, errno);
+		/* FIXME: should handle valid race conditions like hub unplugged
+		 * during directory iteration - this is not an error */
+		return r;
+	}
+
+	while ((entry = readdir(dir))) {
+		uint8_t devaddr;
+
+		if (entry->d_name[0] == '.')
+			continue;
+
+		if (!parse_u8(entry->d_name, &devaddr)) {
+			usbi_dbg(ctx, "unknown dir entry %s", entry->d_name);
+			continue;
+		}
+
+		if (linux_enumerate_device(ctx, busnum, devaddr, NULL)) {
+			usbi_dbg(ctx, "failed to enumerate dir entry %s", entry->d_name);
+			continue;
+		}
+
+		r = 0;
+	}
+
+	closedir(dir);
+	return r;
+}
+
+static int usbfs_get_device_list(struct libusb_context *ctx)
+{
+	struct dirent *entry;
+	DIR *buses;
+	uint8_t busnum, devaddr;
+	int r = 0;
+
+	if (usbdev_names)
+		buses = opendir(USBDEV_PATH);
+	else
+		buses = opendir(USB_DEVTMPFS_PATH);
+
+	if (!buses) {
+		usbi_err(ctx, "opendir buses failed, errno=%d", errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	while ((entry = readdir(buses))) {
+		if (entry->d_name[0] == '.')
+			continue;
+
+		if (usbdev_names) {
+			if (!is_usbdev_entry(entry->d_name, &busnum, &devaddr))
+				continue;
+
+			r = linux_enumerate_device(ctx, busnum, devaddr, NULL);
+			if (r < 0) {
+				usbi_dbg(ctx, "failed to enumerate dir entry %s", entry->d_name);
+				continue;
+			}
+		} else {
+			if (!parse_u8(entry->d_name, &busnum)) {
+				usbi_dbg(ctx, "unknown dir entry %s", entry->d_name);
+				continue;
+			}
+
+			r = usbfs_scan_busdir(ctx, busnum);
+			if (r < 0)
+				break;
+		}
+	}
+
+	closedir(buses);
+	return r;
+
+}
+
+static int sysfs_get_device_list(struct libusb_context *ctx)
+{
+	DIR *devices = opendir(SYSFS_DEVICE_PATH);
+	struct dirent *entry;
+	int num_devices = 0;
+	int num_enumerated = 0;
+
+	if (!devices) {
+		usbi_err(ctx, "opendir devices failed, errno=%d", errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	while ((entry = readdir(devices))) {
+		if ((!isdigit(entry->d_name[0]) && strncmp(entry->d_name, "usb", 3))
+		    || strchr(entry->d_name, ':'))
+			continue;
+
+		num_devices++;
+
+		if (sysfs_scan_device(ctx, entry->d_name)) {
+			usbi_dbg(ctx, "failed to enumerate dir entry %s", entry->d_name);
+			continue;
+		}
+
+		num_enumerated++;
+	}
+
+	closedir(devices);
+
+	/* successful if at least one device was enumerated or no devices were found */
+	if (num_enumerated || !num_devices)
+		return LIBUSB_SUCCESS;
+	else
+		return LIBUSB_ERROR_IO;
+}
+
+static int linux_default_scan_devices(struct libusb_context *ctx)
+{
+	/* we can retrieve device list and descriptors from sysfs or usbfs.
+	 * sysfs is preferable, because if we use usbfs we end up resuming
+	 * any autosuspended USB devices. however, sysfs is not available
+	 * everywhere, so we need a usbfs fallback too.
+	 */
+	if (sysfs_available)
+		return sysfs_get_device_list(ctx);
+	else
+		return usbfs_get_device_list(ctx);
+}
+#endif
+
+static int initialize_handle(struct libusb_device_handle *handle, int fd)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int r;
+
+	hpriv->fd = fd;
+
+	r = ioctl(fd, IOCTL_USBFS_GET_CAPABILITIES, &hpriv->caps);
+	if (r < 0) {
+		if (errno == ENOTTY)
+			usbi_dbg(HANDLE_CTX(handle), "getcap not available");
+		else
+			usbi_err(HANDLE_CTX(handle), "getcap failed, errno=%d", errno);
+		hpriv->caps = USBFS_CAP_BULK_CONTINUATION;
+	}
+
+	return usbi_add_event_source(HANDLE_CTX(handle), hpriv->fd, POLLOUT);
+}
+
+static int op_wrap_sys_device(struct libusb_context *ctx,
+	struct libusb_device_handle *handle, intptr_t sys_dev)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int fd = (int)sys_dev;
+	uint8_t busnum, devaddr;
+	struct usbfs_connectinfo ci;
+	struct libusb_device *dev;
+	int r;
+
+	r = linux_get_device_address(ctx, 1, &busnum, &devaddr, NULL, NULL, fd);
+	if (r < 0) {
+		r = ioctl(fd, IOCTL_USBFS_CONNECTINFO, &ci);
+		if (r < 0) {
+			usbi_err(ctx, "connectinfo failed, errno=%d", errno);
+			return LIBUSB_ERROR_IO;
+		}
+		/* There is no ioctl to get the bus number. We choose 0 here
+		 * as linux starts numbering buses from 1. */
+		busnum = 0;
+		devaddr = ci.devnum;
+	}
+
+	/* Session id is unused as we do not add the device to the list of
+	 * connected devices. */
+	usbi_dbg(ctx, "allocating new device for fd %d", fd);
+	dev = usbi_alloc_device(ctx, 0);
+	if (!dev)
+		return LIBUSB_ERROR_NO_MEM;
+
+	r = initialize_device(dev, busnum, devaddr, NULL, fd);
+	if (r < 0)
+		goto out;
+	r = usbi_sanitize_device(dev);
+	if (r < 0)
+		goto out;
+	/* Consider the device as connected, but do not add it to the managed
+	 * device list. */
+	usbi_atomic_store(&dev->attached, 1);
+	handle->dev = dev;
+
+	r = initialize_handle(handle, fd);
+	hpriv->fd_keep = 1;
+
+out:
+	if (r < 0)
+		libusb_unref_device(dev);
+	return r;
+}
+
+static int op_open(struct libusb_device_handle *handle)
+{
+	int fd, r;
+
+	fd = get_usbfs_fd(handle->dev, O_RDWR, 0);
+	if (fd < 0) {
+		if (fd == LIBUSB_ERROR_NO_DEVICE) {
+			/* device will still be marked as attached if hotplug monitor thread
+			 * hasn't processed remove event yet */
+			usbi_mutex_static_lock(&linux_hotplug_lock);
+			if (usbi_atomic_load(&handle->dev->attached)) {
+				usbi_dbg(HANDLE_CTX(handle), "open failed with no device, but device still attached");
+				linux_device_disconnected(handle->dev->bus_number,
+							  handle->dev->device_address);
+			}
+			usbi_mutex_static_unlock(&linux_hotplug_lock);
+		}
+		return fd;
+	}
+
+	r = initialize_handle(handle, fd);
+	if (r < 0)
+		close(fd);
+
+	return r;
+}
+
+static void op_close(struct libusb_device_handle *dev_handle)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(dev_handle);
+
+	/* fd may have already been removed by POLLERR condition in op_handle_events() */
+	if (!hpriv->fd_removed)
+		usbi_remove_event_source(HANDLE_CTX(dev_handle), hpriv->fd);
+	if (!hpriv->fd_keep)
+		close(hpriv->fd);
+}
+
+static int op_get_configuration(struct libusb_device_handle *handle,
+	uint8_t *config)
+{
+	struct linux_device_priv *priv = usbi_get_device_priv(handle->dev);
+	int active_config;
+	int r;
+
+	if (priv->sysfs_dir) {
+		r = sysfs_get_active_config(handle->dev, &active_config);
+	} else {
+		struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+
+		r = usbfs_get_active_config(handle->dev, hpriv->fd);
+		if (r == LIBUSB_SUCCESS)
+			active_config = priv->active_config;
+	}
+	if (r < 0)
+		return r;
+
+	if (active_config == -1) {
+		usbi_warn(HANDLE_CTX(handle), "device unconfigured");
+		active_config = 0;
+	}
+
+	*config = (uint8_t)active_config;
+
+	return 0;
+}
+
+static int op_set_configuration(struct libusb_device_handle *handle, int config)
+{
+	struct linux_device_priv *priv = usbi_get_device_priv(handle->dev);
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int fd = hpriv->fd;
+	int r = ioctl(fd, IOCTL_USBFS_SETCONFIGURATION, &config);
+
+	if (r < 0) {
+		if (errno == EINVAL)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == EBUSY)
+			return LIBUSB_ERROR_BUSY;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle), "set configuration failed, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	/* if necessary, update our cached active config descriptor */
+	if (!priv->sysfs_dir) {
+		if (config == 0 && !dev_has_config0(handle->dev))
+			config = -1;
+
+		priv->active_config = config;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int claim_interface(struct libusb_device_handle *handle, unsigned int iface)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int fd = hpriv->fd;
+	int r = ioctl(fd, IOCTL_USBFS_CLAIMINTERFACE, &iface);
+
+	if (r < 0) {
+		if (errno == ENOENT)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == EBUSY)
+			return LIBUSB_ERROR_BUSY;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle), "claim interface failed, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+	return 0;
+}
+
+static int release_interface(struct libusb_device_handle *handle, unsigned int iface)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int fd = hpriv->fd;
+	int r = ioctl(fd, IOCTL_USBFS_RELEASEINTERFACE, &iface);
+
+	if (r < 0) {
+		if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle), "release interface failed, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+	return 0;
+}
+
+static int op_set_interface(struct libusb_device_handle *handle, uint8_t interface,
+	uint8_t altsetting)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int fd = hpriv->fd;
+	struct usbfs_setinterface setintf;
+	int r;
+
+	setintf.interface = interface;
+	setintf.altsetting = altsetting;
+	r = ioctl(fd, IOCTL_USBFS_SETINTERFACE, &setintf);
+	if (r < 0) {
+		if (errno == EINVAL)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle), "set interface failed, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+static int op_clear_halt(struct libusb_device_handle *handle,
+	unsigned char endpoint)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int fd = hpriv->fd;
+	unsigned int _endpoint = endpoint;
+	int r = ioctl(fd, IOCTL_USBFS_CLEAR_HALT, &_endpoint);
+
+	if (r < 0) {
+		if (errno == ENOENT)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle), "clear halt failed, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+static int op_reset_device(struct libusb_device_handle *handle)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int fd = hpriv->fd;
+	int r, ret = 0;
+	uint8_t i;
+
+	/* Doing a device reset will cause the usbfs driver to get unbound
+	 * from any interfaces it is bound to. By voluntarily unbinding
+	 * the usbfs driver ourself, we stop the kernel from rebinding
+	 * the interface after reset (which would end up with the interface
+	 * getting bound to the in kernel driver if any). */
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		if (handle->claimed_interfaces & (1UL << i))
+			release_interface(handle, i);
+	}
+
+	usbi_mutex_lock(&handle->lock);
+	r = ioctl(fd, IOCTL_USBFS_RESET, NULL);
+	if (r < 0) {
+		if (errno == ENODEV) {
+			ret = LIBUSB_ERROR_NOT_FOUND;
+			goto out;
+		}
+
+		usbi_err(HANDLE_CTX(handle), "reset failed, errno=%d", errno);
+		ret = LIBUSB_ERROR_OTHER;
+		goto out;
+	}
+
+	/* And re-claim any interfaces which were claimed before the reset */
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		if (!(handle->claimed_interfaces & (1UL << i)))
+			continue;
+		/*
+		 * A driver may have completed modprobing during
+		 * IOCTL_USBFS_RESET, and bound itself as soon as
+		 * IOCTL_USBFS_RESET released the device lock
+		 */
+		r = detach_kernel_driver_and_claim(handle, i);
+		if (r) {
+			usbi_warn(HANDLE_CTX(handle), "failed to re-claim interface %u after reset: %s",
+				  i, libusb_error_name(r));
+			handle->claimed_interfaces &= ~(1UL << i);
+			ret = LIBUSB_ERROR_NOT_FOUND;
+		}
+	}
+out:
+	usbi_mutex_unlock(&handle->lock);
+	return ret;
+}
+
+static int do_streams_ioctl(struct libusb_device_handle *handle, long req,
+	uint32_t num_streams, unsigned char *endpoints, int num_endpoints)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int r, fd = hpriv->fd;
+	struct usbfs_streams *streams;
+
+	if (num_endpoints > 30) /* Max 15 in + 15 out eps */
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	streams = malloc(sizeof(*streams) + num_endpoints);
+	if (!streams)
+		return LIBUSB_ERROR_NO_MEM;
+
+	streams->num_streams = num_streams;
+	streams->num_eps = num_endpoints;
+	memcpy(streams->eps, endpoints, num_endpoints);
+
+	r = ioctl(fd, req, streams);
+
+	free(streams);
+
+	if (r < 0) {
+		if (errno == ENOTTY)
+			return LIBUSB_ERROR_NOT_SUPPORTED;
+		else if (errno == EINVAL)
+			return LIBUSB_ERROR_INVALID_PARAM;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle), "streams-ioctl failed, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+	return r;
+}
+
+static int op_alloc_streams(struct libusb_device_handle *handle,
+	uint32_t num_streams, unsigned char *endpoints, int num_endpoints)
+{
+	return do_streams_ioctl(handle, IOCTL_USBFS_ALLOC_STREAMS,
+				num_streams, endpoints, num_endpoints);
+}
+
+static int op_free_streams(struct libusb_device_handle *handle,
+		unsigned char *endpoints, int num_endpoints)
+{
+	return do_streams_ioctl(handle, IOCTL_USBFS_FREE_STREAMS, 0,
+				endpoints, num_endpoints);
+}
+
+static void *op_dev_mem_alloc(struct libusb_device_handle *handle, size_t len)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	void *buffer;
+
+	buffer = mmap(NULL, len, PROT_READ | PROT_WRITE, MAP_SHARED, hpriv->fd, 0);
+	if (buffer == MAP_FAILED) {
+		usbi_err(HANDLE_CTX(handle), "alloc dev mem failed, errno=%d", errno);
+		return NULL;
+	}
+	return buffer;
+}
+
+static int op_dev_mem_free(struct libusb_device_handle *handle, void *buffer,
+	size_t len)
+{
+	if (munmap(buffer, len) != 0) {
+		usbi_err(HANDLE_CTX(handle), "free dev mem failed, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	} else {
+		return LIBUSB_SUCCESS;
+	}
+}
+
+static int op_kernel_driver_active(struct libusb_device_handle *handle,
+	uint8_t interface)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int fd = hpriv->fd;
+	struct usbfs_getdriver getdrv;
+	int r;
+
+	getdrv.interface = interface;
+	r = ioctl(fd, IOCTL_USBFS_GETDRIVER, &getdrv);
+	if (r < 0) {
+		if (errno == ENODATA)
+			return 0;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle), "get driver failed, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return strcmp(getdrv.driver, "usbfs") != 0;
+}
+
+static int op_detach_kernel_driver(struct libusb_device_handle *handle,
+	uint8_t interface)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int fd = hpriv->fd;
+	struct usbfs_ioctl command;
+	struct usbfs_getdriver getdrv;
+	int r;
+
+	command.ifno = interface;
+	command.ioctl_code = IOCTL_USBFS_DISCONNECT;
+	command.data = NULL;
+
+	getdrv.interface = interface;
+	r = ioctl(fd, IOCTL_USBFS_GETDRIVER, &getdrv);
+	if (r == 0 && !strcmp(getdrv.driver, "usbfs"))
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	r = ioctl(fd, IOCTL_USBFS_IOCTL, &command);
+	if (r < 0) {
+		if (errno == ENODATA)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == EINVAL)
+			return LIBUSB_ERROR_INVALID_PARAM;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle), "detach failed, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return 0;
+}
+
+static int op_attach_kernel_driver(struct libusb_device_handle *handle,
+	uint8_t interface)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int fd = hpriv->fd;
+	struct usbfs_ioctl command;
+	int r;
+
+	command.ifno = interface;
+	command.ioctl_code = IOCTL_USBFS_CONNECT;
+	command.data = NULL;
+
+	r = ioctl(fd, IOCTL_USBFS_IOCTL, &command);
+	if (r < 0) {
+		if (errno == ENODATA)
+			return LIBUSB_ERROR_NOT_FOUND;
+		else if (errno == EINVAL)
+			return LIBUSB_ERROR_INVALID_PARAM;
+		else if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+		else if (errno == EBUSY)
+			return LIBUSB_ERROR_BUSY;
+
+		usbi_err(HANDLE_CTX(handle), "attach failed, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	} else if (r == 0) {
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	return 0;
+}
+
+static int detach_kernel_driver_and_claim(struct libusb_device_handle *handle,
+	uint8_t interface)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	struct usbfs_disconnect_claim dc;
+	int r, fd = hpriv->fd;
+
+	dc.interface = interface;
+	strcpy(dc.driver, "usbfs");
+	dc.flags = USBFS_DISCONNECT_CLAIM_EXCEPT_DRIVER;
+	r = ioctl(fd, IOCTL_USBFS_DISCONNECT_CLAIM, &dc);
+	if (r == 0)
+		return 0;
+	switch (errno) {
+	case ENOTTY:
+		break;
+	case EBUSY:
+		return LIBUSB_ERROR_BUSY;
+	case EINVAL:
+		return LIBUSB_ERROR_INVALID_PARAM;
+	case ENODEV:
+		return LIBUSB_ERROR_NO_DEVICE;
+	default:
+		usbi_err(HANDLE_CTX(handle), "disconnect-and-claim failed, errno=%d", errno);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	/* Fallback code for kernels which don't support the
+	   disconnect-and-claim ioctl */
+	r = op_detach_kernel_driver(handle, interface);
+	if (r != 0 && r != LIBUSB_ERROR_NOT_FOUND)
+		return r;
+
+	return claim_interface(handle, interface);
+}
+
+static int op_claim_interface(struct libusb_device_handle *handle, uint8_t interface)
+{
+	if (handle->auto_detach_kernel_driver)
+		return detach_kernel_driver_and_claim(handle, interface);
+	else
+		return claim_interface(handle, interface);
+}
+
+static int op_release_interface(struct libusb_device_handle *handle, uint8_t interface)
+{
+	int r;
+
+	r = release_interface(handle, interface);
+	if (r)
+		return r;
+
+	if (handle->auto_detach_kernel_driver)
+		op_attach_kernel_driver(handle, interface);
+
+	return 0;
+}
+
+static void op_destroy_device(struct libusb_device *dev)
+{
+	struct linux_device_priv *priv = usbi_get_device_priv(dev);
+
+	free(priv->config_descriptors);
+	free(priv->descriptors);
+	free(priv->sysfs_dir);
+}
+
+/* URBs are discarded in reverse order of submission to avoid races. */
+static int discard_urbs(struct usbi_transfer *itransfer, int first, int last_plus_one)
+{
+	struct libusb_transfer *transfer =
+		USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_transfer_priv *tpriv = usbi_get_transfer_priv(itransfer);
+	struct linux_device_handle_priv *hpriv =
+		usbi_get_device_handle_priv(transfer->dev_handle);
+	int i, ret = 0;
+	struct usbfs_urb *urb;
+
+	for (i = last_plus_one - 1; i >= first; i--) {
+		if (transfer->type == LIBUSB_TRANSFER_TYPE_ISOCHRONOUS)
+			urb = tpriv->iso_urbs[i];
+		else
+			urb = &tpriv->urbs[i];
+
+		if (ioctl(hpriv->fd, IOCTL_USBFS_DISCARDURB, urb) == 0)
+			continue;
+
+		if (errno == EINVAL) {
+			usbi_dbg(TRANSFER_CTX(transfer), "URB not found --> assuming ready to be reaped");
+			if (i == (last_plus_one - 1))
+				ret = LIBUSB_ERROR_NOT_FOUND;
+		} else if (errno == ENODEV) {
+			usbi_dbg(TRANSFER_CTX(transfer), "Device not found for URB --> assuming ready to be reaped");
+			ret = LIBUSB_ERROR_NO_DEVICE;
+		} else {
+			usbi_warn(TRANSFER_CTX(transfer), "unrecognised discard errno %d", errno);
+			ret = LIBUSB_ERROR_OTHER;
+		}
+	}
+	return ret;
+}
+
+static void free_iso_urbs(struct linux_transfer_priv *tpriv)
+{
+	int i;
+
+	for (i = 0; i < tpriv->num_urbs; i++) {
+		struct usbfs_urb *urb = tpriv->iso_urbs[i];
+
+		if (!urb)
+			break;
+		free(urb);
+	}
+
+	free(tpriv->iso_urbs);
+	tpriv->iso_urbs = NULL;
+}
+
+static int submit_bulk_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer =
+		USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_transfer_priv *tpriv = usbi_get_transfer_priv(itransfer);
+	struct linux_device_handle_priv *hpriv =
+		usbi_get_device_handle_priv(transfer->dev_handle);
+	struct usbfs_urb *urbs;
+	int is_out = IS_XFEROUT(transfer);
+	int bulk_buffer_len, use_bulk_continuation;
+	int num_urbs;
+	int last_urb_partial = 0;
+	int r;
+	int i;
+
+	/*
+	 * Older versions of usbfs place a 16kb limit on bulk URBs. We work
+	 * around this by splitting large transfers into 16k blocks, and then
+	 * submit all urbs at once. it would be simpler to submit one urb at
+	 * a time, but there is a big performance gain doing it this way.
+	 *
+	 * Newer versions lift the 16k limit (USBFS_CAP_NO_PACKET_SIZE_LIM),
+	 * using arbitrary large transfers can still be a bad idea though, as
+	 * the kernel needs to allocate physical contiguous memory for this,
+	 * which may fail for large buffers.
+	 *
+	 * The kernel solves this problem by splitting the transfer into
+	 * blocks itself when the host-controller is scatter-gather capable
+	 * (USBFS_CAP_BULK_SCATTER_GATHER), which most controllers are.
+	 *
+	 * Last, there is the issue of short-transfers when splitting, for
+	 * short split-transfers to work reliable USBFS_CAP_BULK_CONTINUATION
+	 * is needed, but this is not always available.
+	 */
+	if (hpriv->caps & USBFS_CAP_BULK_SCATTER_GATHER) {
+		/* Good! Just submit everything in one go */
+		bulk_buffer_len = transfer->length ? transfer->length : 1;
+		use_bulk_continuation = 0;
+	} else if (hpriv->caps & USBFS_CAP_BULK_CONTINUATION) {
+		/* Split the transfers and use bulk-continuation to
+		   avoid issues with short-transfers */
+		bulk_buffer_len = MAX_BULK_BUFFER_LENGTH;
+		use_bulk_continuation = 1;
+	} else if (hpriv->caps & USBFS_CAP_NO_PACKET_SIZE_LIM) {
+		/* Don't split, assume the kernel can alloc the buffer
+		   (otherwise the submit will fail with -ENOMEM) */
+		bulk_buffer_len = transfer->length ? transfer->length : 1;
+		use_bulk_continuation = 0;
+	} else {
+		/* Bad, splitting without bulk-continuation, short transfers
+		   which end before the last urb will not work reliable! */
+		/* Note we don't warn here as this is "normal" on kernels <
+		   2.6.32 and not a problem for most applications */
+		bulk_buffer_len = MAX_BULK_BUFFER_LENGTH;
+		use_bulk_continuation = 0;
+	}
+
+	num_urbs = transfer->length / bulk_buffer_len;
+
+	if (transfer->length == 0) {
+		num_urbs = 1;
+	} else if ((transfer->length % bulk_buffer_len) > 0) {
+		last_urb_partial = 1;
+		num_urbs++;
+	}
+	usbi_dbg(TRANSFER_CTX(transfer), "need %d urbs for new transfer with length %d", num_urbs, transfer->length);
+	urbs = calloc(num_urbs, sizeof(*urbs));
+	if (!urbs)
+		return LIBUSB_ERROR_NO_MEM;
+	tpriv->urbs = urbs;
+	tpriv->num_urbs = num_urbs;
+	tpriv->num_retired = 0;
+	tpriv->reap_action = NORMAL;
+	tpriv->reap_status = LIBUSB_TRANSFER_COMPLETED;
+
+	for (i = 0; i < num_urbs; i++) {
+		struct usbfs_urb *urb = &urbs[i];
+
+		urb->usercontext = itransfer;
+		switch (transfer->type) {
+		case LIBUSB_TRANSFER_TYPE_BULK:
+			urb->type = USBFS_URB_TYPE_BULK;
+			urb->stream_id = 0;
+			break;
+		case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
+			urb->type = USBFS_URB_TYPE_BULK;
+			urb->stream_id = itransfer->stream_id;
+			break;
+		case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+			urb->type = USBFS_URB_TYPE_INTERRUPT;
+			break;
+		}
+		urb->endpoint = transfer->endpoint;
+		urb->buffer = transfer->buffer + (i * bulk_buffer_len);
+
+		/* don't set the short not ok flag for the last URB */
+		if (use_bulk_continuation && !is_out && (i < num_urbs - 1))
+			urb->flags = USBFS_URB_SHORT_NOT_OK;
+
+		if (i == num_urbs - 1 && last_urb_partial)
+			urb->buffer_length = transfer->length % bulk_buffer_len;
+		else if (transfer->length == 0)
+			urb->buffer_length = 0;
+		else
+			urb->buffer_length = bulk_buffer_len;
+
+		if (i > 0 && use_bulk_continuation)
+			urb->flags |= USBFS_URB_BULK_CONTINUATION;
+
+		/* we have already checked that the flag is supported */
+		if (is_out && i == num_urbs - 1 &&
+		    (transfer->flags & LIBUSB_TRANSFER_ADD_ZERO_PACKET))
+			urb->flags |= USBFS_URB_ZERO_PACKET;
+
+		r = ioctl(hpriv->fd, IOCTL_USBFS_SUBMITURB, urb);
+		if (r == 0)
+			continue;
+
+		if (errno == ENODEV) {
+			r = LIBUSB_ERROR_NO_DEVICE;
+		} else if (errno == ENOMEM) {
+			r = LIBUSB_ERROR_NO_MEM;
+		} else {
+			usbi_err(TRANSFER_CTX(transfer), "submiturb failed, errno=%d", errno);
+			r = LIBUSB_ERROR_IO;
+		}
+
+		/* if the first URB submission fails, we can simply free up and
+		 * return failure immediately. */
+		if (i == 0) {
+			usbi_dbg(TRANSFER_CTX(transfer), "first URB failed, easy peasy");
+			free(urbs);
+			tpriv->urbs = NULL;
+			return r;
+		}
+
+		/* if it's not the first URB that failed, the situation is a bit
+		 * tricky. we may need to discard all previous URBs. there are
+		 * complications:
+		 *  - discarding is asynchronous - discarded urbs will be reaped
+		 *    later. the user must not have freed the transfer when the
+		 *    discarded URBs are reaped, otherwise libusb will be using
+		 *    freed memory.
+		 *  - the earlier URBs may have completed successfully and we do
+		 *    not want to throw away any data.
+		 *  - this URB failing may be no error; EREMOTEIO means that
+		 *    this transfer simply didn't need all the URBs we submitted
+		 * so, we report that the transfer was submitted successfully and
+		 * in case of error we discard all previous URBs. later when
+		 * the final reap completes we can report error to the user,
+		 * or success if an earlier URB was completed successfully.
+		 */
+		tpriv->reap_action = errno == EREMOTEIO ? COMPLETED_EARLY : SUBMIT_FAILED;
+
+		/* The URBs we haven't submitted yet we count as already
+		 * retired. */
+		tpriv->num_retired += num_urbs - i;
+
+		/* If we completed short then don't try to discard. */
+		if (tpriv->reap_action == COMPLETED_EARLY)
+			return 0;
+
+		discard_urbs(itransfer, 0, i);
+
+		usbi_dbg(TRANSFER_CTX(transfer), "reporting successful submission but waiting for %d "
+			 "discards before reporting error", i);
+		return 0;
+	}
+
+	return 0;
+}
+
+static int submit_iso_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer =
+		USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_transfer_priv *tpriv = usbi_get_transfer_priv(itransfer);
+	struct linux_device_handle_priv *hpriv =
+		usbi_get_device_handle_priv(transfer->dev_handle);
+	struct usbfs_urb **urbs;
+	int num_packets = transfer->num_iso_packets;
+	int num_packets_remaining;
+	int i, j;
+	int num_urbs;
+	unsigned int packet_len;
+	unsigned int total_len = 0;
+	unsigned char *urb_buffer = transfer->buffer;
+
+	if (num_packets < 1)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	/* usbfs places arbitrary limits on iso URBs. this limit has changed
+	 * at least three times, but we attempt to detect this limit during
+	 * init and check it here. if the kernel rejects the request due to
+	 * its size, we return an error indicating such to the user.
+	 */
+	for (i = 0; i < num_packets; i++) {
+		packet_len = transfer->iso_packet_desc[i].length;
+
+		if (packet_len > max_iso_packet_len) {
+			usbi_warn(TRANSFER_CTX(transfer),
+				  "iso packet length of %u bytes exceeds maximum of %u bytes",
+				  packet_len, max_iso_packet_len);
+			return LIBUSB_ERROR_INVALID_PARAM;
+		}
+
+		total_len += packet_len;
+	}
+
+	if (transfer->length < (int)total_len)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	/* usbfs limits the number of iso packets per URB */
+	num_urbs = (num_packets + (MAX_ISO_PACKETS_PER_URB - 1)) / MAX_ISO_PACKETS_PER_URB;
+
+	usbi_dbg(TRANSFER_CTX(transfer), "need %d urbs for new transfer with length %d", num_urbs, transfer->length);
+
+	urbs = calloc(num_urbs, sizeof(*urbs));
+	if (!urbs)
+		return LIBUSB_ERROR_NO_MEM;
+
+	tpriv->iso_urbs = urbs;
+	tpriv->num_urbs = num_urbs;
+	tpriv->num_retired = 0;
+	tpriv->reap_action = NORMAL;
+	tpriv->iso_packet_offset = 0;
+
+	/* allocate + initialize each URB with the correct number of packets */
+	num_packets_remaining = num_packets;
+	for (i = 0, j = 0; i < num_urbs; i++) {
+		int num_packets_in_urb = MIN(num_packets_remaining, MAX_ISO_PACKETS_PER_URB);
+		struct usbfs_urb *urb;
+		size_t alloc_size;
+		int k;
+
+		alloc_size = sizeof(*urb)
+			+ (num_packets_in_urb * sizeof(struct usbfs_iso_packet_desc));
+		urb = calloc(1, alloc_size);
+		if (!urb) {
+			free_iso_urbs(tpriv);
+			return LIBUSB_ERROR_NO_MEM;
+		}
+		urbs[i] = urb;
+
+		/* populate packet lengths */
+		for (k = 0; k < num_packets_in_urb; j++, k++) {
+			packet_len = transfer->iso_packet_desc[j].length;
+			urb->buffer_length += packet_len;
+			urb->iso_frame_desc[k].length = packet_len;
+		}
+
+		urb->usercontext = itransfer;
+		urb->type = USBFS_URB_TYPE_ISO;
+		/* FIXME: interface for non-ASAP data? */
+		urb->flags = USBFS_URB_ISO_ASAP;
+		urb->endpoint = transfer->endpoint;
+		urb->number_of_packets = num_packets_in_urb;
+		urb->buffer = urb_buffer;
+
+		urb_buffer += urb->buffer_length;
+		num_packets_remaining -= num_packets_in_urb;
+	}
+
+	/* submit URBs */
+	for (i = 0; i < num_urbs; i++) {
+		int r = ioctl(hpriv->fd, IOCTL_USBFS_SUBMITURB, urbs[i]);
+
+		if (r == 0)
+			continue;
+
+		if (errno == ENODEV) {
+			r = LIBUSB_ERROR_NO_DEVICE;
+		} else if (errno == EINVAL) {
+			usbi_warn(TRANSFER_CTX(transfer), "submiturb failed, transfer too large");
+			r = LIBUSB_ERROR_INVALID_PARAM;
+		} else if (errno == EMSGSIZE) {
+			usbi_warn(TRANSFER_CTX(transfer), "submiturb failed, iso packet length too large");
+			r = LIBUSB_ERROR_INVALID_PARAM;
+		} else {
+			usbi_err(TRANSFER_CTX(transfer), "submiturb failed, errno=%d", errno);
+			r = LIBUSB_ERROR_IO;
+		}
+
+		/* if the first URB submission fails, we can simply free up and
+		 * return failure immediately. */
+		if (i == 0) {
+			usbi_dbg(TRANSFER_CTX(transfer), "first URB failed, easy peasy");
+			free_iso_urbs(tpriv);
+			return r;
+		}
+
+		/* if it's not the first URB that failed, the situation is a bit
+		 * tricky. we must discard all previous URBs. there are
+		 * complications:
+		 *  - discarding is asynchronous - discarded urbs will be reaped
+		 *    later. the user must not have freed the transfer when the
+		 *    discarded URBs are reaped, otherwise libusb will be using
+		 *    freed memory.
+		 *  - the earlier URBs may have completed successfully and we do
+		 *    not want to throw away any data.
+		 * so, in this case we discard all the previous URBs BUT we report
+		 * that the transfer was submitted successfully. then later when
+		 * the final discard completes we can report error to the user.
+		 */
+		tpriv->reap_action = SUBMIT_FAILED;
+
+		/* The URBs we haven't submitted yet we count as already
+		 * retired. */
+		tpriv->num_retired = num_urbs - i;
+		discard_urbs(itransfer, 0, i);
+
+		usbi_dbg(TRANSFER_CTX(transfer), "reporting successful submission but waiting for %d "
+			 "discards before reporting error", i);
+		return 0;
+	}
+
+	return 0;
+}
+
+static int submit_control_transfer(struct usbi_transfer *itransfer)
+{
+	struct linux_transfer_priv *tpriv = usbi_get_transfer_priv(itransfer);
+	struct libusb_transfer *transfer =
+		USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_device_handle_priv *hpriv =
+		usbi_get_device_handle_priv(transfer->dev_handle);
+	struct usbfs_urb *urb;
+	int r;
+
+	if (transfer->length - LIBUSB_CONTROL_SETUP_SIZE > MAX_CTRL_BUFFER_LENGTH)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	urb = calloc(1, sizeof(*urb));
+	if (!urb)
+		return LIBUSB_ERROR_NO_MEM;
+	tpriv->urbs = urb;
+	tpriv->num_urbs = 1;
+	tpriv->reap_action = NORMAL;
+
+	urb->usercontext = itransfer;
+	urb->type = USBFS_URB_TYPE_CONTROL;
+	urb->endpoint = transfer->endpoint;
+	urb->buffer = transfer->buffer;
+	urb->buffer_length = transfer->length;
+
+	r = ioctl(hpriv->fd, IOCTL_USBFS_SUBMITURB, urb);
+	if (r < 0) {
+		free(urb);
+		tpriv->urbs = NULL;
+		if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(TRANSFER_CTX(transfer), "submiturb failed, errno=%d", errno);
+		return LIBUSB_ERROR_IO;
+	}
+	return 0;
+}
+
+static int op_submit_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer =
+		USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+		return submit_control_transfer(itransfer);
+	case LIBUSB_TRANSFER_TYPE_BULK:
+	case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
+		return submit_bulk_transfer(itransfer);
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		return submit_bulk_transfer(itransfer);
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		return submit_iso_transfer(itransfer);
+	default:
+		usbi_err(TRANSFER_CTX(transfer), "unknown transfer type %u", transfer->type);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	}
+}
+
+static int op_cancel_transfer(struct usbi_transfer *itransfer)
+{
+	struct linux_transfer_priv *tpriv = usbi_get_transfer_priv(itransfer);
+	struct libusb_transfer *transfer =
+		USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	int r;
+
+	if (!tpriv->urbs)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	r = discard_urbs(itransfer, 0, tpriv->num_urbs);
+	if (r != 0)
+		return r;
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_BULK:
+	case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
+		if (tpriv->reap_action == ERROR)
+			break;
+		/* else, fall through */
+	default:
+		tpriv->reap_action = CANCELLED;
+	}
+
+	return 0;
+}
+
+static void op_clear_transfer_priv(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer =
+		USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_transfer_priv *tpriv = usbi_get_transfer_priv(itransfer);
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+	case LIBUSB_TRANSFER_TYPE_BULK:
+	case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		if (tpriv->urbs) {
+			free(tpriv->urbs);
+			tpriv->urbs = NULL;
+		}
+		break;
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		if (tpriv->iso_urbs) {
+			free_iso_urbs(tpriv);
+			tpriv->iso_urbs = NULL;
+		}
+		break;
+	default:
+		usbi_err(TRANSFER_CTX(transfer), "unknown transfer type %u", transfer->type);
+	}
+}
+
+static int handle_bulk_completion(struct usbi_transfer *itransfer,
+	struct usbfs_urb *urb)
+{
+	struct linux_transfer_priv *tpriv = usbi_get_transfer_priv(itransfer);
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	int urb_idx = urb - tpriv->urbs;
+
+	usbi_mutex_lock(&itransfer->lock);
+	usbi_dbg(TRANSFER_CTX(transfer), "handling completion status %d of bulk urb %d/%d", urb->status,
+		 urb_idx + 1, tpriv->num_urbs);
+
+	tpriv->num_retired++;
+
+	if (tpriv->reap_action != NORMAL) {
+		/* cancelled, submit_fail, or completed early */
+		usbi_dbg(TRANSFER_CTX(transfer), "abnormal reap: urb status %d", urb->status);
+
+		/* even though we're in the process of cancelling, it's possible that
+		 * we may receive some data in these URBs that we don't want to lose.
+		 * examples:
+		 * 1. while the kernel is cancelling all the packets that make up an
+		 *    URB, a few of them might complete. so we get back a successful
+		 *    cancellation *and* some data.
+		 * 2. we receive a short URB which marks the early completion condition,
+		 *    so we start cancelling the remaining URBs. however, we're too
+		 *    slow and another URB completes (or at least completes partially).
+		 *    (this can't happen since we always use BULK_CONTINUATION.)
+		 *
+		 * When this happens, our objectives are not to lose any "surplus" data,
+		 * and also to stick it at the end of the previously-received data
+		 * (closing any holes), so that libusb reports the total amount of
+		 * transferred data and presents it in a contiguous chunk.
+		 */
+		if (urb->actual_length > 0) {
+			unsigned char *target = transfer->buffer + itransfer->transferred;
+
+			usbi_dbg(TRANSFER_CTX(transfer), "received %d bytes of surplus data", urb->actual_length);
+			if (urb->buffer != target) {
+				usbi_dbg(TRANSFER_CTX(transfer), "moving surplus data from offset %zu to offset %zu",
+					 (unsigned char *)urb->buffer - transfer->buffer,
+					 target - transfer->buffer);
+				memmove(target, urb->buffer, urb->actual_length);
+			}
+			itransfer->transferred += urb->actual_length;
+		}
+
+		if (tpriv->num_retired == tpriv->num_urbs) {
+			usbi_dbg(TRANSFER_CTX(transfer), "abnormal reap: last URB handled, reporting");
+			if (tpriv->reap_action != COMPLETED_EARLY &&
+			    tpriv->reap_status == LIBUSB_TRANSFER_COMPLETED)
+				tpriv->reap_status = LIBUSB_TRANSFER_ERROR;
+			goto completed;
+		}
+		goto out_unlock;
+	}
+
+	itransfer->transferred += urb->actual_length;
+
+	/* Many of these errors can occur on *any* urb of a multi-urb
+	 * transfer.  When they do, we tear down the rest of the transfer.
+	 */
+	switch (urb->status) {
+	case 0:
+		break;
+	case -EREMOTEIO: /* short transfer */
+		break;
+	case -ENOENT: /* cancelled */
+	case -ECONNRESET:
+		break;
+	case -ENODEV:
+	case -ESHUTDOWN:
+		usbi_dbg(TRANSFER_CTX(transfer), "device removed");
+		tpriv->reap_status = LIBUSB_TRANSFER_NO_DEVICE;
+		goto cancel_remaining;
+	case -EPIPE:
+		usbi_dbg(TRANSFER_CTX(transfer), "detected endpoint stall");
+		if (tpriv->reap_status == LIBUSB_TRANSFER_COMPLETED)
+			tpriv->reap_status = LIBUSB_TRANSFER_STALL;
+		goto cancel_remaining;
+	case -EOVERFLOW:
+		/* overflow can only ever occur in the last urb */
+		usbi_dbg(TRANSFER_CTX(transfer), "overflow, actual_length=%d", urb->actual_length);
+		if (tpriv->reap_status == LIBUSB_TRANSFER_COMPLETED)
+			tpriv->reap_status = LIBUSB_TRANSFER_OVERFLOW;
+		goto completed;
+	case -ETIME:
+	case -EPROTO:
+	case -EILSEQ:
+	case -ECOMM:
+	case -ENOSR:
+		usbi_dbg(TRANSFER_CTX(transfer), "low-level bus error %d", urb->status);
+		tpriv->reap_action = ERROR;
+		goto cancel_remaining;
+	default:
+		usbi_warn(ITRANSFER_CTX(itransfer), "unrecognised urb status %d", urb->status);
+		tpriv->reap_action = ERROR;
+		goto cancel_remaining;
+	}
+
+	/* if we've reaped all urbs or we got less data than requested then we're
+	 * done */
+	if (tpriv->num_retired == tpriv->num_urbs) {
+		usbi_dbg(TRANSFER_CTX(transfer), "all URBs in transfer reaped --> complete!");
+		goto completed;
+	} else if (urb->actual_length < urb->buffer_length) {
+		usbi_dbg(TRANSFER_CTX(transfer), "short transfer %d/%d --> complete!",
+			 urb->actual_length, urb->buffer_length);
+		if (tpriv->reap_action == NORMAL)
+			tpriv->reap_action = COMPLETED_EARLY;
+	} else {
+		goto out_unlock;
+	}
+
+cancel_remaining:
+	if (tpriv->reap_action == ERROR && tpriv->reap_status == LIBUSB_TRANSFER_COMPLETED)
+		tpriv->reap_status = LIBUSB_TRANSFER_ERROR;
+
+	if (tpriv->num_retired == tpriv->num_urbs) /* nothing to cancel */
+		goto completed;
+
+	/* cancel remaining urbs and wait for their completion before
+	 * reporting results */
+	discard_urbs(itransfer, urb_idx + 1, tpriv->num_urbs);
+
+out_unlock:
+	usbi_mutex_unlock(&itransfer->lock);
+	return 0;
+
+completed:
+	free(tpriv->urbs);
+	tpriv->urbs = NULL;
+	usbi_mutex_unlock(&itransfer->lock);
+	return tpriv->reap_action == CANCELLED ?
+		usbi_handle_transfer_cancellation(itransfer) :
+		usbi_handle_transfer_completion(itransfer, tpriv->reap_status);
+}
+
+static int handle_iso_completion(struct usbi_transfer *itransfer,
+	struct usbfs_urb *urb)
+{
+	struct libusb_transfer *transfer =
+		USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct linux_transfer_priv *tpriv = usbi_get_transfer_priv(itransfer);
+	int num_urbs = tpriv->num_urbs;
+	int urb_idx = 0;
+	int i;
+	enum libusb_transfer_status status = LIBUSB_TRANSFER_COMPLETED;
+
+	usbi_mutex_lock(&itransfer->lock);
+	for (i = 0; i < num_urbs; i++) {
+		if (urb == tpriv->iso_urbs[i]) {
+			urb_idx = i + 1;
+			break;
+		}
+	}
+	if (urb_idx == 0) {
+		usbi_err(TRANSFER_CTX(transfer), "could not locate urb!");
+		usbi_mutex_unlock(&itransfer->lock);
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	usbi_dbg(TRANSFER_CTX(transfer), "handling completion status %d of iso urb %d/%d", urb->status,
+		 urb_idx, num_urbs);
+
+	/* copy isochronous results back in */
+
+	for (i = 0; i < urb->number_of_packets; i++) {
+		struct usbfs_iso_packet_desc *urb_desc = &urb->iso_frame_desc[i];
+		struct libusb_iso_packet_descriptor *lib_desc =
+			&transfer->iso_packet_desc[tpriv->iso_packet_offset++];
+
+		lib_desc->status = LIBUSB_TRANSFER_COMPLETED;
+		switch (urb_desc->status) {
+		case 0:
+			break;
+		case -ENOENT: /* cancelled */
+		case -ECONNRESET:
+			break;
+		case -ENODEV:
+		case -ESHUTDOWN:
+			usbi_dbg(TRANSFER_CTX(transfer), "packet %d - device removed", i);
+			lib_desc->status = LIBUSB_TRANSFER_NO_DEVICE;
+			break;
+		case -EPIPE:
+			usbi_dbg(TRANSFER_CTX(transfer), "packet %d - detected endpoint stall", i);
+			lib_desc->status = LIBUSB_TRANSFER_STALL;
+			break;
+		case -EOVERFLOW:
+			usbi_dbg(TRANSFER_CTX(transfer), "packet %d - overflow error", i);
+			lib_desc->status = LIBUSB_TRANSFER_OVERFLOW;
+			break;
+		case -ETIME:
+		case -EPROTO:
+		case -EILSEQ:
+		case -ECOMM:
+		case -ENOSR:
+		case -EXDEV:
+			usbi_dbg(TRANSFER_CTX(transfer), "packet %d - low-level USB error %d", i, urb_desc->status);
+			lib_desc->status = LIBUSB_TRANSFER_ERROR;
+			break;
+		default:
+			usbi_warn(TRANSFER_CTX(transfer), "packet %d - unrecognised urb status %d",
+				  i, urb_desc->status);
+			lib_desc->status = LIBUSB_TRANSFER_ERROR;
+			break;
+		}
+		lib_desc->actual_length = urb_desc->actual_length;
+	}
+
+	tpriv->num_retired++;
+
+	if (tpriv->reap_action != NORMAL) { /* cancelled or submit_fail */
+		usbi_dbg(TRANSFER_CTX(transfer), "CANCEL: urb status %d", urb->status);
+
+		if (tpriv->num_retired == num_urbs) {
+			usbi_dbg(TRANSFER_CTX(transfer), "CANCEL: last URB handled, reporting");
+			free_iso_urbs(tpriv);
+			if (tpriv->reap_action == CANCELLED) {
+				usbi_mutex_unlock(&itransfer->lock);
+				return usbi_handle_transfer_cancellation(itransfer);
+			} else {
+				usbi_mutex_unlock(&itransfer->lock);
+				return usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_ERROR);
+			}
+		}
+		goto out;
+	}
+
+	switch (urb->status) {
+	case 0:
+		break;
+	case -ENOENT: /* cancelled */
+	case -ECONNRESET:
+		break;
+	case -ESHUTDOWN:
+		usbi_dbg(TRANSFER_CTX(transfer), "device removed");
+		status = LIBUSB_TRANSFER_NO_DEVICE;
+		break;
+	default:
+		usbi_warn(TRANSFER_CTX(transfer), "unrecognised urb status %d", urb->status);
+		status = LIBUSB_TRANSFER_ERROR;
+		break;
+	}
+
+	/* if we've reaped all urbs then we're done */
+	if (tpriv->num_retired == num_urbs) {
+		usbi_dbg(TRANSFER_CTX(transfer), "all URBs in transfer reaped --> complete!");
+		free_iso_urbs(tpriv);
+		usbi_mutex_unlock(&itransfer->lock);
+		return usbi_handle_transfer_completion(itransfer, status);
+	}
+
+out:
+	usbi_mutex_unlock(&itransfer->lock);
+	return 0;
+}
+
+static int handle_control_completion(struct usbi_transfer *itransfer,
+	struct usbfs_urb *urb)
+{
+	struct linux_transfer_priv *tpriv = usbi_get_transfer_priv(itransfer);
+	int status;
+
+	usbi_mutex_lock(&itransfer->lock);
+	usbi_dbg(ITRANSFER_CTX(itransfer), "handling completion status %d", urb->status);
+
+	itransfer->transferred += urb->actual_length;
+
+	if (tpriv->reap_action == CANCELLED) {
+		if (urb->status && urb->status != -ENOENT)
+			usbi_warn(ITRANSFER_CTX(itransfer), "cancel: unrecognised urb status %d",
+				  urb->status);
+		free(tpriv->urbs);
+		tpriv->urbs = NULL;
+		usbi_mutex_unlock(&itransfer->lock);
+		return usbi_handle_transfer_cancellation(itransfer);
+	}
+
+	switch (urb->status) {
+	case 0:
+		status = LIBUSB_TRANSFER_COMPLETED;
+		break;
+	case -ENOENT: /* cancelled */
+		status = LIBUSB_TRANSFER_CANCELLED;
+		break;
+	case -ENODEV:
+	case -ESHUTDOWN:
+		usbi_dbg(ITRANSFER_CTX(itransfer), "device removed");
+		status = LIBUSB_TRANSFER_NO_DEVICE;
+		break;
+	case -EPIPE:
+		usbi_dbg(ITRANSFER_CTX(itransfer), "unsupported control request");
+		status = LIBUSB_TRANSFER_STALL;
+		break;
+	case -EOVERFLOW:
+		usbi_dbg(ITRANSFER_CTX(itransfer), "overflow, actual_length=%d", urb->actual_length);
+		status = LIBUSB_TRANSFER_OVERFLOW;
+		break;
+	case -ETIME:
+	case -EPROTO:
+	case -EILSEQ:
+	case -ECOMM:
+	case -ENOSR:
+		usbi_dbg(ITRANSFER_CTX(itransfer), "low-level bus error %d", urb->status);
+		status = LIBUSB_TRANSFER_ERROR;
+		break;
+	default:
+		usbi_warn(ITRANSFER_CTX(itransfer), "unrecognised urb status %d", urb->status);
+		status = LIBUSB_TRANSFER_ERROR;
+		break;
+	}
+
+	free(tpriv->urbs);
+	tpriv->urbs = NULL;
+	usbi_mutex_unlock(&itransfer->lock);
+	return usbi_handle_transfer_completion(itransfer, status);
+}
+
+static int reap_for_handle(struct libusb_device_handle *handle)
+{
+	struct linux_device_handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int r;
+	struct usbfs_urb *urb = NULL;
+	struct usbi_transfer *itransfer;
+	struct libusb_transfer *transfer;
+
+	r = ioctl(hpriv->fd, IOCTL_USBFS_REAPURBNDELAY, &urb);
+	if (r < 0) {
+		if (errno == EAGAIN)
+			return 1;
+		if (errno == ENODEV)
+			return LIBUSB_ERROR_NO_DEVICE;
+
+		usbi_err(HANDLE_CTX(handle), "reap failed, errno=%d", errno);
+		return LIBUSB_ERROR_IO;
+	}
+
+	itransfer = urb->usercontext;
+	transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+	usbi_dbg(HANDLE_CTX(handle), "urb type=%u status=%d transferred=%d", urb->type, urb->status, urb->actual_length);
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		return handle_iso_completion(itransfer, urb);
+	case LIBUSB_TRANSFER_TYPE_BULK:
+	case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		return handle_bulk_completion(itransfer, urb);
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+		return handle_control_completion(itransfer, urb);
+	default:
+		usbi_err(HANDLE_CTX(handle), "unrecognised transfer type %u", transfer->type);
+		return LIBUSB_ERROR_OTHER;
+	}
+}
+
+static int op_handle_events(struct libusb_context *ctx,
+	void *event_data, unsigned int count, unsigned int num_ready)
+{
+	struct pollfd *fds = event_data;
+	unsigned int n;
+	int r;
+
+	usbi_mutex_lock(&ctx->open_devs_lock);
+	for (n = 0; n < count && num_ready > 0; n++) {
+		struct pollfd *pollfd = &fds[n];
+		struct libusb_device_handle *handle;
+		struct linux_device_handle_priv *hpriv = NULL;
+		int reap_count;
+
+		if (!pollfd->revents)
+			continue;
+
+		num_ready--;
+		for_each_open_device(ctx, handle) {
+			hpriv = usbi_get_device_handle_priv(handle);
+			if (hpriv->fd == pollfd->fd)
+				break;
+		}
+
+		if (!hpriv || hpriv->fd != pollfd->fd) {
+			usbi_err(ctx, "cannot find handle for fd %d",
+				 pollfd->fd);
+			continue;
+		}
+
+		if (pollfd->revents & POLLERR) {
+			/* remove the fd from the pollfd set so that it doesn't continuously
+			 * trigger an event, and flag that it has been removed so op_close()
+			 * doesn't try to remove it a second time */
+			usbi_remove_event_source(HANDLE_CTX(handle), hpriv->fd);
+			hpriv->fd_removed = 1;
+
+			/* device will still be marked as attached if hotplug monitor thread
+			 * hasn't processed remove event yet */
+			usbi_mutex_static_lock(&linux_hotplug_lock);
+			if (usbi_atomic_load(&handle->dev->attached))
+				linux_device_disconnected(handle->dev->bus_number,
+							  handle->dev->device_address);
+			usbi_mutex_static_unlock(&linux_hotplug_lock);
+
+			if (hpriv->caps & USBFS_CAP_REAP_AFTER_DISCONNECT) {
+				do {
+					r = reap_for_handle(handle);
+				} while (r == 0);
+			}
+
+			usbi_handle_disconnect(handle);
+			continue;
+		}
+
+		reap_count = 0;
+		do {
+			r = reap_for_handle(handle);
+		} while (r == 0 && ++reap_count <= 25);
+
+		if (r == 1 || r == LIBUSB_ERROR_NO_DEVICE)
+			continue;
+		else if (r < 0)
+			goto out;
+	}
+
+	r = 0;
+out:
+	usbi_mutex_unlock(&ctx->open_devs_lock);
+	return r;
+}
+
+const struct usbi_os_backend usbi_backend = {
+	.name = "Linux usbfs",
+	.caps = USBI_CAP_HAS_HID_ACCESS|USBI_CAP_SUPPORTS_DETACH_KERNEL_DRIVER,
+	.init = op_init,
+	.exit = op_exit,
+	.set_option = op_set_option,
+	.hotplug_poll = op_hotplug_poll,
+	.get_active_config_descriptor = op_get_active_config_descriptor,
+	.get_config_descriptor = op_get_config_descriptor,
+	.get_config_descriptor_by_value = op_get_config_descriptor_by_value,
+
+	.wrap_sys_device = op_wrap_sys_device,
+	.open = op_open,
+	.close = op_close,
+	.get_configuration = op_get_configuration,
+	.set_configuration = op_set_configuration,
+	.claim_interface = op_claim_interface,
+	.release_interface = op_release_interface,
+
+	.set_interface_altsetting = op_set_interface,
+	.clear_halt = op_clear_halt,
+	.reset_device = op_reset_device,
+
+	.alloc_streams = op_alloc_streams,
+	.free_streams = op_free_streams,
+
+	.dev_mem_alloc = op_dev_mem_alloc,
+	.dev_mem_free = op_dev_mem_free,
+
+	.kernel_driver_active = op_kernel_driver_active,
+	.detach_kernel_driver = op_detach_kernel_driver,
+	.attach_kernel_driver = op_attach_kernel_driver,
+
+	.destroy_device = op_destroy_device,
+
+	.submit_transfer = op_submit_transfer,
+	.cancel_transfer = op_cancel_transfer,
+	.clear_transfer_priv = op_clear_transfer_priv,
+
+	.handle_events = op_handle_events,
+
+	.device_priv_size = sizeof(struct linux_device_priv),
+	.device_handle_priv_size = sizeof(struct linux_device_handle_priv),
+	.transfer_priv_size = sizeof(struct linux_transfer_priv),
+};
diff --git a/src/os/linux_usbfs.h b/src/os/linux_usbfs.h
new file mode 100644
index 0000000..1238ffa
--- /dev/null
+++ b/src/os/linux_usbfs.h
@@ -0,0 +1,211 @@
+/*
+ * usbfs header structures
+ * Copyright © 2007 Daniel Drake <dsd@gentoo.org>
+ * Copyright © 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef LIBUSB_USBFS_H
+#define LIBUSB_USBFS_H
+
+#include <linux/magic.h>
+#include <linux/types.h>
+
+#define SYSFS_MOUNT_PATH	"/sys"
+#define SYSFS_DEVICE_PATH	SYSFS_MOUNT_PATH "/bus/usb/devices"
+
+struct usbfs_ctrltransfer {
+	/* keep in sync with usbdevice_fs.h:usbdevfs_ctrltransfer */
+	__u8 bmRequestType;
+	__u8 bRequest;
+	__u16 wValue;
+	__u16 wIndex;
+	__u16 wLength;
+	__u32 timeout;	/* in milliseconds */
+
+	/* pointer to data */
+	void *data;
+};
+
+struct usbfs_setinterface {
+	/* keep in sync with usbdevice_fs.h:usbdevfs_setinterface */
+	unsigned int interface;
+	unsigned int altsetting;
+};
+
+#define USBFS_MAXDRIVERNAME		255
+
+struct usbfs_getdriver {
+	unsigned int interface;
+	char driver[USBFS_MAXDRIVERNAME + 1];
+};
+
+#define USBFS_URB_SHORT_NOT_OK		0x01
+#define USBFS_URB_ISO_ASAP		0x02
+#define USBFS_URB_BULK_CONTINUATION	0x04
+#define USBFS_URB_QUEUE_BULK		0x10
+#define USBFS_URB_ZERO_PACKET		0x40
+
+#define USBFS_URB_TYPE_ISO		0
+#define USBFS_URB_TYPE_INTERRUPT	1
+#define USBFS_URB_TYPE_CONTROL		2
+#define USBFS_URB_TYPE_BULK		3
+
+struct usbfs_iso_packet_desc {
+	unsigned int length;
+	unsigned int actual_length;
+	unsigned int status;
+};
+
+#define MAX_BULK_BUFFER_LENGTH		16384
+#define MAX_CTRL_BUFFER_LENGTH		4096
+
+#define MAX_ISO_PACKETS_PER_URB		128
+
+struct usbfs_urb {
+	unsigned char type;
+	unsigned char endpoint;
+	int status;
+	unsigned int flags;
+	void *buffer;
+	int buffer_length;
+	int actual_length;
+	int start_frame;
+	union {
+		int number_of_packets;	/* Only used for isoc urbs */
+		unsigned int stream_id;	/* Only used with bulk streams */
+	};
+	int error_count;
+	unsigned int signr;
+	void *usercontext;
+	struct usbfs_iso_packet_desc iso_frame_desc[0];
+};
+
+struct usbfs_connectinfo {
+	unsigned int devnum;
+	unsigned char slow;
+};
+
+struct usbfs_ioctl {
+	int ifno;	/* interface 0..N ; negative numbers reserved */
+	int ioctl_code;	/* MUST encode size + direction of data so the
+			 * macros in <asm/ioctl.h> give correct values */
+	void *data;	/* param buffer (in, or out) */
+};
+
+#define USBFS_CAP_ZERO_PACKET			0x01
+#define USBFS_CAP_BULK_CONTINUATION		0x02
+#define USBFS_CAP_NO_PACKET_SIZE_LIM		0x04
+#define USBFS_CAP_BULK_SCATTER_GATHER		0x08
+#define USBFS_CAP_REAP_AFTER_DISCONNECT		0x10
+
+#define USBFS_DISCONNECT_CLAIM_IF_DRIVER	0x01
+#define USBFS_DISCONNECT_CLAIM_EXCEPT_DRIVER	0x02
+
+struct usbfs_disconnect_claim {
+	unsigned int interface;
+	unsigned int flags;
+	char driver[USBFS_MAXDRIVERNAME + 1];
+};
+
+struct usbfs_streams {
+	unsigned int num_streams; /* Not used by USBDEVFS_FREE_STREAMS */
+	unsigned int num_eps;
+	unsigned char eps[0];
+};
+
+#define USBFS_SPEED_UNKNOWN			0
+#define USBFS_SPEED_LOW				1
+#define USBFS_SPEED_FULL			2
+#define USBFS_SPEED_HIGH			3
+#define USBFS_SPEED_WIRELESS			4
+#define USBFS_SPEED_SUPER			5
+#define USBFS_SPEED_SUPER_PLUS			6
+
+#define IOCTL_USBFS_CONTROL		_IOWR('U', 0, struct usbfs_ctrltransfer)
+#define IOCTL_USBFS_SETINTERFACE	_IOR('U', 4, struct usbfs_setinterface)
+#define IOCTL_USBFS_SETCONFIGURATION	_IOR('U', 5, unsigned int)
+#define IOCTL_USBFS_GETDRIVER		_IOW('U', 8, struct usbfs_getdriver)
+#define IOCTL_USBFS_SUBMITURB		_IOR('U', 10, struct usbfs_urb)
+#define IOCTL_USBFS_DISCARDURB		_IO('U', 11)
+#define IOCTL_USBFS_REAPURBNDELAY	_IOW('U', 13, void *)
+#define IOCTL_USBFS_CLAIMINTERFACE	_IOR('U', 15, unsigned int)
+#define IOCTL_USBFS_RELEASEINTERFACE	_IOR('U', 16, unsigned int)
+#define IOCTL_USBFS_CONNECTINFO		_IOW('U', 17, struct usbfs_connectinfo)
+#define IOCTL_USBFS_IOCTL		_IOWR('U', 18, struct usbfs_ioctl)
+#define IOCTL_USBFS_RESET		_IO('U', 20)
+#define IOCTL_USBFS_CLEAR_HALT		_IOR('U', 21, unsigned int)
+#define IOCTL_USBFS_DISCONNECT		_IO('U', 22)
+#define IOCTL_USBFS_CONNECT		_IO('U', 23)
+#define IOCTL_USBFS_GET_CAPABILITIES	_IOR('U', 26, __u32)
+#define IOCTL_USBFS_DISCONNECT_CLAIM	_IOR('U', 27, struct usbfs_disconnect_claim)
+#define IOCTL_USBFS_ALLOC_STREAMS	_IOR('U', 28, struct usbfs_streams)
+#define IOCTL_USBFS_FREE_STREAMS	_IOR('U', 29, struct usbfs_streams)
+#define IOCTL_USBFS_DROP_PRIVILEGES	_IOW('U', 30, __u32)
+#define IOCTL_USBFS_GET_SPEED		_IO('U', 31)
+
+extern usbi_mutex_static_t linux_hotplug_lock;
+
+#ifdef HAVE_LIBUDEV
+int linux_udev_start_event_monitor(void);
+int linux_udev_stop_event_monitor(void);
+int linux_udev_scan_devices(struct libusb_context *ctx);
+void linux_udev_hotplug_poll(void);
+#else
+int linux_netlink_start_event_monitor(void);
+int linux_netlink_stop_event_monitor(void);
+void linux_netlink_hotplug_poll(void);
+#endif
+
+static inline int linux_start_event_monitor(void)
+{
+#if defined(HAVE_LIBUDEV)
+	return linux_udev_start_event_monitor();
+#elif !defined(__ANDROID__)
+	return linux_netlink_start_event_monitor();
+#else
+	return LIBUSB_SUCCESS;
+#endif
+}
+
+static inline void linux_stop_event_monitor(void)
+{
+#if defined(HAVE_LIBUDEV)
+	linux_udev_stop_event_monitor();
+#elif !defined(__ANDROID__)
+	linux_netlink_stop_event_monitor();
+#endif
+}
+
+static inline void linux_hotplug_poll(void)
+{
+#if defined(HAVE_LIBUDEV)
+	linux_udev_hotplug_poll();
+#elif !defined(__ANDROID__)
+	linux_netlink_hotplug_poll();
+#endif
+}
+
+void linux_hotplug_enumerate(uint8_t busnum, uint8_t devaddr, const char *sys_name);
+void linux_device_disconnected(uint8_t busnum, uint8_t devaddr);
+
+int linux_get_device_address(struct libusb_context *ctx, int detached,
+	uint8_t *busnum, uint8_t *devaddr, const char *dev_node,
+	const char *sys_name, int fd);
+int linux_enumerate_device(struct libusb_context *ctx,
+	uint8_t busnum, uint8_t devaddr, const char *sysfs_dir);
+
+#endif
diff --git a/src/os/netbsd_usb.c b/src/os/netbsd_usb.c
new file mode 100644
index 0000000..74833f6
--- /dev/null
+++ b/src/os/netbsd_usb.c
@@ -0,0 +1,617 @@
+/*
+ * Copyright © 2011 Martin Pieuchot <mpi@openbsd.org>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+
+#include <sys/time.h>
+#include <sys/types.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <dev/usb/usb.h>
+
+#include "libusbi.h"
+
+struct device_priv {
+	char devnode[16];
+	int fd;
+
+	usb_config_descriptor_t *cdesc;		/* active config descriptor */
+};
+
+struct handle_priv {
+	int endpoints[USB_MAX_ENDPOINTS];
+};
+
+/*
+ * Backend functions
+ */
+static int netbsd_get_device_list(struct libusb_context *,
+    struct discovered_devs **);
+static int netbsd_open(struct libusb_device_handle *);
+static void netbsd_close(struct libusb_device_handle *);
+
+static int netbsd_get_active_config_descriptor(struct libusb_device *,
+    void *, size_t);
+static int netbsd_get_config_descriptor(struct libusb_device *, uint8_t,
+    void *, size_t);
+
+static int netbsd_get_configuration(struct libusb_device_handle *, uint8_t *);
+static int netbsd_set_configuration(struct libusb_device_handle *, int);
+
+static int netbsd_claim_interface(struct libusb_device_handle *, uint8_t);
+static int netbsd_release_interface(struct libusb_device_handle *, uint8_t);
+
+static int netbsd_set_interface_altsetting(struct libusb_device_handle *,
+    uint8_t, uint8_t);
+static int netbsd_clear_halt(struct libusb_device_handle *, unsigned char);
+static void netbsd_destroy_device(struct libusb_device *);
+
+static int netbsd_submit_transfer(struct usbi_transfer *);
+static int netbsd_cancel_transfer(struct usbi_transfer *);
+static int netbsd_handle_transfer_completion(struct usbi_transfer *);
+
+/*
+ * Private functions
+ */
+static int _errno_to_libusb(int);
+static int _cache_active_config_descriptor(struct libusb_device *, int);
+static int _sync_control_transfer(struct usbi_transfer *);
+static int _sync_gen_transfer(struct usbi_transfer *);
+static int _access_endpoint(struct libusb_transfer *);
+
+const struct usbi_os_backend usbi_backend = {
+	.name = "Synchronous NetBSD backend",
+	.caps = 0,
+	.get_device_list = netbsd_get_device_list,
+	.open = netbsd_open,
+	.close = netbsd_close,
+
+	.get_active_config_descriptor = netbsd_get_active_config_descriptor,
+	.get_config_descriptor = netbsd_get_config_descriptor,
+
+	.get_configuration = netbsd_get_configuration,
+	.set_configuration = netbsd_set_configuration,
+
+	.claim_interface = netbsd_claim_interface,
+	.release_interface = netbsd_release_interface,
+
+	.set_interface_altsetting = netbsd_set_interface_altsetting,
+	.clear_halt = netbsd_clear_halt,
+
+	.destroy_device = netbsd_destroy_device,
+
+	.submit_transfer = netbsd_submit_transfer,
+	.cancel_transfer = netbsd_cancel_transfer,
+
+	.handle_transfer_completion = netbsd_handle_transfer_completion,
+
+	.device_priv_size = sizeof(struct device_priv),
+	.device_handle_priv_size = sizeof(struct handle_priv),
+};
+
+int
+netbsd_get_device_list(struct libusb_context * ctx,
+	struct discovered_devs **discdevs)
+{
+	struct libusb_device *dev;
+	struct device_priv *dpriv;
+	struct usb_device_info di;
+	usb_device_descriptor_t ddesc;
+	unsigned long session_id;
+	char devnode[16];
+	int fd, err, i;
+
+	usbi_dbg(ctx, " ");
+
+	/* Only ugen(4) is supported */
+	for (i = 0; i < USB_MAX_DEVICES; i++) {
+		/* Control endpoint is always .00 */
+		snprintf(devnode, sizeof(devnode), "/dev/ugen%d.00", i);
+
+		if ((fd = open(devnode, O_RDONLY)) < 0) {
+			if (errno != ENOENT && errno != ENXIO)
+				usbi_err(ctx, "could not open %s", devnode);
+			continue;
+		}
+
+		if (ioctl(fd, USB_GET_DEVICEINFO, &di) < 0)
+			continue;
+
+		session_id = (di.udi_bus << 8 | di.udi_addr);
+		dev = usbi_get_device_by_session_id(ctx, session_id);
+
+		if (dev == NULL) {
+			dev = usbi_alloc_device(ctx, session_id);
+			if (dev == NULL)
+				return (LIBUSB_ERROR_NO_MEM);
+
+			dev->bus_number = di.udi_bus;
+			dev->device_address = di.udi_addr;
+			dev->speed = di.udi_speed;
+
+			dpriv = usbi_get_device_priv(dev);
+			strlcpy(dpriv->devnode, devnode, sizeof(devnode));
+			dpriv->fd = -1;
+
+			if (ioctl(fd, USB_GET_DEVICE_DESC, &ddesc) < 0) {
+				err = errno;
+				goto error;
+			}
+
+			static_assert(sizeof(dev->device_descriptor) == sizeof(ddesc),
+				      "mismatch between libusb and OS device descriptor sizes");
+			memcpy(&dev->device_descriptor, &ddesc, LIBUSB_DT_DEVICE_SIZE);
+			usbi_localize_device_descriptor(&dev->device_descriptor);
+
+			if (_cache_active_config_descriptor(dev, fd)) {
+				err = errno;
+				goto error;
+			}
+
+			if ((err = usbi_sanitize_device(dev)))
+				goto error;
+		}
+		close(fd);
+
+		if (discovered_devs_append(*discdevs, dev) == NULL)
+			return (LIBUSB_ERROR_NO_MEM);
+
+		libusb_unref_device(dev);
+	}
+
+	return (LIBUSB_SUCCESS);
+
+error:
+	close(fd);
+	libusb_unref_device(dev);
+	return _errno_to_libusb(err);
+}
+
+int
+netbsd_open(struct libusb_device_handle *handle)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(handle->dev);
+	struct handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int i;
+
+	dpriv->fd = open(dpriv->devnode, O_RDWR);
+	if (dpriv->fd < 0) {
+		dpriv->fd = open(dpriv->devnode, O_RDONLY);
+		if (dpriv->fd < 0)
+			return _errno_to_libusb(errno);
+	}
+
+	for (i = 0; i < USB_MAX_ENDPOINTS; i++)
+		hpriv->endpoints[i] = -1;
+
+	usbi_dbg(HANDLE_CTX(handle), "open %s: fd %d", dpriv->devnode, dpriv->fd);
+
+	return (LIBUSB_SUCCESS);
+}
+
+void
+netbsd_close(struct libusb_device_handle *handle)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(handle->dev);
+
+	usbi_dbg(HANDLE_CTX(handle), "close: fd %d", dpriv->fd);
+
+	close(dpriv->fd);
+	dpriv->fd = -1;
+}
+
+int
+netbsd_get_active_config_descriptor(struct libusb_device *dev,
+    void *buf, size_t len)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(dev);
+
+	len = MIN(len, (size_t)UGETW(dpriv->cdesc->wTotalLength));
+
+	usbi_dbg(DEVICE_CTX(dev), "len %zu", len);
+
+	memcpy(buf, dpriv->cdesc, len);
+
+	return (int)len;
+}
+
+int
+netbsd_get_config_descriptor(struct libusb_device *dev, uint8_t idx,
+    void *buf, size_t len)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(dev);
+	struct usb_full_desc ufd;
+	int fd, err;
+
+	usbi_dbg(DEVICE_CTX(dev), "index %u, len %zu", idx, len);
+
+	/* A config descriptor may be requested before opening the device */
+	if (dpriv->fd >= 0) {
+		fd = dpriv->fd;
+	} else {
+		fd = open(dpriv->devnode, O_RDONLY);
+		if (fd < 0)
+			return _errno_to_libusb(errno);
+	}
+
+	ufd.ufd_config_index = idx;
+	ufd.ufd_size = len;
+	ufd.ufd_data = buf;
+
+	if ((ioctl(fd, USB_GET_FULL_DESC, &ufd)) < 0) {
+		err = errno;
+		if (dpriv->fd < 0)
+			close(fd);
+		return _errno_to_libusb(err);
+	}
+
+	if (dpriv->fd < 0)
+		close(fd);
+
+	return (int)len;
+}
+
+int
+netbsd_get_configuration(struct libusb_device_handle *handle, uint8_t *config)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(handle->dev);
+	int tmp;
+
+	usbi_dbg(HANDLE_CTX(handle), " ");
+
+	if (ioctl(dpriv->fd, USB_GET_CONFIG, &tmp) < 0)
+		return _errno_to_libusb(errno);
+
+	usbi_dbg(HANDLE_CTX(handle), "configuration %d", tmp);
+	*config = (uint8_t)tmp;
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+netbsd_set_configuration(struct libusb_device_handle *handle, int config)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(handle->dev);
+
+	usbi_dbg(HANDLE_CTX(handle), "configuration %d", config);
+
+	if (ioctl(dpriv->fd, USB_SET_CONFIG, &config) < 0)
+		return _errno_to_libusb(errno);
+
+	return _cache_active_config_descriptor(handle->dev, dpriv->fd);
+}
+
+int
+netbsd_claim_interface(struct libusb_device_handle *handle, uint8_t iface)
+{
+	struct handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int i;
+
+	UNUSED(iface);
+
+	for (i = 0; i < USB_MAX_ENDPOINTS; i++)
+		hpriv->endpoints[i] = -1;
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+netbsd_release_interface(struct libusb_device_handle *handle, uint8_t iface)
+{
+	struct handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int i;
+
+	UNUSED(iface);
+
+	for (i = 0; i < USB_MAX_ENDPOINTS; i++)
+		if (hpriv->endpoints[i] >= 0)
+			close(hpriv->endpoints[i]);
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+netbsd_set_interface_altsetting(struct libusb_device_handle *handle, uint8_t iface,
+    uint8_t altsetting)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(handle->dev);
+	struct usb_alt_interface intf;
+
+	usbi_dbg(HANDLE_CTX(handle), "iface %u, setting %u", iface, altsetting);
+
+	memset(&intf, 0, sizeof(intf));
+
+	intf.uai_interface_index = iface;
+	intf.uai_alt_no = altsetting;
+
+	if (ioctl(dpriv->fd, USB_SET_ALTINTERFACE, &intf) < 0)
+		return _errno_to_libusb(errno);
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+netbsd_clear_halt(struct libusb_device_handle *handle, unsigned char endpoint)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(handle->dev);
+	struct usb_ctl_request req;
+
+	usbi_dbg(HANDLE_CTX(handle), " ");
+
+	req.ucr_request.bmRequestType = UT_WRITE_ENDPOINT;
+	req.ucr_request.bRequest = UR_CLEAR_FEATURE;
+	USETW(req.ucr_request.wValue, UF_ENDPOINT_HALT);
+	USETW(req.ucr_request.wIndex, endpoint);
+	USETW(req.ucr_request.wLength, 0);
+
+	if (ioctl(dpriv->fd, USB_DO_REQUEST, &req) < 0)
+		return _errno_to_libusb(errno);
+
+	return (LIBUSB_SUCCESS);
+}
+
+void
+netbsd_destroy_device(struct libusb_device *dev)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(dev);
+
+	usbi_dbg(DEVICE_CTX(dev), " ");
+
+	free(dpriv->cdesc);
+}
+
+int
+netbsd_submit_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer;
+	int err = 0;
+
+	usbi_dbg(ITRANSFER_CTX(itransfer), " ");
+
+	transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+		err = _sync_control_transfer(itransfer);
+		break;
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		if (IS_XFEROUT(transfer)) {
+			/* Isochronous write is not supported */
+			err = LIBUSB_ERROR_NOT_SUPPORTED;
+			break;
+		}
+		err = _sync_gen_transfer(itransfer);
+		break;
+	case LIBUSB_TRANSFER_TYPE_BULK:
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		if (IS_XFEROUT(transfer) &&
+		    transfer->flags & LIBUSB_TRANSFER_ADD_ZERO_PACKET) {
+			err = LIBUSB_ERROR_NOT_SUPPORTED;
+			break;
+		}
+		err = _sync_gen_transfer(itransfer);
+		break;
+	case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
+		err = LIBUSB_ERROR_NOT_SUPPORTED;
+		break;
+	}
+
+	if (err)
+		return (err);
+
+	usbi_signal_transfer_completion(itransfer);
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+netbsd_cancel_transfer(struct usbi_transfer *itransfer)
+{
+	UNUSED(itransfer);
+
+	usbi_dbg(ITRANSFER_CTX(itransfer), " ");
+
+	return (LIBUSB_ERROR_NOT_SUPPORTED);
+}
+
+int
+netbsd_handle_transfer_completion(struct usbi_transfer *itransfer)
+{
+	return usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_COMPLETED);
+}
+
+int
+_errno_to_libusb(int err)
+{
+	switch (err) {
+	case EIO:
+		return (LIBUSB_ERROR_IO);
+	case EACCES:
+		return (LIBUSB_ERROR_ACCESS);
+	case ENOENT:
+		return (LIBUSB_ERROR_NO_DEVICE);
+	case ENOMEM:
+		return (LIBUSB_ERROR_NO_MEM);
+	case EWOULDBLOCK:
+	case ETIMEDOUT:
+		return (LIBUSB_ERROR_TIMEOUT);
+	}
+
+	usbi_dbg(NULL, "error: %s", strerror(err));
+
+	return (LIBUSB_ERROR_OTHER);
+}
+
+int
+_cache_active_config_descriptor(struct libusb_device *dev, int fd)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(dev);
+	struct usb_config_desc ucd;
+	struct usb_full_desc ufd;
+	void *buf;
+	int len;
+
+	usbi_dbg(DEVICE_CTX(dev), "fd %d", fd);
+
+	ucd.ucd_config_index = USB_CURRENT_CONFIG_INDEX;
+
+	if ((ioctl(fd, USB_GET_CONFIG_DESC, &ucd)) < 0)
+		return _errno_to_libusb(errno);
+
+	usbi_dbg(DEVICE_CTX(dev), "active bLength %d", ucd.ucd_desc.bLength);
+
+	len = UGETW(ucd.ucd_desc.wTotalLength);
+	buf = malloc((size_t)len);
+	if (buf == NULL)
+		return (LIBUSB_ERROR_NO_MEM);
+
+	ufd.ufd_config_index = ucd.ucd_config_index;
+	ufd.ufd_size = len;
+	ufd.ufd_data = buf;
+
+	usbi_dbg(DEVICE_CTX(dev), "index %d, len %d", ufd.ufd_config_index, len);
+
+	if ((ioctl(fd, USB_GET_FULL_DESC, &ufd)) < 0) {
+		free(buf);
+		return _errno_to_libusb(errno);
+	}
+
+	if (dpriv->cdesc)
+		free(dpriv->cdesc);
+	dpriv->cdesc = buf;
+
+	return (0);
+}
+
+int
+_sync_control_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer;
+	struct libusb_control_setup *setup;
+	struct device_priv *dpriv;
+	struct usb_ctl_request req;
+
+	transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	dpriv = usbi_get_device_priv(transfer->dev_handle->dev);
+	setup = (struct libusb_control_setup *)transfer->buffer;
+
+	usbi_dbg(ITRANSFER_CTX(itransfer), "type %d request %d value %d index %d length %d timeout %d",
+	    setup->bmRequestType, setup->bRequest,
+	    libusb_le16_to_cpu(setup->wValue),
+	    libusb_le16_to_cpu(setup->wIndex),
+	    libusb_le16_to_cpu(setup->wLength), transfer->timeout);
+
+	req.ucr_request.bmRequestType = setup->bmRequestType;
+	req.ucr_request.bRequest = setup->bRequest;
+	/* Don't use USETW, libusb already deals with the endianness */
+	(*(uint16_t *)req.ucr_request.wValue) = setup->wValue;
+	(*(uint16_t *)req.ucr_request.wIndex) = setup->wIndex;
+	(*(uint16_t *)req.ucr_request.wLength) = setup->wLength;
+	req.ucr_data = transfer->buffer + LIBUSB_CONTROL_SETUP_SIZE;
+
+	if ((transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) == 0)
+		req.ucr_flags = USBD_SHORT_XFER_OK;
+
+	if ((ioctl(dpriv->fd, USB_SET_TIMEOUT, &transfer->timeout)) < 0)
+		return _errno_to_libusb(errno);
+
+	if ((ioctl(dpriv->fd, USB_DO_REQUEST, &req)) < 0)
+		return _errno_to_libusb(errno);
+
+	itransfer->transferred = req.ucr_actlen;
+
+	usbi_dbg(ITRANSFER_CTX(itransfer), "transferred %d", itransfer->transferred);
+
+	return (0);
+}
+
+int
+_access_endpoint(struct libusb_transfer *transfer)
+{
+	struct handle_priv *hpriv;
+	struct device_priv *dpriv;
+	char *s, devnode[16];
+	int fd, endpt;
+	mode_t mode;
+
+	hpriv = usbi_get_device_handle_priv(transfer->dev_handle);
+	dpriv = usbi_get_device_priv(transfer->dev_handle->dev);
+
+	endpt = UE_GET_ADDR(transfer->endpoint);
+	mode = IS_XFERIN(transfer) ? O_RDONLY : O_WRONLY;
+
+	usbi_dbg(TRANSFER_CTX(transfer), "endpoint %d mode %d", endpt, mode);
+
+	if (hpriv->endpoints[endpt] < 0) {
+		/* Pick the right node given the control one */
+		strlcpy(devnode, dpriv->devnode, sizeof(devnode));
+		s = strchr(devnode, '.');
+		snprintf(s, 4, ".%02d", endpt);
+
+		/* We may need to read/write to the same endpoint later. */
+		if (((fd = open(devnode, O_RDWR)) < 0) && (errno == ENXIO))
+			if ((fd = open(devnode, mode)) < 0)
+				return (-1);
+
+		hpriv->endpoints[endpt] = fd;
+	}
+
+	return (hpriv->endpoints[endpt]);
+}
+
+int
+_sync_gen_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer;
+	int fd, nr = 1;
+
+	transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+	/*
+	 * Bulk, Interrupt or Isochronous transfer depends on the
+	 * endpoint and thus the node to open.
+	 */
+	if ((fd = _access_endpoint(transfer)) < 0)
+		return _errno_to_libusb(errno);
+
+	if ((ioctl(fd, USB_SET_TIMEOUT, &transfer->timeout)) < 0)
+		return _errno_to_libusb(errno);
+
+	if (IS_XFERIN(transfer)) {
+		if ((transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) == 0)
+			if ((ioctl(fd, USB_SET_SHORT_XFER, &nr)) < 0)
+				return _errno_to_libusb(errno);
+
+		nr = read(fd, transfer->buffer, transfer->length);
+	} else {
+		nr = write(fd, transfer->buffer, transfer->length);
+	}
+
+	if (nr < 0)
+		return _errno_to_libusb(errno);
+
+	itransfer->transferred = nr;
+
+	return (0);
+}
diff --git a/src/os/null_usb.c b/src/os/null_usb.c
new file mode 100644
index 0000000..0cd531d
--- /dev/null
+++ b/src/os/null_usb.c
@@ -0,0 +1,111 @@
+/*
+ * Copyright © 2019 Pino Toscano <toscano.pino@tiscali.it>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "libusbi.h"
+
+static int
+null_get_device_list(struct libusb_context * ctx,
+	struct discovered_devs **discdevs)
+{
+	return LIBUSB_SUCCESS;
+}
+
+static int
+null_open(struct libusb_device_handle *handle)
+{
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static void
+null_close(struct libusb_device_handle *handle)
+{
+}
+
+static int
+null_get_active_config_descriptor(struct libusb_device *dev,
+    void *buf, size_t len)
+{
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static int
+null_get_config_descriptor(struct libusb_device *dev, uint8_t idx,
+    void *buf, size_t len)
+{
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static int
+null_set_configuration(struct libusb_device_handle *handle, int config)
+{
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static int
+null_claim_interface(struct libusb_device_handle *handle, uint8_t iface)
+{
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static int
+null_release_interface(struct libusb_device_handle *handle, uint8_t iface)
+{
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static int
+null_set_interface_altsetting(struct libusb_device_handle *handle, uint8_t iface,
+    uint8_t altsetting)
+{
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static int
+null_clear_halt(struct libusb_device_handle *handle, unsigned char endpoint)
+{
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static int
+null_submit_transfer(struct usbi_transfer *itransfer)
+{
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static int
+null_cancel_transfer(struct usbi_transfer *itransfer)
+{
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+const struct usbi_os_backend usbi_backend = {
+	.name = "Null backend",
+	.caps = 0,
+	.get_device_list = null_get_device_list,
+	.open = null_open,
+	.close = null_close,
+	.get_active_config_descriptor = null_get_active_config_descriptor,
+	.get_config_descriptor = null_get_config_descriptor,
+	.set_configuration = null_set_configuration,
+	.claim_interface = null_claim_interface,
+	.release_interface = null_release_interface,
+	.set_interface_altsetting = null_set_interface_altsetting,
+	.clear_halt = null_clear_halt,
+	.submit_transfer = null_submit_transfer,
+	.cancel_transfer = null_cancel_transfer,
+};
diff --git a/src/os/openbsd_usb.c b/src/os/openbsd_usb.c
new file mode 100644
index 0000000..9a5c604
--- /dev/null
+++ b/src/os/openbsd_usb.c
@@ -0,0 +1,700 @@
+/*
+ * Copyright © 2011-2013 Martin Pieuchot <mpi@openbsd.org>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+
+#include <sys/time.h>
+#include <sys/types.h>
+
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+#include <dev/usb/usb.h>
+
+#include "libusbi.h"
+
+struct device_priv {
+	char *devname;				/* name of the ugen(4) node */
+	int fd;					/* device file descriptor */
+
+	usb_config_descriptor_t *cdesc;		/* active config descriptor */
+};
+
+struct handle_priv {
+	int endpoints[USB_MAX_ENDPOINTS];
+};
+
+/*
+ * Backend functions
+ */
+static int obsd_get_device_list(struct libusb_context *,
+    struct discovered_devs **);
+static int obsd_open(struct libusb_device_handle *);
+static void obsd_close(struct libusb_device_handle *);
+
+static int obsd_get_active_config_descriptor(struct libusb_device *,
+    void *, size_t);
+static int obsd_get_config_descriptor(struct libusb_device *, uint8_t,
+    void *, size_t);
+
+static int obsd_get_configuration(struct libusb_device_handle *, uint8_t *);
+static int obsd_set_configuration(struct libusb_device_handle *, int);
+
+static int obsd_claim_interface(struct libusb_device_handle *, uint8_t);
+static int obsd_release_interface(struct libusb_device_handle *, uint8_t);
+
+static int obsd_set_interface_altsetting(struct libusb_device_handle *, uint8_t,
+    uint8_t);
+static int obsd_clear_halt(struct libusb_device_handle *, unsigned char);
+static void obsd_destroy_device(struct libusb_device *);
+
+static int obsd_submit_transfer(struct usbi_transfer *);
+static int obsd_cancel_transfer(struct usbi_transfer *);
+static int obsd_handle_transfer_completion(struct usbi_transfer *);
+
+/*
+ * Private functions
+ */
+static int _errno_to_libusb(int);
+static int _cache_active_config_descriptor(struct libusb_device *);
+static int _sync_control_transfer(struct usbi_transfer *);
+static int _sync_gen_transfer(struct usbi_transfer *);
+static int _access_endpoint(struct libusb_transfer *);
+
+static int _bus_open(int);
+
+
+const struct usbi_os_backend usbi_backend = {
+	.name = "Synchronous OpenBSD backend",
+	.get_device_list = obsd_get_device_list,
+	.open = obsd_open,
+	.close = obsd_close,
+
+	.get_active_config_descriptor = obsd_get_active_config_descriptor,
+	.get_config_descriptor = obsd_get_config_descriptor,
+
+	.get_configuration = obsd_get_configuration,
+	.set_configuration = obsd_set_configuration,
+
+	.claim_interface = obsd_claim_interface,
+	.release_interface = obsd_release_interface,
+
+	.set_interface_altsetting = obsd_set_interface_altsetting,
+	.clear_halt = obsd_clear_halt,
+	.destroy_device = obsd_destroy_device,
+
+	.submit_transfer = obsd_submit_transfer,
+	.cancel_transfer = obsd_cancel_transfer,
+
+	.handle_transfer_completion = obsd_handle_transfer_completion,
+
+	.device_priv_size = sizeof(struct device_priv),
+	.device_handle_priv_size = sizeof(struct handle_priv),
+};
+
+#define DEVPATH	"/dev/"
+#define USBDEV	DEVPATH "usb"
+
+int
+obsd_get_device_list(struct libusb_context * ctx,
+	struct discovered_devs **discdevs)
+{
+	struct discovered_devs *ddd;
+	struct libusb_device *dev;
+	struct device_priv *dpriv;
+	struct usb_device_info di;
+	struct usb_device_ddesc dd;
+	unsigned long session_id;
+	char devices[USB_MAX_DEVICES];
+	char busnode[16];
+	char *udevname;
+	int fd, addr, i, j;
+
+	usbi_dbg(ctx, " ");
+
+	for (i = 0; i < 8; i++) {
+		snprintf(busnode, sizeof(busnode), USBDEV "%d", i);
+
+		if ((fd = open(busnode, O_RDWR)) < 0) {
+			if (errno != ENOENT && errno != ENXIO)
+				usbi_err(ctx, "could not open %s", busnode);
+			continue;
+		}
+
+		bzero(devices, sizeof(devices));
+		for (addr = 1; addr < USB_MAX_DEVICES; addr++) {
+			if (devices[addr])
+				continue;
+
+			di.udi_addr = addr;
+			if (ioctl(fd, USB_DEVICEINFO, &di) < 0)
+				continue;
+
+			/*
+			 * XXX If ugen(4) is attached to the USB device
+			 * it will be used.
+			 */
+			udevname = NULL;
+			for (j = 0; j < USB_MAX_DEVNAMES; j++)
+				if (!strncmp("ugen", di.udi_devnames[j], 4)) {
+					udevname = strdup(di.udi_devnames[j]);
+					break;
+				}
+
+			session_id = (di.udi_bus << 8 | di.udi_addr);
+			dev = usbi_get_device_by_session_id(ctx, session_id);
+
+			if (dev == NULL) {
+				dev = usbi_alloc_device(ctx, session_id);
+				if (dev == NULL) {
+					close(fd);
+					return (LIBUSB_ERROR_NO_MEM);
+				}
+
+				dev->bus_number = di.udi_bus;
+				dev->device_address = di.udi_addr;
+				dev->speed = di.udi_speed;
+				dev->port_number = di.udi_port;
+
+				dpriv = usbi_get_device_priv(dev);
+				dpriv->fd = -1;
+				dpriv->devname = udevname;
+
+				dd.udd_bus = di.udi_bus;
+				dd.udd_addr = di.udi_addr;
+				if (ioctl(fd, USB_DEVICE_GET_DDESC, &dd) < 0) {
+					libusb_unref_device(dev);
+					continue;
+				}
+
+				static_assert(sizeof(dev->device_descriptor) == sizeof(dd.udd_desc),
+					      "mismatch between libusb and OS device descriptor sizes");
+				memcpy(&dev->device_descriptor, &dd.udd_desc, LIBUSB_DT_DEVICE_SIZE);
+				usbi_localize_device_descriptor(&dev->device_descriptor);
+
+				if (_cache_active_config_descriptor(dev)) {
+					libusb_unref_device(dev);
+					continue;
+				}
+
+				if (usbi_sanitize_device(dev)) {
+					libusb_unref_device(dev);
+					continue;
+				}
+			}
+
+			ddd = discovered_devs_append(*discdevs, dev);
+			if (ddd == NULL) {
+				close(fd);
+				return (LIBUSB_ERROR_NO_MEM);
+			}
+			libusb_unref_device(dev);
+
+			*discdevs = ddd;
+			devices[addr] = 1;
+		}
+
+		close(fd);
+	}
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+obsd_open(struct libusb_device_handle *handle)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(handle->dev);
+	char devnode[16];
+
+	if (dpriv->devname) {
+		int fd;
+		/*
+		 * Only open ugen(4) attached devices read-write, all
+		 * read-only operations are done through the bus node.
+		 */
+		snprintf(devnode, sizeof(devnode), DEVPATH "%s.00",
+		    dpriv->devname);
+		fd = open(devnode, O_RDWR);
+		if (fd < 0)
+			return _errno_to_libusb(errno);
+		dpriv->fd = fd;
+
+		usbi_dbg(HANDLE_CTX(handle), "open %s: fd %d", devnode, dpriv->fd);
+	}
+
+	return (LIBUSB_SUCCESS);
+}
+
+void
+obsd_close(struct libusb_device_handle *handle)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(handle->dev);
+
+	if (dpriv->devname) {
+		usbi_dbg(HANDLE_CTX(handle), "close: fd %d", dpriv->fd);
+
+		close(dpriv->fd);
+		dpriv->fd = -1;
+	}
+}
+
+int
+obsd_get_active_config_descriptor(struct libusb_device *dev,
+    void *buf, size_t len)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(dev);
+
+	len = MIN(len, (size_t)UGETW(dpriv->cdesc->wTotalLength));
+
+	usbi_dbg(DEVICE_CTX(dev), "len %zu", len);
+
+	memcpy(buf, dpriv->cdesc, len);
+
+	return ((int)len);
+}
+
+int
+obsd_get_config_descriptor(struct libusb_device *dev, uint8_t idx,
+    void *buf, size_t len)
+{
+	struct usb_device_fdesc udf;
+	int fd, err;
+
+	if ((fd = _bus_open(dev->bus_number)) < 0)
+		return _errno_to_libusb(errno);
+
+	udf.udf_bus = dev->bus_number;
+	udf.udf_addr = dev->device_address;
+	udf.udf_config_index = idx;
+	udf.udf_size = len;
+	udf.udf_data = buf;
+
+	usbi_dbg(DEVICE_CTX(dev), "index %d, len %zu", udf.udf_config_index, len);
+
+	if (ioctl(fd, USB_DEVICE_GET_FDESC, &udf) < 0) {
+		err = errno;
+		close(fd);
+		return _errno_to_libusb(err);
+	}
+	close(fd);
+
+	return ((int)len);
+}
+
+int
+obsd_get_configuration(struct libusb_device_handle *handle, uint8_t *config)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(handle->dev);
+
+	*config = dpriv->cdesc->bConfigurationValue;
+
+	usbi_dbg(HANDLE_CTX(handle), "bConfigurationValue %u", *config);
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+obsd_set_configuration(struct libusb_device_handle *handle, int config)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(handle->dev);
+
+	if (dpriv->devname == NULL)
+		return (LIBUSB_ERROR_NOT_SUPPORTED);
+
+	usbi_dbg(HANDLE_CTX(handle), "bConfigurationValue %d", config);
+
+	if (ioctl(dpriv->fd, USB_SET_CONFIG, &config) < 0)
+		return _errno_to_libusb(errno);
+
+	return _cache_active_config_descriptor(handle->dev);
+}
+
+int
+obsd_claim_interface(struct libusb_device_handle *handle, uint8_t iface)
+{
+	struct handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int i;
+
+	UNUSED(iface);
+
+	for (i = 0; i < USB_MAX_ENDPOINTS; i++)
+		hpriv->endpoints[i] = -1;
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+obsd_release_interface(struct libusb_device_handle *handle, uint8_t iface)
+{
+	struct handle_priv *hpriv = usbi_get_device_handle_priv(handle);
+	int i;
+
+	UNUSED(iface);
+
+	for (i = 0; i < USB_MAX_ENDPOINTS; i++)
+		if (hpriv->endpoints[i] >= 0)
+			close(hpriv->endpoints[i]);
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+obsd_set_interface_altsetting(struct libusb_device_handle *handle, uint8_t iface,
+    uint8_t altsetting)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(handle->dev);
+	struct usb_alt_interface intf;
+
+	if (dpriv->devname == NULL)
+		return (LIBUSB_ERROR_NOT_SUPPORTED);
+
+	usbi_dbg(HANDLE_CTX(handle), "iface %u, setting %u", iface, altsetting);
+
+	memset(&intf, 0, sizeof(intf));
+
+	intf.uai_interface_index = iface;
+	intf.uai_alt_no = altsetting;
+
+	if (ioctl(dpriv->fd, USB_SET_ALTINTERFACE, &intf) < 0)
+		return _errno_to_libusb(errno);
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+obsd_clear_halt(struct libusb_device_handle *handle, unsigned char endpoint)
+{
+	struct usb_ctl_request req;
+	int fd, err;
+
+	if ((fd = _bus_open(handle->dev->bus_number)) < 0)
+		return _errno_to_libusb(errno);
+
+	usbi_dbg(HANDLE_CTX(handle), " ");
+
+	req.ucr_addr = handle->dev->device_address;
+	req.ucr_request.bmRequestType = UT_WRITE_ENDPOINT;
+	req.ucr_request.bRequest = UR_CLEAR_FEATURE;
+	USETW(req.ucr_request.wValue, UF_ENDPOINT_HALT);
+	USETW(req.ucr_request.wIndex, endpoint);
+	USETW(req.ucr_request.wLength, 0);
+
+	if (ioctl(fd, USB_REQUEST, &req) < 0) {
+		err = errno;
+		close(fd);
+		return _errno_to_libusb(err);
+	}
+	close(fd);
+
+	return (LIBUSB_SUCCESS);
+}
+
+void
+obsd_destroy_device(struct libusb_device *dev)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(dev);
+
+	usbi_dbg(DEVICE_CTX(dev), " ");
+
+	free(dpriv->cdesc);
+	free(dpriv->devname);
+}
+
+int
+obsd_submit_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer;
+	int err = 0;
+
+	usbi_dbg(ITRANSFER_CTX(itransfer), " ");
+
+	transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+		err = _sync_control_transfer(itransfer);
+		break;
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		if (IS_XFEROUT(transfer)) {
+			/* Isochronous write is not supported */
+			err = LIBUSB_ERROR_NOT_SUPPORTED;
+			break;
+		}
+		err = _sync_gen_transfer(itransfer);
+		break;
+	case LIBUSB_TRANSFER_TYPE_BULK:
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		if (IS_XFEROUT(transfer) &&
+		    transfer->flags & LIBUSB_TRANSFER_ADD_ZERO_PACKET) {
+			err = LIBUSB_ERROR_NOT_SUPPORTED;
+			break;
+		}
+		err = _sync_gen_transfer(itransfer);
+		break;
+	case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
+		err = LIBUSB_ERROR_NOT_SUPPORTED;
+		break;
+	}
+
+	if (err)
+		return (err);
+
+	usbi_signal_transfer_completion(itransfer);
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+obsd_cancel_transfer(struct usbi_transfer *itransfer)
+{
+	UNUSED(itransfer);
+
+	usbi_dbg(ITRANSFER_CTX(itransfer), " ");
+
+	return (LIBUSB_ERROR_NOT_SUPPORTED);
+}
+
+int
+obsd_handle_transfer_completion(struct usbi_transfer *itransfer)
+{
+	return usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_COMPLETED);
+}
+
+int
+_errno_to_libusb(int err)
+{
+	usbi_dbg(NULL, "error: %s (%d)", strerror(err), err);
+
+	switch (err) {
+	case EIO:
+		return (LIBUSB_ERROR_IO);
+	case EACCES:
+		return (LIBUSB_ERROR_ACCESS);
+	case ENOENT:
+		return (LIBUSB_ERROR_NO_DEVICE);
+	case ENOMEM:
+		return (LIBUSB_ERROR_NO_MEM);
+	case ETIMEDOUT:
+		return (LIBUSB_ERROR_TIMEOUT);
+	}
+
+	return (LIBUSB_ERROR_OTHER);
+}
+
+int
+_cache_active_config_descriptor(struct libusb_device *dev)
+{
+	struct device_priv *dpriv = usbi_get_device_priv(dev);
+	struct usb_device_cdesc udc;
+	struct usb_device_fdesc udf;
+	void *buf;
+	int fd, len, err;
+
+	if ((fd = _bus_open(dev->bus_number)) < 0)
+		return _errno_to_libusb(errno);
+
+	usbi_dbg(DEVICE_CTX(dev), "fd %d, addr %d", fd, dev->device_address);
+
+	udc.udc_bus = dev->bus_number;
+	udc.udc_addr = dev->device_address;
+	udc.udc_config_index = USB_CURRENT_CONFIG_INDEX;
+	if (ioctl(fd, USB_DEVICE_GET_CDESC, &udc) < 0) {
+		err = errno;
+		close(fd);
+		return _errno_to_libusb(errno);
+	}
+
+	usbi_dbg(DEVICE_CTX(dev), "active bLength %d", udc.udc_desc.bLength);
+
+	len = UGETW(udc.udc_desc.wTotalLength);
+	buf = malloc((size_t)len);
+	if (buf == NULL)
+		return (LIBUSB_ERROR_NO_MEM);
+
+	udf.udf_bus = dev->bus_number;
+	udf.udf_addr = dev->device_address;
+	udf.udf_config_index = udc.udc_config_index;
+	udf.udf_size = len;
+	udf.udf_data = buf;
+
+	usbi_dbg(DEVICE_CTX(dev), "index %d, len %d", udf.udf_config_index, len);
+
+	if (ioctl(fd, USB_DEVICE_GET_FDESC, &udf) < 0) {
+		err = errno;
+		close(fd);
+		free(buf);
+		return _errno_to_libusb(err);
+	}
+	close(fd);
+
+	if (dpriv->cdesc)
+		free(dpriv->cdesc);
+	dpriv->cdesc = buf;
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+_sync_control_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer;
+	struct libusb_control_setup *setup;
+	struct device_priv *dpriv;
+	struct usb_ctl_request req;
+
+	transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	dpriv = usbi_get_device_priv(transfer->dev_handle->dev);
+	setup = (struct libusb_control_setup *)transfer->buffer;
+
+	usbi_dbg(ITRANSFER_CTX(itransfer), "type 0x%x request 0x%x value 0x%x index %d length %d timeout %d",
+	    setup->bmRequestType, setup->bRequest,
+	    libusb_le16_to_cpu(setup->wValue),
+	    libusb_le16_to_cpu(setup->wIndex),
+	    libusb_le16_to_cpu(setup->wLength), transfer->timeout);
+
+	req.ucr_addr = transfer->dev_handle->dev->device_address;
+	req.ucr_request.bmRequestType = setup->bmRequestType;
+	req.ucr_request.bRequest = setup->bRequest;
+	/* Don't use USETW, libusb already deals with the endianness */
+	(*(uint16_t *)req.ucr_request.wValue) = setup->wValue;
+	(*(uint16_t *)req.ucr_request.wIndex) = setup->wIndex;
+	(*(uint16_t *)req.ucr_request.wLength) = setup->wLength;
+	req.ucr_data = transfer->buffer + LIBUSB_CONTROL_SETUP_SIZE;
+
+	if ((transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) == 0)
+		req.ucr_flags = USBD_SHORT_XFER_OK;
+
+	if (dpriv->devname == NULL) {
+		/*
+		 * XXX If the device is not attached to ugen(4) it is
+		 * XXX still possible to submit a control transfer but
+		 * XXX with the default timeout only.
+		 */
+		int fd, err;
+
+		if ((fd = _bus_open(transfer->dev_handle->dev->bus_number)) < 0)
+			return _errno_to_libusb(errno);
+
+		if ((ioctl(fd, USB_REQUEST, &req)) < 0) {
+			err = errno;
+			close(fd);
+			return _errno_to_libusb(err);
+		}
+		close(fd);
+	} else {
+		if ((ioctl(dpriv->fd, USB_SET_TIMEOUT, &transfer->timeout)) < 0)
+			return _errno_to_libusb(errno);
+
+		if ((ioctl(dpriv->fd, USB_DO_REQUEST, &req)) < 0)
+			return _errno_to_libusb(errno);
+	}
+
+	itransfer->transferred = req.ucr_actlen;
+
+	usbi_dbg(ITRANSFER_CTX(itransfer), "transferred %d", itransfer->transferred);
+
+	return (0);
+}
+
+int
+_access_endpoint(struct libusb_transfer *transfer)
+{
+	struct handle_priv *hpriv;
+	struct device_priv *dpriv;
+	char devnode[16];
+	int fd, endpt;
+	mode_t mode;
+
+	hpriv = usbi_get_device_handle_priv(transfer->dev_handle);
+	dpriv = usbi_get_device_priv(transfer->dev_handle->dev);
+
+	endpt = UE_GET_ADDR(transfer->endpoint);
+	mode = IS_XFERIN(transfer) ? O_RDONLY : O_WRONLY;
+
+	usbi_dbg(TRANSFER_CTX(transfer), "endpoint %d mode %d", endpt, mode);
+
+	if (hpriv->endpoints[endpt] < 0) {
+		/* Pick the right endpoint node */
+		snprintf(devnode, sizeof(devnode), DEVPATH "%s.%02d",
+		    dpriv->devname, endpt);
+
+		/* We may need to read/write to the same endpoint later. */
+		if (((fd = open(devnode, O_RDWR)) < 0) && (errno == ENXIO))
+			if ((fd = open(devnode, mode)) < 0)
+				return (-1);
+
+		hpriv->endpoints[endpt] = fd;
+	}
+
+	return (hpriv->endpoints[endpt]);
+}
+
+int
+_sync_gen_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer;
+	struct device_priv *dpriv;
+	int fd, nr = 1;
+
+	transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	dpriv = usbi_get_device_priv(transfer->dev_handle->dev);
+
+	if (dpriv->devname == NULL)
+		return (LIBUSB_ERROR_NOT_SUPPORTED);
+
+	/*
+	 * Bulk, Interrupt or Isochronous transfer depends on the
+	 * endpoint and thus the node to open.
+	 */
+	if ((fd = _access_endpoint(transfer)) < 0)
+		return _errno_to_libusb(errno);
+
+	if ((ioctl(fd, USB_SET_TIMEOUT, &transfer->timeout)) < 0)
+		return _errno_to_libusb(errno);
+
+	if (IS_XFERIN(transfer)) {
+		if ((transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) == 0)
+			if ((ioctl(fd, USB_SET_SHORT_XFER, &nr)) < 0)
+				return _errno_to_libusb(errno);
+
+		nr = read(fd, transfer->buffer, transfer->length);
+	} else {
+		nr = write(fd, transfer->buffer, transfer->length);
+	}
+
+	if (nr < 0)
+		return _errno_to_libusb(errno);
+
+	itransfer->transferred = nr;
+
+	return (0);
+}
+
+int
+_bus_open(int number)
+{
+	char busnode[16];
+
+	snprintf(busnode, sizeof(busnode), USBDEV "%d", number);
+
+	return open(busnode, O_RDWR);
+}
diff --git a/src/os/sunos_usb.c b/src/os/sunos_usb.c
new file mode 100644
index 0000000..28b167f
--- /dev/null
+++ b/src/os/sunos_usb.c
@@ -0,0 +1,1609 @@
+/*
+ *
+ * Copyright (c) 2016, Oracle and/or its affiliates.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+
+#include <sys/time.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <strings.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <wait.h>
+#include <unistd.h>
+#include <aio.h>
+#include <libdevinfo.h>
+#include <sys/nvpair.h>
+#include <sys/devctl.h>
+#include <sys/usb/clients/ugen/usb_ugen.h>
+#include <sys/usb/usba.h>
+#include <sys/pci.h>
+
+#include "libusbi.h"
+#include "sunos_usb.h"
+
+#define UPDATEDRV_PATH	"/usr/sbin/update_drv"
+#define UPDATEDRV	"update_drv"
+
+#define	DEFAULT_LISTSIZE	6
+
+typedef struct {
+	int	nargs;
+	int	listsize;
+	char	**string;
+} string_list_t;
+
+/*
+ * Backend functions
+ */
+static int sunos_get_device_list(struct libusb_context *,
+    struct discovered_devs **);
+static int sunos_open(struct libusb_device_handle *);
+static void sunos_close(struct libusb_device_handle *);
+static int sunos_get_active_config_descriptor(struct libusb_device *,
+    void *, size_t);
+static int sunos_get_config_descriptor(struct libusb_device *, uint8_t,
+    void *, size_t);
+static int sunos_get_configuration(struct libusb_device_handle *, uint8_t *);
+static int sunos_set_configuration(struct libusb_device_handle *, int);
+static int sunos_claim_interface(struct libusb_device_handle *, uint8_t);
+static int sunos_release_interface(struct libusb_device_handle *, uint8_t);
+static int sunos_set_interface_altsetting(struct libusb_device_handle *,
+    uint8_t, uint8_t);
+static int sunos_clear_halt(struct libusb_device_handle *, unsigned char);
+static void sunos_destroy_device(struct libusb_device *);
+static int sunos_submit_transfer(struct usbi_transfer *);
+static int sunos_cancel_transfer(struct usbi_transfer *);
+static int sunos_handle_transfer_completion(struct usbi_transfer *);
+static int sunos_kernel_driver_active(struct libusb_device_handle *, uint8_t);
+static int sunos_detach_kernel_driver(struct libusb_device_handle *, uint8_t);
+static int sunos_attach_kernel_driver(struct libusb_device_handle *, uint8_t);
+static int sunos_usb_open_ep0(sunos_dev_handle_priv_t *hpriv, sunos_dev_priv_t *dpriv);
+static int sunos_usb_ioctl(struct libusb_device *dev, int cmd);
+
+static int sunos_get_link(di_devlink_t devlink, void *arg)
+{
+	walk_link_t *larg = (walk_link_t *)arg;
+	const char *p;
+	const char *q;
+
+	if (larg->path) {
+		char *content = (char *)di_devlink_content(devlink);
+		char *start = strstr(content, "/devices/");
+		start += strlen("/devices");
+		usbi_dbg(NULL, "%s", start);
+
+		/* line content must have minor node */
+		if (start == NULL ||
+		    strncmp(start, larg->path, larg->len) != 0 ||
+		    start[larg->len] != ':')
+			return (DI_WALK_CONTINUE);
+	}
+
+	p = di_devlink_path(devlink);
+	q = strrchr(p, '/');
+	usbi_dbg(NULL, "%s", q);
+
+	*(larg->linkpp) = strndup(p, strlen(p) - strlen(q));
+
+	return (DI_WALK_TERMINATE);
+}
+
+
+static int sunos_physpath_to_devlink(
+	const char *node_path, const char *match, char **link_path)
+{
+	walk_link_t larg;
+	di_devlink_handle_t hdl;
+
+	*link_path = NULL;
+	larg.linkpp = link_path;
+	if ((hdl = di_devlink_init(NULL, 0)) == NULL) {
+		usbi_dbg(NULL, "di_devlink_init failure");
+		return (-1);
+	}
+
+	larg.len = strlen(node_path);
+	larg.path = (char *)node_path;
+
+	(void) di_devlink_walk(hdl, match, NULL, DI_PRIMARY_LINK,
+	    (void *)&larg, sunos_get_link);
+
+	(void) di_devlink_fini(&hdl);
+
+	if (*link_path == NULL) {
+		usbi_dbg(NULL, "there is no devlink for this path");
+		return (-1);
+	}
+
+	return 0;
+}
+
+static int
+sunos_usb_ioctl(struct libusb_device *dev, int cmd)
+{
+	int fd;
+	nvlist_t *nvlist;
+	char *end;
+	char *phypath;
+	char *hubpath;
+	char path_arg[PATH_MAX];
+	sunos_dev_priv_t *dpriv;
+	devctl_ap_state_t devctl_ap_state;
+	struct devctl_iocdata iocdata;
+
+	dpriv = usbi_get_device_priv(dev);
+	phypath = dpriv->phypath;
+
+	end = strrchr(phypath, '/');
+	if (end == NULL)
+		return (-1);
+	hubpath = strndup(phypath, end - phypath);
+	if (hubpath == NULL)
+		return (-1);
+
+	end = strrchr(hubpath, '@');
+	if (end == NULL) {
+		free(hubpath);
+		return (-1);
+	}
+	end++;
+	usbi_dbg(DEVICE_CTX(dev), "unitaddr: %s", end);
+
+	nvlist_alloc(&nvlist, NV_UNIQUE_NAME_TYPE, KM_NOSLEEP);
+	nvlist_add_int32(nvlist, "port", dev->port_number);
+	//find the hub path
+	snprintf(path_arg, sizeof(path_arg), "/devices%s:hubd", hubpath);
+	usbi_dbg(DEVICE_CTX(dev), "ioctl hub path: %s", path_arg);
+
+	fd = open(path_arg, O_RDONLY);
+	if (fd < 0) {
+		usbi_err(DEVICE_CTX(dev), "open failed: errno %d (%s)", errno, strerror(errno));
+		nvlist_free(nvlist);
+		free(hubpath);
+		return (-1);
+	}
+
+	memset(&iocdata, 0, sizeof(iocdata));
+	memset(&devctl_ap_state, 0, sizeof(devctl_ap_state));
+
+	nvlist_pack(nvlist, (char **)&iocdata.nvl_user, &iocdata.nvl_usersz, NV_ENCODE_NATIVE, 0);
+
+	iocdata.cmd = DEVCTL_AP_GETSTATE;
+	iocdata.flags = 0;
+	iocdata.c_nodename = (char *)"hub";
+	iocdata.c_unitaddr = end;
+	iocdata.cpyout_buf = &devctl_ap_state;
+	usbi_dbg(DEVICE_CTX(dev), "%p, %" PRIuPTR, iocdata.nvl_user, iocdata.nvl_usersz);
+
+	errno = 0;
+	if (ioctl(fd, DEVCTL_AP_GETSTATE, &iocdata) == -1) {
+		usbi_err(DEVICE_CTX(dev), "ioctl failed: fd %d, cmd %x, errno %d (%s)",
+			 fd, DEVCTL_AP_GETSTATE, errno, strerror(errno));
+	} else {
+		usbi_dbg(DEVICE_CTX(dev), "dev rstate: %d", devctl_ap_state.ap_rstate);
+		usbi_dbg(DEVICE_CTX(dev), "dev ostate: %d", devctl_ap_state.ap_ostate);
+	}
+
+	errno = 0;
+	iocdata.cmd = cmd;
+	if (ioctl(fd, (int)cmd, &iocdata) != 0) {
+		usbi_err(DEVICE_CTX(dev), "ioctl failed: fd %d, cmd %x, errno %d (%s)",
+			 fd, cmd, errno, strerror(errno));
+		sleep(2);
+	}
+
+	close(fd);
+	free(iocdata.nvl_user);
+	nvlist_free(nvlist);
+	free(hubpath);
+
+	return (-errno);
+}
+
+static int
+sunos_kernel_driver_active(struct libusb_device_handle *dev_handle, uint8_t interface)
+{
+	sunos_dev_priv_t *dpriv = usbi_get_device_priv(dev_handle->dev);
+
+	UNUSED(interface);
+
+	usbi_dbg(HANDLE_CTX(dev_handle), "%s", dpriv->ugenpath);
+
+	return (dpriv->ugenpath == NULL);
+}
+
+/*
+ * Private functions
+ */
+static int _errno_to_libusb(int);
+static int sunos_usb_get_status(struct libusb_context *ctx, int fd);
+
+static string_list_t *
+sunos_new_string_list(void)
+{
+	string_list_t *list;
+
+	list = calloc(1, sizeof(string_list_t));
+	if (list == NULL)
+		return (NULL);
+	list->string = calloc(DEFAULT_LISTSIZE, sizeof(char *));
+	if (list->string == NULL) {
+		free(list);
+		return (NULL);
+	}
+	list->nargs = 0;
+	list->listsize = DEFAULT_LISTSIZE;
+
+	return (list);
+}
+
+static int
+sunos_append_to_string_list(string_list_t *list, const char *arg)
+{
+	char	*str = strdup(arg);
+
+	if (str == NULL)
+		return (-1);
+
+	if ((list->nargs + 1) == list->listsize) { /* +1 is for NULL */
+		char	**tmp = realloc(list->string,
+		    sizeof(char *) * (list->listsize + 1));
+		if (tmp == NULL) {
+			free(str);
+			return (-1);
+		}
+		list->string = tmp;
+		list->string[list->listsize++] = NULL;
+	}
+	list->string[list->nargs++] = str;
+
+	return (0);
+}
+
+static void
+sunos_free_string_list(string_list_t *list)
+{
+	int	i;
+
+	for (i = 0; i < list->nargs; i++) {
+		free(list->string[i]);
+	}
+
+	free(list->string);
+	free(list);
+}
+
+static char **
+sunos_build_argv_list(string_list_t *list)
+{
+	return (list->string);
+}
+
+
+static int
+sunos_exec_command(struct libusb_context *ctx, const char *path,
+	string_list_t *list)
+{
+	pid_t pid;
+	int status;
+	int waitstat;
+	int exit_status;
+	char **argv_list;
+
+	argv_list = sunos_build_argv_list(list);
+	if (argv_list == NULL)
+		return (-1);
+
+	pid = fork();
+	if (pid == 0) {
+		/* child */
+		execv(path, argv_list);
+		_exit(127);
+	} else if (pid > 0) {
+		/* parent */
+		do {
+			waitstat = waitpid(pid, &status, 0);
+		} while ((waitstat == -1 && errno == EINTR) ||
+			 (waitstat == 0 && !WIFEXITED(status) && !WIFSIGNALED(status)));
+
+		if (waitstat == 0) {
+			if (WIFEXITED(status))
+				exit_status = WEXITSTATUS(status);
+			else
+				exit_status = WTERMSIG(status);
+		} else {
+			usbi_err(ctx, "waitpid failed: errno %d (%s)", errno, strerror(errno));
+			exit_status = -1;
+		}
+	} else {
+		/* fork failed */
+		usbi_err(ctx, "fork failed: errno %d (%s)", errno, strerror(errno));
+		exit_status = -1;
+	}
+
+	return (exit_status);
+}
+
+static int
+sunos_detach_kernel_driver(struct libusb_device_handle *dev_handle,
+	uint8_t interface_number)
+{
+	struct libusb_context *ctx = HANDLE_CTX(dev_handle);
+	string_list_t *list;
+	char path_arg[PATH_MAX];
+	sunos_dev_priv_t *dpriv;
+	int r;
+
+	UNUSED(interface_number);
+
+	dpriv = usbi_get_device_priv(dev_handle->dev);
+	snprintf(path_arg, sizeof(path_arg), "\'\"%s\"\'", dpriv->phypath);
+	usbi_dbg(HANDLE_CTX(dev_handle), "%s", path_arg);
+
+	list = sunos_new_string_list();
+	if (list == NULL)
+		return (LIBUSB_ERROR_NO_MEM);
+
+	/* attach ugen driver */
+	r = 0;
+	r |= sunos_append_to_string_list(list, UPDATEDRV);
+	r |= sunos_append_to_string_list(list, "-a"); /* add rule */
+	r |= sunos_append_to_string_list(list, "-i"); /* specific device */
+	r |= sunos_append_to_string_list(list, path_arg); /* physical path */
+	r |= sunos_append_to_string_list(list, "ugen");
+	if (r) {
+		sunos_free_string_list(list);
+		return (LIBUSB_ERROR_NO_MEM);
+	}
+
+	r = sunos_exec_command(ctx, UPDATEDRV_PATH, list);
+	sunos_free_string_list(list);
+	if (r < 0)
+		return (LIBUSB_ERROR_OTHER);
+
+	/* reconfigure the driver node */
+	r = 0;
+	r |= sunos_usb_ioctl(dev_handle->dev, DEVCTL_AP_DISCONNECT);
+	r |= sunos_usb_ioctl(dev_handle->dev, DEVCTL_AP_CONFIGURE);
+	if (r)
+		usbi_warn(HANDLE_CTX(dev_handle), "one or more ioctls failed");
+
+	snprintf(path_arg, sizeof(path_arg), "^usb/%x.%x",
+	    dev_handle->dev->device_descriptor.idVendor,
+	    dev_handle->dev->device_descriptor.idProduct);
+	sunos_physpath_to_devlink(dpriv->phypath, path_arg, &dpriv->ugenpath);
+
+	if (access(dpriv->ugenpath, F_OK) == -1) {
+		usbi_err(HANDLE_CTX(dev_handle), "fail to detach kernel driver");
+		return (LIBUSB_ERROR_IO);
+	}
+
+	return sunos_usb_open_ep0(usbi_get_device_handle_priv(dev_handle), dpriv);
+}
+
+static int
+sunos_attach_kernel_driver(struct libusb_device_handle *dev_handle,
+	uint8_t interface_number)
+{
+	struct libusb_context *ctx = HANDLE_CTX(dev_handle);
+	string_list_t *list;
+	char path_arg[PATH_MAX];
+	sunos_dev_priv_t *dpriv;
+	int r;
+
+	UNUSED(interface_number);
+
+	/* we open the dev in detach driver, so we need close it first. */
+	sunos_close(dev_handle);
+
+	dpriv = usbi_get_device_priv(dev_handle->dev);
+	snprintf(path_arg, sizeof(path_arg), "\'\"%s\"\'", dpriv->phypath);
+	usbi_dbg(HANDLE_CTX(dev_handle), "%s", path_arg);
+
+	list = sunos_new_string_list();
+	if (list == NULL)
+		return (LIBUSB_ERROR_NO_MEM);
+
+	/* detach ugen driver */
+	r = 0;
+	r |= sunos_append_to_string_list(list, UPDATEDRV);
+	r |= sunos_append_to_string_list(list, "-d"); /* add rule */
+	r |= sunos_append_to_string_list(list, "-i"); /* specific device */
+	r |= sunos_append_to_string_list(list, path_arg); /* physical path */
+	r |= sunos_append_to_string_list(list, "ugen");
+	if (r) {
+		sunos_free_string_list(list);
+		return (LIBUSB_ERROR_NO_MEM);
+	}
+
+	r = sunos_exec_command(ctx, UPDATEDRV_PATH, list);
+	sunos_free_string_list(list);
+	if (r < 0)
+		return (LIBUSB_ERROR_OTHER);
+
+	/* reconfigure the driver node */
+	r = 0;
+	r |= sunos_usb_ioctl(dev_handle->dev, DEVCTL_AP_CONFIGURE);
+	r |= sunos_usb_ioctl(dev_handle->dev, DEVCTL_AP_DISCONNECT);
+	r |= sunos_usb_ioctl(dev_handle->dev, DEVCTL_AP_CONFIGURE);
+	if (r)
+		usbi_warn(HANDLE_CTX(dev_handle), "one or more ioctls failed");
+
+	return 0;
+}
+
+static int
+sunos_fill_in_dev_info(di_node_t node, struct libusb_device *dev)
+{
+	int	proplen;
+	int	*i, n, *addr, *port_prop;
+	char	*phypath;
+	uint8_t	*rdata;
+	sunos_dev_priv_t	*dpriv = usbi_get_device_priv(dev);
+	char	match_str[PATH_MAX];
+
+	/* Device descriptors */
+	proplen = di_prop_lookup_bytes(DDI_DEV_T_ANY, node,
+	    "usb-dev-descriptor", &rdata);
+	if (proplen <= 0) {
+		return (LIBUSB_ERROR_IO);
+	}
+	bcopy(rdata, &dev->device_descriptor, LIBUSB_DT_DEVICE_SIZE);
+
+	/* Raw configuration descriptors */
+	proplen = di_prop_lookup_bytes(DDI_DEV_T_ANY, node,
+	    "usb-raw-cfg-descriptors", &rdata);
+	if (proplen <= 0) {
+		usbi_dbg(DEVICE_CTX(dev), "can't find raw config descriptors");
+
+		return (LIBUSB_ERROR_IO);
+	}
+	dpriv->raw_cfgdescr = calloc(1, proplen);
+	if (dpriv->raw_cfgdescr == NULL) {
+		return (LIBUSB_ERROR_NO_MEM);
+	} else {
+		bcopy(rdata, dpriv->raw_cfgdescr, proplen);
+		dpriv->cfgvalue = ((struct libusb_config_descriptor *)
+		    rdata)->bConfigurationValue;
+	}
+
+	n = di_prop_lookup_ints(DDI_DEV_T_ANY, node, "reg", &port_prop);
+
+	if ((n != 1) || (*port_prop <= 0)) {
+		return (LIBUSB_ERROR_IO);
+	}
+	dev->port_number = *port_prop;
+
+	/* device physical path */
+	phypath = di_devfs_path(node);
+	if (phypath) {
+		dpriv->phypath = strdup(phypath);
+		snprintf(match_str, sizeof(match_str), "^usb/%x.%x",
+		    dev->device_descriptor.idVendor,
+		    dev->device_descriptor.idProduct);
+		usbi_dbg(DEVICE_CTX(dev), "match is %s", match_str);
+		sunos_physpath_to_devlink(dpriv->phypath, match_str,  &dpriv->ugenpath);
+		di_devfs_path_free(phypath);
+
+	} else {
+		free(dpriv->raw_cfgdescr);
+
+		return (LIBUSB_ERROR_IO);
+	}
+
+	/* address */
+	n = di_prop_lookup_ints(DDI_DEV_T_ANY, node, "assigned-address", &addr);
+	if (n != 1 || *addr == 0) {
+		usbi_dbg(DEVICE_CTX(dev), "can't get address");
+	} else {
+		dev->device_address = *addr;
+	}
+
+	/* speed */
+	if (di_prop_lookup_ints(DDI_DEV_T_ANY, node, "low-speed", &i) >= 0) {
+		dev->speed = LIBUSB_SPEED_LOW;
+	} else if (di_prop_lookup_ints(DDI_DEV_T_ANY, node, "high-speed", &i) >= 0) {
+		dev->speed = LIBUSB_SPEED_HIGH;
+	} else if (di_prop_lookup_ints(DDI_DEV_T_ANY, node, "full-speed", &i) >= 0) {
+		dev->speed = LIBUSB_SPEED_FULL;
+	} else if (di_prop_lookup_ints(DDI_DEV_T_ANY, node, "super-speed", &i) >= 0) {
+		dev->speed = LIBUSB_SPEED_SUPER;
+	}
+
+	usbi_dbg(DEVICE_CTX(dev), "vid=%x pid=%x, path=%s, bus_nmber=0x%x, port_number=%d, speed=%d",
+	    dev->device_descriptor.idVendor, dev->device_descriptor.idProduct,
+	    dpriv->phypath, dev->bus_number, dev->port_number, dev->speed);
+
+	return (LIBUSB_SUCCESS);
+}
+
+static int
+sunos_add_devices(di_devlink_t link, void *arg)
+{
+	struct devlink_cbarg	*largs = (struct devlink_cbarg *)arg;
+	struct node_args	*nargs;
+	di_node_t		myself, dn;
+	uint64_t		session_id = 0;
+	uint64_t		sid = 0;
+	uint64_t		bdf = 0;
+	struct libusb_device	*dev;
+	sunos_dev_priv_t	*devpriv;
+	int			n, *j;
+	int			i = 0;
+	int			*addr_prop;
+	uint8_t			bus_number = 0;
+	uint32_t *		regbuf = NULL;
+	uint32_t		reg;
+
+	UNUSED(link);
+
+	nargs = (struct node_args *)largs->nargs;
+	myself = largs->myself;
+
+	/*
+	 * Construct session ID.
+	 * session ID = dev_addr | hub addr |parent hub addr|...|root hub bdf
+	 * 		8 bits       8bits          8 bits               16bits
+	 */
+	if (myself == DI_NODE_NIL)
+		return (DI_WALK_CONTINUE);
+
+	dn = myself;
+	/* find the root hub */
+	while (di_prop_lookup_ints(DDI_DEV_T_ANY, dn, "root-hub", &j) != 0) {
+		usbi_dbg(NULL, "find_root_hub:%s", di_devfs_path(dn));
+		n = di_prop_lookup_ints(DDI_DEV_T_ANY, dn,
+				"assigned-address", &addr_prop);
+		session_id |= ((addr_prop[0] & 0xff) << i++ * 8);
+		dn = di_parent_node(dn);
+	}
+
+	/* dn is the root hub node */
+	n = di_prop_lookup_ints(DDI_DEV_T_ANY, dn, "reg", (int **)&regbuf);
+	reg = regbuf[0];
+	bdf = (PCI_REG_BUS_G(reg) << 8) | (PCI_REG_DEV_G(reg) << 3) | PCI_REG_FUNC_G(reg);
+	/* bdf must larger than i*8 bits */
+	session_id |= (bdf << i * 8);
+	bus_number = (PCI_REG_DEV_G(reg) << 3) | PCI_REG_FUNC_G(reg);
+
+	usbi_dbg(NULL, "device bus address=%s:%x, name:%s",
+	    di_bus_addr(myself), bus_number, di_node_name(dn));
+	usbi_dbg(NULL, "session id org:%" PRIx64, session_id);
+
+	/* dn is the usb device */
+	for (dn = di_child_node(myself); dn != DI_NODE_NIL; dn = di_sibling_node(dn)) {
+		usbi_dbg(NULL, "device path:%s", di_devfs_path(dn));
+		/* skip hub devices, because its driver can not been unload */
+		if (di_prop_lookup_ints(DDI_DEV_T_ANY, dn, "usb-port-count", &addr_prop) != -1)
+			continue;
+		/* usb_addr */
+		n = di_prop_lookup_ints(DDI_DEV_T_ANY, dn,
+		    "assigned-address", &addr_prop);
+		if ((n != 1) || (addr_prop[0] == 0)) {
+			usbi_dbg(NULL, "cannot get valid usb_addr");
+			continue;
+		}
+
+		sid = (session_id << 8) | (addr_prop[0] & 0xff) ;
+		usbi_dbg(NULL, "session id %" PRIX64, sid);
+
+		dev = usbi_get_device_by_session_id(nargs->ctx, sid);
+		if (dev == NULL) {
+			dev = usbi_alloc_device(nargs->ctx, sid);
+			if (dev == NULL) {
+				usbi_dbg(NULL, "can't alloc device");
+				continue;
+			}
+			devpriv = usbi_get_device_priv(dev);
+			dev->bus_number = bus_number;
+
+			if (sunos_fill_in_dev_info(dn, dev) != LIBUSB_SUCCESS) {
+				libusb_unref_device(dev);
+				usbi_dbg(NULL, "get information fail");
+				continue;
+			}
+			if (usbi_sanitize_device(dev) < 0) {
+				libusb_unref_device(dev);
+				usbi_dbg(NULL, "sanatize failed: ");
+				return (DI_WALK_TERMINATE);
+			}
+		} else {
+			devpriv = usbi_get_device_priv(dev);
+			usbi_dbg(NULL, "Dev %s exists", devpriv->ugenpath);
+		}
+
+		if (discovered_devs_append(*(nargs->discdevs), dev) == NULL) {
+			usbi_dbg(NULL, "cannot append device");
+		}
+
+		/*
+		 * we alloc and hence ref this dev. We don't need to ref it
+		 * hereafter. Front end or app should take care of their ref.
+		 */
+		libusb_unref_device(dev);
+
+		usbi_dbg(NULL, "Device %s %s id=0x%" PRIx64 ", devcount:%" PRIuPTR
+		    ", bdf=%" PRIx64,
+		    devpriv->ugenpath, di_devfs_path(dn), (uint64_t)sid,
+		    (*nargs->discdevs)->len, bdf);
+	}
+
+	return (DI_WALK_CONTINUE);
+}
+
+static int
+sunos_walk_minor_node_link(di_node_t node, void *args)
+{
+        di_minor_t minor = DI_MINOR_NIL;
+        char *minor_path;
+        struct devlink_cbarg arg;
+	struct node_args *nargs = (struct node_args *)args;
+	di_devlink_handle_t devlink_hdl = nargs->dlink_hdl;
+
+	/* walk each minor to find usb devices */
+        while ((minor = di_minor_next(node, minor)) != DI_MINOR_NIL) {
+                minor_path = di_devfs_minor_path(minor);
+                arg.nargs = args;
+		arg.myself = node;
+                arg.minor = minor;
+                (void) di_devlink_walk(devlink_hdl,
+		    "^usb/hub[0-9]+", minor_path,
+		    DI_PRIMARY_LINK, (void *)&arg, sunos_add_devices);
+                di_devfs_path_free(minor_path);
+        }
+
+	/* switch to a different node */
+	nargs->last_ugenpath = NULL;
+
+	return (DI_WALK_CONTINUE);
+}
+
+int
+sunos_get_device_list(struct libusb_context * ctx,
+	struct discovered_devs **discdevs)
+{
+	di_node_t root_node;
+	struct node_args args;
+	di_devlink_handle_t devlink_hdl;
+
+	args.ctx = ctx;
+	args.discdevs = discdevs;
+	args.last_ugenpath = NULL;
+	if ((root_node = di_init("/", DINFOCPYALL)) == DI_NODE_NIL) {
+		usbi_dbg(ctx, "di_int() failed: errno %d (%s)", errno, strerror(errno));
+		return (LIBUSB_ERROR_IO);
+	}
+
+	if ((devlink_hdl = di_devlink_init(NULL, 0)) == NULL) {
+		di_fini(root_node);
+		usbi_dbg(ctx, "di_devlink_init() failed: errno %d (%s)", errno, strerror(errno));
+
+		return (LIBUSB_ERROR_IO);
+	}
+	args.dlink_hdl = devlink_hdl;
+
+	/* walk each node to find USB devices */
+	if (di_walk_node(root_node, DI_WALK_SIBFIRST, &args,
+	    sunos_walk_minor_node_link) == -1) {
+		usbi_dbg(ctx, "di_walk_node() failed: errno %d (%s)", errno, strerror(errno));
+		di_fini(root_node);
+
+		return (LIBUSB_ERROR_IO);
+	}
+
+	di_fini(root_node);
+	di_devlink_fini(&devlink_hdl);
+
+	usbi_dbg(ctx, "%zu devices", (*discdevs)->len);
+
+	return ((*discdevs)->len);
+}
+
+static int
+sunos_usb_open_ep0(sunos_dev_handle_priv_t *hpriv, sunos_dev_priv_t *dpriv)
+{
+	char filename[PATH_MAX + 1];
+
+	if (hpriv->eps[0].datafd > 0) {
+		return (LIBUSB_SUCCESS);
+	}
+	snprintf(filename, PATH_MAX, "%s/cntrl0", dpriv->ugenpath);
+
+	usbi_dbg(NULL, "opening %s", filename);
+	hpriv->eps[0].datafd = open(filename, O_RDWR);
+	if (hpriv->eps[0].datafd < 0) {
+		return(_errno_to_libusb(errno));
+	}
+
+	snprintf(filename, PATH_MAX, "%s/cntrl0stat", dpriv->ugenpath);
+	hpriv->eps[0].statfd = open(filename, O_RDONLY);
+	if (hpriv->eps[0].statfd < 0) {
+		close(hpriv->eps[0].datafd);
+		hpriv->eps[0].datafd = -1;
+
+		return(_errno_to_libusb(errno));
+	}
+
+	return (LIBUSB_SUCCESS);
+}
+
+static void
+sunos_usb_close_all_eps(sunos_dev_handle_priv_t *hdev)
+{
+	int i;
+
+	/* not close ep0 */
+	for (i = 1; i < USB_MAXENDPOINTS; i++) {
+		if (hdev->eps[i].datafd != -1) {
+			(void) close(hdev->eps[i].datafd);
+			hdev->eps[i].datafd = -1;
+		}
+		if (hdev->eps[i].statfd != -1) {
+			(void) close(hdev->eps[i].statfd);
+			hdev->eps[i].statfd = -1;
+		}
+	}
+}
+
+static void
+sunos_usb_close_ep0(sunos_dev_handle_priv_t *hdev)
+{
+	if (hdev->eps[0].datafd >= 0) {
+		close(hdev->eps[0].datafd);
+		close(hdev->eps[0].statfd);
+		hdev->eps[0].datafd = -1;
+		hdev->eps[0].statfd = -1;
+	}
+}
+
+static uchar_t
+sunos_usb_ep_index(uint8_t ep_addr)
+{
+	return ((ep_addr & LIBUSB_ENDPOINT_ADDRESS_MASK) +
+	    ((ep_addr & LIBUSB_ENDPOINT_DIR_MASK) ? 16 : 0));
+}
+
+static int
+sunos_find_interface(struct libusb_device_handle *hdev,
+    uint8_t endpoint, uint8_t *interface)
+{
+	struct libusb_config_descriptor *config;
+	int r;
+	int iface_idx;
+
+	r = libusb_get_active_config_descriptor(hdev->dev, &config);
+	if (r < 0) {
+		return (LIBUSB_ERROR_INVALID_PARAM);
+	}
+
+	for (iface_idx = 0; iface_idx < config->bNumInterfaces; iface_idx++) {
+		const struct libusb_interface *iface =
+		    &config->interface[iface_idx];
+		int altsetting_idx;
+
+		for (altsetting_idx = 0; altsetting_idx < iface->num_altsetting;
+		    altsetting_idx++) {
+			const struct libusb_interface_descriptor *altsetting =
+			    &iface->altsetting[altsetting_idx];
+			int ep_idx;
+
+			for (ep_idx = 0; ep_idx < altsetting->bNumEndpoints;
+			    ep_idx++) {
+				const struct libusb_endpoint_descriptor *ep =
+					&altsetting->endpoint[ep_idx];
+				if (ep->bEndpointAddress == endpoint) {
+					*interface = iface_idx;
+					libusb_free_config_descriptor(config);
+
+					return (LIBUSB_SUCCESS);
+				}
+			}
+		}
+	}
+	libusb_free_config_descriptor(config);
+
+	return (LIBUSB_ERROR_INVALID_PARAM);
+}
+
+static int
+sunos_check_device_and_status_open(struct libusb_device_handle *hdl,
+    uint8_t ep_addr, int ep_type)
+{
+	char	filename[PATH_MAX + 1], statfilename[PATH_MAX + 1];
+	char	cfg_num[16], alt_num[16];
+	int	fd, fdstat, mode;
+	uint8_t	ifc = 0;
+	uint8_t	ep_index;
+	sunos_dev_handle_priv_t *hpriv;
+
+	usbi_dbg(HANDLE_CTX(hdl), "open ep 0x%02x", ep_addr);
+	hpriv = usbi_get_device_handle_priv(hdl);
+	ep_index = sunos_usb_ep_index(ep_addr);
+	/* ep already opened */
+	if ((hpriv->eps[ep_index].datafd > 0) &&
+	    (hpriv->eps[ep_index].statfd > 0)) {
+		usbi_dbg(HANDLE_CTX(hdl), "ep 0x%02x already opened, return success",
+			ep_addr);
+
+		return (0);
+	}
+
+	if (sunos_find_interface(hdl, ep_addr, &ifc) < 0) {
+		usbi_dbg(HANDLE_CTX(hdl), "can't find interface for endpoint 0x%02x",
+		    ep_addr);
+
+		return (EACCES);
+	}
+
+	/* create filename */
+	if (hpriv->config_index > 0) {
+		(void) snprintf(cfg_num, sizeof(cfg_num), "cfg%d",
+		    hpriv->config_index + 1);
+	} else {
+		bzero(cfg_num, sizeof(cfg_num));
+	}
+
+	if (hpriv->altsetting[ifc] > 0) {
+		(void) snprintf(alt_num, sizeof(alt_num), ".%d",
+		    hpriv->altsetting[ifc]);
+	} else {
+		bzero(alt_num, sizeof(alt_num));
+	}
+
+	(void) snprintf(filename, PATH_MAX, "%s/%sif%d%s%s%d",
+	    hpriv->dpriv->ugenpath, cfg_num, ifc, alt_num,
+	    (ep_addr & LIBUSB_ENDPOINT_DIR_MASK) ? "in" :
+	    "out", (ep_addr & LIBUSB_ENDPOINT_ADDRESS_MASK));
+	(void) snprintf(statfilename, PATH_MAX, "%sstat", filename);
+
+	/*
+	 * In case configuration has been switched, the xfer endpoint needs
+	 * to be opened before the status endpoint, due to a ugen issue.
+	 * However, to enable the one transfer mode for an Interrupt-In pipe,
+	 * the status endpoint needs to be opened before the xfer endpoint.
+	 * So, open the xfer mode first and close it immediately
+	 * as a workaround. This will handle the configuration switch.
+	 * Then, open the status endpoint.  If for an Interrupt-in pipe,
+	 * write the USB_EP_INTR_ONE_XFER control to the status endpoint
+	 * to enable the one transfer mode.  Then, re-open the xfer mode.
+	 */
+	if (ep_type == LIBUSB_TRANSFER_TYPE_ISOCHRONOUS) {
+		mode = O_RDWR;
+	} else if (ep_addr & LIBUSB_ENDPOINT_IN) {
+		mode = O_RDONLY;
+	} else {
+		mode = O_WRONLY;
+	}
+	/* Open the xfer endpoint first */
+	if ((fd = open(filename, mode)) == -1) {
+		usbi_dbg(HANDLE_CTX(hdl), "can't open %s: errno %d (%s)", filename, errno,
+		    strerror(errno));
+
+		return (errno);
+	}
+	/* And immediately close the xfer endpoint */
+	(void) close(fd);
+
+	/*
+	 * Open the status endpoint.
+	 * If for an Interrupt-IN pipe, need to enable the one transfer mode
+	 * by writing USB_EP_INTR_ONE_XFER control to the status endpoint
+	 * before opening the xfer endpoint
+	 */
+	if ((ep_type == LIBUSB_TRANSFER_TYPE_INTERRUPT) &&
+	    (ep_addr & LIBUSB_ENDPOINT_IN)) {
+		char	control = USB_EP_INTR_ONE_XFER;
+		ssize_t	count;
+
+		/* Open the status endpoint with RDWR */
+		if ((fdstat = open(statfilename, O_RDWR)) == -1) {
+			usbi_dbg(HANDLE_CTX(hdl), "can't open %s RDWR: errno %d (%s)",
+				statfilename, errno, strerror(errno));
+
+			return (errno);
+		} else {
+			count = write(fdstat, &control, sizeof(control));
+			if (count != 1) {
+				/* this should have worked */
+				usbi_dbg(HANDLE_CTX(hdl), "can't write to %s: errno %d (%s)",
+					statfilename, errno, strerror(errno));
+				(void) close(fdstat);
+
+				return (errno);
+			}
+		}
+	} else {
+		if ((fdstat = open(statfilename, O_RDONLY)) == -1) {
+			usbi_dbg(HANDLE_CTX(hdl), "can't open %s: errno %d (%s)", statfilename, errno,
+				strerror(errno));
+
+			return (errno);
+		}
+	}
+
+	/* Re-open the xfer endpoint */
+	if ((fd = open(filename, mode)) == -1) {
+		usbi_dbg(HANDLE_CTX(hdl), "can't open %s: errno %d (%s)", filename, errno,
+			strerror(errno));
+		(void) close(fdstat);
+
+		return (errno);
+	}
+
+	hpriv->eps[ep_index].datafd = fd;
+	hpriv->eps[ep_index].statfd = fdstat;
+	usbi_dbg(HANDLE_CTX(hdl), "ep=0x%02x datafd=%d, statfd=%d", ep_addr, fd, fdstat);
+
+	return (0);
+}
+
+int
+sunos_open(struct libusb_device_handle *handle)
+{
+	sunos_dev_handle_priv_t	*hpriv;
+	sunos_dev_priv_t	*dpriv;
+	int	i;
+	int	ret;
+
+	hpriv = usbi_get_device_handle_priv(handle);
+	dpriv = usbi_get_device_priv(handle->dev);
+	hpriv->dpriv = dpriv;
+
+	/* set all file descriptors to "closed" */
+	for (i = 0; i < USB_MAXENDPOINTS; i++) {
+		hpriv->eps[i].datafd = -1;
+		hpriv->eps[i].statfd = -1;
+	}
+
+	if (sunos_kernel_driver_active(handle, 0)) {
+		/* pretend we can open the device */
+		return (LIBUSB_SUCCESS);
+	}
+
+	if ((ret = sunos_usb_open_ep0(hpriv, dpriv)) != LIBUSB_SUCCESS) {
+		usbi_dbg(HANDLE_CTX(handle), "fail: %d", ret);
+		return (ret);
+	}
+
+	return (LIBUSB_SUCCESS);
+}
+
+void
+sunos_close(struct libusb_device_handle *handle)
+{
+	sunos_dev_handle_priv_t *hpriv;
+
+	usbi_dbg(HANDLE_CTX(handle), " ");
+
+	hpriv = usbi_get_device_handle_priv(handle);
+
+	sunos_usb_close_all_eps(hpriv);
+	sunos_usb_close_ep0(hpriv);
+}
+
+int
+sunos_get_active_config_descriptor(struct libusb_device *dev,
+    void *buf, size_t len)
+{
+	sunos_dev_priv_t *dpriv = usbi_get_device_priv(dev);
+	struct libusb_config_descriptor *cfg;
+	int proplen;
+	di_node_t node;
+	uint8_t	*rdata;
+
+	/*
+	 * Keep raw configuration descriptors updated, in case config
+	 * has ever been changed through setCfg.
+	 */
+	if ((node = di_init(dpriv->phypath, DINFOCPYALL)) == DI_NODE_NIL) {
+		usbi_dbg(DEVICE_CTX(dev), "di_int() failed: errno %d (%s)", errno,
+			strerror(errno));
+		return (LIBUSB_ERROR_IO);
+	}
+	proplen = di_prop_lookup_bytes(DDI_DEV_T_ANY, node,
+	    "usb-raw-cfg-descriptors", &rdata);
+	if (proplen <= 0) {
+		usbi_dbg(DEVICE_CTX(dev), "can't find raw config descriptors");
+
+		return (LIBUSB_ERROR_IO);
+	}
+	dpriv->raw_cfgdescr = realloc(dpriv->raw_cfgdescr, proplen);
+	if (dpriv->raw_cfgdescr == NULL) {
+		return (LIBUSB_ERROR_NO_MEM);
+	} else {
+		bcopy(rdata, dpriv->raw_cfgdescr, proplen);
+		dpriv->cfgvalue = ((struct libusb_config_descriptor *)
+		    rdata)->bConfigurationValue;
+	}
+	di_fini(node);
+
+	cfg = (struct libusb_config_descriptor *)dpriv->raw_cfgdescr;
+	len = MIN(len, libusb_le16_to_cpu(cfg->wTotalLength));
+	memcpy(buf, dpriv->raw_cfgdescr, len);
+	usbi_dbg(DEVICE_CTX(dev), "path:%s len %zu", dpriv->phypath, len);
+
+	return (len);
+}
+
+int
+sunos_get_config_descriptor(struct libusb_device *dev, uint8_t idx,
+    void *buf, size_t len)
+{
+	UNUSED(idx);
+	/* XXX */
+	return(sunos_get_active_config_descriptor(dev, buf, len));
+}
+
+int
+sunos_get_configuration(struct libusb_device_handle *handle, uint8_t *config)
+{
+	sunos_dev_priv_t *dpriv = usbi_get_device_priv(handle->dev);
+
+	*config = dpriv->cfgvalue;
+
+	usbi_dbg(HANDLE_CTX(handle), "bConfigurationValue %u", *config);
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+sunos_set_configuration(struct libusb_device_handle *handle, int config)
+{
+	sunos_dev_priv_t *dpriv = usbi_get_device_priv(handle->dev);
+	sunos_dev_handle_priv_t *hpriv;
+
+	usbi_dbg(HANDLE_CTX(handle), "bConfigurationValue %d", config);
+	hpriv = usbi_get_device_handle_priv(handle);
+
+	if (dpriv->ugenpath == NULL)
+		return (LIBUSB_ERROR_NOT_SUPPORTED);
+
+	if (config < 1)
+		return (LIBUSB_ERROR_NOT_SUPPORTED);
+
+	dpriv->cfgvalue = config;
+	hpriv->config_index = config - 1;
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+sunos_claim_interface(struct libusb_device_handle *handle, uint8_t iface)
+{
+	UNUSED(handle);
+
+	usbi_dbg(HANDLE_CTX(handle), "iface %u", iface);
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+sunos_release_interface(struct libusb_device_handle *handle, uint8_t iface)
+{
+	sunos_dev_handle_priv_t *hpriv = usbi_get_device_handle_priv(handle);
+
+	usbi_dbg(HANDLE_CTX(handle), "iface %u", iface);
+
+	/* XXX: can we release it? */
+	hpriv->altsetting[iface] = 0;
+
+	return (LIBUSB_SUCCESS);
+}
+
+int
+sunos_set_interface_altsetting(struct libusb_device_handle *handle, uint8_t iface,
+    uint8_t altsetting)
+{
+	sunos_dev_priv_t *dpriv = usbi_get_device_priv(handle->dev);
+	sunos_dev_handle_priv_t *hpriv = usbi_get_device_handle_priv(handle);
+
+	usbi_dbg(HANDLE_CTX(handle), "iface %u, setting %u", iface, altsetting);
+
+	if (dpriv->ugenpath == NULL)
+		return (LIBUSB_ERROR_NOT_FOUND);
+
+	/* XXX: can we switch altsetting? */
+	hpriv->altsetting[iface] = altsetting;
+
+	return (LIBUSB_SUCCESS);
+}
+
+static void
+usb_dump_data(const void *data, size_t size)
+{
+	const uint8_t *p = data;
+	size_t i;
+
+	if (getenv("LIBUSB_DEBUG") == NULL) {
+		return;
+	}
+
+	(void) fprintf(stderr, "data dump:");
+	for (i = 0; i < size; i++) {
+		if (i % 16 == 0) {
+			(void) fprintf(stderr, "\n%08zx	", i);
+		}
+		(void) fprintf(stderr, "%02x ", p[i]);
+	}
+	(void) fprintf(stderr, "\n");
+}
+
+static void
+sunos_async_callback(union sigval arg)
+{
+	struct sunos_transfer_priv *tpriv =
+	    (struct sunos_transfer_priv *)arg.sival_ptr;
+	struct libusb_transfer *xfer = tpriv->transfer;
+	struct aiocb *aiocb = &tpriv->aiocb;
+	int ret;
+	sunos_dev_handle_priv_t *hpriv;
+	uint8_t ep;
+	libusb_device_handle *dev_handle;
+
+	dev_handle = xfer->dev_handle;
+
+	/* libusb can forcibly interrupt transfer in do_close() */
+	if (dev_handle != NULL) {
+		hpriv = usbi_get_device_handle_priv(dev_handle);
+		ep = sunos_usb_ep_index(xfer->endpoint);
+
+		ret = aio_error(aiocb);
+		if (ret != 0) {
+			xfer->status = sunos_usb_get_status(TRANSFER_CTX(xfer), hpriv->eps[ep].statfd);
+		} else {
+			xfer->actual_length =
+			    LIBUSB_TRANSFER_TO_USBI_TRANSFER(xfer)->transferred =
+			    aio_return(aiocb);
+		}
+
+		usb_dump_data(xfer->buffer, xfer->actual_length);
+
+		usbi_dbg(TRANSFER_CTX(xfer), "ret=%d, len=%d, actual_len=%d", ret, xfer->length,
+		    xfer->actual_length);
+
+		/* async notification */
+		usbi_signal_transfer_completion(LIBUSB_TRANSFER_TO_USBI_TRANSFER(xfer));
+	}
+}
+
+static int
+sunos_do_async_io(struct libusb_transfer *transfer)
+{
+	int ret = -1;
+	struct aiocb *aiocb;
+	sunos_dev_handle_priv_t *hpriv;
+	uint8_t ep;
+	struct sunos_transfer_priv *tpriv;
+
+	usbi_dbg(TRANSFER_CTX(transfer), " ");
+
+	tpriv = usbi_get_transfer_priv(LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer));
+	hpriv = usbi_get_device_handle_priv(transfer->dev_handle);
+	ep = sunos_usb_ep_index(transfer->endpoint);
+
+	tpriv->transfer = transfer;
+	aiocb = &tpriv->aiocb;
+	bzero(aiocb, sizeof(*aiocb));
+	aiocb->aio_fildes = hpriv->eps[ep].datafd;
+	aiocb->aio_buf = transfer->buffer;
+	aiocb->aio_nbytes = transfer->length;
+	aiocb->aio_lio_opcode =
+	    ((transfer->endpoint & LIBUSB_ENDPOINT_DIR_MASK) ==
+	    LIBUSB_ENDPOINT_IN) ? LIO_READ:LIO_WRITE;
+	aiocb->aio_sigevent.sigev_notify = SIGEV_THREAD;
+	aiocb->aio_sigevent.sigev_value.sival_ptr = tpriv;
+	aiocb->aio_sigevent.sigev_notify_function = sunos_async_callback;
+
+	if (aiocb->aio_lio_opcode == LIO_READ) {
+		ret = aio_read(aiocb);
+	} else {
+		ret = aio_write(aiocb);
+	}
+
+	return (ret);
+}
+
+/* return the number of bytes read/written */
+static ssize_t
+usb_do_io(struct libusb_context *ctx, int fd, int stat_fd, void *data, size_t size, int flag, int *status)
+{
+	int error;
+	ssize_t ret = -1;
+
+	usbi_dbg(ctx, "usb_do_io(): datafd=%d statfd=%d size=0x%zx flag=%s",
+	    fd, stat_fd, size, flag? "WRITE":"READ");
+
+	switch (flag) {
+	case READ:
+		errno = 0;
+		ret = read(fd, data, size);
+		usb_dump_data(data, size);
+		break;
+	case WRITE:
+		usb_dump_data(data, size);
+		errno = 0;
+		ret = write(fd, data, size);
+		break;
+	}
+
+	usbi_dbg(ctx, "usb_do_io(): amount=%zd", ret);
+
+	if (ret < 0) {
+		int save_errno = errno;
+
+		usbi_dbg(ctx, "TID=%x io %s errno %d (%s)", pthread_self(),
+		    flag?"WRITE":"READ", errno, strerror(errno));
+
+		/* sunos_usb_get_status will do a read and overwrite errno */
+		error = sunos_usb_get_status(ctx, stat_fd);
+		usbi_dbg(ctx, "io status=%d errno %d (%s)", error,
+			save_errno, strerror(save_errno));
+
+		if (status) {
+			*status = save_errno;
+		}
+
+		return (save_errno);
+
+	} else if (status) {
+		*status = 0;
+	}
+
+	return (ret);
+}
+
+static int
+solaris_submit_ctrl_on_default(struct libusb_transfer *transfer)
+{
+	ssize_t		ret = -1, setup_ret;
+	int		status;
+	sunos_dev_handle_priv_t *hpriv;
+	struct		libusb_device_handle *hdl = transfer->dev_handle;
+	uint16_t	wLength;
+	uint8_t		*data = transfer->buffer;
+
+	hpriv = usbi_get_device_handle_priv(hdl);
+	wLength = transfer->length - LIBUSB_CONTROL_SETUP_SIZE;
+
+	if (hpriv->eps[0].datafd == -1) {
+		usbi_dbg(TRANSFER_CTX(transfer), "ep0 not opened");
+
+		return (LIBUSB_ERROR_NOT_FOUND);
+	}
+
+	if ((data[0] & LIBUSB_ENDPOINT_DIR_MASK) == LIBUSB_ENDPOINT_IN) {
+		usbi_dbg(TRANSFER_CTX(transfer), "IN request");
+		ret = usb_do_io(TRANSFER_CTX(transfer), hpriv->eps[0].datafd,
+		    hpriv->eps[0].statfd, data, LIBUSB_CONTROL_SETUP_SIZE,
+		    WRITE, &status);
+	} else {
+		usbi_dbg(TRANSFER_CTX(transfer), "OUT request");
+		ret = usb_do_io(TRANSFER_CTX(transfer), hpriv->eps[0].datafd, hpriv->eps[0].statfd,
+		    transfer->buffer, transfer->length, WRITE,
+		    (int *)&transfer->status);
+	}
+
+	setup_ret = ret;
+	if (ret < (ssize_t)LIBUSB_CONTROL_SETUP_SIZE) {
+		usbi_dbg(TRANSFER_CTX(transfer), "error sending control msg: %zd", ret);
+
+		return (LIBUSB_ERROR_IO);
+	}
+
+	ret = transfer->length - LIBUSB_CONTROL_SETUP_SIZE;
+
+	/* Read the remaining bytes for IN request */
+	if ((wLength) && ((data[0] & LIBUSB_ENDPOINT_DIR_MASK) ==
+	    LIBUSB_ENDPOINT_IN)) {
+		usbi_dbg(TRANSFER_CTX(transfer), "DATA: %d", transfer->length - (int)setup_ret);
+		ret = usb_do_io(TRANSFER_CTX(transfer), hpriv->eps[0].datafd,
+			hpriv->eps[0].statfd,
+			transfer->buffer + LIBUSB_CONTROL_SETUP_SIZE,
+			wLength, READ, (int *)&transfer->status);
+	}
+
+	if (ret >= 0) {
+		LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer)->transferred = ret;
+	}
+	usbi_dbg(TRANSFER_CTX(transfer), "Done: ctrl data bytes %zd", ret);
+
+	/**
+	 * Sync transfer handling.
+ 	 * We should release transfer lock here and later get it back
+	 * as usbi_handle_transfer_completion() takes its own transfer lock.
+	 */
+	usbi_mutex_unlock(&LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer)->lock);
+	ret = usbi_handle_transfer_completion(LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer),
+	    transfer->status);
+	usbi_mutex_lock(&LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer)->lock);
+
+	return (ret);
+}
+
+int
+sunos_clear_halt(struct libusb_device_handle *handle, unsigned char endpoint)
+{
+	int ret;
+
+	usbi_dbg(HANDLE_CTX(handle), "endpoint=0x%02x", endpoint);
+
+	ret = libusb_control_transfer(handle, LIBUSB_ENDPOINT_OUT |
+	    LIBUSB_RECIPIENT_ENDPOINT | LIBUSB_REQUEST_TYPE_STANDARD,
+	    LIBUSB_REQUEST_CLEAR_FEATURE, 0, endpoint, NULL, 0, 1000);
+
+	usbi_dbg(HANDLE_CTX(handle), "ret=%d", ret);
+
+	return (ret);
+}
+
+void
+sunos_destroy_device(struct libusb_device *dev)
+{
+	sunos_dev_priv_t *dpriv = usbi_get_device_priv(dev);
+
+	usbi_dbg(DEVICE_CTX(dev), "destroy everything");
+	free(dpriv->raw_cfgdescr);
+	free(dpriv->ugenpath);
+	free(dpriv->phypath);
+}
+
+int
+sunos_submit_transfer(struct usbi_transfer *itransfer)
+{
+	struct	libusb_transfer *transfer;
+	struct	libusb_device_handle *hdl;
+	int	err = 0;
+
+	transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	hdl = transfer->dev_handle;
+
+	err = sunos_check_device_and_status_open(hdl,
+	    transfer->endpoint, transfer->type);
+	if (err < 0) {
+
+		return (_errno_to_libusb(err));
+	}
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+		/* sync transfer */
+		usbi_dbg(ITRANSFER_CTX(itransfer), "CTRL transfer: %d", transfer->length);
+		err = solaris_submit_ctrl_on_default(transfer);
+		break;
+
+	case LIBUSB_TRANSFER_TYPE_BULK:
+		/* fallthru */
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		if (transfer->type == LIBUSB_TRANSFER_TYPE_BULK)
+			usbi_dbg(ITRANSFER_CTX(itransfer), "BULK transfer: %d", transfer->length);
+		else
+			usbi_dbg(ITRANSFER_CTX(itransfer), "INTR transfer: %d", transfer->length);
+		err = sunos_do_async_io(transfer);
+		break;
+
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		/* Isochronous/Stream is not supported */
+
+		/* fallthru */
+	case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
+		if (transfer->type == LIBUSB_TRANSFER_TYPE_ISOCHRONOUS)
+			usbi_dbg(ITRANSFER_CTX(itransfer), "ISOC transfer: %d", transfer->length);
+		else
+			usbi_dbg(ITRANSFER_CTX(itransfer), "BULK STREAM transfer: %d", transfer->length);
+		err = LIBUSB_ERROR_NOT_SUPPORTED;
+		break;
+	}
+
+	return (err);
+}
+
+int
+sunos_cancel_transfer(struct usbi_transfer *itransfer)
+{
+	sunos_xfer_priv_t	*tpriv;
+	sunos_dev_handle_priv_t	*hpriv;
+	struct libusb_transfer	*transfer;
+	struct aiocb	*aiocb;
+	uint8_t		ep;
+	int		ret;
+
+	tpriv = usbi_get_transfer_priv(itransfer);
+	aiocb = &tpriv->aiocb;
+	transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	hpriv = usbi_get_device_handle_priv(transfer->dev_handle);
+	ep = sunos_usb_ep_index(transfer->endpoint);
+
+	ret = aio_cancel(hpriv->eps[ep].datafd, aiocb);
+
+	usbi_dbg(ITRANSFER_CTX(itransfer), "aio->fd=%d fd=%d ret = %d, %s", aiocb->aio_fildes,
+	    hpriv->eps[ep].datafd, ret, (ret == AIO_CANCELED)?
+	    strerror(0):strerror(errno));
+
+	if (ret != AIO_CANCELED) {
+		ret = _errno_to_libusb(errno);
+	} else {
+	/*
+	 * we don't need to call usbi_handle_transfer_cancellation(),
+	 * because we'll handle everything in sunos_async_callback.
+	 */
+		ret = LIBUSB_SUCCESS;
+	}
+
+	return (ret);
+}
+
+int
+sunos_handle_transfer_completion(struct usbi_transfer *itransfer)
+{
+	return usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_COMPLETED);
+}
+
+int
+_errno_to_libusb(int err)
+{
+	usbi_dbg(NULL, "error: %s (%d)", strerror(err), err);
+
+	switch (err) {
+	case EIO:
+		return (LIBUSB_ERROR_IO);
+	case EACCES:
+		return (LIBUSB_ERROR_ACCESS);
+	case ENOENT:
+		return (LIBUSB_ERROR_NO_DEVICE);
+	case ENOMEM:
+		return (LIBUSB_ERROR_NO_MEM);
+	case ETIMEDOUT:
+		return (LIBUSB_ERROR_TIMEOUT);
+	}
+
+	return (LIBUSB_ERROR_OTHER);
+}
+
+/*
+ * sunos_usb_get_status:
+ *	gets status of endpoint
+ *
+ * Returns: ugen's last cmd status
+ */
+static int
+sunos_usb_get_status(struct libusb_context *ctx, int fd)
+{
+	int status;
+	ssize_t ret;
+
+	usbi_dbg(ctx, "sunos_usb_get_status(): fd=%d", fd);
+
+	ret = read(fd, &status, sizeof(status));
+	if (ret == sizeof(status)) {
+		switch (status) {
+		case USB_LC_STAT_NOERROR:
+			usbi_dbg(ctx, "No Error");
+			break;
+		case USB_LC_STAT_CRC:
+			usbi_dbg(ctx, "CRC Timeout Detected\n");
+			break;
+		case USB_LC_STAT_BITSTUFFING:
+			usbi_dbg(ctx, "Bit Stuffing Violation\n");
+			break;
+		case USB_LC_STAT_DATA_TOGGLE_MM:
+			usbi_dbg(ctx, "Data Toggle Mismatch\n");
+			break;
+		case USB_LC_STAT_STALL:
+			usbi_dbg(ctx, "End Point Stalled\n");
+			break;
+		case USB_LC_STAT_DEV_NOT_RESP:
+			usbi_dbg(ctx, "Device is Not Responding\n");
+			break;
+		case USB_LC_STAT_PID_CHECKFAILURE:
+			usbi_dbg(ctx, "PID Check Failure\n");
+			break;
+		case USB_LC_STAT_UNEXP_PID:
+			usbi_dbg(ctx, "Unexpected PID\n");
+			break;
+		case USB_LC_STAT_DATA_OVERRUN:
+			usbi_dbg(ctx, "Data Exceeded Size\n");
+			break;
+		case USB_LC_STAT_DATA_UNDERRUN:
+			usbi_dbg(ctx, "Less data received\n");
+			break;
+		case USB_LC_STAT_BUFFER_OVERRUN:
+			usbi_dbg(ctx, "Buffer Size Exceeded\n");
+			break;
+		case USB_LC_STAT_BUFFER_UNDERRUN:
+			usbi_dbg(ctx, "Buffer Underrun\n");
+			break;
+		case USB_LC_STAT_TIMEOUT:
+			usbi_dbg(ctx, "Command Timed Out\n");
+			break;
+		case USB_LC_STAT_NOT_ACCESSED:
+			usbi_dbg(ctx, "Not Accessed by h/w\n");
+			break;
+		case USB_LC_STAT_UNSPECIFIED_ERR:
+			usbi_dbg(ctx, "Unspecified Error\n");
+			break;
+		case USB_LC_STAT_NO_BANDWIDTH:
+			usbi_dbg(ctx, "No Bandwidth\n");
+			break;
+		case USB_LC_STAT_HW_ERR:
+			usbi_dbg(ctx, "Host Controller h/w Error\n");
+			break;
+		case USB_LC_STAT_SUSPENDED:
+			usbi_dbg(ctx, "Device was Suspended\n");
+			break;
+		case USB_LC_STAT_DISCONNECTED:
+			usbi_dbg(ctx, "Device was Disconnected\n");
+			break;
+		case USB_LC_STAT_INTR_BUF_FULL:
+			usbi_dbg(ctx, "Interrupt buffer was full\n");
+			break;
+		case USB_LC_STAT_INVALID_REQ:
+			usbi_dbg(ctx, "Request was Invalid\n");
+			break;
+		case USB_LC_STAT_INTERRUPTED:
+			usbi_dbg(ctx, "Request was Interrupted\n");
+			break;
+		case USB_LC_STAT_NO_RESOURCES:
+			usbi_dbg(ctx, "No resources available for "
+			    "request\n");
+			break;
+		case USB_LC_STAT_INTR_POLLING_FAILED:
+			usbi_dbg(ctx, "Failed to Restart Poll");
+			break;
+		default:
+			usbi_dbg(ctx, "Error Not Determined %d\n",
+			    status);
+			break;
+		}
+	} else {
+		usbi_dbg(ctx, "read stat error: %s",strerror(errno));
+		status = -1;
+	}
+
+	return (status);
+}
+
+const struct usbi_os_backend usbi_backend = {
+        .name = "Solaris",
+        .caps = 0,
+        .get_device_list = sunos_get_device_list,
+        .get_active_config_descriptor = sunos_get_active_config_descriptor,
+        .get_config_descriptor = sunos_get_config_descriptor,
+        .open = sunos_open,
+        .close = sunos_close,
+        .get_configuration = sunos_get_configuration,
+        .set_configuration = sunos_set_configuration,
+        .claim_interface = sunos_claim_interface,
+        .release_interface = sunos_release_interface,
+        .set_interface_altsetting = sunos_set_interface_altsetting,
+        .clear_halt = sunos_clear_halt,
+        .kernel_driver_active = sunos_kernel_driver_active,
+        .detach_kernel_driver = sunos_detach_kernel_driver,
+        .attach_kernel_driver = sunos_attach_kernel_driver,
+        .destroy_device = sunos_destroy_device,
+        .submit_transfer = sunos_submit_transfer,
+        .cancel_transfer = sunos_cancel_transfer,
+        .handle_transfer_completion = sunos_handle_transfer_completion,
+        .device_priv_size = sizeof(sunos_dev_priv_t),
+        .device_handle_priv_size = sizeof(sunos_dev_handle_priv_t),
+        .transfer_priv_size = sizeof(sunos_xfer_priv_t),
+};
diff --git a/src/os/sunos_usb.h b/src/os/sunos_usb.h
new file mode 100644
index 0000000..2988398
--- /dev/null
+++ b/src/os/sunos_usb.h
@@ -0,0 +1,79 @@
+/*
+ *
+ * Copyright (c) 2016, Oracle and/or its affiliates.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef	LIBUSB_SUNOS_H
+#define	LIBUSB_SUNOS_H
+
+#include <libdevinfo.h>
+#include <pthread.h>
+#include "libusbi.h"
+
+#define	READ	0
+#define	WRITE	1
+
+typedef struct sunos_device_priv {
+	uint8_t	cfgvalue;		/* active config value */
+	uint8_t	*raw_cfgdescr;		/* active config descriptor */
+	char	*ugenpath;		/* name of the ugen(4) node */
+	char	*phypath;		/* physical path */
+} sunos_dev_priv_t;
+
+typedef	struct endpoint {
+	int datafd;	/* data file */
+	int statfd;	/* state file */
+} sunos_ep_priv_t;
+
+typedef struct sunos_device_handle_priv {
+	uint8_t			altsetting[USB_MAXINTERFACES];	/* a interface's alt */
+	uint8_t			config_index;
+	sunos_ep_priv_t		eps[USB_MAXENDPOINTS];
+	sunos_dev_priv_t	*dpriv; /* device private */
+} sunos_dev_handle_priv_t;
+
+typedef	struct sunos_transfer_priv {
+	struct aiocb		aiocb;
+	struct libusb_transfer	*transfer;
+} sunos_xfer_priv_t;
+
+struct node_args {
+	struct libusb_context	*ctx;
+	struct discovered_devs	**discdevs;
+	const char		*last_ugenpath;
+	di_devlink_handle_t	dlink_hdl;
+};
+
+struct devlink_cbarg {
+	struct node_args	*nargs;	/* di node walk arguments */
+	di_node_t		myself;	/* the di node */
+	di_minor_t		minor;
+};
+
+typedef struct walk_link {
+	char *path;
+	int len;
+	char **linkpp;
+} walk_link_t;
+
+/* AIO callback args */
+struct aio_callback_args{
+	struct libusb_transfer *transfer;
+	struct aiocb aiocb;
+};
+
+#endif /* LIBUSB_SUNOS_H */
diff --git a/src/os/threads_posix.c b/src/os/threads_posix.c
new file mode 100644
index 0000000..0e0e221
--- /dev/null
+++ b/src/os/threads_posix.c
@@ -0,0 +1,129 @@
+/*
+ * libusb synchronization using POSIX Threads
+ *
+ * Copyright © 2011 Vitali Lovich <vlovich@aliph.com>
+ * Copyright © 2011 Peter Stuge <peter@stuge.se>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "libusbi.h"
+
+#include <errno.h>
+#if defined(__ANDROID__)
+# include <unistd.h>
+#elif defined(__HAIKU__)
+# include <os/kernel/OS.h>
+#elif defined(__linux__)
+# include <sys/syscall.h>
+# include <unistd.h>
+#elif defined(__NetBSD__)
+# include <lwp.h>
+#elif defined(__OpenBSD__)
+# define _BSD_SOURCE
+# include <sys/syscall.h>
+# include <unistd.h>
+#elif defined(__sun__)
+# include <sys/lwp.h>
+#endif
+
+void usbi_cond_init(pthread_cond_t *cond)
+{
+#ifdef HAVE_PTHREAD_CONDATTR_SETCLOCK
+	pthread_condattr_t condattr;
+
+	PTHREAD_CHECK(pthread_condattr_init(&condattr));
+	PTHREAD_CHECK(pthread_condattr_setclock(&condattr, CLOCK_MONOTONIC));
+	PTHREAD_CHECK(pthread_cond_init(cond, &condattr));
+	PTHREAD_CHECK(pthread_condattr_destroy(&condattr));
+#else
+	PTHREAD_CHECK(pthread_cond_init(cond, NULL));
+#endif
+}
+
+int usbi_cond_timedwait(pthread_cond_t *cond,
+	pthread_mutex_t *mutex, const struct timeval *tv)
+{
+	struct timespec timeout;
+	int r;
+
+#ifdef HAVE_PTHREAD_CONDATTR_SETCLOCK
+	usbi_get_monotonic_time(&timeout);
+#else
+	usbi_get_real_time(&timeout);
+#endif
+
+	timeout.tv_sec += tv->tv_sec;
+	timeout.tv_nsec += tv->tv_usec * 1000L;
+	if (timeout.tv_nsec >= NSEC_PER_SEC) {
+		timeout.tv_nsec -= NSEC_PER_SEC;
+		timeout.tv_sec++;
+	}
+
+	r = pthread_cond_timedwait(cond, mutex, &timeout);
+	if (r == 0)
+		return 0;
+	else if (r == ETIMEDOUT)
+		return LIBUSB_ERROR_TIMEOUT;
+	else
+		return LIBUSB_ERROR_OTHER;
+}
+
+unsigned int usbi_get_tid(void)
+{
+	static _Thread_local unsigned int tl_tid;
+	int tid;
+
+	if (tl_tid)
+		return tl_tid;
+
+#if defined(__ANDROID__)
+	tid = gettid();
+#elif defined(__APPLE__)
+#ifdef HAVE_PTHREAD_THREADID_NP
+	uint64_t thread_id;
+
+	if (pthread_threadid_np(NULL, &thread_id) == 0)
+		tid = (int)thread_id;
+	else
+		tid = -1;
+#else
+	tid = (int)pthread_mach_thread_np(pthread_self());
+#endif
+#elif defined(__HAIKU__)
+	tid = get_pthread_thread_id(pthread_self());
+#elif defined(__linux__)
+	tid = (int)syscall(SYS_gettid);
+#elif defined(__NetBSD__)
+	tid = _lwp_self();
+#elif defined(__OpenBSD__)
+	/* The following only works with OpenBSD > 5.1 as it requires
+	 * real thread support. For 5.1 and earlier, -1 is returned. */
+	tid = syscall(SYS_getthrid);
+#elif defined(__sun__)
+	tid = _lwp_self();
+#else
+	tid = -1;
+#endif
+
+	if (tid == -1) {
+		/* If we don't have a thread ID, at least return a unique
+		 * value that can be used to distinguish individual
+		 * threads. */
+		tid = (int)(intptr_t)pthread_self();
+	}
+
+	return tl_tid = (unsigned int)tid;
+}
diff --git a/src/os/threads_posix.h b/src/os/threads_posix.h
new file mode 100644
index 0000000..9322834
--- /dev/null
+++ b/src/os/threads_posix.h
@@ -0,0 +1,98 @@
+/*
+ * libusb synchronization using POSIX Threads
+ *
+ * Copyright © 2010 Peter Stuge <peter@stuge.se>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef LIBUSB_THREADS_POSIX_H
+#define LIBUSB_THREADS_POSIX_H
+
+#include <pthread.h>
+
+#define PTHREAD_CHECK(expression)	ASSERT_EQ(expression, 0)
+
+#define USBI_MUTEX_INITIALIZER	PTHREAD_MUTEX_INITIALIZER
+typedef pthread_mutex_t usbi_mutex_static_t;
+static inline void usbi_mutex_static_lock(usbi_mutex_static_t *mutex)
+{
+	PTHREAD_CHECK(pthread_mutex_lock(mutex));
+}
+static inline void usbi_mutex_static_unlock(usbi_mutex_static_t *mutex)
+{
+	PTHREAD_CHECK(pthread_mutex_unlock(mutex));
+}
+
+typedef pthread_mutex_t usbi_mutex_t;
+static inline void usbi_mutex_init(usbi_mutex_t *mutex)
+{
+	PTHREAD_CHECK(pthread_mutex_init(mutex, NULL));
+}
+static inline void usbi_mutex_lock(usbi_mutex_t *mutex)
+{
+	PTHREAD_CHECK(pthread_mutex_lock(mutex));
+}
+static inline void usbi_mutex_unlock(usbi_mutex_t *mutex)
+{
+	PTHREAD_CHECK(pthread_mutex_unlock(mutex));
+}
+static inline int usbi_mutex_trylock(usbi_mutex_t *mutex)
+{
+	return pthread_mutex_trylock(mutex) == 0;
+}
+static inline void usbi_mutex_destroy(usbi_mutex_t *mutex)
+{
+	PTHREAD_CHECK(pthread_mutex_destroy(mutex));
+}
+
+typedef pthread_cond_t usbi_cond_t;
+void usbi_cond_init(pthread_cond_t *cond);
+static inline void usbi_cond_wait(usbi_cond_t *cond, usbi_mutex_t *mutex)
+{
+	PTHREAD_CHECK(pthread_cond_wait(cond, mutex));
+}
+int usbi_cond_timedwait(usbi_cond_t *cond,
+	usbi_mutex_t *mutex, const struct timeval *tv);
+static inline void usbi_cond_broadcast(usbi_cond_t *cond)
+{
+	PTHREAD_CHECK(pthread_cond_broadcast(cond));
+}
+static inline void usbi_cond_destroy(usbi_cond_t *cond)
+{
+	PTHREAD_CHECK(pthread_cond_destroy(cond));
+}
+
+typedef pthread_key_t usbi_tls_key_t;
+static inline void usbi_tls_key_create(usbi_tls_key_t *key)
+{
+	PTHREAD_CHECK(pthread_key_create(key, NULL));
+}
+static inline void *usbi_tls_key_get(usbi_tls_key_t key)
+{
+	return pthread_getspecific(key);
+}
+static inline void usbi_tls_key_set(usbi_tls_key_t key, void *ptr)
+{
+	PTHREAD_CHECK(pthread_setspecific(key, ptr));
+}
+static inline void usbi_tls_key_delete(usbi_tls_key_t key)
+{
+	PTHREAD_CHECK(pthread_key_delete(key));
+}
+
+unsigned int usbi_get_tid(void);
+
+#endif /* LIBUSB_THREADS_POSIX_H */
diff --git a/src/os/threads_windows.c b/src/os/threads_windows.c
new file mode 100644
index 0000000..4a57f42
--- /dev/null
+++ b/src/os/threads_windows.c
@@ -0,0 +1,40 @@
+/*
+ * libusb synchronization on Microsoft Windows
+ *
+ * Copyright © 2010 Michael Plante <michael.plante@gmail.com>
+ * Copyright © 2020 Chris Dickens <christopher.a.dickens@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include "libusbi.h"
+
+int usbi_cond_timedwait(usbi_cond_t *cond,
+	usbi_mutex_t *mutex, const struct timeval *tv)
+{
+	DWORD millis;
+
+	millis = (DWORD)(tv->tv_sec * 1000L) + (tv->tv_usec / 1000L);
+	/* round up to next millisecond */
+	if (tv->tv_usec % 1000L)
+		millis++;
+
+	if (SleepConditionVariableCS(cond, mutex, millis))
+		return 0;
+	else if (GetLastError() == ERROR_TIMEOUT)
+		return LIBUSB_ERROR_TIMEOUT;
+	else
+		return LIBUSB_ERROR_OTHER;
+}
diff --git a/src/os/threads_windows.h b/src/os/threads_windows.h
new file mode 100644
index 0000000..dfef158
--- /dev/null
+++ b/src/os/threads_windows.h
@@ -0,0 +1,113 @@
+/*
+ * libusb synchronization on Microsoft Windows
+ *
+ * Copyright © 2010 Michael Plante <michael.plante@gmail.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef LIBUSB_THREADS_WINDOWS_H
+#define LIBUSB_THREADS_WINDOWS_H
+
+#define WINAPI_CHECK(expression)	ASSERT_NE(expression, 0)
+
+#define USBI_MUTEX_INITIALIZER	0L
+typedef LONG usbi_mutex_static_t;
+static inline void usbi_mutex_static_lock(usbi_mutex_static_t *mutex)
+{
+	while (InterlockedExchange(mutex, 1L) == 1L)
+		SleepEx(0, TRUE);
+}
+static inline void usbi_mutex_static_unlock(usbi_mutex_static_t *mutex)
+{
+	InterlockedExchange(mutex, 0L);
+}
+
+typedef CRITICAL_SECTION usbi_mutex_t;
+static inline void usbi_mutex_init(usbi_mutex_t *mutex)
+{
+	InitializeCriticalSection(mutex);
+}
+static inline void usbi_mutex_lock(usbi_mutex_t *mutex)
+{
+	EnterCriticalSection(mutex);
+}
+static inline void usbi_mutex_unlock(usbi_mutex_t *mutex)
+{
+	LeaveCriticalSection(mutex);
+}
+static inline int usbi_mutex_trylock(usbi_mutex_t *mutex)
+{
+	return TryEnterCriticalSection(mutex) != 0;
+}
+static inline void usbi_mutex_destroy(usbi_mutex_t *mutex)
+{
+	DeleteCriticalSection(mutex);
+}
+
+#if !defined(HAVE_STRUCT_TIMESPEC) && !defined(_TIMESPEC_DEFINED)
+#define HAVE_STRUCT_TIMESPEC 1
+#define _TIMESPEC_DEFINED 1
+struct timespec {
+	long tv_sec;
+	long tv_nsec;
+};
+#endif /* HAVE_STRUCT_TIMESPEC || _TIMESPEC_DEFINED */
+
+typedef CONDITION_VARIABLE usbi_cond_t;
+static inline void usbi_cond_init(usbi_cond_t *cond)
+{
+	InitializeConditionVariable(cond);
+}
+static inline void usbi_cond_wait(usbi_cond_t *cond, usbi_mutex_t *mutex)
+{
+	WINAPI_CHECK(SleepConditionVariableCS(cond, mutex, INFINITE));
+}
+int usbi_cond_timedwait(usbi_cond_t *cond,
+	usbi_mutex_t *mutex, const struct timeval *tv);
+static inline void usbi_cond_broadcast(usbi_cond_t *cond)
+{
+	WakeAllConditionVariable(cond);
+}
+static inline void usbi_cond_destroy(usbi_cond_t *cond)
+{
+	UNUSED(cond);
+}
+
+typedef DWORD usbi_tls_key_t;
+static inline void usbi_tls_key_create(usbi_tls_key_t *key)
+{
+	*key = TlsAlloc();
+	assert(*key != TLS_OUT_OF_INDEXES);
+}
+static inline void *usbi_tls_key_get(usbi_tls_key_t key)
+{
+	return TlsGetValue(key);
+}
+static inline void usbi_tls_key_set(usbi_tls_key_t key, void *ptr)
+{
+	WINAPI_CHECK(TlsSetValue(key, ptr));
+}
+static inline void usbi_tls_key_delete(usbi_tls_key_t key)
+{
+	WINAPI_CHECK(TlsFree(key));
+}
+
+static inline unsigned int usbi_get_tid(void)
+{
+	return (unsigned int)GetCurrentThreadId();
+}
+
+#endif /* LIBUSB_THREADS_WINDOWS_H */
diff --git a/src/os/windows_common.c b/src/os/windows_common.c
new file mode 100644
index 0000000..eefd01e
--- /dev/null
+++ b/src/os/windows_common.c
@@ -0,0 +1,904 @@
+/*
+ * windows backend for libusb 1.0
+ * Copyright © 2009-2012 Pete Batard <pete@akeo.ie>
+ * With contributions from Michael Plante, Orin Eman et al.
+ * Parts of this code adapted from libusb-win32-v1 by Stephan Meyer
+ * HID Reports IOCTLs inspired from HIDAPI by Alan Ott, Signal 11 Software
+ * Hash table functions adapted from glibc, by Ulrich Drepper et al.
+ * Major code testing contribution by Xiaofan Chen
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+
+#include <stdio.h>
+
+#include "libusbi.h"
+#include "windows_common.h"
+
+#define EPOCH_TIME	UINT64_C(116444736000000000)	// 1970.01.01 00:00:000 in MS Filetime
+
+#define STATUS_SUCCESS	((ULONG_PTR)0UL)
+
+// Public
+enum windows_version windows_version = WINDOWS_UNDEFINED;
+
+// Global variables for init/exit
+static unsigned int init_count;
+static bool usbdk_available;
+
+/*
+* Converts a windows error to human readable string
+* uses retval as errorcode, or, if 0, use GetLastError()
+*/
+#if defined(ENABLE_LOGGING)
+const char *windows_error_str(DWORD error_code)
+{
+	static char err_string[256];
+
+	DWORD size;
+	int len;
+
+	if (error_code == 0)
+		error_code = GetLastError();
+
+	len = sprintf(err_string, "[%lu] ", ULONG_CAST(error_code));
+
+	// Translate codes returned by SetupAPI. The ones we are dealing with are either
+	// in 0x0000xxxx or 0xE000xxxx and can be distinguished from standard error codes.
+	// See http://msdn.microsoft.com/en-us/library/windows/hardware/ff545011.aspx
+	switch (error_code & 0xE0000000) {
+	case 0:
+		error_code = HRESULT_FROM_WIN32(error_code); // Still leaves ERROR_SUCCESS unmodified
+		break;
+	case 0xE0000000:
+		error_code = 0x80000000 | (FACILITY_SETUPAPI << 16) | (error_code & 0x0000FFFF);
+		break;
+	default:
+		break;
+	}
+
+	size = FormatMessageA(FORMAT_MESSAGE_FROM_SYSTEM|FORMAT_MESSAGE_IGNORE_INSERTS,
+			NULL, error_code, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT),
+			&err_string[len], sizeof(err_string) - len, NULL);
+	if (size == 0) {
+		DWORD format_error = GetLastError();
+		if (format_error)
+			snprintf(err_string, sizeof(err_string),
+				"Windows error code %lu (FormatMessage error code %lu)",
+				ULONG_CAST(error_code), ULONG_CAST(format_error));
+		else
+			snprintf(err_string, sizeof(err_string), "Unknown error code %lu",
+				ULONG_CAST(error_code));
+	} else {
+		// Remove CRLF from end of message, if present
+		size_t pos = len + size - 2;
+		if (err_string[pos] == '\r')
+			err_string[pos] = '\0';
+	}
+
+	return err_string;
+}
+#endif
+
+/*
+ * Dynamically loads a DLL from the Windows system directory.  Unlike the
+ * LoadLibraryA() function, this function will not search through any
+ * directories to try and find the library.
+ */
+HMODULE load_system_library(struct libusb_context *ctx, const char *name)
+{
+	char library_path[MAX_PATH];
+	char *filename_start;
+	UINT length;
+
+	length = GetSystemDirectoryA(library_path, sizeof(library_path));
+	if ((length == 0) || (length >= (UINT)sizeof(library_path))) {
+		usbi_err(ctx, "program assertion failed - could not get system directory");
+		return NULL;
+	}
+
+	filename_start = library_path + length;
+	// Append '\' + name + ".dll" + NUL
+	length += 1 + (UINT)strlen(name) + 4 + 1;
+	if (length >= (UINT)sizeof(library_path)) {
+		usbi_err(ctx, "program assertion failed - library path buffer overflow");
+		return NULL;
+	}
+
+	sprintf(filename_start, "\\%s.dll", name);
+	return LoadLibraryA(library_path);
+}
+
+/* Hash table functions - modified From glibc 2.3.2:
+   [Aho,Sethi,Ullman] Compilers: Principles, Techniques and Tools, 1986
+   [Knuth]            The Art of Computer Programming, part 3 (6.4)  */
+
+#define HTAB_SIZE 1021UL	// *MUST* be a prime number!!
+
+typedef struct htab_entry {
+	unsigned long used;
+	char *str;
+} htab_entry;
+
+static htab_entry *htab_table;
+static usbi_mutex_t htab_mutex;
+static unsigned long htab_filled;
+
+/* Before using the hash table we must allocate memory for it.
+   We allocate one element more as the found prime number says.
+   This is done for more effective indexing as explained in the
+   comment for the hash function.  */
+static bool htab_create(struct libusb_context *ctx)
+{
+	if (htab_table != NULL) {
+		usbi_err(ctx, "program assertion failed - hash table already allocated");
+		return true;
+	}
+
+	// Create a mutex
+	usbi_mutex_init(&htab_mutex);
+
+	usbi_dbg(ctx, "using %lu entries hash table", HTAB_SIZE);
+	htab_filled = 0;
+
+	// allocate memory and zero out.
+	htab_table = calloc(HTAB_SIZE + 1, sizeof(htab_entry));
+	if (htab_table == NULL) {
+		usbi_err(ctx, "could not allocate space for hash table");
+		return false;
+	}
+
+	return true;
+}
+
+/* After using the hash table it has to be destroyed.  */
+static void htab_destroy(void)
+{
+	unsigned long i;
+
+	if (htab_table == NULL)
+		return;
+
+	for (i = 0; i < HTAB_SIZE; i++)
+		free(htab_table[i].str);
+
+	safe_free(htab_table);
+
+	usbi_mutex_destroy(&htab_mutex);
+}
+
+/* This is the search function. It uses double hashing with open addressing.
+   We use a trick to speed up the lookup. The table is created with one
+   more element available. This enables us to use the index zero special.
+   This index will never be used because we store the first hash index in
+   the field used where zero means not used. Every other value means used.
+   The used field can be used as a first fast comparison for equality of
+   the stored and the parameter value. This helps to prevent unnecessary
+   expensive calls of strcmp.  */
+unsigned long htab_hash(const char *str)
+{
+	unsigned long hval, hval2;
+	unsigned long idx;
+	unsigned long r = 5381UL;
+	int c;
+	const char *sz = str;
+
+	if (str == NULL)
+		return 0;
+
+	// Compute main hash value (algorithm suggested by Nokia)
+	while ((c = *sz++) != 0)
+		r = ((r << 5) + r) + c;
+	if (r == 0)
+		++r;
+
+	// compute table hash: simply take the modulus
+	hval = r % HTAB_SIZE;
+	if (hval == 0)
+		++hval;
+
+	// Try the first index
+	idx = hval;
+
+	// Mutually exclusive access (R/W lock would be better)
+	usbi_mutex_lock(&htab_mutex);
+
+	if (htab_table[idx].used) {
+		if ((htab_table[idx].used == hval) && (strcmp(str, htab_table[idx].str) == 0))
+			goto out_unlock; // existing hash
+
+		usbi_dbg(NULL, "hash collision ('%s' vs '%s')", str, htab_table[idx].str);
+
+		// Second hash function, as suggested in [Knuth]
+		hval2 = 1UL + hval % (HTAB_SIZE - 2);
+
+		do {
+			// Because size is prime this guarantees to step through all available indexes
+			if (idx <= hval2)
+				idx = HTAB_SIZE + idx - hval2;
+			else
+				idx -= hval2;
+
+			// If we visited all entries leave the loop unsuccessfully
+			if (idx == hval)
+				break;
+
+			// If entry is found use it.
+			if ((htab_table[idx].used == hval) && (strcmp(str, htab_table[idx].str) == 0))
+				goto out_unlock;
+		} while (htab_table[idx].used);
+	}
+
+	// Not found => New entry
+
+	// If the table is full return an error
+	if (htab_filled >= HTAB_SIZE) {
+		usbi_err(NULL, "hash table is full (%lu entries)", HTAB_SIZE);
+		idx = 0UL;
+		goto out_unlock;
+	}
+
+	htab_table[idx].str = _strdup(str);
+	if (htab_table[idx].str == NULL) {
+		usbi_err(NULL, "could not duplicate string for hash table");
+		idx = 0UL;
+		goto out_unlock;
+	}
+
+	htab_table[idx].used = hval;
+	++htab_filled;
+
+out_unlock:
+	usbi_mutex_unlock(&htab_mutex);
+
+	return idx;
+}
+
+enum libusb_transfer_status usbd_status_to_libusb_transfer_status(USBD_STATUS status)
+{
+	if (USBD_SUCCESS(status))
+		return LIBUSB_TRANSFER_COMPLETED;
+
+	switch (status) {
+	case USBD_STATUS_TIMEOUT:
+		return LIBUSB_TRANSFER_TIMED_OUT;
+	case USBD_STATUS_CANCELED:
+		return LIBUSB_TRANSFER_CANCELLED;
+	case USBD_STATUS_ENDPOINT_HALTED:
+		return LIBUSB_TRANSFER_STALL;
+	case USBD_STATUS_DEVICE_GONE:
+		return LIBUSB_TRANSFER_NO_DEVICE;
+	default:
+		usbi_dbg(NULL, "USBD_STATUS 0x%08lx translated to LIBUSB_TRANSFER_ERROR", ULONG_CAST(status));
+		return LIBUSB_TRANSFER_ERROR;
+	}
+}
+
+/*
+ * Make a transfer complete synchronously
+ */
+void windows_force_sync_completion(struct usbi_transfer *itransfer, ULONG size)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct windows_context_priv *priv = usbi_get_context_priv(TRANSFER_CTX(transfer));
+	struct windows_transfer_priv *transfer_priv = usbi_get_transfer_priv(itransfer);
+	OVERLAPPED *overlapped = &transfer_priv->overlapped;
+
+	usbi_dbg(TRANSFER_CTX(transfer), "transfer %p, length %lu", transfer, ULONG_CAST(size));
+
+	overlapped->Internal = (ULONG_PTR)STATUS_SUCCESS;
+	overlapped->InternalHigh = (ULONG_PTR)size;
+
+	if (!PostQueuedCompletionStatus(priv->completion_port, (DWORD)size, (ULONG_PTR)transfer->dev_handle, overlapped))
+		usbi_err(TRANSFER_CTX(transfer), "failed to post I/O completion: %s", windows_error_str(0));
+}
+
+/* Windows version detection */
+static BOOL is_x64(void)
+{
+	BOOL ret = FALSE;
+
+	// Detect if we're running a 32 or 64 bit system
+	if (sizeof(uintptr_t) < 8) {
+		IsWow64Process(GetCurrentProcess(), &ret);
+	} else {
+		ret = TRUE;
+	}
+
+	return ret;
+}
+
+static enum windows_version get_windows_version(void)
+{
+	enum windows_version winver;
+	OSVERSIONINFOEXA vi, vi2;
+	unsigned major, minor, version;
+	ULONGLONG major_equal, minor_equal;
+	const char *w, *arch;
+	bool ws;
+
+	memset(&vi, 0, sizeof(vi));
+	vi.dwOSVersionInfoSize = sizeof(vi);
+	if (!GetVersionExA((OSVERSIONINFOA *)&vi)) {
+		memset(&vi, 0, sizeof(vi));
+		vi.dwOSVersionInfoSize = sizeof(OSVERSIONINFOA);
+		if (!GetVersionExA((OSVERSIONINFOA *)&vi))
+			return WINDOWS_UNDEFINED;
+	}
+
+	if (vi.dwPlatformId != VER_PLATFORM_WIN32_NT)
+		return WINDOWS_UNDEFINED;
+
+	if ((vi.dwMajorVersion > 6) || ((vi.dwMajorVersion == 6) && (vi.dwMinorVersion >= 2))) {
+		// Starting with Windows 8.1 Preview, GetVersionEx() does no longer report the actual OS version
+		// See: http://msdn.microsoft.com/en-us/library/windows/desktop/dn302074.aspx
+
+		major_equal = VerSetConditionMask(0, VER_MAJORVERSION, VER_EQUAL);
+		for (major = vi.dwMajorVersion; major <= 9; major++) {
+			memset(&vi2, 0, sizeof(vi2));
+			vi2.dwOSVersionInfoSize = sizeof(vi2);
+			vi2.dwMajorVersion = major;
+			if (!VerifyVersionInfoA(&vi2, VER_MAJORVERSION, major_equal))
+				continue;
+
+			if (vi.dwMajorVersion < major) {
+				vi.dwMajorVersion = major;
+				vi.dwMinorVersion = 0;
+			}
+
+			minor_equal = VerSetConditionMask(0, VER_MINORVERSION, VER_EQUAL);
+			for (minor = vi.dwMinorVersion; minor <= 9; minor++) {
+				memset(&vi2, 0, sizeof(vi2));
+				vi2.dwOSVersionInfoSize = sizeof(vi2);
+				vi2.dwMinorVersion = minor;
+				if (!VerifyVersionInfoA(&vi2, VER_MINORVERSION, minor_equal))
+					continue;
+
+				vi.dwMinorVersion = minor;
+				break;
+			}
+
+			break;
+		}
+	}
+
+	if ((vi.dwMajorVersion > 0xf) || (vi.dwMinorVersion > 0xf))
+		return WINDOWS_UNDEFINED;
+
+	ws = (vi.wProductType <= VER_NT_WORKSTATION);
+	version = vi.dwMajorVersion << 4 | vi.dwMinorVersion;
+	switch (version) {
+	case 0x50: winver = WINDOWS_2000;  w = "2000"; break;
+	case 0x51: winver = WINDOWS_XP;	   w = "XP";   break;
+	case 0x52: winver = WINDOWS_2003;  w = "2003"; break;
+	case 0x60: winver = WINDOWS_VISTA; w = (ws ? "Vista" : "2008");	 break;
+	case 0x61: winver = WINDOWS_7;	   w = (ws ? "7" : "2008_R2");	 break;
+	case 0x62: winver = WINDOWS_8;	   w = (ws ? "8" : "2012");	 break;
+	case 0x63: winver = WINDOWS_8_1;   w = (ws ? "8.1" : "2012_R2"); break;
+	case 0x64: // Early Windows 10 Insider Previews and Windows Server 2017 Technical Preview 1 used version 6.4
+	case 0xA0: winver = WINDOWS_10;	   w = (ws ? "10" : "2016");	 break;
+	default:
+		if (version < 0x50)
+			return WINDOWS_UNDEFINED;
+		winver = WINDOWS_11_OR_LATER;
+		w = "11 or later";
+	}
+
+	arch = is_x64() ? "64-bit" : "32-bit";
+
+	if (vi.wServicePackMinor)
+		usbi_dbg(NULL, "Windows %s SP%u.%u %s", w, vi.wServicePackMajor, vi.wServicePackMinor, arch);
+	else if (vi.wServicePackMajor)
+		usbi_dbg(NULL, "Windows %s SP%u %s", w, vi.wServicePackMajor, arch);
+	else
+		usbi_dbg(NULL, "Windows %s %s", w, arch);
+
+	return winver;
+}
+
+static unsigned __stdcall windows_iocp_thread(void *arg)
+{
+	struct libusb_context *ctx = arg;
+	struct windows_context_priv *priv = usbi_get_context_priv(ctx);
+	HANDLE iocp = priv->completion_port;
+	DWORD num_bytes;
+	ULONG_PTR completion_key;
+	OVERLAPPED *overlapped;
+	struct libusb_device_handle *dev_handle;
+	struct libusb_device_handle *opened_device_handle;
+	struct windows_device_handle_priv *handle_priv;
+	struct windows_transfer_priv *transfer_priv;
+	struct usbi_transfer *itransfer;
+	bool found;
+
+	usbi_dbg(ctx, "I/O completion thread started");
+
+	while (true) {
+		overlapped = NULL;
+		if (!GetQueuedCompletionStatus(iocp, &num_bytes, &completion_key, &overlapped, INFINITE) && (overlapped == NULL)) {
+			usbi_err(ctx, "GetQueuedCompletionStatus failed: %s", windows_error_str(0));
+			break;
+		}
+
+		if (overlapped == NULL) {
+			// Signal to quit
+			if (completion_key != (ULONG_PTR)ctx)
+				usbi_err(ctx, "program assertion failed - overlapped is NULL");
+			break;
+		}
+
+		// Find the transfer associated with the OVERLAPPED that just completed.
+		// If we cannot find a match, the I/O operation originated from outside of libusb
+		// (e.g. within libusbK) and we need to ignore it.
+		dev_handle = (struct libusb_device_handle *)completion_key;
+
+		found = false;
+		transfer_priv = NULL;
+
+		// Issue 912: lock opened device handles in context to search the current device handle
+		// to avoid accessing unallocated memory after device has been closed
+		usbi_mutex_lock(&ctx->open_devs_lock);
+		for_each_open_device(ctx, opened_device_handle) {
+			if (dev_handle == opened_device_handle) {
+				handle_priv = usbi_get_device_handle_priv(dev_handle);
+
+				usbi_mutex_lock(&dev_handle->lock);
+				list_for_each_entry(transfer_priv, &handle_priv->active_transfers, list, struct windows_transfer_priv) {
+					if (overlapped == &transfer_priv->overlapped) {
+						// This OVERLAPPED belongs to us, remove the transfer from the device handle's list
+						list_del(&transfer_priv->list);
+						found = true;
+						break;
+					}
+				}
+				usbi_mutex_unlock(&dev_handle->lock);
+			}
+		}
+		usbi_mutex_unlock(&ctx->open_devs_lock);
+
+		if (!found) {
+			usbi_dbg(ctx, "ignoring overlapped %p for handle %p (device %u.%u)",
+				overlapped, dev_handle, dev_handle->dev->bus_number, dev_handle->dev->device_address);
+			continue;
+		}
+
+		itransfer = (struct usbi_transfer *)((unsigned char *)transfer_priv + PTR_ALIGN(sizeof(*transfer_priv)));
+		usbi_dbg(ctx, "transfer %p completed, length %lu",
+			 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer), ULONG_CAST(num_bytes));
+		usbi_signal_transfer_completion(itransfer);
+	}
+
+	usbi_dbg(ctx, "I/O completion thread exiting");
+
+	return 0;
+}
+
+static int windows_init(struct libusb_context *ctx)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(ctx);
+	bool winusb_backend_init = false;
+	int r;
+
+	// NB: concurrent usage supposes that init calls are equally balanced with
+	// exit calls. If init is called more than exit, we will not exit properly
+	if (++init_count == 1) { // First init?
+		windows_version = get_windows_version();
+		if (windows_version == WINDOWS_UNDEFINED) {
+			usbi_err(ctx, "failed to detect Windows version");
+			r = LIBUSB_ERROR_NOT_SUPPORTED;
+			goto init_exit;
+		} else if (windows_version < WINDOWS_VISTA) {
+			usbi_err(ctx, "Windows version is too old");
+			r = LIBUSB_ERROR_NOT_SUPPORTED;
+			goto init_exit;
+		}
+
+		if (!htab_create(ctx)) {
+			r = LIBUSB_ERROR_NO_MEM;
+			goto init_exit;
+		}
+
+		r = winusb_backend.init(ctx);
+		if (r != LIBUSB_SUCCESS)
+			goto init_exit;
+		winusb_backend_init = true;
+
+		r = usbdk_backend.init(ctx);
+		if (r == LIBUSB_SUCCESS) {
+			usbi_dbg(ctx, "UsbDk backend is available");
+			usbdk_available = true;
+		} else {
+			usbi_info(ctx, "UsbDk backend is not available");
+			// Do not report this as an error
+		}
+	}
+
+	// By default, new contexts will use the WinUSB backend
+	priv->backend = &winusb_backend;
+
+	r = LIBUSB_ERROR_NO_MEM;
+
+	// Use an I/O completion port to manage all transfers for this context
+	priv->completion_port = CreateIoCompletionPort(INVALID_HANDLE_VALUE, NULL, 0, 1);
+	if (priv->completion_port == NULL) {
+		usbi_err(ctx, "failed to create I/O completion port: %s", windows_error_str(0));
+		goto init_exit;
+	}
+
+	// And a dedicated thread to wait for I/O completions
+	priv->completion_port_thread = (HANDLE)_beginthreadex(NULL, 0, windows_iocp_thread, ctx, 0, NULL);
+	if (priv->completion_port_thread == NULL) {
+		usbi_err(ctx, "failed to create I/O completion port thread");
+		CloseHandle(priv->completion_port);
+		goto init_exit;
+	}
+
+	r = LIBUSB_SUCCESS;
+
+init_exit: // Holds semaphore here
+	if ((init_count == 1) && (r != LIBUSB_SUCCESS)) { // First init failed?
+		if (usbdk_available) {
+			usbdk_backend.exit(ctx);
+			usbdk_available = false;
+		}
+		if (winusb_backend_init)
+			winusb_backend.exit(ctx);
+		htab_destroy();
+		--init_count;
+	}
+
+	return r;
+}
+
+static void windows_exit(struct libusb_context *ctx)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(ctx);
+
+	// A NULL completion status will indicate to the thread that it is time to exit
+	if (!PostQueuedCompletionStatus(priv->completion_port, 0, (ULONG_PTR)ctx, NULL))
+		usbi_err(ctx, "failed to post I/O completion: %s", windows_error_str(0));
+
+	if (WaitForSingleObject(priv->completion_port_thread, INFINITE) == WAIT_FAILED)
+		usbi_err(ctx, "failed to wait for I/O completion port thread: %s", windows_error_str(0));
+
+	CloseHandle(priv->completion_port_thread);
+	CloseHandle(priv->completion_port);
+
+	// Only works if exits and inits are balanced exactly
+	if (--init_count == 0) { // Last exit
+		if (usbdk_available) {
+			usbdk_backend.exit(ctx);
+			usbdk_available = false;
+		}
+		winusb_backend.exit(ctx);
+		htab_destroy();
+	}
+}
+
+static int windows_set_option(struct libusb_context *ctx, enum libusb_option option, va_list ap)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(ctx);
+
+	UNUSED(ap);
+
+	if (option == LIBUSB_OPTION_USE_USBDK) {
+		if (!usbdk_available) {
+			usbi_err(ctx, "UsbDk backend not available");
+			return LIBUSB_ERROR_NOT_FOUND;
+		}
+		usbi_dbg(ctx, "switching context %p to use UsbDk backend", ctx);
+		priv->backend = &usbdk_backend;
+		return LIBUSB_SUCCESS;
+	}
+
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static int windows_get_device_list(struct libusb_context *ctx, struct discovered_devs **discdevs)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(ctx);
+	return priv->backend->get_device_list(ctx, discdevs);
+}
+
+static int windows_open(struct libusb_device_handle *dev_handle)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(HANDLE_CTX(dev_handle));
+	struct windows_device_handle_priv *handle_priv = usbi_get_device_handle_priv(dev_handle);
+
+	list_init(&handle_priv->active_transfers);
+	return priv->backend->open(dev_handle);
+}
+
+static void windows_close(struct libusb_device_handle *dev_handle)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(HANDLE_CTX(dev_handle));
+	priv->backend->close(dev_handle);
+}
+
+static int windows_get_active_config_descriptor(struct libusb_device *dev,
+	void *buffer, size_t len)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(DEVICE_CTX(dev));
+	return priv->backend->get_active_config_descriptor(dev, buffer, len);
+}
+
+static int windows_get_config_descriptor(struct libusb_device *dev,
+	uint8_t config_index, void *buffer, size_t len)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(DEVICE_CTX(dev));
+	return priv->backend->get_config_descriptor(dev, config_index, buffer, len);
+}
+
+static int windows_get_config_descriptor_by_value(struct libusb_device *dev,
+	uint8_t bConfigurationValue, void **buffer)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(DEVICE_CTX(dev));
+	return priv->backend->get_config_descriptor_by_value(dev, bConfigurationValue, buffer);
+}
+
+static int windows_get_configuration(struct libusb_device_handle *dev_handle, uint8_t *config)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(HANDLE_CTX(dev_handle));
+	return priv->backend->get_configuration(dev_handle, config);
+}
+
+static int windows_set_configuration(struct libusb_device_handle *dev_handle, int config)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(HANDLE_CTX(dev_handle));
+	if (config == -1)
+		config = 0;
+	return priv->backend->set_configuration(dev_handle, (uint8_t)config);
+}
+
+static int windows_claim_interface(struct libusb_device_handle *dev_handle, uint8_t interface_number)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(HANDLE_CTX(dev_handle));
+	return priv->backend->claim_interface(dev_handle, interface_number);
+}
+
+static int windows_release_interface(struct libusb_device_handle *dev_handle, uint8_t interface_number)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(HANDLE_CTX(dev_handle));
+	return priv->backend->release_interface(dev_handle, interface_number);
+}
+
+static int windows_set_interface_altsetting(struct libusb_device_handle *dev_handle,
+	uint8_t interface_number, uint8_t altsetting)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(HANDLE_CTX(dev_handle));
+	return priv->backend->set_interface_altsetting(dev_handle, interface_number, altsetting);
+}
+
+static int windows_clear_halt(struct libusb_device_handle *dev_handle, unsigned char endpoint)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(HANDLE_CTX(dev_handle));
+	return priv->backend->clear_halt(dev_handle, endpoint);
+}
+
+static int windows_reset_device(struct libusb_device_handle *dev_handle)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(HANDLE_CTX(dev_handle));
+	return priv->backend->reset_device(dev_handle);
+}
+
+static void windows_destroy_device(struct libusb_device *dev)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(DEVICE_CTX(dev));
+	priv->backend->destroy_device(dev);
+}
+
+static int windows_submit_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct libusb_device_handle *dev_handle = transfer->dev_handle;
+	struct libusb_context *ctx = HANDLE_CTX(dev_handle);
+	struct windows_context_priv *priv = usbi_get_context_priv(ctx);
+	struct windows_device_handle_priv *handle_priv = usbi_get_device_handle_priv(dev_handle);
+	struct windows_transfer_priv *transfer_priv = usbi_get_transfer_priv(itransfer);
+	int r;
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+	case LIBUSB_TRANSFER_TYPE_BULK:
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		break;
+	case LIBUSB_TRANSFER_TYPE_BULK_STREAM:
+		usbi_warn(ctx, "bulk stream transfers are not yet supported on this platform");
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+	default:
+		usbi_err(ctx, "unknown endpoint type %d", transfer->type);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	}
+
+	if (transfer_priv->handle != NULL) {
+		usbi_err(ctx, "program assertion failed - transfer HANDLE is not NULL");
+		transfer_priv->handle = NULL;
+	}
+
+	// Add transfer to the device handle's list
+	usbi_mutex_lock(&dev_handle->lock);
+	list_add_tail(&transfer_priv->list, &handle_priv->active_transfers);
+	usbi_mutex_unlock(&dev_handle->lock);
+
+	r = priv->backend->submit_transfer(itransfer);
+	if (r != LIBUSB_SUCCESS) {
+		// Remove the unsuccessful transfer from the device handle's list
+		usbi_mutex_lock(&dev_handle->lock);
+		list_del(&transfer_priv->list);
+		usbi_mutex_unlock(&dev_handle->lock);
+
+		// Always call the backend's clear_transfer_priv() function on failure
+		priv->backend->clear_transfer_priv(itransfer);
+		transfer_priv->handle = NULL;
+		return r;
+	}
+
+	// The backend should set the HANDLE used for each submitted transfer
+	// by calling set_transfer_priv_handle()
+	if (transfer_priv->handle == NULL)
+		usbi_err(ctx, "program assertion failed - transfer HANDLE is NULL after transfer was submitted");
+
+	return r;
+}
+
+static int windows_cancel_transfer(struct usbi_transfer *itransfer)
+{
+	struct windows_context_priv *priv = usbi_get_context_priv(ITRANSFER_CTX(itransfer));
+	struct windows_transfer_priv *transfer_priv = usbi_get_transfer_priv(itransfer);
+
+	// Try CancelIoEx() on the transfer
+	// If that fails, fall back to the backend's cancel_transfer()
+	// function if it is available
+	if (CancelIoEx(transfer_priv->handle, &transfer_priv->overlapped))
+		return LIBUSB_SUCCESS;
+	else if (GetLastError() == ERROR_NOT_FOUND)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	if (priv->backend->cancel_transfer)
+		return priv->backend->cancel_transfer(itransfer);
+
+	usbi_warn(ITRANSFER_CTX(itransfer), "cancellation not supported for this transfer's driver");
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static int windows_handle_transfer_completion(struct usbi_transfer *itransfer)
+{
+	struct libusb_context *ctx = ITRANSFER_CTX(itransfer);
+	struct windows_context_priv *priv = usbi_get_context_priv(ctx);
+	const struct windows_backend *backend = priv->backend;
+	struct windows_transfer_priv *transfer_priv = usbi_get_transfer_priv(itransfer);
+	enum libusb_transfer_status status, istatus;
+	DWORD result, bytes_transferred;
+
+	if (GetOverlappedResult(transfer_priv->handle, &transfer_priv->overlapped, &bytes_transferred, FALSE))
+		result = NO_ERROR;
+	else
+		result = GetLastError();
+
+	usbi_dbg(ctx, "handling transfer %p completion with errcode %lu, length %lu",
+		 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer), ULONG_CAST(result), ULONG_CAST(bytes_transferred));
+
+	switch (result) {
+	case NO_ERROR:
+		status = backend->copy_transfer_data(itransfer, bytes_transferred);
+		break;
+	case ERROR_GEN_FAILURE:
+		usbi_dbg(ctx, "detected endpoint stall");
+		status = LIBUSB_TRANSFER_STALL;
+		break;
+	case ERROR_SEM_TIMEOUT:
+		usbi_dbg(ctx, "detected semaphore timeout");
+		status = LIBUSB_TRANSFER_TIMED_OUT;
+		break;
+	case ERROR_OPERATION_ABORTED:
+		istatus = backend->copy_transfer_data(itransfer, bytes_transferred);
+		if (istatus != LIBUSB_TRANSFER_COMPLETED)
+			usbi_dbg(ctx, "failed to copy partial data in aborted operation: %d", (int)istatus);
+
+		usbi_dbg(ctx, "detected operation aborted");
+		status = LIBUSB_TRANSFER_CANCELLED;
+		break;
+	case ERROR_FILE_NOT_FOUND:
+	case ERROR_DEVICE_NOT_CONNECTED:
+	case ERROR_NO_SUCH_DEVICE:
+		usbi_dbg(ctx, "detected device removed");
+		status = LIBUSB_TRANSFER_NO_DEVICE;
+		break;
+	default:
+		usbi_err(ctx, "detected I/O error %lu: %s",
+			ULONG_CAST(result), windows_error_str(result));
+		status = LIBUSB_TRANSFER_ERROR;
+		break;
+	}
+
+	transfer_priv->handle = NULL;
+
+	// Backend-specific cleanup
+	backend->clear_transfer_priv(itransfer);
+
+	if (status == LIBUSB_TRANSFER_CANCELLED)
+		return usbi_handle_transfer_cancellation(itransfer);
+	else
+		return usbi_handle_transfer_completion(itransfer, status);
+}
+
+void usbi_get_monotonic_time(struct timespec *tp)
+{
+	static LONG hires_counter_init;
+	static uint64_t hires_ticks_to_ps;
+	static uint64_t hires_frequency;
+	LARGE_INTEGER hires_counter;
+
+	if (InterlockedExchange(&hires_counter_init, 1L) == 0L) {
+		LARGE_INTEGER li_frequency;
+
+		// Microsoft says that the QueryPerformanceFrequency() and
+		// QueryPerformanceCounter() functions always succeed on XP and later
+		QueryPerformanceFrequency(&li_frequency);
+
+		// The hires frequency can go as high as 4 GHz, so we'll use a conversion
+		// to picoseconds to compute the tv_nsecs part
+		hires_frequency = li_frequency.QuadPart;
+		hires_ticks_to_ps = UINT64_C(1000000000000) / hires_frequency;
+	}
+
+	QueryPerformanceCounter(&hires_counter);
+	tp->tv_sec = (long)(hires_counter.QuadPart / hires_frequency);
+	tp->tv_nsec = (long)(((hires_counter.QuadPart % hires_frequency) * hires_ticks_to_ps) / UINT64_C(1000));
+}
+
+// NB: MSVC6 does not support named initializers.
+const struct usbi_os_backend usbi_backend = {
+	"Windows",
+	USBI_CAP_HAS_HID_ACCESS,
+	windows_init,
+	windows_exit,
+	windows_set_option,
+	windows_get_device_list,
+	NULL,	/* hotplug_poll */
+	NULL,	/* wrap_sys_device */
+	windows_open,
+	windows_close,
+	windows_get_active_config_descriptor,
+	windows_get_config_descriptor,
+	windows_get_config_descriptor_by_value,
+	windows_get_configuration,
+	windows_set_configuration,
+	windows_claim_interface,
+	windows_release_interface,
+	windows_set_interface_altsetting,
+	windows_clear_halt,
+	windows_reset_device,
+	NULL,	/* alloc_streams */
+	NULL,	/* free_streams */
+	NULL,	/* dev_mem_alloc */
+	NULL,	/* dev_mem_free */
+	NULL,	/* kernel_driver_active */
+	NULL,	/* detach_kernel_driver */
+	NULL,	/* attach_kernel_driver */
+	windows_destroy_device,
+	windows_submit_transfer,
+	windows_cancel_transfer,
+	NULL,	/* clear_transfer_priv */
+	NULL,	/* handle_events */
+	windows_handle_transfer_completion,
+	sizeof(struct windows_context_priv),
+	sizeof(union windows_device_priv),
+	sizeof(struct windows_device_handle_priv),
+	sizeof(struct windows_transfer_priv),
+};
diff --git a/src/os/windows_common.h b/src/os/windows_common.h
new file mode 100644
index 0000000..792a31e
--- /dev/null
+++ b/src/os/windows_common.h
@@ -0,0 +1,415 @@
+/*
+ * Windows backend common header for libusb 1.0
+ *
+ * This file brings together header code common between
+ * the desktop Windows backends.
+ * Copyright © 2012-2013 RealVNC Ltd.
+ * Copyright © 2009-2012 Pete Batard <pete@akeo.ie>
+ * Copyright © 2014-2020 Chris Dickens <christopher.a.dickens@gmail.com>
+ * With contributions from Michael Plante, Orin Eman et al.
+ * Parts of this code adapted from libusb-win32-v1 by Stephan Meyer
+ * Major code testing contribution by Xiaofan Chen
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef LIBUSB_WINDOWS_COMMON_H
+#define LIBUSB_WINDOWS_COMMON_H
+
+#include <stdbool.h>
+
+/*
+ * Workaround for the mess that exists with the DWORD and ULONG types.
+ * Visual Studio unconditionally defines these types as 'unsigned long'
+ * and a long is always 32-bits, even on 64-bit builds. GCC on the other
+ * hand varies the width of a long, matching it to the build. To make
+ * matters worse, the platform headers for these GCC builds define a
+ * DWORD/ULONG to be 'unsigned long' on 32-bit builds and 'unsigned int'
+ * on 64-bit builds. This creates a great deal of warnings for compilers
+ * that support printf format checking since it will never actually be
+ * an unsigned long.
+ */
+#if defined(_MSC_VER)
+#define ULONG_CAST(x)	(x)
+#else
+#define ULONG_CAST(x)	((unsigned long)(x))
+#endif
+
+#if defined(__CYGWIN__)
+#define _stricmp strcasecmp
+#define _strdup strdup
+// _beginthreadex is MSVCRT => unavailable for cygwin. Fallback to using CreateThread
+#define _beginthreadex(a, b, c, d, e, f) CreateThread(a, b, (LPTHREAD_START_ROUTINE)c, d, e, (LPDWORD)f)
+#else
+#include <process.h>
+#endif
+
+#define safe_free(p) do {if (p != NULL) {free((void *)p); p = NULL;}} while (0)
+
+/*
+ * API macros - leveraged from libusb-win32 1.x
+ */
+#define DLL_STRINGIFY(s) #s
+
+/*
+ * Macros for handling DLL themselves
+ */
+#define DLL_HANDLE_NAME(name) __dll_##name##_handle
+
+#define DLL_DECLARE_HANDLE(name)					\
+	static HMODULE DLL_HANDLE_NAME(name)
+
+#define DLL_GET_HANDLE(ctx, name)					\
+	do {								\
+		DLL_HANDLE_NAME(name) = load_system_library(ctx,	\
+				DLL_STRINGIFY(name));			\
+		if (!DLL_HANDLE_NAME(name))				\
+			return false;					\
+	} while (0)
+
+#define DLL_FREE_HANDLE(name)						\
+	do {								\
+		if (DLL_HANDLE_NAME(name)) {				\
+			FreeLibrary(DLL_HANDLE_NAME(name));		\
+			DLL_HANDLE_NAME(name) = NULL;			\
+		}							\
+	} while (0)
+
+/*
+ * Macros for handling functions within a DLL
+ */
+#define DLL_FUNC_NAME(name) __dll_##name##_func_t
+
+#define DLL_DECLARE_FUNC_PREFIXNAME(api, ret, prefixname, name, args)	\
+	typedef ret (api * DLL_FUNC_NAME(name))args;			\
+	static DLL_FUNC_NAME(name) prefixname
+
+#define DLL_DECLARE_FUNC(api, ret, name, args)				\
+	DLL_DECLARE_FUNC_PREFIXNAME(api, ret, name, name, args)
+#define DLL_DECLARE_FUNC_PREFIXED(api, ret, prefix, name, args)		\
+	DLL_DECLARE_FUNC_PREFIXNAME(api, ret, prefix##name, name, args)
+
+#define DLL_LOAD_FUNC_PREFIXNAME(dll, prefixname, name, ret_on_failure)	\
+	do {								\
+		HMODULE h = DLL_HANDLE_NAME(dll);			\
+		prefixname = (DLL_FUNC_NAME(name))GetProcAddress(h,	\
+				DLL_STRINGIFY(name));			\
+		if (prefixname)						\
+			break;						\
+		prefixname = (DLL_FUNC_NAME(name))GetProcAddress(h,	\
+				DLL_STRINGIFY(name) DLL_STRINGIFY(A));	\
+		if (prefixname)						\
+			break;						\
+		prefixname = (DLL_FUNC_NAME(name))GetProcAddress(h,	\
+				DLL_STRINGIFY(name) DLL_STRINGIFY(W));	\
+		if (prefixname)						\
+			break;						\
+		if (ret_on_failure)					\
+			return false;					\
+	} while (0)
+
+#define DLL_LOAD_FUNC(dll, name, ret_on_failure)			\
+	DLL_LOAD_FUNC_PREFIXNAME(dll, name, name, ret_on_failure)
+#define DLL_LOAD_FUNC_PREFIXED(dll, prefix, name, ret_on_failure)	\
+	DLL_LOAD_FUNC_PREFIXNAME(dll, prefix##name, name, ret_on_failure)
+
+// https://msdn.microsoft.com/en-us/library/windows/hardware/ff539136(v=vs.85).aspx
+#if !defined(USBD_SUCCESS)
+typedef LONG USBD_STATUS;
+
+#define USBD_SUCCESS(Status)		((USBD_STATUS)(Status) >= 0)
+
+#define USBD_STATUS_ENDPOINT_HALTED	((USBD_STATUS)0xC0000030L)
+#define USBD_STATUS_TIMEOUT		((USBD_STATUS)0xC0006000L)
+#define USBD_STATUS_DEVICE_GONE		((USBD_STATUS)0xC0007000L)
+#define USBD_STATUS_CANCELED		((USBD_STATUS)0xC0010000L)
+#endif
+
+// error code added with Windows SDK 10.0.18362
+#ifndef ERROR_NO_SUCH_DEVICE
+#define ERROR_NO_SUCH_DEVICE	433L
+#endif
+
+/* Windows versions */
+enum windows_version {
+	WINDOWS_UNDEFINED,
+	WINDOWS_2000,
+	WINDOWS_XP,
+	WINDOWS_2003,	// Also XP x64
+	WINDOWS_VISTA,
+	WINDOWS_7,
+	WINDOWS_8,
+	WINDOWS_8_1,
+	WINDOWS_10,
+	WINDOWS_11_OR_LATER
+};
+
+extern enum windows_version windows_version;
+
+#include <pshpack1.h>
+
+typedef struct USB_DEVICE_DESCRIPTOR {
+	UCHAR  bLength;
+	UCHAR  bDescriptorType;
+	USHORT bcdUSB;
+	UCHAR  bDeviceClass;
+	UCHAR  bDeviceSubClass;
+	UCHAR  bDeviceProtocol;
+	UCHAR  bMaxPacketSize0;
+	USHORT idVendor;
+	USHORT idProduct;
+	USHORT bcdDevice;
+	UCHAR  iManufacturer;
+	UCHAR  iProduct;
+	UCHAR  iSerialNumber;
+	UCHAR  bNumConfigurations;
+} USB_DEVICE_DESCRIPTOR, *PUSB_DEVICE_DESCRIPTOR;
+
+typedef struct USB_CONFIGURATION_DESCRIPTOR {
+	UCHAR  bLength;
+	UCHAR  bDescriptorType;
+	USHORT wTotalLength;
+	UCHAR  bNumInterfaces;
+	UCHAR  bConfigurationValue;
+	UCHAR  iConfiguration;
+	UCHAR  bmAttributes;
+	UCHAR  MaxPower;
+} USB_CONFIGURATION_DESCRIPTOR, *PUSB_CONFIGURATION_DESCRIPTOR;
+
+#include <poppack.h>
+
+#define MAX_DEVICE_ID_LEN	200
+
+typedef struct USB_DK_DEVICE_ID {
+	WCHAR DeviceID[MAX_DEVICE_ID_LEN];
+	WCHAR InstanceID[MAX_DEVICE_ID_LEN];
+} USB_DK_DEVICE_ID, *PUSB_DK_DEVICE_ID;
+
+typedef struct USB_DK_DEVICE_INFO {
+	USB_DK_DEVICE_ID ID;
+	ULONG64 FilterID;
+	ULONG64 Port;
+	ULONG64 Speed;
+	USB_DEVICE_DESCRIPTOR DeviceDescriptor;
+} USB_DK_DEVICE_INFO, *PUSB_DK_DEVICE_INFO;
+
+typedef struct USB_DK_ISO_TRANSFER_RESULT {
+	ULONG64 ActualLength;
+	ULONG64 TransferResult;
+} USB_DK_ISO_TRANSFER_RESULT, *PUSB_DK_ISO_TRANSFER_RESULT;
+
+typedef struct USB_DK_GEN_TRANSFER_RESULT {
+	ULONG64 BytesTransferred;
+	ULONG64 UsbdStatus; // USBD_STATUS code
+} USB_DK_GEN_TRANSFER_RESULT, *PUSB_DK_GEN_TRANSFER_RESULT;
+
+typedef struct USB_DK_TRANSFER_RESULT {
+	USB_DK_GEN_TRANSFER_RESULT GenResult;
+	PVOID64 IsochronousResultsArray; // array of USB_DK_ISO_TRANSFER_RESULT
+} USB_DK_TRANSFER_RESULT, *PUSB_DK_TRANSFER_RESULT;
+
+typedef struct USB_DK_TRANSFER_REQUEST {
+	ULONG64 EndpointAddress;
+	PVOID64 Buffer;
+	ULONG64 BufferLength;
+	ULONG64 TransferType;
+	ULONG64 IsochronousPacketsArraySize;
+	PVOID64 IsochronousPacketsArray;
+	USB_DK_TRANSFER_RESULT Result;
+} USB_DK_TRANSFER_REQUEST, *PUSB_DK_TRANSFER_REQUEST;
+
+struct usbdk_device_priv {
+	USB_DK_DEVICE_ID ID;
+	PUSB_CONFIGURATION_DESCRIPTOR *config_descriptors;
+	HANDLE redirector_handle;
+	HANDLE system_handle;
+	uint8_t active_configuration;
+};
+
+struct winusb_device_priv {
+	bool initialized;
+	bool root_hub;
+	uint8_t active_config;
+	uint8_t depth; // distance to HCD
+	const struct windows_usb_api_backend *apib;
+	char *dev_id;
+	char *path;  // device interface path
+	int sub_api; // for WinUSB-like APIs
+	struct {
+		char *path; // each interface needs a device interface path,
+		const struct windows_usb_api_backend *apib; // an API backend (multiple drivers support),
+		int sub_api;
+		int8_t nb_endpoints; // and a set of endpoint addresses (USB_MAXENDPOINTS)
+		uint8_t *endpoint;
+		int current_altsetting;
+		bool restricted_functionality;  // indicates if the interface functionality is restricted
+						// by Windows (eg. HID keyboards or mice cannot do R/W)
+	} usb_interface[USB_MAXINTERFACES];
+	struct hid_device_priv *hid;
+	PUSB_CONFIGURATION_DESCRIPTOR *config_descriptor; // list of pointers to the cached config descriptors
+	GUID class_guid; // checked for change during re-enumeration
+};
+
+struct usbdk_device_handle_priv {
+	// Not currently used
+	char dummy;
+};
+ 
+enum WINUSB_ZLP {
+	WINUSB_ZLP_UNSET = 0,
+	WINUSB_ZLP_OFF = 1,
+	WINUSB_ZLP_ON = 2
+};
+
+struct winusb_device_handle_priv {
+	int active_interface;
+	struct {
+		HANDLE dev_handle; // WinUSB needs an extra handle for the file
+		HANDLE api_handle; // used by the API to communicate with the device
+		uint8_t zlp[USB_MAXENDPOINTS]; // Current per-endpoint SHORT_PACKET_TERMINATE status (enum WINUSB_ZLP)
+	} interface_handle[USB_MAXINTERFACES];
+	int autoclaim_count[USB_MAXINTERFACES]; // For auto-release
+};
+
+struct usbdk_transfer_priv {
+	USB_DK_TRANSFER_REQUEST request;
+	PULONG64 IsochronousPacketsArray;
+	PUSB_DK_ISO_TRANSFER_RESULT IsochronousResultsArray;
+};
+
+struct winusb_transfer_priv {
+	uint8_t interface_number;
+
+	uint8_t *hid_buffer; // 1 byte extended data buffer, required for HID
+	uint8_t *hid_dest;   // transfer buffer destination, required for HID
+	size_t hid_expected_size;
+
+	// For isochronous transfers with LibUSBk driver:
+	void *iso_context;
+
+	// For isochronous transfers with Microsoft WinUSB driver:
+	void *isoch_buffer_handle; // The isoch_buffer_handle to free at the end of the transfer
+	BOOL iso_break_stream;	// Whether the isoch. stream was to be continued in the last call of libusb_submit_transfer.
+							// As we this structure is zeroed out upon initialization, we need to use inverse logic here.
+	libusb_transfer_cb_fn iso_user_callback; // Original transfer callback of the user. Might be used for isochronous transfers.
+};
+
+struct windows_backend {
+	int (*init)(struct libusb_context *ctx);
+	void (*exit)(struct libusb_context *ctx);
+	int (*get_device_list)(struct libusb_context *ctx,
+		struct discovered_devs **discdevs);
+	int (*open)(struct libusb_device_handle *dev_handle);
+	void (*close)(struct libusb_device_handle *dev_handle);
+	int (*get_active_config_descriptor)(struct libusb_device *device,
+		void *buffer, size_t len);
+	int (*get_config_descriptor)(struct libusb_device *device,
+		uint8_t config_index, void *buffer, size_t len);
+	int (*get_config_descriptor_by_value)(struct libusb_device *device,
+		uint8_t bConfigurationValue, void **buffer);
+	int (*get_configuration)(struct libusb_device_handle *dev_handle, uint8_t *config);
+	int (*set_configuration)(struct libusb_device_handle *dev_handle, uint8_t config);
+	int (*claim_interface)(struct libusb_device_handle *dev_handle, uint8_t interface_number);
+	int (*release_interface)(struct libusb_device_handle *dev_handle, uint8_t interface_number);
+	int (*set_interface_altsetting)(struct libusb_device_handle *dev_handle,
+		uint8_t interface_number, uint8_t altsetting);
+	int (*clear_halt)(struct libusb_device_handle *dev_handle,
+		unsigned char endpoint);
+	int (*reset_device)(struct libusb_device_handle *dev_handle);
+	void (*destroy_device)(struct libusb_device *dev);
+	int (*submit_transfer)(struct usbi_transfer *itransfer);
+	int (*cancel_transfer)(struct usbi_transfer *itransfer);
+	void (*clear_transfer_priv)(struct usbi_transfer *itransfer);
+	enum libusb_transfer_status (*copy_transfer_data)(struct usbi_transfer *itransfer, DWORD length);
+};
+
+struct windows_context_priv {
+	const struct windows_backend *backend;
+	HANDLE completion_port;
+	HANDLE completion_port_thread;
+};
+
+union windows_device_priv {
+	struct usbdk_device_priv usbdk_priv;
+	struct winusb_device_priv winusb_priv;
+};
+
+struct windows_device_handle_priv {
+	struct list_head active_transfers;
+	union {
+		struct usbdk_device_handle_priv usbdk_priv;
+		struct winusb_device_handle_priv winusb_priv;
+	};
+};
+
+struct windows_transfer_priv {
+	OVERLAPPED overlapped;
+	HANDLE handle;
+	struct list_head list;
+	union {
+		struct usbdk_transfer_priv usbdk_priv;
+		struct winusb_transfer_priv winusb_priv;
+	};
+};
+
+static inline struct usbdk_device_handle_priv *get_usbdk_device_handle_priv(struct libusb_device_handle *dev_handle)
+{
+	struct windows_device_handle_priv *handle_priv = usbi_get_device_handle_priv(dev_handle);
+	return &handle_priv->usbdk_priv;
+}
+
+static inline struct winusb_device_handle_priv *get_winusb_device_handle_priv(struct libusb_device_handle *dev_handle)
+{
+	struct windows_device_handle_priv *handle_priv = usbi_get_device_handle_priv(dev_handle);
+	return &handle_priv->winusb_priv;
+}
+
+static inline OVERLAPPED *get_transfer_priv_overlapped(struct usbi_transfer *itransfer)
+{
+	struct windows_transfer_priv *transfer_priv = usbi_get_transfer_priv(itransfer);
+	return &transfer_priv->overlapped;
+}
+
+static inline void set_transfer_priv_handle(struct usbi_transfer *itransfer, HANDLE handle)
+{
+	struct windows_transfer_priv *transfer_priv = usbi_get_transfer_priv(itransfer);
+	transfer_priv->handle = handle;
+}
+
+static inline struct usbdk_transfer_priv *get_usbdk_transfer_priv(struct usbi_transfer *itransfer)
+{
+	struct windows_transfer_priv *transfer_priv = usbi_get_transfer_priv(itransfer);
+	return &transfer_priv->usbdk_priv;
+}
+
+static inline struct winusb_transfer_priv *get_winusb_transfer_priv(struct usbi_transfer *itransfer)
+{
+	struct windows_transfer_priv *transfer_priv = usbi_get_transfer_priv(itransfer);
+	return &transfer_priv->winusb_priv;
+}
+
+extern const struct windows_backend usbdk_backend;
+extern const struct windows_backend winusb_backend;
+
+HMODULE load_system_library(struct libusb_context *ctx, const char *name);
+unsigned long htab_hash(const char *str);
+enum libusb_transfer_status usbd_status_to_libusb_transfer_status(USBD_STATUS status);
+void windows_force_sync_completion(struct usbi_transfer *itransfer, ULONG size);
+
+#if defined(ENABLE_LOGGING)
+const char *windows_error_str(DWORD error_code);
+#endif
+
+#endif
diff --git a/src/os/windows_usbdk.c b/src/os/windows_usbdk.c
new file mode 100644
index 0000000..9f52b48
--- /dev/null
+++ b/src/os/windows_usbdk.c
@@ -0,0 +1,724 @@
+/*
+ * windows UsbDk backend for libusb 1.0
+ * Copyright © 2014 Red Hat, Inc.
+
+ * Authors:
+ * Dmitry Fleytman <dmitry@daynix.com>
+ * Pavel Gurvich <pavel@daynix.com>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+
+#include <windows.h>
+#include <stdio.h>
+
+#include "libusbi.h"
+#include "windows_usbdk.h"
+
+#if !defined(STATUS_SUCCESS)
+typedef LONG NTSTATUS;
+#define STATUS_SUCCESS			((NTSTATUS)0x00000000L)
+#endif
+
+#if !defined(STATUS_CANCELLED)
+#define STATUS_CANCELLED		((NTSTATUS)0xC0000120L)
+#endif
+
+#if !defined(STATUS_REQUEST_CANCELED)
+#define STATUS_REQUEST_CANCELED		((NTSTATUS)0xC0000703L)
+#endif
+
+static struct {
+	HMODULE module;
+
+	USBDK_GET_DEVICES_LIST			GetDevicesList;
+	USBDK_RELEASE_DEVICES_LIST		ReleaseDevicesList;
+	USBDK_START_REDIRECT			StartRedirect;
+	USBDK_STOP_REDIRECT			StopRedirect;
+	USBDK_GET_CONFIGURATION_DESCRIPTOR	GetConfigurationDescriptor;
+	USBDK_RELEASE_CONFIGURATION_DESCRIPTOR	ReleaseConfigurationDescriptor;
+	USBDK_READ_PIPE				ReadPipe;
+	USBDK_WRITE_PIPE			WritePipe;
+	USBDK_ABORT_PIPE			AbortPipe;
+	USBDK_RESET_PIPE			ResetPipe;
+	USBDK_SET_ALTSETTING			SetAltsetting;
+	USBDK_RESET_DEVICE			ResetDevice;
+	USBDK_GET_REDIRECTOR_SYSTEM_HANDLE	GetRedirectorSystemHandle;
+} usbdk_helper;
+
+static FARPROC get_usbdk_proc_addr(struct libusb_context *ctx, LPCSTR api_name)
+{
+	FARPROC api_ptr = GetProcAddress(usbdk_helper.module, api_name);
+
+	if (api_ptr == NULL)
+		usbi_err(ctx, "UsbDkHelper API %s not found: %s", api_name, windows_error_str(0));
+
+	return api_ptr;
+}
+
+static void unload_usbdk_helper_dll(void)
+{
+	if (usbdk_helper.module != NULL) {
+		FreeLibrary(usbdk_helper.module);
+		usbdk_helper.module = NULL;
+	}
+}
+
+static int load_usbdk_helper_dll(struct libusb_context *ctx)
+{
+	usbdk_helper.module = load_system_library(ctx, "UsbDkHelper");
+	if (usbdk_helper.module == NULL) {
+		usbi_err(ctx, "Failed to load UsbDkHelper.dll: %s", windows_error_str(0));
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	usbdk_helper.GetDevicesList = (USBDK_GET_DEVICES_LIST)get_usbdk_proc_addr(ctx, "UsbDk_GetDevicesList");
+	if (usbdk_helper.GetDevicesList == NULL)
+		goto error_unload;
+
+	usbdk_helper.ReleaseDevicesList = (USBDK_RELEASE_DEVICES_LIST)get_usbdk_proc_addr(ctx, "UsbDk_ReleaseDevicesList");
+	if (usbdk_helper.ReleaseDevicesList == NULL)
+		goto error_unload;
+
+	usbdk_helper.StartRedirect = (USBDK_START_REDIRECT)get_usbdk_proc_addr(ctx, "UsbDk_StartRedirect");
+	if (usbdk_helper.StartRedirect == NULL)
+		goto error_unload;
+
+	usbdk_helper.StopRedirect = (USBDK_STOP_REDIRECT)get_usbdk_proc_addr(ctx, "UsbDk_StopRedirect");
+	if (usbdk_helper.StopRedirect == NULL)
+		goto error_unload;
+
+	usbdk_helper.GetConfigurationDescriptor = (USBDK_GET_CONFIGURATION_DESCRIPTOR)get_usbdk_proc_addr(ctx, "UsbDk_GetConfigurationDescriptor");
+	if (usbdk_helper.GetConfigurationDescriptor == NULL)
+		goto error_unload;
+
+	usbdk_helper.ReleaseConfigurationDescriptor = (USBDK_RELEASE_CONFIGURATION_DESCRIPTOR)get_usbdk_proc_addr(ctx, "UsbDk_ReleaseConfigurationDescriptor");
+	if (usbdk_helper.ReleaseConfigurationDescriptor == NULL)
+		goto error_unload;
+
+	usbdk_helper.ReadPipe = (USBDK_READ_PIPE)get_usbdk_proc_addr(ctx, "UsbDk_ReadPipe");
+	if (usbdk_helper.ReadPipe == NULL)
+		goto error_unload;
+
+	usbdk_helper.WritePipe = (USBDK_WRITE_PIPE)get_usbdk_proc_addr(ctx, "UsbDk_WritePipe");
+	if (usbdk_helper.WritePipe == NULL)
+		goto error_unload;
+
+	usbdk_helper.AbortPipe = (USBDK_ABORT_PIPE)get_usbdk_proc_addr(ctx, "UsbDk_AbortPipe");
+	if (usbdk_helper.AbortPipe == NULL)
+		goto error_unload;
+
+	usbdk_helper.ResetPipe = (USBDK_RESET_PIPE)get_usbdk_proc_addr(ctx, "UsbDk_ResetPipe");
+	if (usbdk_helper.ResetPipe == NULL)
+		goto error_unload;
+
+	usbdk_helper.SetAltsetting = (USBDK_SET_ALTSETTING)get_usbdk_proc_addr(ctx, "UsbDk_SetAltsetting");
+	if (usbdk_helper.SetAltsetting == NULL)
+		goto error_unload;
+
+	usbdk_helper.ResetDevice = (USBDK_RESET_DEVICE)get_usbdk_proc_addr(ctx, "UsbDk_ResetDevice");
+	if (usbdk_helper.ResetDevice == NULL)
+		goto error_unload;
+
+	usbdk_helper.GetRedirectorSystemHandle = (USBDK_GET_REDIRECTOR_SYSTEM_HANDLE)get_usbdk_proc_addr(ctx, "UsbDk_GetRedirectorSystemHandle");
+	if (usbdk_helper.GetRedirectorSystemHandle == NULL)
+		goto error_unload;
+
+	return LIBUSB_SUCCESS;
+
+error_unload:
+	FreeLibrary(usbdk_helper.module);
+	usbdk_helper.module = NULL;
+	return LIBUSB_ERROR_NOT_FOUND;
+}
+
+typedef SC_HANDLE (WINAPI *POPENSCMANAGERA)(LPCSTR, LPCSTR, DWORD);
+typedef SC_HANDLE (WINAPI *POPENSERVICEA)(SC_HANDLE, LPCSTR, DWORD);
+typedef BOOL (WINAPI *PCLOSESERVICEHANDLE)(SC_HANDLE);
+
+static int usbdk_init(struct libusb_context *ctx)
+{
+	POPENSCMANAGERA pOpenSCManagerA;
+	POPENSERVICEA pOpenServiceA;
+	PCLOSESERVICEHANDLE pCloseServiceHandle;
+	SC_HANDLE managerHandle;
+	SC_HANDLE serviceHandle;
+	HMODULE h;
+
+	h = load_system_library(ctx, "Advapi32");
+	if (h == NULL) {
+		usbi_warn(ctx, "failed to open Advapi32\n");
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	pOpenSCManagerA = (POPENSCMANAGERA)GetProcAddress(h, "OpenSCManagerA");
+	if (pOpenSCManagerA == NULL) {
+		usbi_warn(ctx, "failed to find %s in Advapi32\n", "OpenSCManagerA");
+		goto error_free_library;
+	}
+	pOpenServiceA = (POPENSERVICEA)GetProcAddress(h, "OpenServiceA");
+	if (pOpenServiceA == NULL) {
+		usbi_warn(ctx, "failed to find %s in Advapi32\n", "OpenServiceA");
+		goto error_free_library;
+	}
+	pCloseServiceHandle = (PCLOSESERVICEHANDLE)GetProcAddress(h, "CloseServiceHandle");
+	if (pCloseServiceHandle == NULL) {
+		usbi_warn(ctx, "failed to find %s in Advapi32\n", "CloseServiceHandle");
+		goto error_free_library;
+	}
+
+	managerHandle = pOpenSCManagerA(NULL, NULL, SC_MANAGER_CONNECT);
+	if (managerHandle == NULL) {
+		usbi_warn(ctx, "failed to open service control manager: %s", windows_error_str(0));
+		goto error_free_library;
+	}
+
+	serviceHandle = pOpenServiceA(managerHandle, "UsbDk", GENERIC_READ);
+	pCloseServiceHandle(managerHandle);
+
+	if (serviceHandle == NULL) {
+		if (GetLastError() != ERROR_SERVICE_DOES_NOT_EXIST)
+			usbi_warn(ctx, "failed to open UsbDk service: %s", windows_error_str(0));
+		FreeLibrary(h);
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	pCloseServiceHandle(serviceHandle);
+	FreeLibrary(h);
+
+	return load_usbdk_helper_dll(ctx);
+
+error_free_library:
+	FreeLibrary(h);
+	return LIBUSB_ERROR_OTHER;
+}
+
+static void usbdk_exit(struct libusb_context *ctx)
+{
+	UNUSED(ctx);
+	unload_usbdk_helper_dll();
+}
+
+static int usbdk_get_session_id_for_device(struct libusb_context *ctx,
+	PUSB_DK_DEVICE_ID id, unsigned long *session_id)
+{
+	char dev_identity[ARRAYSIZE(id->DeviceID) + ARRAYSIZE(id->InstanceID) + 1];
+
+	if (snprintf(dev_identity, sizeof(dev_identity), "%S%S", id->DeviceID, id->InstanceID) == -1) {
+		usbi_warn(ctx, "cannot form device identity");
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+	}
+
+	*session_id = htab_hash(dev_identity);
+
+	return LIBUSB_SUCCESS;
+}
+
+static void usbdk_release_config_descriptors(struct usbdk_device_priv *priv, uint8_t count)
+{
+	uint8_t i;
+
+	for (i = 0; i < count; i++)
+		usbdk_helper.ReleaseConfigurationDescriptor(priv->config_descriptors[i]);
+
+	free(priv->config_descriptors);
+	priv->config_descriptors = NULL;
+}
+
+static int usbdk_cache_config_descriptors(struct libusb_context *ctx,
+	struct usbdk_device_priv *priv, PUSB_DK_DEVICE_INFO info)
+{
+	uint8_t i;
+	USB_DK_CONFIG_DESCRIPTOR_REQUEST Request;
+	Request.ID = info->ID;
+
+	priv->config_descriptors = calloc(info->DeviceDescriptor.bNumConfigurations, sizeof(PUSB_CONFIGURATION_DESCRIPTOR));
+	if (priv->config_descriptors == NULL) {
+		usbi_err(ctx, "failed to allocate configuration descriptors holder");
+		return LIBUSB_ERROR_NO_MEM;
+	}
+
+	for (i = 0; i < info->DeviceDescriptor.bNumConfigurations; i++) {
+		ULONG Length;
+
+		Request.Index = i;
+		if (!usbdk_helper.GetConfigurationDescriptor(&Request, &priv->config_descriptors[i], &Length)) {
+			usbi_err(ctx, "failed to retrieve configuration descriptors");
+			usbdk_release_config_descriptors(priv, i);
+			return LIBUSB_ERROR_OTHER;
+		}
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static inline int usbdk_device_priv_init(struct libusb_context *ctx, struct libusb_device *dev, PUSB_DK_DEVICE_INFO info)
+{
+	struct usbdk_device_priv *priv = usbi_get_device_priv(dev);
+
+	priv->ID = info->ID;
+	priv->active_configuration = 0;
+
+	return usbdk_cache_config_descriptors(ctx, priv, info);
+}
+
+static void usbdk_device_init(struct libusb_device *dev, PUSB_DK_DEVICE_INFO info)
+{
+	dev->bus_number = (uint8_t)info->FilterID;
+	dev->port_number = (uint8_t)info->Port;
+	dev->parent_dev = NULL;
+
+	// Addresses in libusb are 1-based
+	dev->device_address = (uint8_t)(info->Port + 1);
+
+	static_assert(sizeof(dev->device_descriptor) == sizeof(info->DeviceDescriptor),
+		      "mismatch between libusb and OS device descriptor sizes");
+	memcpy(&dev->device_descriptor, &info->DeviceDescriptor, LIBUSB_DT_DEVICE_SIZE);
+	usbi_localize_device_descriptor(&dev->device_descriptor);
+
+	switch (info->Speed) {
+	case LowSpeed:
+		dev->speed = LIBUSB_SPEED_LOW;
+		break;
+	case FullSpeed:
+		dev->speed = LIBUSB_SPEED_FULL;
+		break;
+	case HighSpeed:
+		dev->speed = LIBUSB_SPEED_HIGH;
+		break;
+	case SuperSpeed:
+		dev->speed = LIBUSB_SPEED_SUPER;
+		break;
+	case NoSpeed:
+	default:
+		dev->speed = LIBUSB_SPEED_UNKNOWN;
+		break;
+	}
+}
+
+static int usbdk_get_device_list(struct libusb_context *ctx, struct discovered_devs **_discdevs)
+{
+	int r = LIBUSB_SUCCESS;
+	ULONG i;
+	struct discovered_devs *discdevs = NULL;
+	ULONG dev_number;
+	PUSB_DK_DEVICE_INFO devices;
+
+	if (!usbdk_helper.GetDevicesList(&devices, &dev_number))
+		return LIBUSB_ERROR_OTHER;
+
+	for (i = 0; i < dev_number; i++) {
+		unsigned long session_id;
+		struct libusb_device *dev = NULL;
+
+		if (usbdk_get_session_id_for_device(ctx, &devices[i].ID, &session_id))
+			continue;
+
+		dev = usbi_get_device_by_session_id(ctx, session_id);
+		if (dev == NULL) {
+			dev = usbi_alloc_device(ctx, session_id);
+			if (dev == NULL) {
+				usbi_err(ctx, "failed to allocate a new device structure");
+				continue;
+			}
+
+			usbdk_device_init(dev, &devices[i]);
+			if (usbdk_device_priv_init(ctx, dev, &devices[i]) != LIBUSB_SUCCESS) {
+				libusb_unref_device(dev);
+				continue;
+			}
+		}
+
+		discdevs = discovered_devs_append(*_discdevs, dev);
+		libusb_unref_device(dev);
+		if (!discdevs) {
+			usbi_err(ctx, "cannot append new device to list");
+			r = LIBUSB_ERROR_NO_MEM;
+			goto func_exit;
+		}
+
+		*_discdevs = discdevs;
+	}
+
+func_exit:
+	usbdk_helper.ReleaseDevicesList(devices);
+	return r;
+}
+
+static int usbdk_get_config_descriptor(struct libusb_device *dev, uint8_t config_index, void *buffer, size_t len)
+{
+	struct usbdk_device_priv *priv = usbi_get_device_priv(dev);
+	PUSB_CONFIGURATION_DESCRIPTOR config_header;
+	size_t size;
+
+	config_header = (PUSB_CONFIGURATION_DESCRIPTOR)priv->config_descriptors[config_index];
+
+	size = min(config_header->wTotalLength, len);
+	memcpy(buffer, config_header, size);
+	return (int)size;
+}
+
+static int usbdk_get_config_descriptor_by_value(struct libusb_device *dev, uint8_t bConfigurationValue,
+	void **buffer)
+{
+	struct usbdk_device_priv *priv = usbi_get_device_priv(dev);
+	PUSB_CONFIGURATION_DESCRIPTOR config_header;
+	uint8_t index;
+
+	for (index = 0; index < dev->device_descriptor.bNumConfigurations; index++) {
+		config_header = priv->config_descriptors[index];
+		if (config_header->bConfigurationValue == bConfigurationValue) {
+			*buffer = priv->config_descriptors[index];
+			return (int)config_header->wTotalLength;
+		}
+	}
+
+	return LIBUSB_ERROR_NOT_FOUND;
+}
+
+static int usbdk_get_active_config_descriptor(struct libusb_device *dev, void *buffer, size_t len)
+{
+	struct usbdk_device_priv *priv = usbi_get_device_priv(dev);
+
+	return usbdk_get_config_descriptor(dev, priv->active_configuration, buffer, len);
+}
+
+static int usbdk_open(struct libusb_device_handle *dev_handle)
+{
+	struct libusb_device *dev = dev_handle->dev;
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	struct windows_context_priv *priv = usbi_get_context_priv(ctx);
+	struct usbdk_device_priv *device_priv = usbi_get_device_priv(dev);
+
+	device_priv->redirector_handle = usbdk_helper.StartRedirect(&device_priv->ID);
+	if (device_priv->redirector_handle == INVALID_HANDLE_VALUE) {
+		usbi_err(ctx, "Redirector startup failed");
+		device_priv->redirector_handle = NULL;
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	device_priv->system_handle = usbdk_helper.GetRedirectorSystemHandle(device_priv->redirector_handle);
+
+	if (CreateIoCompletionPort(device_priv->system_handle, priv->completion_port, (ULONG_PTR)dev_handle, 0) == NULL) {
+		usbi_err(ctx, "failed to associate handle to I/O completion port: %s", windows_error_str(0));
+		usbdk_helper.StopRedirect(device_priv->redirector_handle);
+		device_priv->system_handle = NULL;
+		device_priv->redirector_handle = NULL;
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static void usbdk_close(struct libusb_device_handle *dev_handle)
+{
+	struct usbdk_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	if (!usbdk_helper.StopRedirect(priv->redirector_handle))
+		usbi_err(HANDLE_CTX(dev_handle), "Redirector shutdown failed");
+
+	priv->system_handle = NULL;
+	priv->redirector_handle = NULL;
+}
+
+static int usbdk_get_configuration(struct libusb_device_handle *dev_handle, uint8_t *config)
+{
+	struct usbdk_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	*config = priv->active_configuration;
+
+	return LIBUSB_SUCCESS;
+}
+
+static int usbdk_set_configuration(struct libusb_device_handle *dev_handle, uint8_t config)
+{
+	UNUSED(dev_handle);
+	UNUSED(config);
+	return LIBUSB_SUCCESS;
+}
+
+static int usbdk_claim_interface(struct libusb_device_handle *dev_handle, uint8_t iface)
+{
+	UNUSED(dev_handle);
+	UNUSED(iface);
+	return LIBUSB_SUCCESS;
+}
+
+static int usbdk_set_interface_altsetting(struct libusb_device_handle *dev_handle, uint8_t iface, uint8_t altsetting)
+{
+	struct usbdk_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	if (!usbdk_helper.SetAltsetting(priv->redirector_handle, iface, altsetting)) {
+		usbi_err(HANDLE_CTX(dev_handle), "SetAltsetting failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_NO_DEVICE;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int usbdk_release_interface(struct libusb_device_handle *dev_handle, uint8_t iface)
+{
+	UNUSED(dev_handle);
+	UNUSED(iface);
+	return LIBUSB_SUCCESS;
+}
+
+static int usbdk_clear_halt(struct libusb_device_handle *dev_handle, unsigned char endpoint)
+{
+	struct usbdk_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	if (!usbdk_helper.ResetPipe(priv->redirector_handle, endpoint)) {
+		usbi_err(HANDLE_CTX(dev_handle), "ResetPipe failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_NO_DEVICE;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int usbdk_reset_device(struct libusb_device_handle *dev_handle)
+{
+	struct usbdk_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	if (!usbdk_helper.ResetDevice(priv->redirector_handle)) {
+		usbi_err(HANDLE_CTX(dev_handle), "ResetDevice failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_NO_DEVICE;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static void usbdk_destroy_device(struct libusb_device *dev)
+{
+	struct usbdk_device_priv *priv = usbi_get_device_priv(dev);
+
+	if (priv->config_descriptors != NULL)
+		usbdk_release_config_descriptors(priv, dev->device_descriptor.bNumConfigurations);
+}
+
+static void usbdk_clear_transfer_priv(struct usbi_transfer *itransfer)
+{
+	struct usbdk_transfer_priv *transfer_priv = get_usbdk_transfer_priv(itransfer);
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+	if (transfer->type == LIBUSB_TRANSFER_TYPE_ISOCHRONOUS) {
+		safe_free(transfer_priv->IsochronousPacketsArray);
+		safe_free(transfer_priv->IsochronousResultsArray);
+	}
+}
+
+static int usbdk_do_control_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct usbdk_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	struct usbdk_transfer_priv *transfer_priv = get_usbdk_transfer_priv(itransfer);
+	OVERLAPPED *overlapped = get_transfer_priv_overlapped(itransfer);
+	TransferResult transResult;
+
+	transfer_priv->request.Buffer = (PVOID64)transfer->buffer;
+	transfer_priv->request.BufferLength = transfer->length;
+	transfer_priv->request.TransferType = ControlTransferType;
+
+	set_transfer_priv_handle(itransfer, priv->system_handle);
+
+	if (transfer->buffer[0] & LIBUSB_ENDPOINT_IN)
+		transResult = usbdk_helper.ReadPipe(priv->redirector_handle, &transfer_priv->request, overlapped);
+	else
+		transResult = usbdk_helper.WritePipe(priv->redirector_handle, &transfer_priv->request, overlapped);
+
+	switch (transResult) {
+	case TransferSuccess:
+		windows_force_sync_completion(itransfer, (ULONG)transfer_priv->request.Result.GenResult.BytesTransferred);
+		break;
+	case TransferSuccessAsync:
+		break;
+	case TransferFailure:
+		usbi_err(TRANSFER_CTX(transfer), "ControlTransfer failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_IO;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int usbdk_do_bulk_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct usbdk_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	struct usbdk_transfer_priv *transfer_priv = get_usbdk_transfer_priv(itransfer);
+	OVERLAPPED *overlapped = get_transfer_priv_overlapped(itransfer);
+	TransferResult transferRes;
+
+	transfer_priv->request.Buffer = (PVOID64)transfer->buffer;
+	transfer_priv->request.BufferLength = transfer->length;
+	transfer_priv->request.EndpointAddress = transfer->endpoint;
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_BULK:
+		transfer_priv->request.TransferType = BulkTransferType;
+		break;
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		transfer_priv->request.TransferType = InterruptTransferType;
+		break;
+	}
+
+	set_transfer_priv_handle(itransfer, priv->system_handle);
+
+	if (IS_XFERIN(transfer))
+		transferRes = usbdk_helper.ReadPipe(priv->redirector_handle, &transfer_priv->request, overlapped);
+	else
+		transferRes = usbdk_helper.WritePipe(priv->redirector_handle, &transfer_priv->request, overlapped);
+
+	switch (transferRes) {
+	case TransferSuccess:
+		windows_force_sync_completion(itransfer, (ULONG)transfer_priv->request.Result.GenResult.BytesTransferred);
+		break;
+	case TransferSuccessAsync:
+		break;
+	case TransferFailure:
+		usbi_err(TRANSFER_CTX(transfer), "ReadPipe/WritePipe failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_IO;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int usbdk_do_iso_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct usbdk_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	struct usbdk_transfer_priv *transfer_priv = get_usbdk_transfer_priv(itransfer);
+	OVERLAPPED *overlapped = get_transfer_priv_overlapped(itransfer);
+	TransferResult transferRes;
+	int i;
+
+	transfer_priv->request.Buffer = (PVOID64)transfer->buffer;
+	transfer_priv->request.BufferLength = transfer->length;
+	transfer_priv->request.EndpointAddress = transfer->endpoint;
+	transfer_priv->request.TransferType = IsochronousTransferType;
+	transfer_priv->request.IsochronousPacketsArraySize = transfer->num_iso_packets;
+	transfer_priv->IsochronousPacketsArray = malloc(transfer->num_iso_packets * sizeof(ULONG64));
+	transfer_priv->request.IsochronousPacketsArray = (PVOID64)transfer_priv->IsochronousPacketsArray;
+	if (!transfer_priv->IsochronousPacketsArray) {
+		usbi_err(TRANSFER_CTX(transfer), "Allocation of IsochronousPacketsArray failed");
+		return LIBUSB_ERROR_NO_MEM;
+	}
+
+	transfer_priv->IsochronousResultsArray = malloc(transfer->num_iso_packets * sizeof(USB_DK_ISO_TRANSFER_RESULT));
+	transfer_priv->request.Result.IsochronousResultsArray = (PVOID64)transfer_priv->IsochronousResultsArray;
+	if (!transfer_priv->IsochronousResultsArray) {
+		usbi_err(TRANSFER_CTX(transfer), "Allocation of isochronousResultsArray failed");
+		return LIBUSB_ERROR_NO_MEM;
+	}
+
+	for (i = 0; i < transfer->num_iso_packets; i++)
+		transfer_priv->IsochronousPacketsArray[i] = transfer->iso_packet_desc[i].length;
+
+	set_transfer_priv_handle(itransfer, priv->system_handle);
+
+	if (IS_XFERIN(transfer))
+		transferRes = usbdk_helper.ReadPipe(priv->redirector_handle, &transfer_priv->request, overlapped);
+	else
+		transferRes = usbdk_helper.WritePipe(priv->redirector_handle, &transfer_priv->request, overlapped);
+
+	switch (transferRes) {
+	case TransferSuccess:
+		windows_force_sync_completion(itransfer, (ULONG)transfer_priv->request.Result.GenResult.BytesTransferred);
+		break;
+	case TransferSuccessAsync:
+		break;
+	case TransferFailure:
+		return LIBUSB_ERROR_IO;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int usbdk_submit_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+		return usbdk_do_control_transfer(itransfer);
+	case LIBUSB_TRANSFER_TYPE_BULK:
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		if (IS_XFEROUT(transfer) && (transfer->flags & LIBUSB_TRANSFER_ADD_ZERO_PACKET))
+			return LIBUSB_ERROR_NOT_SUPPORTED; //TODO: Check whether we can support this in UsbDk
+		return usbdk_do_bulk_transfer(itransfer);
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		return usbdk_do_iso_transfer(itransfer);
+	default:
+		// Should not get here since windows_submit_transfer() validates
+		// the transfer->type field
+		usbi_err(TRANSFER_CTX(transfer), "unsupported endpoint type %d", transfer->type);
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+	}
+}
+
+static enum libusb_transfer_status usbdk_copy_transfer_data(struct usbi_transfer *itransfer, DWORD length)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct usbdk_transfer_priv *transfer_priv = get_usbdk_transfer_priv(itransfer);
+
+	UNUSED(length);
+
+	if (transfer->type == LIBUSB_TRANSFER_TYPE_ISOCHRONOUS) {
+		ULONG64 i;
+
+		for (i = 0; i < transfer_priv->request.IsochronousPacketsArraySize; i++) {
+			struct libusb_iso_packet_descriptor *lib_desc = &transfer->iso_packet_desc[i];
+
+			switch (transfer_priv->IsochronousResultsArray[i].TransferResult) {
+			case STATUS_SUCCESS:
+			case STATUS_CANCELLED:
+			case STATUS_REQUEST_CANCELED:
+				lib_desc->status = LIBUSB_TRANSFER_COMPLETED; // == ERROR_SUCCESS
+				break;
+			default:
+				lib_desc->status = LIBUSB_TRANSFER_ERROR; // ERROR_UNKNOWN_EXCEPTION;
+				break;
+			}
+
+			lib_desc->actual_length = (unsigned int)transfer_priv->IsochronousResultsArray[i].ActualLength;
+		}
+	}
+
+	itransfer->transferred += (int)transfer_priv->request.Result.GenResult.BytesTransferred;
+	return usbd_status_to_libusb_transfer_status((USBD_STATUS)transfer_priv->request.Result.GenResult.UsbdStatus);
+}
+
+const struct windows_backend usbdk_backend = {
+	usbdk_init,
+	usbdk_exit,
+	usbdk_get_device_list,
+	usbdk_open,
+	usbdk_close,
+	usbdk_get_active_config_descriptor,
+	usbdk_get_config_descriptor,
+	usbdk_get_config_descriptor_by_value,
+	usbdk_get_configuration,
+	usbdk_set_configuration,
+	usbdk_claim_interface,
+	usbdk_release_interface,
+	usbdk_set_interface_altsetting,
+	usbdk_clear_halt,
+	usbdk_reset_device,
+	usbdk_destroy_device,
+	usbdk_submit_transfer,
+	NULL,	/* cancel_transfer */
+	usbdk_clear_transfer_priv,
+	usbdk_copy_transfer_data,
+};
diff --git a/src/os/windows_usbdk.h b/src/os/windows_usbdk.h
new file mode 100644
index 0000000..0eb3779
--- /dev/null
+++ b/src/os/windows_usbdk.h
@@ -0,0 +1,106 @@
+/*
+* windows UsbDk backend for libusb 1.0
+* Copyright © 2014 Red Hat, Inc.
+
+* Authors:
+* Dmitry Fleytman <dmitry@daynix.com>
+* Pavel Gurvich <pavel@daynix.com>
+*
+* This library is free software; you can redistribute it and/or
+* modify it under the terms of the GNU Lesser General Public
+* License as published by the Free Software Foundation; either
+* version 2.1 of the License, or (at your option) any later version.
+*
+* This library is distributed in the hope that it will be useful,
+* but WITHOUT ANY WARRANTY; without even the implied warranty of
+* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+* Lesser General Public License for more details.
+*
+* You should have received a copy of the GNU Lesser General Public
+* License along with this library; if not, write to the Free Software
+* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+*/
+
+#ifndef LIBUSB_WINDOWS_USBDK_H
+#define LIBUSB_WINDOWS_USBDK_H
+
+#include "windows_common.h"
+
+typedef struct USB_DK_CONFIG_DESCRIPTOR_REQUEST {
+	USB_DK_DEVICE_ID ID;
+	ULONG64 Index;
+} USB_DK_CONFIG_DESCRIPTOR_REQUEST, *PUSB_DK_CONFIG_DESCRIPTOR_REQUEST;
+
+typedef enum {
+	TransferFailure = 0,
+	TransferSuccess,
+	TransferSuccessAsync
+} TransferResult;
+
+typedef enum {
+	NoSpeed = 0,
+	LowSpeed,
+	FullSpeed,
+	HighSpeed,
+	SuperSpeed
+} USB_DK_DEVICE_SPEED;
+
+typedef enum {
+	ControlTransferType,
+	BulkTransferType,
+	InterruptTransferType,
+	IsochronousTransferType
+} USB_DK_TRANSFER_TYPE;
+
+typedef BOOL (__cdecl *USBDK_GET_DEVICES_LIST)(
+	PUSB_DK_DEVICE_INFO *DeviceInfo,
+	PULONG DeviceNumber
+);
+typedef void (__cdecl *USBDK_RELEASE_DEVICES_LIST)(
+	PUSB_DK_DEVICE_INFO DeviceInfo
+);
+typedef HANDLE (__cdecl *USBDK_START_REDIRECT)(
+	PUSB_DK_DEVICE_ID DeviceId
+);
+typedef BOOL (__cdecl *USBDK_STOP_REDIRECT)(
+	HANDLE DeviceHandle
+);
+typedef BOOL (__cdecl *USBDK_GET_CONFIGURATION_DESCRIPTOR)(
+	PUSB_DK_CONFIG_DESCRIPTOR_REQUEST Request,
+	PUSB_CONFIGURATION_DESCRIPTOR *Descriptor,
+	PULONG Length
+);
+typedef void (__cdecl *USBDK_RELEASE_CONFIGURATION_DESCRIPTOR)(
+	PUSB_CONFIGURATION_DESCRIPTOR Descriptor
+);
+typedef TransferResult (__cdecl *USBDK_WRITE_PIPE)(
+	HANDLE DeviceHandle,
+	PUSB_DK_TRANSFER_REQUEST Request,
+	LPOVERLAPPED lpOverlapped
+);
+typedef TransferResult (__cdecl *USBDK_READ_PIPE)(
+	HANDLE DeviceHandle,
+	PUSB_DK_TRANSFER_REQUEST Request,
+	LPOVERLAPPED lpOverlapped
+);
+typedef BOOL (__cdecl *USBDK_ABORT_PIPE)(
+	HANDLE DeviceHandle,
+	ULONG64 PipeAddress
+);
+typedef BOOL (__cdecl *USBDK_RESET_PIPE)(
+	HANDLE DeviceHandle,
+	ULONG64 PipeAddress
+);
+typedef BOOL (__cdecl *USBDK_SET_ALTSETTING)(
+	HANDLE DeviceHandle,
+	ULONG64 InterfaceIdx,
+	ULONG64 AltSettingIdx
+);
+typedef BOOL (__cdecl *USBDK_RESET_DEVICE)(
+	HANDLE DeviceHandle
+);
+typedef HANDLE (__cdecl *USBDK_GET_REDIRECTOR_SYSTEM_HANDLE)(
+	HANDLE DeviceHandle
+);
+
+#endif
diff --git a/src/os/windows_winusb.c b/src/os/windows_winusb.c
new file mode 100644
index 0000000..a03d6a5
--- /dev/null
+++ b/src/os/windows_winusb.c
@@ -0,0 +1,4527 @@
+/*
+ * windows backend for libusb 1.0
+ * Copyright © 2009-2012 Pete Batard <pete@akeo.ie>
+ * Copyright © 2016-2018 Chris Dickens <christopher.a.dickens@gmail.com>
+ * With contributions from Michael Plante, Orin Eman et al.
+ * Parts of this code adapted from libusb-win32-v1 by Stephan Meyer
+ * HID Reports IOCTLs inspired from HIDAPI by Alan Ott, Signal 11 Software
+ * Hash table functions adapted from glibc, by Ulrich Drepper et al.
+ * Major code testing contribution by Xiaofan Chen
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#include <config.h>
+
+#include <windows.h>
+#include <setupapi.h>
+#include <ctype.h>
+#include <stdio.h>
+
+#include "libusbi.h"
+#include "windows_winusb.h"
+
+#define HANDLE_VALID(h) (((h) != NULL) && ((h) != INVALID_HANDLE_VALUE))
+
+// The below macro is used in conjunction with safe loops.
+#define LOOP_BREAK(err)				\
+	{					\
+		r = err;			\
+		continue;			\
+	}
+
+// WinUSB-like API prototypes
+static bool winusbx_init(struct libusb_context *ctx);
+static void winusbx_exit(void);
+static int winusbx_open(int sub_api, struct libusb_device_handle *dev_handle);
+static void winusbx_close(int sub_api, struct libusb_device_handle *dev_handle);
+static int winusbx_configure_endpoints(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface);
+static int winusbx_claim_interface(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface);
+static int winusbx_release_interface(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface);
+static int winusbx_submit_control_transfer(int sub_api, struct usbi_transfer *itransfer);
+static int winusbx_set_interface_altsetting(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface, uint8_t altsetting);
+static int winusbx_submit_iso_transfer(int sub_api, struct usbi_transfer *itransfer);
+static int winusbx_submit_bulk_transfer(int sub_api, struct usbi_transfer *itransfer);
+static int winusbx_clear_halt(int sub_api, struct libusb_device_handle *dev_handle, unsigned char endpoint);
+static int winusbx_cancel_transfer(int sub_api, struct usbi_transfer *itransfer);
+static int winusbx_reset_device(int sub_api, struct libusb_device_handle *dev_handle);
+static enum libusb_transfer_status winusbx_copy_transfer_data(int sub_api, struct usbi_transfer *itransfer, DWORD length);
+// HID API prototypes
+static bool hid_init(struct libusb_context *ctx);
+static void hid_exit(void);
+static int hid_open(int sub_api, struct libusb_device_handle *dev_handle);
+static void hid_close(int sub_api, struct libusb_device_handle *dev_handle);
+static int hid_claim_interface(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface);
+static int hid_release_interface(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface);
+static int hid_set_interface_altsetting(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface, uint8_t altsetting);
+static int hid_submit_control_transfer(int sub_api, struct usbi_transfer *itransfer);
+static int hid_submit_bulk_transfer(int sub_api, struct usbi_transfer *itransfer);
+static int hid_clear_halt(int sub_api, struct libusb_device_handle *dev_handle, unsigned char endpoint);
+static int hid_reset_device(int sub_api, struct libusb_device_handle *dev_handle);
+static enum libusb_transfer_status hid_copy_transfer_data(int sub_api, struct usbi_transfer *itransfer, DWORD length);
+// Composite API prototypes
+static int composite_open(int sub_api, struct libusb_device_handle *dev_handle);
+static void composite_close(int sub_api, struct libusb_device_handle *dev_handle);
+static int composite_claim_interface(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface);
+static int composite_set_interface_altsetting(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface, uint8_t altsetting);
+static int composite_release_interface(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface);
+static int composite_submit_control_transfer(int sub_api, struct usbi_transfer *itransfer);
+static int composite_submit_bulk_transfer(int sub_api, struct usbi_transfer *itransfer);
+static int composite_submit_iso_transfer(int sub_api, struct usbi_transfer *itransfer);
+static int composite_clear_halt(int sub_api, struct libusb_device_handle *dev_handle, unsigned char endpoint);
+static int composite_cancel_transfer(int sub_api, struct usbi_transfer *itransfer);
+static int composite_reset_device(int sub_api, struct libusb_device_handle *dev_handle);
+static enum libusb_transfer_status composite_copy_transfer_data(int sub_api, struct usbi_transfer *itransfer, DWORD length);
+
+static usbi_mutex_t autoclaim_lock;
+
+// API globals
+static struct winusb_interface WinUSBX[SUB_API_MAX];
+#define CHECK_WINUSBX_AVAILABLE(sub_api)		\
+	do {						\
+		if (sub_api == SUB_API_NOTSET)		\
+			sub_api = priv->sub_api;	\
+		if (WinUSBX[sub_api].hDll == NULL)	\
+			return LIBUSB_ERROR_ACCESS;	\
+	} while (0)
+
+#define CHECK_HID_AVAILABLE				\
+	do {						\
+		if (DLL_HANDLE_NAME(hid) == NULL)	\
+			return LIBUSB_ERROR_ACCESS;	\
+	} while (0)
+
+#if defined(ENABLE_LOGGING)
+static const char *guid_to_string(const GUID *guid, char guid_string[MAX_GUID_STRING_LENGTH])
+{
+	if (guid == NULL) {
+		guid_string[0] = '\0';
+		return guid_string;
+	}
+
+	sprintf(guid_string, "{%08X-%04X-%04X-%02X%02X-%02X%02X%02X%02X%02X%02X}",
+		(unsigned int)guid->Data1, guid->Data2, guid->Data3,
+		guid->Data4[0], guid->Data4[1], guid->Data4[2], guid->Data4[3],
+		guid->Data4[4], guid->Data4[5], guid->Data4[6], guid->Data4[7]);
+
+	return guid_string;
+}
+#endif
+
+static bool string_to_guid(const char guid_string[MAX_GUID_STRING_LENGTH], GUID *guid)
+{
+	unsigned short tmp[4];
+	int num_chars = -1;
+	char extra;
+	int r;
+
+	// Unfortunately MinGW complains that '%hhx' is not a valid format specifier,
+	// even though Visual Studio 2013 and later support it. Rather than complicating
+	// the logic in this function with '#ifdef's, use a temporary array on the stack
+	// to store the conversions.
+	r = sscanf(guid_string, "{%8x-%4hx-%4hx-%4hx-%4hx%4hx%4hx}%n%c",
+		(unsigned int *)&guid->Data1, &guid->Data2, &guid->Data3,
+		&tmp[0], &tmp[1], &tmp[2], &tmp[3], &num_chars, &extra);
+
+	if ((r != 7) || (num_chars != 38))
+		return false;
+
+	// Extract the bytes from the 2-byte shorts
+	guid->Data4[0] = (unsigned char)((tmp[0] >> 8) & 0xFF);
+	guid->Data4[1] = (unsigned char)(tmp[0] & 0xFF);
+	guid->Data4[2] = (unsigned char)((tmp[1] >> 8) & 0xFF);
+	guid->Data4[3] = (unsigned char)(tmp[1] & 0xFF);
+	guid->Data4[4] = (unsigned char)((tmp[2] >> 8) & 0xFF);
+	guid->Data4[5] = (unsigned char)(tmp[2] & 0xFF);
+	guid->Data4[6] = (unsigned char)((tmp[3] >> 8) & 0xFF);
+	guid->Data4[7] = (unsigned char)(tmp[3] & 0xFF);
+
+	return true;
+}
+
+/*
+ * Normalize Microsoft's paths: return a duplicate of the given path
+ * with all characters converted to uppercase
+ */
+static char *normalize_path(const char *path)
+{
+	char *ret_path = _strdup(path);
+	char *p;
+
+	if (ret_path == NULL)
+		return NULL;
+
+	for (p = ret_path; *p != '\0'; p++)
+		*p = (char)toupper((unsigned char)*p);
+
+	return ret_path;
+}
+
+/*
+ * Cfgmgr32, AdvAPI32, OLE32 and SetupAPI DLL functions
+ */
+static bool init_dlls(struct libusb_context *ctx)
+{
+	DLL_GET_HANDLE(ctx, Cfgmgr32);
+	DLL_LOAD_FUNC(Cfgmgr32, CM_Get_Parent, true);
+	DLL_LOAD_FUNC(Cfgmgr32, CM_Get_Child, true);
+
+	// Prefixed to avoid conflict with header files
+	DLL_GET_HANDLE(ctx, AdvAPI32);
+	DLL_LOAD_FUNC_PREFIXED(AdvAPI32, p, RegQueryValueExA, true);
+	DLL_LOAD_FUNC_PREFIXED(AdvAPI32, p, RegCloseKey, true);
+
+	DLL_GET_HANDLE(ctx, SetupAPI);
+	DLL_LOAD_FUNC_PREFIXED(SetupAPI, p, SetupDiGetClassDevsA, true);
+	DLL_LOAD_FUNC_PREFIXED(SetupAPI, p, SetupDiEnumDeviceInfo, true);
+	DLL_LOAD_FUNC_PREFIXED(SetupAPI, p, SetupDiEnumDeviceInterfaces, true);
+	DLL_LOAD_FUNC_PREFIXED(SetupAPI, p, SetupDiGetDeviceInstanceIdA, true);
+	DLL_LOAD_FUNC_PREFIXED(SetupAPI, p, SetupDiGetDeviceInterfaceDetailA, true);
+	DLL_LOAD_FUNC_PREFIXED(SetupAPI, p, SetupDiGetDeviceRegistryPropertyA, true);
+	DLL_LOAD_FUNC_PREFIXED(SetupAPI, p, SetupDiDestroyDeviceInfoList, true);
+	DLL_LOAD_FUNC_PREFIXED(SetupAPI, p, SetupDiOpenDevRegKey, true);
+	DLL_LOAD_FUNC_PREFIXED(SetupAPI, p, SetupDiOpenDeviceInterfaceRegKey, true);
+
+	return true;
+}
+
+static void exit_dlls(void)
+{
+	DLL_FREE_HANDLE(SetupAPI);
+	DLL_FREE_HANDLE(AdvAPI32);
+	DLL_FREE_HANDLE(Cfgmgr32);
+}
+
+/*
+ * enumerate interfaces for the whole USB class
+ *
+ * Parameters:
+ * dev_info: a pointer to a dev_info list
+ * dev_info_data: a pointer to an SP_DEVINFO_DATA to be filled (or NULL if not needed)
+ * enumerator: the generic USB class for which to retrieve interface details
+ * index: zero based index of the interface in the device info list
+ *
+ * Note: it is the responsibility of the caller to free the DEVICE_INTERFACE_DETAIL_DATA
+ * structure returned and call this function repeatedly using the same guid (with an
+ * incremented index starting at zero) until all interfaces have been returned.
+ */
+static bool get_devinfo_data(struct libusb_context *ctx,
+	HDEVINFO *dev_info, SP_DEVINFO_DATA *dev_info_data, const char *enumerator, unsigned _index)
+{
+	if (_index == 0) {
+		*dev_info = pSetupDiGetClassDevsA(NULL, enumerator, NULL, DIGCF_PRESENT|DIGCF_ALLCLASSES);
+		if (*dev_info == INVALID_HANDLE_VALUE) {
+			usbi_err(ctx, "could not obtain device info set for PnP enumerator '%s': %s",
+				enumerator, windows_error_str(0));
+			return false;
+		}
+	}
+
+	dev_info_data->cbSize = sizeof(SP_DEVINFO_DATA);
+	if (!pSetupDiEnumDeviceInfo(*dev_info, _index, dev_info_data)) {
+		if (GetLastError() != ERROR_NO_MORE_ITEMS)
+			usbi_err(ctx, "could not obtain device info data for PnP enumerator '%s' index %u: %s",
+				enumerator, _index, windows_error_str(0));
+
+		pSetupDiDestroyDeviceInfoList(*dev_info);
+		*dev_info = INVALID_HANDLE_VALUE;
+		return false;
+	}
+	return true;
+}
+
+/*
+ * enumerate interfaces for a specific GUID
+ *
+ * Parameters:
+ * dev_info: a pointer to a dev_info list
+ * dev_info_data: a pointer to an SP_DEVINFO_DATA to be filled (or NULL if not needed)
+ * guid: the GUID for which to retrieve interface details
+ * index: zero based index of the interface in the device info list
+ *
+ * Note: it is the responsibility of the caller to free the DEVICE_INTERFACE_DETAIL_DATA
+ * structure returned and call this function repeatedly using the same guid (with an
+ * incremented index starting at zero) until all interfaces have been returned.
+ */
+static int get_interface_details(struct libusb_context *ctx, HDEVINFO dev_info,
+	PSP_DEVINFO_DATA dev_info_data, LPCGUID guid, DWORD *_index, char **dev_interface_path)
+{
+	SP_DEVICE_INTERFACE_DATA dev_interface_data;
+	PSP_DEVICE_INTERFACE_DETAIL_DATA_A dev_interface_details;
+	char guid_string[MAX_GUID_STRING_LENGTH];
+	DWORD size;
+
+	dev_info_data->cbSize = sizeof(SP_DEVINFO_DATA);
+	dev_interface_data.cbSize = sizeof(SP_DEVICE_INTERFACE_DATA);
+	for (;;) {
+		if (!pSetupDiEnumDeviceInfo(dev_info, *_index, dev_info_data)) {
+			if (GetLastError() != ERROR_NO_MORE_ITEMS) {
+				usbi_err(ctx, "Could not obtain device info data for %s index %lu: %s",
+					guid_to_string(guid, guid_string), ULONG_CAST(*_index), windows_error_str(0));
+				return LIBUSB_ERROR_OTHER;
+			}
+
+			// No more devices
+			return LIBUSB_SUCCESS;
+		}
+
+		// Always advance the index for the next iteration
+		(*_index)++;
+
+		if (pSetupDiEnumDeviceInterfaces(dev_info, dev_info_data, guid, 0, &dev_interface_data))
+			break;
+
+		if (GetLastError() != ERROR_NO_MORE_ITEMS) {
+			usbi_err(ctx, "Could not obtain interface data for %s devInst %lX: %s",
+				guid_to_string(guid, guid_string), ULONG_CAST(dev_info_data->DevInst), windows_error_str(0));
+			return LIBUSB_ERROR_OTHER;
+		}
+
+		// Device does not have an interface matching this GUID, skip
+	}
+
+	// Read interface data (dummy + actual) to access the device path
+	if (!pSetupDiGetDeviceInterfaceDetailA(dev_info, &dev_interface_data, NULL, 0, &size, NULL)) {
+		// The dummy call should fail with ERROR_INSUFFICIENT_BUFFER
+		if (GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
+			usbi_err(ctx, "could not access interface data (dummy) for %s devInst %lX: %s",
+				guid_to_string(guid, guid_string), ULONG_CAST(dev_info_data->DevInst), windows_error_str(0));
+			return LIBUSB_ERROR_OTHER;
+		}
+	} else {
+		usbi_err(ctx, "program assertion failed - http://msdn.microsoft.com/en-us/library/ms792901.aspx is wrong");
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	dev_interface_details = malloc(size);
+	if (dev_interface_details == NULL) {
+		usbi_err(ctx, "could not allocate interface data for %s devInst %lX",
+			guid_to_string(guid, guid_string), ULONG_CAST(dev_info_data->DevInst));
+		return LIBUSB_ERROR_NO_MEM;
+	}
+
+	dev_interface_details->cbSize = sizeof(SP_DEVICE_INTERFACE_DETAIL_DATA_A);
+	if (!pSetupDiGetDeviceInterfaceDetailA(dev_info, &dev_interface_data,
+		dev_interface_details, size, NULL, NULL)) {
+		usbi_err(ctx, "could not access interface data (actual) for %s devInst %lX: %s",
+			guid_to_string(guid, guid_string), ULONG_CAST(dev_info_data->DevInst), windows_error_str(0));
+		free(dev_interface_details);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	*dev_interface_path = normalize_path(dev_interface_details->DevicePath);
+	free(dev_interface_details);
+
+	if (*dev_interface_path == NULL) {
+		usbi_err(ctx, "could not allocate interface path for %s devInst %lX",
+			guid_to_string(guid, guid_string), ULONG_CAST(dev_info_data->DevInst));
+		return LIBUSB_ERROR_NO_MEM;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+/* For libusb0 filter */
+static int get_interface_details_filter(struct libusb_context *ctx, HDEVINFO *dev_info,
+	DWORD _index, char *filter_path, char **dev_interface_path)
+{
+	const GUID *libusb0_guid = &GUID_DEVINTERFACE_LIBUSB0_FILTER;
+	SP_DEVICE_INTERFACE_DATA dev_interface_data;
+	PSP_DEVICE_INTERFACE_DETAIL_DATA_A dev_interface_details;
+	HKEY hkey_dev_interface;
+	DWORD size;
+	int err = LIBUSB_ERROR_OTHER;
+
+	if (_index == 0) {
+		*dev_info = pSetupDiGetClassDevsA(libusb0_guid, NULL, NULL, DIGCF_PRESENT | DIGCF_DEVICEINTERFACE);
+		if (*dev_info == INVALID_HANDLE_VALUE) {
+			usbi_err(ctx, "could not obtain device info set: %s", windows_error_str(0));
+			return LIBUSB_ERROR_OTHER;
+		}
+	}
+
+	dev_interface_data.cbSize = sizeof(SP_DEVICE_INTERFACE_DATA);
+	if (!pSetupDiEnumDeviceInterfaces(*dev_info, NULL, libusb0_guid, _index, &dev_interface_data)) {
+		if (GetLastError() != ERROR_NO_MORE_ITEMS) {
+			usbi_err(ctx, "Could not obtain interface data for index %lu: %s",
+				ULONG_CAST(_index), windows_error_str(0));
+			goto err_exit;
+		}
+
+		pSetupDiDestroyDeviceInfoList(*dev_info);
+		*dev_info = INVALID_HANDLE_VALUE;
+		return LIBUSB_SUCCESS;
+	}
+
+	// Read interface data (dummy + actual) to access the device path
+	if (!pSetupDiGetDeviceInterfaceDetailA(*dev_info, &dev_interface_data, NULL, 0, &size, NULL)) {
+		// The dummy call should fail with ERROR_INSUFFICIENT_BUFFER
+		if (GetLastError() != ERROR_INSUFFICIENT_BUFFER) {
+			usbi_err(ctx, "could not access interface data (dummy) for index %lu: %s",
+				ULONG_CAST(_index), windows_error_str(0));
+			goto err_exit;
+		}
+	} else {
+		usbi_err(ctx, "program assertion failed - http://msdn.microsoft.com/en-us/library/ms792901.aspx is wrong");
+		goto err_exit;
+	}
+
+	dev_interface_details = malloc(size);
+	if (dev_interface_details == NULL) {
+		usbi_err(ctx, "could not allocate interface data for index %lu", ULONG_CAST(_index));
+		err = LIBUSB_ERROR_NO_MEM;
+		goto err_exit;
+	}
+
+	dev_interface_details->cbSize = sizeof(SP_DEVICE_INTERFACE_DETAIL_DATA_A);
+	if (!pSetupDiGetDeviceInterfaceDetailA(*dev_info, &dev_interface_data, dev_interface_details, size, NULL, NULL)) {
+		usbi_err(ctx, "could not access interface data (actual) for index %lu: %s",
+			ULONG_CAST(_index), windows_error_str(0));
+		free(dev_interface_details);
+		goto err_exit;
+	}
+
+	*dev_interface_path = normalize_path(dev_interface_details->DevicePath);
+	free(dev_interface_details);
+
+	if (*dev_interface_path == NULL) {
+		usbi_err(ctx, "could not allocate interface path for index %lu", ULONG_CAST(_index));
+		err = LIBUSB_ERROR_NO_MEM;
+		goto err_exit;
+	}
+
+	// [trobinso] lookup the libusb0 symbolic index.
+	hkey_dev_interface = pSetupDiOpenDeviceInterfaceRegKey(*dev_info, &dev_interface_data, 0, KEY_READ);
+	if (hkey_dev_interface != INVALID_HANDLE_VALUE) {
+		DWORD libusb0_symboliclink_index = 0;
+		DWORD value_length = sizeof(DWORD);
+		LONG status;
+
+		status = pRegQueryValueExA(hkey_dev_interface, "LUsb0", NULL, NULL,
+			(LPBYTE)&libusb0_symboliclink_index, &value_length);
+		if (status == ERROR_SUCCESS) {
+			if (libusb0_symboliclink_index < 256) {
+				// libusb0.sys is connected to this device instance.
+				// If the the device interface guid is {F9F3FF14-AE21-48A0-8A25-8011A7A931D9} then it's a filter.
+				sprintf(filter_path, "\\\\.\\libusb0-%04u", (unsigned int)libusb0_symboliclink_index);
+				usbi_dbg(ctx, "assigned libusb0 symbolic link %s", filter_path);
+			} else {
+				// libusb0.sys was connected to this device instance at one time; but not anymore.
+			}
+		}
+		pRegCloseKey(hkey_dev_interface);
+	} else {
+		usbi_warn(ctx, "could not open device interface registry key for index %lu: %s",
+			ULONG_CAST(_index), windows_error_str(0));
+		// TODO: should this be an error?
+	}
+
+	return LIBUSB_SUCCESS;
+
+err_exit:
+	pSetupDiDestroyDeviceInfoList(*dev_info);
+	*dev_info = INVALID_HANDLE_VALUE;
+	return err;
+}
+
+/*
+ * Returns the first known ancestor of a device
+ */
+static struct libusb_device *get_ancestor(struct libusb_context *ctx,
+	DEVINST devinst, PDEVINST _parent_devinst)
+{
+	struct libusb_device *dev = NULL;
+	DEVINST parent_devinst;
+
+	while (dev == NULL) {
+		if (CM_Get_Parent(&parent_devinst, devinst, 0) != CR_SUCCESS)
+			break;
+		devinst = parent_devinst;
+		dev = usbi_get_device_by_session_id(ctx, (unsigned long)devinst);
+	}
+
+	if ((dev != NULL) && (_parent_devinst != NULL))
+		*_parent_devinst = devinst;
+
+	return dev;
+}
+
+/*
+ * Determine which interface the given endpoint address belongs to
+ */
+static int get_interface_by_endpoint(struct libusb_config_descriptor *conf_desc, uint8_t ep)
+{
+	const struct libusb_interface *intf;
+	const struct libusb_interface_descriptor *intf_desc;
+	uint8_t i, k;
+	int j;
+
+	for (i = 0; i < conf_desc->bNumInterfaces; i++) {
+		intf = &conf_desc->interface[i];
+		for (j = 0; j < intf->num_altsetting; j++) {
+			intf_desc = &intf->altsetting[j];
+			for (k = 0; k < intf_desc->bNumEndpoints; k++) {
+				if (intf_desc->endpoint[k].bEndpointAddress == ep) {
+					usbi_dbg(NULL, "found endpoint %02X on interface %d", intf_desc->bInterfaceNumber, i);
+					return intf_desc->bInterfaceNumber;
+				}
+			}
+		}
+	}
+
+	usbi_dbg(NULL, "endpoint %02X not found on any interface", ep);
+	return LIBUSB_ERROR_NOT_FOUND;
+}
+
+/*
+ * Open a device and associate the HANDLE with the context's I/O completion port
+ */
+static HANDLE windows_open(struct libusb_device_handle *dev_handle, const char *path, DWORD access)
+{
+	struct libusb_context *ctx = HANDLE_CTX(dev_handle);
+	struct windows_context_priv *priv = usbi_get_context_priv(ctx);
+	HANDLE handle;
+
+	handle = CreateFileA(path, access, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, FILE_FLAG_OVERLAPPED, NULL);
+	if (handle == INVALID_HANDLE_VALUE)
+		return handle;
+
+	if (CreateIoCompletionPort(handle, priv->completion_port, (ULONG_PTR)dev_handle, 0) == NULL) {
+		usbi_err(ctx, "failed to associate handle to I/O completion port: %s", windows_error_str(0));
+		CloseHandle(handle);
+		return INVALID_HANDLE_VALUE;
+	}
+
+	return handle;
+}
+
+/*
+ * Populate the endpoints addresses of the device_priv interface helper structs
+ */
+static int windows_assign_endpoints(struct libusb_device_handle *dev_handle, uint8_t iface, uint8_t altsetting)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	struct libusb_config_descriptor *conf_desc;
+	const struct libusb_interface_descriptor *if_desc;
+	int i, r;
+
+	r = libusb_get_active_config_descriptor(dev_handle->dev, &conf_desc);
+	if (r != LIBUSB_SUCCESS) {
+		usbi_warn(HANDLE_CTX(dev_handle), "could not read config descriptor: error %d", r);
+		return r;
+	}
+
+	if_desc = &conf_desc->interface[iface].altsetting[altsetting];
+	safe_free(priv->usb_interface[iface].endpoint);
+
+	if (if_desc->bNumEndpoints == 0) {
+		usbi_dbg(HANDLE_CTX(dev_handle), "no endpoints found for interface %u", iface);
+	} else {
+		priv->usb_interface[iface].endpoint = malloc(if_desc->bNumEndpoints);
+		if (priv->usb_interface[iface].endpoint == NULL) {
+			libusb_free_config_descriptor(conf_desc);
+			return LIBUSB_ERROR_NO_MEM;
+		}
+		priv->usb_interface[iface].nb_endpoints = if_desc->bNumEndpoints;
+		for (i = 0; i < if_desc->bNumEndpoints; i++) {
+			priv->usb_interface[iface].endpoint[i] = if_desc->endpoint[i].bEndpointAddress;
+			usbi_dbg(HANDLE_CTX(dev_handle), "(re)assigned endpoint %02X to interface %u", priv->usb_interface[iface].endpoint[i], iface);
+		}
+	}
+	libusb_free_config_descriptor(conf_desc);
+
+	// Extra init may be required to configure endpoints
+	if (priv->apib->configure_endpoints)
+		r = priv->apib->configure_endpoints(SUB_API_NOTSET, dev_handle, iface);
+
+	if (r == LIBUSB_SUCCESS)
+		priv->usb_interface[iface].current_altsetting = altsetting;
+
+	return r;
+}
+
+// Lookup for a match in the list of API driver names
+// return -1 if not found, driver match number otherwise
+static int get_sub_api(char *driver, int api)
+{
+	const char sep_str[2] = {LIST_SEPARATOR, 0};
+	char *tok, *tmp_str;
+	size_t len = strlen(driver);
+	int i;
+
+	if (len == 0)
+		return SUB_API_NOTSET;
+
+	tmp_str = _strdup(driver);
+	if (tmp_str == NULL)
+		return SUB_API_NOTSET;
+
+	tok = strtok(tmp_str, sep_str);
+	while (tok != NULL) {
+		for (i = 0; i < usb_api_backend[api].nb_driver_names; i++) {
+			if (_stricmp(tok, usb_api_backend[api].driver_name_list[i]) == 0) {
+				free(tmp_str);
+				return i;
+			}
+		}
+		tok = strtok(NULL, sep_str);
+	}
+
+	free(tmp_str);
+	return SUB_API_NOTSET;
+}
+
+/*
+ * auto-claiming and auto-release helper functions
+ */
+static int auto_claim(struct libusb_transfer *transfer, int *interface_number, int api_type)
+{
+	struct winusb_device_handle_priv *handle_priv =
+		get_winusb_device_handle_priv(transfer->dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	int current_interface = *interface_number;
+	int r = LIBUSB_SUCCESS;
+
+	switch (api_type) {
+	case USB_API_WINUSBX:
+	case USB_API_HID:
+		break;
+	default:
+		return LIBUSB_ERROR_INVALID_PARAM;
+	}
+
+	usbi_mutex_lock(&autoclaim_lock);
+	if (current_interface < 0) { // No serviceable interface was found
+		for (current_interface = 0; current_interface < USB_MAXINTERFACES; current_interface++) {
+			// Must claim an interface of the same API type
+			if ((priv->usb_interface[current_interface].apib->id == api_type)
+					&& (libusb_claim_interface(transfer->dev_handle, current_interface) == LIBUSB_SUCCESS)) {
+				usbi_dbg(TRANSFER_CTX(transfer), "auto-claimed interface %d for control request", current_interface);
+				if (handle_priv->autoclaim_count[current_interface] != 0)
+					usbi_err(TRANSFER_CTX(transfer), "program assertion failed - autoclaim_count was nonzero");
+				handle_priv->autoclaim_count[current_interface]++;
+				break;
+			}
+		}
+		if (current_interface == USB_MAXINTERFACES) {
+			usbi_err(TRANSFER_CTX(transfer), "could not auto-claim any interface");
+			r = LIBUSB_ERROR_NOT_FOUND;
+		}
+	} else {
+		// If we have a valid interface that was autoclaimed, we must increment
+		// its autoclaim count so that we can prevent an early release.
+		if (handle_priv->autoclaim_count[current_interface] != 0)
+			handle_priv->autoclaim_count[current_interface]++;
+	}
+	usbi_mutex_unlock(&autoclaim_lock);
+
+	*interface_number = current_interface;
+	return r;
+}
+
+static void auto_release(struct usbi_transfer *itransfer)
+{
+	struct winusb_transfer_priv *transfer_priv = get_winusb_transfer_priv(itransfer);
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	libusb_device_handle *dev_handle = transfer->dev_handle;
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	int r;
+
+	usbi_mutex_lock(&autoclaim_lock);
+	if (handle_priv->autoclaim_count[transfer_priv->interface_number] > 0) {
+		handle_priv->autoclaim_count[transfer_priv->interface_number]--;
+		if (handle_priv->autoclaim_count[transfer_priv->interface_number] == 0) {
+			r = libusb_release_interface(dev_handle, transfer_priv->interface_number);
+			if (r == LIBUSB_SUCCESS)
+				usbi_dbg(ITRANSFER_CTX(itransfer), "auto-released interface %d", transfer_priv->interface_number);
+			else
+				usbi_dbg(ITRANSFER_CTX(itransfer), "failed to auto-release interface %d (%s)",
+					transfer_priv->interface_number, libusb_error_name((enum libusb_error)r));
+		}
+	}
+	usbi_mutex_unlock(&autoclaim_lock);
+}
+
+/*
+ * init: libusb backend init function
+ */
+static int winusb_init(struct libusb_context *ctx)
+{
+	int i;
+
+	// Load DLL imports
+	if (!init_dlls(ctx)) {
+		usbi_err(ctx, "could not resolve DLL functions");
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	// Initialize the low level APIs (we don't care about errors at this stage)
+	for (i = 0; i < USB_API_MAX; i++) {
+		if (usb_api_backend[i].init && !usb_api_backend[i].init(ctx))
+			usbi_warn(ctx, "error initializing %s backend",
+				usb_api_backend[i].designation);
+	}
+
+	// We need a lock for proper auto-release
+	usbi_mutex_init(&autoclaim_lock);
+
+	return LIBUSB_SUCCESS;
+}
+
+/*
+* exit: libusb backend deinitialization function
+*/
+static void winusb_exit(struct libusb_context *ctx)
+{
+	int i;
+
+	UNUSED(ctx);
+
+	usbi_mutex_destroy(&autoclaim_lock);
+
+	for (i = 0; i < USB_API_MAX; i++) {
+		if (usb_api_backend[i].exit)
+			usb_api_backend[i].exit();
+	}
+
+	exit_dlls();
+}
+
+/*
+ * fetch and cache all the config descriptors through I/O
+ */
+static void cache_config_descriptors(struct libusb_device *dev, HANDLE hub_handle)
+{
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev);
+	DWORD size, ret_size;
+	uint8_t i, num_configurations;
+
+	USB_CONFIGURATION_DESCRIPTOR_SHORT cd_buf_short; // dummy request
+	PUSB_DESCRIPTOR_REQUEST cd_buf_actual = NULL;    // actual request
+	PUSB_CONFIGURATION_DESCRIPTOR cd_data;
+
+	num_configurations = dev->device_descriptor.bNumConfigurations;
+	if (num_configurations == 0)
+		return;
+
+	assert(sizeof(USB_DESCRIPTOR_REQUEST) == USB_DESCRIPTOR_REQUEST_SIZE);
+
+	priv->config_descriptor = calloc(num_configurations, sizeof(PUSB_CONFIGURATION_DESCRIPTOR));
+	if (priv->config_descriptor == NULL) {
+		usbi_err(ctx, "could not allocate configuration descriptor array for '%s'", priv->dev_id);
+		return;
+	}
+
+	for (i = 0; i <= num_configurations; i++) {
+		safe_free(cd_buf_actual);
+
+		if (i == num_configurations)
+			break;
+
+		size = sizeof(cd_buf_short);
+		memset(&cd_buf_short.desc, 0, sizeof(cd_buf_short.desc));
+
+		cd_buf_short.req.ConnectionIndex = (ULONG)dev->port_number;
+		cd_buf_short.req.SetupPacket.bmRequest = LIBUSB_ENDPOINT_IN;
+		cd_buf_short.req.SetupPacket.bRequest = LIBUSB_REQUEST_GET_DESCRIPTOR;
+		cd_buf_short.req.SetupPacket.wValue = (LIBUSB_DT_CONFIG << 8) | i;
+		cd_buf_short.req.SetupPacket.wIndex = 0;
+		cd_buf_short.req.SetupPacket.wLength = (USHORT)sizeof(USB_CONFIGURATION_DESCRIPTOR);
+
+		// Dummy call to get the required data size. Initial failures are reported as info rather
+		// than error as they can occur for non-penalizing situations, such as with some hubs.
+		// coverity[tainted_data_argument]
+		if (!DeviceIoControl(hub_handle, IOCTL_USB_GET_DESCRIPTOR_FROM_NODE_CONNECTION, &cd_buf_short, size,
+			&cd_buf_short, size, &ret_size, NULL)) {
+			usbi_info(ctx, "could not access configuration descriptor %u (dummy) for '%s': %s", i, priv->dev_id, windows_error_str(0));
+			continue;
+		}
+
+		if ((ret_size != size) || (cd_buf_short.desc.wTotalLength < sizeof(USB_CONFIGURATION_DESCRIPTOR))) {
+			usbi_info(ctx, "unexpected configuration descriptor %u size (dummy) for '%s'", i, priv->dev_id);
+			continue;
+		}
+
+		size = sizeof(USB_DESCRIPTOR_REQUEST) + cd_buf_short.desc.wTotalLength;
+		cd_buf_actual = malloc(size);
+		if (cd_buf_actual == NULL) {
+			usbi_err(ctx, "could not allocate configuration descriptor %u buffer for '%s'", i, priv->dev_id);
+			continue;
+		}
+
+		// Actual call
+		cd_buf_actual->ConnectionIndex = (ULONG)dev->port_number;
+		cd_buf_actual->SetupPacket.bmRequest = LIBUSB_ENDPOINT_IN;
+		cd_buf_actual->SetupPacket.bRequest = LIBUSB_REQUEST_GET_DESCRIPTOR;
+		cd_buf_actual->SetupPacket.wValue = (LIBUSB_DT_CONFIG << 8) | i;
+		cd_buf_actual->SetupPacket.wIndex = 0;
+		cd_buf_actual->SetupPacket.wLength = cd_buf_short.desc.wTotalLength;
+
+		if (!DeviceIoControl(hub_handle, IOCTL_USB_GET_DESCRIPTOR_FROM_NODE_CONNECTION, cd_buf_actual, size,
+			cd_buf_actual, size, &ret_size, NULL)) {
+			usbi_err(ctx, "could not access configuration descriptor %u (actual) for '%s': %s", i, priv->dev_id, windows_error_str(0));
+			continue;
+		}
+
+		cd_data = (PUSB_CONFIGURATION_DESCRIPTOR)((UCHAR *)cd_buf_actual + USB_DESCRIPTOR_REQUEST_SIZE);
+
+		if ((size != ret_size) || (cd_data->wTotalLength != cd_buf_short.desc.wTotalLength)) {
+			usbi_err(ctx, "unexpected configuration descriptor %u size (actual) for '%s'", i, priv->dev_id);
+			continue;
+		}
+
+		if (cd_data->bDescriptorType != LIBUSB_DT_CONFIG) {
+			usbi_err(ctx, "descriptor %u not a configuration descriptor for '%s'", i, priv->dev_id);
+			continue;
+		}
+
+		usbi_dbg(ctx, "cached config descriptor %u (bConfigurationValue=%u, %u bytes)",
+			i, cd_data->bConfigurationValue, cd_data->wTotalLength);
+
+		// Cache the descriptor
+		priv->config_descriptor[i] = cd_data;
+		cd_buf_actual = NULL;
+	}
+}
+
+#define ROOT_HUB_FS_CONFIG_DESC_LENGTH		0x19
+#define ROOT_HUB_HS_CONFIG_DESC_LENGTH		0x19
+#define ROOT_HUB_SS_CONFIG_DESC_LENGTH		0x1f
+#define CONFIG_DESC_WTOTAL_LENGTH_OFFSET	0x02
+#define CONFIG_DESC_EP_MAX_PACKET_OFFSET	0x16
+#define CONFIG_DESC_EP_BINTERVAL_OFFSET		0x18
+
+static const uint8_t root_hub_config_descriptor_template[] = {
+	// Configuration Descriptor
+	LIBUSB_DT_CONFIG_SIZE,		// bLength
+	LIBUSB_DT_CONFIG,		// bDescriptorType
+	0x00, 0x00,			// wTotalLength (filled in)
+	0x01,				// bNumInterfaces
+	0x01,				// bConfigurationValue
+	0x00,				// iConfiguration
+	0xc0,				// bmAttributes (reserved + self-powered)
+	0x00,				// bMaxPower
+	// Interface Descriptor
+	LIBUSB_DT_INTERFACE_SIZE,	// bLength
+	LIBUSB_DT_INTERFACE,		// bDescriptorType
+	0x00,				// bInterfaceNumber
+	0x00,				// bAlternateSetting
+	0x01,				// bNumEndpoints
+	LIBUSB_CLASS_HUB,		// bInterfaceClass
+	0x00,				// bInterfaceSubClass
+	0x00,				// bInterfaceProtocol
+	0x00,				// iInterface
+	// Endpoint Descriptor
+	LIBUSB_DT_ENDPOINT_SIZE,	// bLength
+	LIBUSB_DT_ENDPOINT,		// bDescriptorType
+	0x81,				// bEndpointAddress
+	0x03,				// bmAttributes (Interrupt)
+	0x00, 0x00,			// wMaxPacketSize (filled in)
+	0x00,				// bInterval (filled in)
+	// SuperSpeed Endpoint Companion Descriptor
+	LIBUSB_DT_SS_ENDPOINT_COMPANION_SIZE,	// bLength
+	LIBUSB_DT_SS_ENDPOINT_COMPANION,	// bDescriptorType
+	0x00,					// bMaxBurst
+	0x00,					// bmAttributes
+	0x02, 0x00				// wBytesPerInterval
+};
+
+static int alloc_root_hub_config_desc(struct libusb_device *dev, ULONG num_ports,
+	uint8_t config_desc_length, uint8_t ep_interval)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev);
+	uint8_t *ptr;
+
+	priv->config_descriptor = malloc(sizeof(*priv->config_descriptor));
+	if (priv->config_descriptor == NULL)
+		return LIBUSB_ERROR_NO_MEM;
+
+	// Most config descriptors come from cache_config_descriptors() which obtains the
+	// descriptors from the hub using an allocated USB_DESCRIPTOR_REQUEST structure.
+	// To avoid an extra malloc + memcpy we just hold on to the USB_DESCRIPTOR_REQUEST
+	// structure we already have and back up the pointer in windows_device_priv_release()
+	// when freeing the descriptors. To keep a single execution path, we need to offset
+	// the pointer here by the same amount.
+	ptr = malloc(USB_DESCRIPTOR_REQUEST_SIZE + config_desc_length);
+	if (ptr == NULL)
+		return LIBUSB_ERROR_NO_MEM;
+
+	ptr += USB_DESCRIPTOR_REQUEST_SIZE;
+
+	memcpy(ptr, root_hub_config_descriptor_template, config_desc_length);
+	ptr[CONFIG_DESC_WTOTAL_LENGTH_OFFSET] = config_desc_length;
+	ptr[CONFIG_DESC_EP_MAX_PACKET_OFFSET] = (uint8_t)((num_ports + 7) / 8);
+	ptr[CONFIG_DESC_EP_BINTERVAL_OFFSET] = ep_interval;
+
+	priv->config_descriptor[0] = (PUSB_CONFIGURATION_DESCRIPTOR)ptr;
+	priv->active_config = 1;
+
+	return 0;
+}
+
+static int init_root_hub(struct libusb_device *dev)
+{
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev);
+	USB_NODE_CONNECTION_INFORMATION_EX conn_info;
+	USB_NODE_CONNECTION_INFORMATION_EX_V2 conn_info_v2;
+	USB_NODE_INFORMATION hub_info;
+	enum libusb_speed speed = LIBUSB_SPEED_UNKNOWN;
+	uint8_t config_desc_length;
+	uint8_t ep_interval;
+	HANDLE handle;
+	ULONG port_number, num_ports;
+	DWORD size;
+	int r;
+
+	// Determining the speed of a root hub is painful. Microsoft does not directly report the speed
+	// capabilities of the root hub itself, only its ports and/or connected devices. Therefore we
+	// are forced to query each individual port of the root hub to try and infer the root hub's
+	// speed. Note that we have to query all ports because the presence of a device on that port
+	// changes if/how Windows returns any useful speed information.
+	handle = CreateFileA(priv->path, GENERIC_WRITE, FILE_SHARE_WRITE, NULL, OPEN_EXISTING, 0, NULL);
+	if (handle == INVALID_HANDLE_VALUE) {
+		usbi_err(ctx, "could not open root hub %s: %s", priv->path, windows_error_str(0));
+		return LIBUSB_ERROR_ACCESS;
+	}
+
+	if (!DeviceIoControl(handle, IOCTL_USB_GET_NODE_INFORMATION, NULL, 0, &hub_info, sizeof(hub_info), &size, NULL)) {
+		usbi_warn(ctx, "could not get root hub info for '%s': %s", priv->dev_id, windows_error_str(0));
+		CloseHandle(handle);
+		return LIBUSB_ERROR_ACCESS;
+	}
+
+	num_ports = hub_info.u.HubInformation.HubDescriptor.bNumberOfPorts;
+	usbi_dbg(ctx, "root hub '%s' reports %lu ports", priv->dev_id, ULONG_CAST(num_ports));
+
+	if (windows_version >= WINDOWS_8) {
+		// Windows 8 and later is better at reporting the speed capabilities of the root hub,
+		// but it is not perfect. If no device is attached to the port being queried, the
+		// returned information will only indicate whether that port supports USB 3.0 signalling.
+		// That is not enough information to distinguish between SuperSpeed and SuperSpeed Plus.
+		for (port_number = 1; port_number <= num_ports; port_number++) {
+			conn_info_v2.ConnectionIndex = port_number;
+			conn_info_v2.Length = sizeof(conn_info_v2);
+			conn_info_v2.SupportedUsbProtocols.Usb300 = 1;
+			if (!DeviceIoControl(handle, IOCTL_USB_GET_NODE_CONNECTION_INFORMATION_EX_V2,
+				&conn_info_v2, sizeof(conn_info_v2), &conn_info_v2, sizeof(conn_info_v2), &size, NULL)) {
+				usbi_warn(ctx, "could not get node connection information (V2) for root hub '%s' port %lu: %s",
+					priv->dev_id, ULONG_CAST(port_number), windows_error_str(0));
+				break;
+			}
+
+			if (conn_info_v2.Flags.DeviceIsSuperSpeedPlusCapableOrHigher)
+				speed = MAX(speed, LIBUSB_SPEED_SUPER_PLUS);
+			else if (conn_info_v2.Flags.DeviceIsSuperSpeedCapableOrHigher || conn_info_v2.SupportedUsbProtocols.Usb300)
+				speed = MAX(speed, LIBUSB_SPEED_SUPER);
+			else if (conn_info_v2.SupportedUsbProtocols.Usb200)
+				speed = MAX(speed, LIBUSB_SPEED_HIGH);
+			else
+				speed = MAX(speed, LIBUSB_SPEED_FULL);
+		}
+
+		if (speed != LIBUSB_SPEED_UNKNOWN)
+			goto make_descriptors;
+	}
+
+	// At this point the speed is still not known, most likely because we are executing on
+	// Windows 7 or earlier. The following hackery peeks into the root hub's Device ID and
+	// tries to extract speed information from it, based on observed naming conventions.
+	// If this does not work, we will query individual ports of the root hub.
+	if (strstr(priv->dev_id, "ROOT_HUB31") != NULL)
+		speed = LIBUSB_SPEED_SUPER_PLUS;
+	else if (strstr(priv->dev_id, "ROOT_HUB30") != NULL)
+		speed = LIBUSB_SPEED_SUPER;
+	else if (strstr(priv->dev_id, "ROOT_HUB20") != NULL)
+		speed = LIBUSB_SPEED_HIGH;
+
+	if (speed != LIBUSB_SPEED_UNKNOWN)
+		goto make_descriptors;
+
+	// Windows only reports speed information about a connected device. This means that a root
+	// hub with no connected devices or devices that are all operating at a speed less than the
+	// highest speed that the root hub supports will not give us the correct speed.
+	for (port_number = 1; port_number <= num_ports; port_number++) {
+		conn_info.ConnectionIndex = port_number;
+		if (!DeviceIoControl(handle, IOCTL_USB_GET_NODE_CONNECTION_INFORMATION_EX, &conn_info, sizeof(conn_info),
+			&conn_info, sizeof(conn_info), &size, NULL)) {
+			usbi_warn(ctx, "could not get node connection information for root hub '%s' port %lu: %s",
+				priv->dev_id, ULONG_CAST(port_number), windows_error_str(0));
+			continue;
+		}
+
+		if (conn_info.ConnectionStatus != DeviceConnected)
+			continue;
+
+		if (conn_info.Speed == UsbHighSpeed) {
+			speed = LIBUSB_SPEED_HIGH;
+			break;
+		}
+	}
+
+make_descriptors:
+	CloseHandle(handle);
+
+	dev->device_descriptor.bLength = LIBUSB_DT_DEVICE_SIZE;
+	dev->device_descriptor.bDescriptorType = LIBUSB_DT_DEVICE;
+	dev->device_descriptor.bDeviceClass = LIBUSB_CLASS_HUB;
+	if ((dev->device_descriptor.idVendor == 0) && (dev->device_descriptor.idProduct == 0)) {
+		dev->device_descriptor.idVendor = 0x1d6b;	// Linux Foundation
+		dev->device_descriptor.idProduct = (uint16_t)speed;
+	}
+	dev->device_descriptor.bcdDevice = 0x0100;
+	dev->device_descriptor.bNumConfigurations = 1;
+
+	switch (speed) {
+	case LIBUSB_SPEED_SUPER_PLUS:
+		dev->device_descriptor.bcdUSB = 0x0310;
+		config_desc_length = ROOT_HUB_SS_CONFIG_DESC_LENGTH;
+		ep_interval = 0x0c;	// 256ms
+		break;
+	case LIBUSB_SPEED_SUPER:
+		dev->device_descriptor.bcdUSB = 0x0300;
+		config_desc_length = ROOT_HUB_SS_CONFIG_DESC_LENGTH;
+		ep_interval = 0x0c;	// 256ms
+		break;
+	case LIBUSB_SPEED_HIGH:
+		dev->device_descriptor.bcdUSB = 0x0200;
+		config_desc_length = ROOT_HUB_HS_CONFIG_DESC_LENGTH;
+		ep_interval = 0x0c;	// 256ms
+		break;
+	case LIBUSB_SPEED_LOW:		// Not used, but keeps compiler happy
+	case LIBUSB_SPEED_UNKNOWN:
+		// This case means absolutely no information about this root hub was determined.
+		// There is not much choice than to be pessimistic and label this as a
+		// full-speed device.
+		speed = LIBUSB_SPEED_FULL;
+		// fallthrough
+	case LIBUSB_SPEED_FULL:
+		dev->device_descriptor.bcdUSB = 0x0110;
+		config_desc_length = ROOT_HUB_FS_CONFIG_DESC_LENGTH;
+		ep_interval = 0xff;	// 255ms
+		break;
+	default:			// Impossible, buts keeps compiler happy
+		usbi_err(ctx, "program assertion failed - unknown root hub speed");
+		return LIBUSB_ERROR_INVALID_PARAM;
+	}
+
+	if (speed >= LIBUSB_SPEED_SUPER) {
+		dev->device_descriptor.bDeviceProtocol = 0x03;	// USB 3.0 Hub
+		dev->device_descriptor.bMaxPacketSize0 = 0x09;	// 2^9 bytes
+	} else {
+		dev->device_descriptor.bMaxPacketSize0 = 0x40;	// 64 bytes
+	}
+
+	dev->speed = speed;
+
+	r = alloc_root_hub_config_desc(dev, num_ports, config_desc_length, ep_interval);
+	if (r)
+		usbi_err(ctx, "could not allocate config descriptor for root hub '%s'", priv->dev_id);
+
+	return r;
+}
+
+/*
+ * Populate a libusb device structure
+ */
+static int init_device(struct libusb_device *dev, struct libusb_device *parent_dev,
+	uint8_t port_number, DEVINST devinst)
+{
+	struct libusb_context *ctx = NULL;
+	struct libusb_device *tmp_dev;
+	struct winusb_device_priv *priv, *parent_priv, *tmp_priv;
+	USB_NODE_CONNECTION_INFORMATION_EX conn_info;
+	USB_NODE_CONNECTION_INFORMATION_EX_V2 conn_info_v2;
+	HANDLE hub_handle;
+	DWORD size;
+	uint8_t bus_number, depth;
+	int r;
+	int ginfotimeout;
+
+	priv = usbi_get_device_priv(dev);
+
+	// If the device is already initialized, we can stop here
+	if (priv->initialized)
+		return LIBUSB_SUCCESS;
+
+	if (parent_dev != NULL) { // Not a HCD root hub
+		ctx = DEVICE_CTX(dev);
+		parent_priv = usbi_get_device_priv(parent_dev);
+		if (parent_priv->apib->id != USB_API_HUB) {
+			usbi_warn(ctx, "parent for device '%s' is not a hub", priv->dev_id);
+			return LIBUSB_ERROR_NOT_FOUND;
+		}
+
+		// Calculate depth and fetch bus number
+		bus_number = parent_dev->bus_number;
+		if (bus_number == 0) {
+			tmp_dev = get_ancestor(ctx, devinst, &devinst);
+			if (tmp_dev != parent_dev) {
+				usbi_err(ctx, "program assertion failed - first ancestor is not parent");
+				return LIBUSB_ERROR_NOT_FOUND;
+			}
+			libusb_unref_device(tmp_dev);
+
+			for (depth = 1; bus_number == 0; depth++) {
+				tmp_dev = get_ancestor(ctx, devinst, &devinst);
+				if (tmp_dev == NULL) {
+					usbi_warn(ctx, "ancestor for device '%s' not found at depth %u", priv->dev_id, depth);
+					return LIBUSB_ERROR_NO_DEVICE;
+				}
+				if (tmp_dev->bus_number != 0) {
+					bus_number = tmp_dev->bus_number;
+					tmp_priv = usbi_get_device_priv(tmp_dev);
+					depth += tmp_priv->depth;
+				}
+				libusb_unref_device(tmp_dev);
+			}
+		} else {
+			depth = parent_priv->depth + 1;
+		}
+
+		if (bus_number == 0) {
+			usbi_err(ctx, "program assertion failed - bus number not found for '%s'", priv->dev_id);
+			return LIBUSB_ERROR_NOT_FOUND;
+		}
+
+		dev->bus_number = bus_number;
+		dev->port_number = port_number;
+		dev->parent_dev = parent_dev;
+		priv->depth = depth;
+
+		hub_handle = CreateFileA(parent_priv->path, GENERIC_WRITE, FILE_SHARE_WRITE, NULL, OPEN_EXISTING, 0, NULL);
+		if (hub_handle == INVALID_HANDLE_VALUE) {
+			usbi_warn(ctx, "could not open hub %s: %s", parent_priv->path, windows_error_str(0));
+			return LIBUSB_ERROR_ACCESS;
+		}
+
+		conn_info.ConnectionIndex = (ULONG)port_number;
+		// coverity[tainted_data_argument]
+		ginfotimeout = 20;
+		do {
+			if (!DeviceIoControl(hub_handle, IOCTL_USB_GET_NODE_CONNECTION_INFORMATION_EX, &conn_info, sizeof(conn_info),
+				&conn_info, sizeof(conn_info), &size, NULL)) {
+				usbi_warn(ctx, "could not get node connection information for device '%s': %s",
+					priv->dev_id, windows_error_str(0));
+				CloseHandle(hub_handle);
+				return LIBUSB_ERROR_NO_DEVICE;
+			}
+
+			if (conn_info.ConnectionStatus == NoDeviceConnected) {
+				usbi_err(ctx, "device '%s' is no longer connected!", priv->dev_id);
+				CloseHandle(hub_handle);
+				return LIBUSB_ERROR_NO_DEVICE;
+			}
+
+			if ((conn_info.DeviceDescriptor.bLength != LIBUSB_DT_DEVICE_SIZE)
+				 || (conn_info.DeviceDescriptor.bDescriptorType != LIBUSB_DT_DEVICE)) {
+				SleepEx(50, TRUE);
+				continue;
+			}
+
+			static_assert(sizeof(dev->device_descriptor) == sizeof(conn_info.DeviceDescriptor),
+				      "mismatch between libusb and OS device descriptor sizes");
+			memcpy(&dev->device_descriptor, &conn_info.DeviceDescriptor, LIBUSB_DT_DEVICE_SIZE);
+			usbi_localize_device_descriptor(&dev->device_descriptor);
+
+			priv->active_config = conn_info.CurrentConfigurationValue;
+			if (priv->active_config == 0) {
+				usbi_dbg(ctx, "0x%x:0x%x found %u configurations (not configured)",
+					dev->device_descriptor.idVendor,
+					dev->device_descriptor.idProduct,
+					dev->device_descriptor.bNumConfigurations);
+				SleepEx(50, TRUE);
+			}
+		} while (priv->active_config == 0 && --ginfotimeout >= 0);
+
+		if ((conn_info.DeviceDescriptor.bLength != LIBUSB_DT_DEVICE_SIZE)
+			 || (conn_info.DeviceDescriptor.bDescriptorType != LIBUSB_DT_DEVICE)) {
+			usbi_err(ctx, "device '%s' has invalid descriptor!", priv->dev_id);
+			CloseHandle(hub_handle);
+			return LIBUSB_ERROR_OTHER;
+		}
+
+		if (priv->active_config == 0) {
+			usbi_info(ctx, "0x%x:0x%x found %u configurations but device isn't configured, "
+				"forcing current configuration to 1",
+				dev->device_descriptor.idVendor,
+				dev->device_descriptor.idProduct,
+				dev->device_descriptor.bNumConfigurations);
+			priv->active_config = 1;
+		} else {
+			usbi_dbg(ctx, "found %u configurations (current config: %u)", dev->device_descriptor.bNumConfigurations, priv->active_config);
+		}
+
+		// Cache as many config descriptors as we can
+		cache_config_descriptors(dev, hub_handle);
+
+		// In their great wisdom, Microsoft decided to BREAK the USB speed report between Windows 7 and Windows 8
+		if (windows_version >= WINDOWS_8) {
+			conn_info_v2.ConnectionIndex = (ULONG)port_number;
+			conn_info_v2.Length = sizeof(USB_NODE_CONNECTION_INFORMATION_EX_V2);
+			conn_info_v2.SupportedUsbProtocols.Usb300 = 1;
+			if (!DeviceIoControl(hub_handle, IOCTL_USB_GET_NODE_CONNECTION_INFORMATION_EX_V2,
+				&conn_info_v2, sizeof(conn_info_v2), &conn_info_v2, sizeof(conn_info_v2), &size, NULL)) {
+				usbi_warn(ctx, "could not get node connection information (V2) for device '%s': %s",
+					priv->dev_id,  windows_error_str(0));
+			} else if (conn_info_v2.Flags.DeviceIsOperatingAtSuperSpeedPlusOrHigher) {
+				conn_info.Speed = UsbSuperSpeedPlus;
+			} else if (conn_info_v2.Flags.DeviceIsOperatingAtSuperSpeedOrHigher) {
+				conn_info.Speed = UsbSuperSpeed;
+			}
+		}
+
+		CloseHandle(hub_handle);
+
+		if (conn_info.DeviceAddress > UINT8_MAX)
+			usbi_err(ctx, "program assertion failed - device address overflow");
+
+		dev->device_address = (uint8_t)conn_info.DeviceAddress;
+
+		switch (conn_info.Speed) {
+		case UsbLowSpeed: dev->speed = LIBUSB_SPEED_LOW; break;
+		case UsbFullSpeed: dev->speed = LIBUSB_SPEED_FULL; break;
+		case UsbHighSpeed: dev->speed = LIBUSB_SPEED_HIGH; break;
+		case UsbSuperSpeed: dev->speed = LIBUSB_SPEED_SUPER; break;
+		case UsbSuperSpeedPlus: dev->speed = LIBUSB_SPEED_SUPER_PLUS; break;
+		default:
+			usbi_warn(ctx, "unknown device speed %u", conn_info.Speed);
+			break;
+		}
+	} else {
+		r = init_root_hub(dev);
+		if (r)
+			return r;
+	}
+
+	r = usbi_sanitize_device(dev);
+	if (r)
+		return r;
+
+	priv->initialized = true;
+
+	usbi_dbg(ctx, "(bus: %u, addr: %u, depth: %u, port: %u): '%s'",
+		dev->bus_number, dev->device_address, priv->depth, dev->port_number, priv->dev_id);
+
+	return LIBUSB_SUCCESS;
+}
+
+static bool get_dev_port_number(HDEVINFO dev_info, SP_DEVINFO_DATA *dev_info_data, DWORD *port_nr)
+{
+	char buffer[MAX_KEY_LENGTH];
+	DWORD size;
+
+	// First try SPDRP_LOCATION_INFORMATION, which returns a REG_SZ. The string *may* have a format
+	// similar to "Port_#0002.Hub_#000D", in which case we can extract the port number. However, we
+	// cannot extract the port if the returned string does not follow this format.
+	if (pSetupDiGetDeviceRegistryPropertyA(dev_info, dev_info_data, SPDRP_LOCATION_INFORMATION,
+			NULL, (PBYTE)buffer, sizeof(buffer), NULL)) {
+		// Check for the required format.
+		if (strncmp(buffer, "Port_#", 6) == 0) {
+			*port_nr = atoi(buffer + 6);
+			return true;
+		}
+	}
+
+	// Next try SPDRP_LOCATION_PATHS, which returns a REG_MULTI_SZ (but we only examine the first
+	// string in it). Each path has a format similar to,
+	// "PCIROOT(B2)#PCI(0300)#PCI(0000)#USBROOT(0)#USB(1)#USB(2)#USBMI(3)", and the port number is
+	// the number within the last "USB(x)" token.
+	if (pSetupDiGetDeviceRegistryPropertyA(dev_info, dev_info_data, SPDRP_LOCATION_PATHS,
+			NULL, (PBYTE)buffer, sizeof(buffer), NULL)) {
+		// Find the last "#USB(x)" substring
+		for (char *token = strrchr(buffer, '#'); token != NULL; token = strrchr(buffer, '#')) {
+			if (strncmp(token, "#USB(", 5) == 0) {
+				*port_nr = atoi(token + 5);
+				return true;
+			}
+			// Shorten the string and try again.
+			*token = '\0';
+		}
+	}
+
+	// Lastly, try SPDRP_ADDRESS, which returns a REG_DWORD. The address *may* be the port number,
+	// which is true for the Microsoft driver but may not be true for other drivers. However, we
+	// have no other options here but to accept what it returns.
+	return pSetupDiGetDeviceRegistryPropertyA(dev_info, dev_info_data, SPDRP_ADDRESS,
+			NULL, (PBYTE)port_nr, sizeof(*port_nr), &size) && (size == sizeof(*port_nr));
+}
+
+static int enumerate_hcd_root_hub(struct libusb_context *ctx, const char *dev_id,
+	uint8_t bus_number, DEVINST devinst)
+{
+	struct libusb_device *dev;
+	struct winusb_device_priv *priv;
+	unsigned long session_id;
+	DEVINST child_devinst;
+
+	if (CM_Get_Child(&child_devinst, devinst, 0) != CR_SUCCESS) {
+		usbi_warn(ctx, "could not get child devinst for '%s'", dev_id);
+		return LIBUSB_SUCCESS;
+	}
+
+	session_id = (unsigned long)child_devinst;
+	dev = usbi_get_device_by_session_id(ctx, session_id);
+	if (dev == NULL) {
+		usbi_err(ctx, "program assertion failed - HCD '%s' child not found", dev_id);
+		return LIBUSB_SUCCESS;
+	}
+
+	if (dev->bus_number == 0) {
+		// Only do this once
+		usbi_dbg(ctx, "assigning HCD '%s' bus number %u", dev_id, bus_number);
+		dev->bus_number = bus_number;
+
+		if (sscanf(dev_id, "PCI\\VEN_%04hx&DEV_%04hx%*s", &dev->device_descriptor.idVendor, &dev->device_descriptor.idProduct) != 2)
+			usbi_warn(ctx, "could not infer VID/PID of HCD root hub from '%s'", dev_id);
+
+		priv = usbi_get_device_priv(dev);
+		priv->root_hub = true;
+	}
+
+	libusb_unref_device(dev);
+	return LIBUSB_SUCCESS;
+}
+
+// Returns the api type, or 0 if not found/unsupported
+static void get_api_type(HDEVINFO *dev_info, SP_DEVINFO_DATA *dev_info_data,
+	int *api, int *sub_api)
+{
+	// Precedence for filter drivers vs driver is in the order of this array
+	struct driver_lookup lookup[3] = {
+		{"\0\0", SPDRP_SERVICE, "driver"},
+		{"\0\0", SPDRP_UPPERFILTERS, "upper filter driver"},
+		{"\0\0", SPDRP_LOWERFILTERS, "lower filter driver"}
+	};
+	DWORD size, reg_type;
+	unsigned k, l;
+	int i, j;
+
+	// Check the service & filter names to know the API we should use
+	for (k = 0; k < 3; k++) {
+		if (pSetupDiGetDeviceRegistryPropertyA(*dev_info, dev_info_data, lookup[k].reg_prop,
+			&reg_type, (PBYTE)lookup[k].list, MAX_KEY_LENGTH, &size)) {
+			// Turn the REG_SZ SPDRP_SERVICE into REG_MULTI_SZ
+			if (lookup[k].reg_prop == SPDRP_SERVICE)
+				// our buffers are MAX_KEY_LENGTH + 1 so we can overflow if needed
+				lookup[k].list[strlen(lookup[k].list) + 1] = 0;
+
+			// MULTI_SZ is a pain to work with. Turn it into something much more manageable
+			// NB: none of the driver names we check against contain LIST_SEPARATOR,
+			// (currently ';'), so even if an unsupported one does, it's not an issue
+			for (l = 0; (lookup[k].list[l] != 0) || (lookup[k].list[l + 1] != 0); l++) {
+				if (lookup[k].list[l] == 0)
+					lookup[k].list[l] = LIST_SEPARATOR;
+			}
+			usbi_dbg(NULL, "%s(s): %s", lookup[k].designation, lookup[k].list);
+		} else {
+			if (GetLastError() != ERROR_INVALID_DATA)
+				usbi_dbg(NULL, "could not access %s: %s", lookup[k].designation, windows_error_str(0));
+			lookup[k].list[0] = 0;
+		}
+	}
+
+	for (i = 2; i < USB_API_MAX; i++) {
+		for (k = 0; k < 3; k++) {
+			j = get_sub_api(lookup[k].list, i);
+			if (j >= 0) {
+				usbi_dbg(NULL, "matched %s name against %s", lookup[k].designation,
+					(i != USB_API_WINUSBX) ? usb_api_backend[i].designation : usb_api_backend[i].driver_name_list[j]);
+				*api = i;
+				*sub_api = j;
+				return;
+			}
+		}
+	}
+}
+
+static int set_composite_interface(struct libusb_context *ctx, struct libusb_device *dev,
+	char *dev_interface_path, char *device_id, int api, int sub_api)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev);
+	int interface_number;
+	const char *mi_str;
+
+	// Because MI_## are not necessarily in sequential order (some composite
+	// devices will have only MI_00 & MI_03 for instance), we retrieve the actual
+	// interface number from the path's MI value
+	mi_str = strstr(device_id, "MI_");
+	if ((mi_str != NULL) && isdigit((unsigned char)mi_str[3]) && isdigit((unsigned char)mi_str[4])) {
+		interface_number = ((mi_str[3] - '0') * 10) + (mi_str[4] - '0');
+	} else {
+		usbi_warn(ctx, "failure to read interface number for %s, using default value", device_id);
+		interface_number = 0;
+	}
+
+	if (interface_number >= USB_MAXINTERFACES) {
+		usbi_warn(ctx, "interface %d too large - ignoring interface path %s", interface_number, dev_interface_path);
+		return LIBUSB_ERROR_ACCESS;
+	}
+
+	if (priv->usb_interface[interface_number].path != NULL) {
+		if (api == USB_API_HID) {
+			// HID devices can have multiple collections (COL##) for each MI_## interface
+			usbi_dbg(ctx, "interface[%d] already set - ignoring HID collection: %s",
+				interface_number, device_id);
+			return LIBUSB_ERROR_ACCESS;
+		}
+		// In other cases, just use the latest data
+		safe_free(priv->usb_interface[interface_number].path);
+	}
+
+	usbi_dbg(ctx, "interface[%d] = %s", interface_number, dev_interface_path);
+	priv->usb_interface[interface_number].path = dev_interface_path;
+	priv->usb_interface[interface_number].apib = &usb_api_backend[api];
+	priv->usb_interface[interface_number].sub_api = sub_api;
+	if ((api == USB_API_HID) && (priv->hid == NULL)) {
+		priv->hid = calloc(1, sizeof(struct hid_device_priv));
+		if (priv->hid == NULL)
+			return LIBUSB_ERROR_NO_MEM;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int set_hid_interface(struct libusb_context *ctx, struct libusb_device *dev,
+	char *dev_interface_path)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev);
+	uint8_t i;
+
+	if (priv->hid == NULL) {
+		usbi_err(ctx, "program assertion failed - parent is not HID");
+		return LIBUSB_ERROR_NO_DEVICE;
+	} else if (priv->hid->nb_interfaces == USB_MAXINTERFACES) {
+		usbi_err(ctx, "program assertion failed - max USB interfaces reached for HID device");
+		return LIBUSB_ERROR_NO_DEVICE;
+	}
+
+	for (i = 0; i < priv->hid->nb_interfaces; i++) {
+		if ((priv->usb_interface[i].path != NULL) && strcmp(priv->usb_interface[i].path, dev_interface_path) == 0) {
+			usbi_dbg(ctx, "interface[%u] already set to %s", i, dev_interface_path);
+			return LIBUSB_ERROR_ACCESS;
+		}
+	}
+
+	priv->usb_interface[priv->hid->nb_interfaces].path = dev_interface_path;
+	priv->usb_interface[priv->hid->nb_interfaces].apib = &usb_api_backend[USB_API_HID];
+	usbi_dbg(ctx, "interface[%u] = %s", priv->hid->nb_interfaces, dev_interface_path);
+	priv->hid->nb_interfaces++;
+	return LIBUSB_SUCCESS;
+}
+
+/*
+ * get_device_list: libusb backend device enumeration function
+ */
+static int winusb_get_device_list(struct libusb_context *ctx, struct discovered_devs **_discdevs)
+{
+	struct discovered_devs *discdevs;
+	HDEVINFO *dev_info, dev_info_intf, dev_info_enum;
+	SP_DEVINFO_DATA dev_info_data;
+	DWORD _index = 0;
+	GUID hid_guid;
+	int r = LIBUSB_SUCCESS;
+	int api, sub_api;
+	unsigned int pass, i, j;
+	char enumerator[16];
+	char dev_id[MAX_PATH_LENGTH];
+	struct libusb_device *dev, *parent_dev;
+	struct winusb_device_priv *priv, *parent_priv;
+	char *dev_interface_path = NULL;
+	unsigned long session_id;
+	DWORD size, port_nr, reg_type, install_state;
+	HKEY key;
+	char guid_string[MAX_GUID_STRING_LENGTH];
+	GUID *if_guid;
+	LONG s;
+#define HUB_PASS 0
+#define DEV_PASS 1
+#define HCD_PASS 2
+#define GEN_PASS 3
+#define HID_PASS 4
+#define EXT_PASS 5
+	// Keep a list of guids that will be enumerated
+#define GUID_SIZE_STEP 8
+	const GUID **guid_list, **new_guid_list;
+	unsigned int guid_size = GUID_SIZE_STEP;
+	unsigned int nb_guids;
+	// Keep a list of PnP enumerator strings that are found
+	const char *usb_enumerator[8] = { "USB" };
+	unsigned int nb_usb_enumerators = 1;
+	unsigned int usb_enum_index = 0;
+	// Keep a list of newly allocated devs to unref
+#define UNREF_SIZE_STEP 16
+	libusb_device **unref_list, **new_unref_list;
+	unsigned int unref_size = UNREF_SIZE_STEP;
+	unsigned int unref_cur = 0;
+
+	// PASS 1 : (re)enumerate HCDs (allows for HCD hotplug)
+	// PASS 2 : (re)enumerate HUBS
+	// PASS 3 : (re)enumerate generic USB devices (including driverless)
+	//           and list additional USB device interface GUIDs to explore
+	// PASS 4 : (re)enumerate master USB devices that have a device interface
+	// PASS 5+: (re)enumerate device interfaced GUIDs (including HID) and
+	//           set the device interfaces.
+
+	// Init the GUID table
+	guid_list = malloc(guid_size * sizeof(void *));
+	if (guid_list == NULL) {
+		usbi_err(ctx, "failed to alloc guid list");
+		return LIBUSB_ERROR_NO_MEM;
+	}
+
+	guid_list[HUB_PASS] = &GUID_DEVINTERFACE_USB_HUB;
+	guid_list[DEV_PASS] = &GUID_DEVINTERFACE_USB_DEVICE;
+	guid_list[HCD_PASS] = &GUID_DEVINTERFACE_USB_HOST_CONTROLLER;
+	guid_list[GEN_PASS] = NULL;
+	if (HidD_GetHidGuid != NULL) {
+		HidD_GetHidGuid(&hid_guid);
+		guid_list[HID_PASS] = &hid_guid;
+	} else {
+		guid_list[HID_PASS] = NULL;
+	}
+	nb_guids = EXT_PASS;
+
+	unref_list = malloc(unref_size * sizeof(void *));
+	if (unref_list == NULL) {
+		usbi_err(ctx, "failed to alloc unref list");
+		free((void *)guid_list);
+		return LIBUSB_ERROR_NO_MEM;
+	}
+
+	dev_info_intf = pSetupDiGetClassDevsA(NULL, NULL, NULL, DIGCF_ALLCLASSES | DIGCF_PRESENT | DIGCF_DEVICEINTERFACE);
+	if (dev_info_intf == INVALID_HANDLE_VALUE) {
+		usbi_err(ctx, "failed to obtain device info list: %s", windows_error_str(0));
+		free(unref_list);
+		free((void *)guid_list);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	for (pass = 0; ((pass < nb_guids) && (r == LIBUSB_SUCCESS)); pass++) {
+//#define ENUM_DEBUG
+#if defined(ENABLE_LOGGING) && defined(ENUM_DEBUG)
+		const char * const passname[] = {"HUB", "DEV", "HCD", "GEN", "HID", "EXT"};
+		usbi_dbg(ctx, "#### PROCESSING %ss %s", passname[MIN(pass, EXT_PASS)], guid_to_string(guid_list[pass], guid_string));
+#endif
+		if ((pass == HID_PASS) && (guid_list[HID_PASS] == NULL))
+			continue;
+
+		dev_info = (pass != GEN_PASS) ? &dev_info_intf : &dev_info_enum;
+
+		for (i = 0; ; i++) {
+			// safe loop: free up any (unprotected) dynamic resource
+			// NB: this is always executed before breaking the loop
+			safe_free(dev_interface_path);
+			priv = parent_priv = NULL;
+			dev = parent_dev = NULL;
+
+			// Safe loop: end of loop conditions
+			if (r != LIBUSB_SUCCESS)
+				break;
+
+			if ((pass == HCD_PASS) && (i == UINT8_MAX)) {
+				usbi_warn(ctx, "program assertion failed - found more than %u buses, skipping the rest", UINT8_MAX);
+				break;
+			}
+
+			if (pass != GEN_PASS) {
+				// Except for GEN, all passes deal with device interfaces
+				r = get_interface_details(ctx, *dev_info, &dev_info_data, guid_list[pass], &_index, &dev_interface_path);
+				if ((r != LIBUSB_SUCCESS) || (dev_interface_path == NULL)) {
+					_index = 0;
+					break;
+				}
+			} else {
+				// Workaround for a Nec/Renesas USB 3.0 driver bug where root hubs are
+				// being listed under the "NUSB3" PnP Symbolic Name rather than "USB".
+				// The Intel USB 3.0 driver behaves similar, but uses "IUSB3"
+				// The Intel Alpine Ridge USB 3.1 driver uses "IARUSB3"
+				for (; usb_enum_index < nb_usb_enumerators; usb_enum_index++) {
+					if (get_devinfo_data(ctx, dev_info, &dev_info_data, usb_enumerator[usb_enum_index], i))
+						break;
+					i = 0;
+				}
+				if (usb_enum_index == nb_usb_enumerators)
+					break;
+			}
+
+			// Read the Device ID path
+			if (!pSetupDiGetDeviceInstanceIdA(*dev_info, &dev_info_data, dev_id, sizeof(dev_id), NULL)) {
+				usbi_warn(ctx, "could not read the device instance ID for devInst %lX, skipping",
+					  ULONG_CAST(dev_info_data.DevInst));
+				continue;
+			}
+
+#ifdef ENUM_DEBUG
+			usbi_dbg(ctx, "PRO: %s", dev_id);
+#endif
+
+			// Set API to use or get additional data from generic pass
+			api = USB_API_UNSUPPORTED;
+			sub_api = SUB_API_NOTSET;
+			switch (pass) {
+			case HCD_PASS:
+				break;
+			case HUB_PASS:
+				api = USB_API_HUB;
+				// Fetch the PnP enumerator class for this hub
+				// This will allow us to enumerate all classes during the GEN pass
+				if (!pSetupDiGetDeviceRegistryPropertyA(*dev_info, &dev_info_data, SPDRP_ENUMERATOR_NAME,
+					NULL, (PBYTE)enumerator, sizeof(enumerator), NULL)) {
+					usbi_err(ctx, "could not read enumerator string for device '%s': %s", dev_id, windows_error_str(0));
+					LOOP_BREAK(LIBUSB_ERROR_OTHER);
+				}
+				for (j = 0; j < nb_usb_enumerators; j++) {
+					if (strcmp(usb_enumerator[j], enumerator) == 0)
+						break;
+				}
+				if (j == nb_usb_enumerators) {
+					usbi_dbg(ctx, "found new PnP enumerator string '%s'", enumerator);
+					if (nb_usb_enumerators < ARRAYSIZE(usb_enumerator)) {
+						usb_enumerator[nb_usb_enumerators] = _strdup(enumerator);
+						if (usb_enumerator[nb_usb_enumerators] != NULL) {
+							nb_usb_enumerators++;
+						} else {
+							usbi_err(ctx, "could not allocate enumerator string '%s'", enumerator);
+							LOOP_BREAK(LIBUSB_ERROR_NO_MEM);
+						}
+					} else {
+						usbi_warn(ctx, "too many enumerator strings, some devices may not be accessible");
+					}
+				}
+				break;
+			case GEN_PASS:
+				// We use the GEN pass to detect driverless devices...
+				if (!pSetupDiGetDeviceRegistryPropertyA(*dev_info, &dev_info_data, SPDRP_DRIVER,
+					NULL, NULL, 0, NULL) && (GetLastError() != ERROR_INSUFFICIENT_BUFFER)) {
+					usbi_info(ctx, "The following device has no driver: '%s'", dev_id);
+					usbi_info(ctx, "libusb will not be able to access it");
+				}
+				// ...and to add the additional device interface GUIDs
+				key = pSetupDiOpenDevRegKey(*dev_info, &dev_info_data, DICS_FLAG_GLOBAL, 0, DIREG_DEV, KEY_READ);
+				if (key == INVALID_HANDLE_VALUE)
+					break;
+				// Look for both DeviceInterfaceGUIDs *and* DeviceInterfaceGUID, in that order
+				// If multiple GUIDs just process the first and ignore the others
+				size = sizeof(guid_string);
+				s = pRegQueryValueExA(key, "DeviceInterfaceGUIDs", NULL, &reg_type,
+					(LPBYTE)guid_string, &size);
+				if (s == ERROR_FILE_NOT_FOUND)
+					s = pRegQueryValueExA(key, "DeviceInterfaceGUID", NULL, &reg_type,
+						(LPBYTE)guid_string, &size);
+				pRegCloseKey(key);
+				if (s == ERROR_FILE_NOT_FOUND) {
+					break; /* no DeviceInterfaceGUID registered */
+				} else if (s != ERROR_SUCCESS && s != ERROR_MORE_DATA) {
+					usbi_warn(ctx, "unexpected error from pRegQueryValueExA for '%s'", dev_id);
+					break;
+				}
+				// https://docs.microsoft.com/en-us/windows/win32/api/winreg/nf-winreg-regqueryvalueexa#remarks
+				// - "string may not have been stored with the proper terminating null characters"
+				// - "Note that REG_MULTI_SZ strings could have two terminating null characters"
+			        if ((reg_type == REG_SZ && size >= sizeof(guid_string) - sizeof(char))
+				    || (reg_type == REG_MULTI_SZ && size >= sizeof(guid_string) - 2 * sizeof(char))) {
+					if (nb_guids == guid_size) {
+						new_guid_list = realloc((void *)guid_list, (guid_size + GUID_SIZE_STEP) * sizeof(void *));
+						if (new_guid_list == NULL) {
+							usbi_err(ctx, "failed to realloc guid list");
+							LOOP_BREAK(LIBUSB_ERROR_NO_MEM);
+						}
+						guid_list = new_guid_list;
+						guid_size += GUID_SIZE_STEP;
+					}
+					if_guid = malloc(sizeof(*if_guid));
+					if (if_guid == NULL) {
+						usbi_err(ctx, "failed to alloc if_guid");
+						LOOP_BREAK(LIBUSB_ERROR_NO_MEM);
+					}
+					if (!string_to_guid(guid_string, if_guid)) {
+						usbi_warn(ctx, "device '%s' has malformed DeviceInterfaceGUID string '%s', skipping", dev_id, guid_string);
+						free(if_guid);
+					} else {
+						// Check if we've already seen this GUID
+						for (j = EXT_PASS; j < nb_guids; j++) {
+							if (memcmp(guid_list[j], if_guid, sizeof(*if_guid)) == 0)
+								break;
+						}
+						if (j == nb_guids) {
+							usbi_dbg(ctx, "extra GUID: %s", guid_string);
+							guid_list[nb_guids++] = if_guid;
+						} else {
+							// Duplicate, ignore
+							free(if_guid);
+						}
+					}
+				} else {
+					usbi_warn(ctx, "unexpected type/size of DeviceInterfaceGUID for '%s'", dev_id);
+				}
+				break;
+			case HID_PASS:
+				api = USB_API_HID;
+				break;
+			default:
+				// Get the API type (after checking that the driver installation is OK)
+				if ((!pSetupDiGetDeviceRegistryPropertyA(*dev_info, &dev_info_data, SPDRP_INSTALL_STATE,
+					NULL, (PBYTE)&install_state, sizeof(install_state), &size)) || (size != sizeof(install_state))) {
+					usbi_warn(ctx, "could not detect installation state of driver for '%s': %s",
+						dev_id, windows_error_str(0));
+				} else if (install_state != 0) {
+					usbi_warn(ctx, "driver for device '%s' is reporting an issue (code: %lu) - skipping",
+						dev_id, ULONG_CAST(install_state));
+					continue;
+				}
+				get_api_type(dev_info, &dev_info_data, &api, &sub_api);
+				break;
+			}
+
+			// Find parent device (for the passes that need it)
+			if (pass >= GEN_PASS) {
+				parent_dev = get_ancestor(ctx, dev_info_data.DevInst, NULL);
+				if (parent_dev == NULL) {
+					// Root hubs will not have a parent
+					dev = usbi_get_device_by_session_id(ctx, (unsigned long)dev_info_data.DevInst);
+					if (dev != NULL) {
+						priv = usbi_get_device_priv(dev);
+						if (priv->root_hub)
+							goto track_unref;
+						libusb_unref_device(dev);
+					}
+
+					usbi_dbg(ctx, "unlisted ancestor for '%s' (non USB HID, newly connected, etc.) - ignoring", dev_id);
+					continue;
+				}
+
+				parent_priv = usbi_get_device_priv(parent_dev);
+				// virtual USB devices are also listed during GEN - don't process these yet
+				if ((pass == GEN_PASS) && (parent_priv->apib->id != USB_API_HUB)) {
+					libusb_unref_device(parent_dev);
+					continue;
+				}
+			}
+
+			// Create new or match existing device, using the devInst as session id
+			if ((pass <= GEN_PASS) && (pass != HCD_PASS)) {	// For subsequent passes, we'll lookup the parent
+				// These are the passes that create "new" devices
+				session_id = (unsigned long)dev_info_data.DevInst;
+				dev = usbi_get_device_by_session_id(ctx, session_id);
+				if (dev == NULL) {
+				alloc_device:
+					usbi_dbg(ctx, "allocating new device for session [%lX]", session_id);
+					dev = usbi_alloc_device(ctx, session_id);
+					if (dev == NULL)
+						LOOP_BREAK(LIBUSB_ERROR_NO_MEM);
+
+					priv = winusb_device_priv_init(dev);
+					priv->dev_id = _strdup(dev_id);
+					priv->class_guid = dev_info_data.ClassGuid;
+					if (priv->dev_id == NULL) {
+						libusb_unref_device(dev);
+						LOOP_BREAK(LIBUSB_ERROR_NO_MEM);
+					}
+				} else {
+					usbi_dbg(ctx, "found existing device for session [%lX]", session_id);
+
+					priv = usbi_get_device_priv(dev);
+					if (strcmp(priv->dev_id, dev_id) != 0) {
+						usbi_dbg(ctx, "device instance ID for session [%lX] changed", session_id);
+						usbi_disconnect_device(dev);
+						libusb_unref_device(dev);
+						goto alloc_device;
+					}
+					if (!IsEqualGUID(&priv->class_guid, &dev_info_data.ClassGuid)) {
+						usbi_dbg(ctx, "device class GUID for session [%lX] changed", session_id);
+						usbi_disconnect_device(dev);
+						libusb_unref_device(dev);
+						goto alloc_device;
+					}
+				}
+
+			track_unref:
+				// Keep track of devices that need unref
+				if (unref_cur == unref_size) {
+					new_unref_list = realloc(unref_list, (unref_size + UNREF_SIZE_STEP) * sizeof(void *));
+					if (new_unref_list == NULL) {
+						usbi_err(ctx, "could not realloc list for unref - aborting");
+						LOOP_BREAK(LIBUSB_ERROR_NO_MEM);
+					}
+					unref_list = new_unref_list;
+					unref_size += UNREF_SIZE_STEP;
+				}
+				unref_list[unref_cur++] = dev;
+			}
+
+			// Setup device
+			switch (pass) {
+			case HUB_PASS:
+			case DEV_PASS:
+				// If the device has already been setup, don't do it again
+				if (priv->path != NULL)
+					break;
+				// Take care of API initialization
+				priv->path = dev_interface_path;
+				dev_interface_path = NULL;
+				priv->apib = &usb_api_backend[api];
+				priv->sub_api = sub_api;
+				switch (api) {
+				case USB_API_COMPOSITE:
+				case USB_API_HUB:
+					break;
+				case USB_API_HID:
+					priv->hid = calloc(1, sizeof(struct hid_device_priv));
+					if (priv->hid == NULL)
+						LOOP_BREAK(LIBUSB_ERROR_NO_MEM);
+					break;
+				default:
+					// For other devices, the first interface is the same as the device
+					priv->usb_interface[0].path = _strdup(priv->path);
+					if (priv->usb_interface[0].path == NULL)
+						LOOP_BREAK(LIBUSB_ERROR_NO_MEM);
+					// The following is needed if we want API calls to work for both simple
+					// and composite devices.
+					for (j = 0; j < USB_MAXINTERFACES; j++)
+						priv->usb_interface[j].apib = &usb_api_backend[api];
+					break;
+				}
+				break;
+			case HCD_PASS:
+				r = enumerate_hcd_root_hub(ctx, dev_id, (uint8_t)(i + 1), dev_info_data.DevInst);
+				break;
+			case GEN_PASS:
+				port_nr = 0;
+				if (!get_dev_port_number(*dev_info, &dev_info_data, &port_nr))
+					usbi_warn(ctx, "could not retrieve port number for device '%s': %s", dev_id, windows_error_str(0));
+				r = init_device(dev, parent_dev, (uint8_t)port_nr, dev_info_data.DevInst);
+				if (r == LIBUSB_SUCCESS) {
+					// Append device to the list of discovered devices
+					discdevs = discovered_devs_append(*_discdevs, dev);
+					if (!discdevs)
+						LOOP_BREAK(LIBUSB_ERROR_NO_MEM);
+
+					*_discdevs = discdevs;
+				} else {
+					// Failed to initialize a single device doesn't stop us from enumerating all other devices,
+					// but we skip it (don't add to list of discovered devices)
+					usbi_warn(ctx, "failed to initialize device '%s'", priv->dev_id);
+					r = LIBUSB_SUCCESS;
+				}
+				break;
+			default: // HID_PASS and later
+				if (parent_priv->apib->id == USB_API_HID || parent_priv->apib->id == USB_API_COMPOSITE) {
+					if (parent_priv->apib->id == USB_API_HID) {
+						usbi_dbg(ctx, "setting HID interface for [%lX]:", parent_dev->session_data);
+						r = set_hid_interface(ctx, parent_dev, dev_interface_path);
+					} else {
+						usbi_dbg(ctx, "setting composite interface for [%lX]:", parent_dev->session_data);
+						r = set_composite_interface(ctx, parent_dev, dev_interface_path, dev_id, api, sub_api);
+					}
+					switch (r) {
+					case LIBUSB_SUCCESS:
+						dev_interface_path = NULL;
+						break;
+					case LIBUSB_ERROR_ACCESS:
+						// interface has already been set => make sure dev_interface_path is freed then
+						r = LIBUSB_SUCCESS;
+						break;
+					default:
+						LOOP_BREAK(r);
+						break;
+					}
+				}
+				libusb_unref_device(parent_dev);
+				break;
+			}
+		}
+	}
+
+	pSetupDiDestroyDeviceInfoList(dev_info_intf);
+
+	// Free any additional GUIDs
+	for (pass = EXT_PASS; pass < nb_guids; pass++)
+		free((void *)guid_list[pass]);
+	free((void *)guid_list);
+
+	// Free any PnP enumerator strings
+	for (i = 1; i < nb_usb_enumerators; i++)
+		free((void *)usb_enumerator[i]);
+
+	// Unref newly allocated devs
+	for (i = 0; i < unref_cur; i++)
+		libusb_unref_device(unref_list[i]);
+	free(unref_list);
+
+	return r;
+}
+
+static int winusb_get_config_descriptor(struct libusb_device *dev, uint8_t config_index, void *buffer, size_t len)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev);
+	PUSB_CONFIGURATION_DESCRIPTOR config_header;
+
+	if ((priv->config_descriptor == NULL) || (priv->config_descriptor[config_index] == NULL))
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	config_header = priv->config_descriptor[config_index];
+
+	len = MIN(len, config_header->wTotalLength);
+	memcpy(buffer, config_header, len);
+	return (int)len;
+}
+
+static int winusb_get_config_descriptor_by_value(struct libusb_device *dev, uint8_t bConfigurationValue,
+	void **buffer)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev);
+	PUSB_CONFIGURATION_DESCRIPTOR config_header;
+	uint8_t index;
+
+	if (priv->config_descriptor == NULL)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	for (index = 0; index < dev->device_descriptor.bNumConfigurations; index++) {
+		config_header = priv->config_descriptor[index];
+		if (config_header == NULL)
+			continue;
+		if (config_header->bConfigurationValue == bConfigurationValue) {
+			*buffer = config_header;
+			return (int)config_header->wTotalLength;
+		}
+	}
+
+	return LIBUSB_ERROR_NOT_FOUND;
+}
+
+/*
+ * return the cached copy of the active config descriptor
+ */
+static int winusb_get_active_config_descriptor(struct libusb_device *dev, void *buffer, size_t len)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev);
+	void *config_desc;
+	int r;
+
+	if (priv->active_config == 0)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	r = winusb_get_config_descriptor_by_value(dev, priv->active_config, &config_desc);
+	if (r < 0)
+		return r;
+
+	len = MIN(len, (size_t)r);
+	memcpy(buffer, config_desc, len);
+	return (int)len;
+}
+
+static int winusb_open(struct libusb_device_handle *dev_handle)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	CHECK_SUPPORTED_API(priv->apib, open);
+
+	return priv->apib->open(SUB_API_NOTSET, dev_handle);
+}
+
+static void winusb_close(struct libusb_device_handle *dev_handle)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	if (priv->apib->close)
+		priv->apib->close(SUB_API_NOTSET, dev_handle);
+}
+
+static int winusb_get_configuration(struct libusb_device_handle *dev_handle, uint8_t *config)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	*config = priv->active_config;
+	return LIBUSB_SUCCESS;
+}
+
+/*
+ * from http://msdn.microsoft.com/en-us/library/ms793522.aspx: "The port driver
+ * does not currently expose a service that allows higher-level drivers to set
+ * the configuration."
+ */
+static int winusb_set_configuration(struct libusb_device_handle *dev_handle, uint8_t config)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	int r = LIBUSB_SUCCESS;
+
+	r = libusb_control_transfer(dev_handle, LIBUSB_ENDPOINT_OUT |
+		LIBUSB_REQUEST_TYPE_STANDARD | LIBUSB_RECIPIENT_DEVICE,
+		LIBUSB_REQUEST_SET_CONFIGURATION, config,
+		0, NULL, 0, 1000);
+
+	if (r == LIBUSB_SUCCESS)
+		priv->active_config = config;
+
+	return r;
+}
+
+static int winusb_claim_interface(struct libusb_device_handle *dev_handle, uint8_t iface)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	int r;
+
+	CHECK_SUPPORTED_API(priv->apib, claim_interface);
+
+	safe_free(priv->usb_interface[iface].endpoint);
+	priv->usb_interface[iface].nb_endpoints = 0;
+
+	r = priv->apib->claim_interface(SUB_API_NOTSET, dev_handle, iface);
+
+	if (r == LIBUSB_SUCCESS)
+		r = windows_assign_endpoints(dev_handle, iface, 0);
+
+	return r;
+}
+
+static int winusb_set_interface_altsetting(struct libusb_device_handle *dev_handle, uint8_t iface, uint8_t altsetting)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	int r;
+
+	CHECK_SUPPORTED_API(priv->apib, set_interface_altsetting);
+
+	safe_free(priv->usb_interface[iface].endpoint);
+	priv->usb_interface[iface].nb_endpoints = 0;
+
+	r = priv->apib->set_interface_altsetting(SUB_API_NOTSET, dev_handle, iface, altsetting);
+
+	if (r == LIBUSB_SUCCESS)
+		r = windows_assign_endpoints(dev_handle, iface, altsetting);
+
+	return r;
+}
+
+static int winusb_release_interface(struct libusb_device_handle *dev_handle, uint8_t iface)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	CHECK_SUPPORTED_API(priv->apib, release_interface);
+
+	return priv->apib->release_interface(SUB_API_NOTSET, dev_handle, iface);
+}
+
+static int winusb_clear_halt(struct libusb_device_handle *dev_handle, unsigned char endpoint)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	CHECK_SUPPORTED_API(priv->apib, clear_halt);
+
+	return priv->apib->clear_halt(SUB_API_NOTSET, dev_handle, endpoint);
+}
+
+static int winusb_reset_device(struct libusb_device_handle *dev_handle)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	CHECK_SUPPORTED_API(priv->apib, reset_device);
+
+	return priv->apib->reset_device(SUB_API_NOTSET, dev_handle);
+}
+
+static void winusb_destroy_device(struct libusb_device *dev)
+{
+	winusb_device_priv_release(dev);
+}
+
+static void winusb_clear_transfer_priv(struct usbi_transfer *itransfer)
+{
+	struct winusb_transfer_priv *transfer_priv = get_winusb_transfer_priv(itransfer);
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	int sub_api = priv->sub_api;
+
+	safe_free(transfer_priv->hid_buffer);
+
+	if (transfer->type == LIBUSB_TRANSFER_TYPE_ISOCHRONOUS && sub_api == SUB_API_WINUSB) {
+		if (transfer_priv->isoch_buffer_handle != NULL) {
+			if (WinUSBX[sub_api].UnregisterIsochBuffer(transfer_priv->isoch_buffer_handle)) {
+				transfer_priv->isoch_buffer_handle = NULL;
+			} else {
+				usbi_warn(TRANSFER_CTX(transfer), "failed to unregister WinUSB isoch buffer: %s", windows_error_str(0));
+			}
+		}
+	}
+
+	safe_free(transfer_priv->iso_context);
+
+	// When auto claim is in use, attempt to release the auto-claimed interface
+	auto_release(itransfer);
+}
+
+static int winusb_submit_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	int (*transfer_fn)(int, struct usbi_transfer *);
+
+	switch (transfer->type) {
+	case LIBUSB_TRANSFER_TYPE_CONTROL:
+		transfer_fn = priv->apib->submit_control_transfer;
+		break;
+	case LIBUSB_TRANSFER_TYPE_BULK:
+	case LIBUSB_TRANSFER_TYPE_INTERRUPT:
+		transfer_fn = priv->apib->submit_bulk_transfer;
+		break;
+	case LIBUSB_TRANSFER_TYPE_ISOCHRONOUS:
+		transfer_fn = priv->apib->submit_iso_transfer;
+		break;
+	default:
+		// Should not get here since windows_submit_transfer() validates
+		// the transfer->type field
+		usbi_err(TRANSFER_CTX(transfer), "unknown endpoint type %d", transfer->type);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	}
+
+	if (transfer_fn == NULL) {
+		usbi_warn(TRANSFER_CTX(transfer),
+			"unsupported transfer type %d (unrecognized device driver)",
+			transfer->type);
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+	}
+
+	return transfer_fn(SUB_API_NOTSET, itransfer);
+}
+
+static int winusb_cancel_transfer(struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+
+	CHECK_SUPPORTED_API(priv->apib, cancel_transfer);
+
+	return priv->apib->cancel_transfer(SUB_API_NOTSET, itransfer);
+}
+
+static enum libusb_transfer_status winusb_copy_transfer_data(struct usbi_transfer *itransfer, DWORD length)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+
+	if (priv->apib->copy_transfer_data == NULL) {
+		usbi_err(TRANSFER_CTX(transfer), "program assertion failed - no function to copy transfer data");
+		return LIBUSB_TRANSFER_ERROR;
+	}
+
+	return priv->apib->copy_transfer_data(SUB_API_NOTSET, itransfer, length);
+}
+
+// NB: MSVC6 does not support named initializers.
+const struct windows_backend winusb_backend = {
+	winusb_init,
+	winusb_exit,
+	winusb_get_device_list,
+	winusb_open,
+	winusb_close,
+	winusb_get_active_config_descriptor,
+	winusb_get_config_descriptor,
+	winusb_get_config_descriptor_by_value,
+	winusb_get_configuration,
+	winusb_set_configuration,
+	winusb_claim_interface,
+	winusb_release_interface,
+	winusb_set_interface_altsetting,
+	winusb_clear_halt,
+	winusb_reset_device,
+	winusb_destroy_device,
+	winusb_submit_transfer,
+	winusb_cancel_transfer,
+	winusb_clear_transfer_priv,
+	winusb_copy_transfer_data,
+};
+
+/*
+ * USB API backends
+ */
+
+static const char * const composite_driver_names[] = {"USBCCGP"};
+static const char * const winusbx_driver_names[] = {"libusbK", "libusb0", "WinUSB"};
+static const char * const hid_driver_names[] = {"HIDUSB", "MOUHID", "KBDHID"};
+const struct windows_usb_api_backend usb_api_backend[USB_API_MAX] = {
+	{
+		USB_API_UNSUPPORTED,
+		"Unsupported API",
+		NULL,	/* driver_name_list */
+		0,	/* nb_driver_names */
+		NULL,	/* init */
+		NULL,	/* exit */
+		NULL,	/* open */
+		NULL,	/* close */
+		NULL,	/* configure_endpoints */
+		NULL,	/* claim_interface */
+		NULL,	/* set_interface_altsetting */
+		NULL,	/* release_interface */
+		NULL,	/* clear_halt */
+		NULL,	/* reset_device */
+		NULL,	/* submit_bulk_transfer */
+		NULL,	/* submit_iso_transfer */
+		NULL,	/* submit_control_transfer */
+		NULL,	/* cancel_transfer */
+		NULL,	/* copy_transfer_data */
+	},
+	{
+		USB_API_HUB,
+		"HUB API",
+		NULL,	/* driver_name_list */
+		0,	/* nb_driver_names */
+		NULL,	/* init */
+		NULL,	/* exit */
+		NULL,	/* open */
+		NULL,	/* close */
+		NULL,	/* configure_endpoints */
+		NULL,	/* claim_interface */
+		NULL,	/* set_interface_altsetting */
+		NULL,	/* release_interface */
+		NULL,	/* clear_halt */
+		NULL,	/* reset_device */
+		NULL,	/* submit_bulk_transfer */
+		NULL,	/* submit_iso_transfer */
+		NULL,	/* submit_control_transfer */
+		NULL,	/* cancel_transfer */
+		NULL,	/* copy_transfer_data */
+	},
+	{
+		USB_API_COMPOSITE,
+		"Composite API",
+		composite_driver_names,
+		ARRAYSIZE(composite_driver_names),
+		NULL,	/* init */
+		NULL,	/* exit */
+		composite_open,
+		composite_close,
+		NULL,	/* configure_endpoints */
+		composite_claim_interface,
+		composite_set_interface_altsetting,
+		composite_release_interface,
+		composite_clear_halt,
+		composite_reset_device,
+		composite_submit_bulk_transfer,
+		composite_submit_iso_transfer,
+		composite_submit_control_transfer,
+		composite_cancel_transfer,
+		composite_copy_transfer_data,
+	},
+	{
+		USB_API_WINUSBX,
+		"WinUSB-like APIs",
+		winusbx_driver_names,
+		ARRAYSIZE(winusbx_driver_names),
+		winusbx_init,
+		winusbx_exit,
+		winusbx_open,
+		winusbx_close,
+		winusbx_configure_endpoints,
+		winusbx_claim_interface,
+		winusbx_set_interface_altsetting,
+		winusbx_release_interface,
+		winusbx_clear_halt,
+		winusbx_reset_device,
+		winusbx_submit_bulk_transfer,
+		winusbx_submit_iso_transfer,
+		winusbx_submit_control_transfer,
+		winusbx_cancel_transfer,
+		winusbx_copy_transfer_data,
+	},
+	{
+		USB_API_HID,
+		"HID API",
+		hid_driver_names,
+		ARRAYSIZE(hid_driver_names),
+		hid_init,
+		hid_exit,
+		hid_open,
+		hid_close,
+		NULL,	/* configure_endpoints */
+		hid_claim_interface,
+		hid_set_interface_altsetting,
+		hid_release_interface,
+		hid_clear_halt,
+		hid_reset_device,
+		hid_submit_bulk_transfer,
+		NULL,	/* submit_iso_transfer */
+		hid_submit_control_transfer,
+		NULL,	/* cancel_transfer */
+		hid_copy_transfer_data,
+	},
+};
+
+
+/*
+ * WinUSB-like (WinUSB, libusb0/libusbK through libusbk DLL) API functions
+ */
+#define WinUSB_Set(h, fn, required)										\
+	do {											\
+		WinUSBX[SUB_API_WINUSB].fn = (WinUsb_##fn##_t)GetProcAddress(h, "WinUsb_" #fn);	\
+		if (required && (WinUSBX[SUB_API_WINUSB].fn == NULL)) {				\
+			usbi_err(ctx, "GetProcAddress() failed for WinUsb_%s", #fn);		\
+			goto cleanup_winusb;							\
+		}										\
+	} while (0)
+
+#define libusbK_Set(sub_api, fn, required)								\
+	do {											\
+		pLibK_GetProcAddress((PVOID *)&WinUSBX[sub_api].fn, sub_api, KUSB_FNID_##fn);	\
+		if (required && (WinUSBX[sub_api].fn == NULL)) {				\
+			usbi_err(ctx, "LibK_GetProcAddress() failed for LibK_%s", #fn);		\
+			goto cleanup_libusbk;							\
+		}										\
+	} while (0)
+
+static bool winusbx_init(struct libusb_context *ctx)
+{
+	HMODULE hWinUSB, hlibusbK;
+
+	hWinUSB = load_system_library(ctx, "WinUSB");
+	if (hWinUSB != NULL) {
+		WinUSB_Set(hWinUSB, AbortPipe, true);
+		WinUSB_Set(hWinUSB, ControlTransfer, true);
+		WinUSB_Set(hWinUSB, FlushPipe, true);
+		WinUSB_Set(hWinUSB, Free, true);
+		WinUSB_Set(hWinUSB, GetAssociatedInterface, true);
+		WinUSB_Set(hWinUSB, Initialize, true);
+		WinUSB_Set(hWinUSB, ReadPipe, true);
+		WinUSB_Set(hWinUSB, ResetPipe, true);
+		WinUSB_Set(hWinUSB, SetCurrentAlternateSetting, true);
+		WinUSB_Set(hWinUSB, SetPipePolicy, true);
+		WinUSB_Set(hWinUSB, WritePipe, true);
+
+		// Check for isochronous transfers support (available starting with Windows 8.1)
+		WinUSB_Set(hWinUSB, ReadIsochPipeAsap, false);
+		if (WinUSBX[SUB_API_WINUSB].ReadIsochPipeAsap != NULL) {
+			WinUSB_Set(hWinUSB, QueryPipeEx, true);
+			WinUSB_Set(hWinUSB, RegisterIsochBuffer, true);
+			WinUSB_Set(hWinUSB, UnregisterIsochBuffer, true);
+			WinUSB_Set(hWinUSB, WriteIsochPipeAsap, true);
+		}
+
+		WinUSBX[SUB_API_WINUSB].hDll = hWinUSB;
+
+		usbi_info(ctx, "WinUSB DLL available (%s isoch support)",
+			(WinUSBX[SUB_API_WINUSB].ReadIsochPipeAsap != NULL) ? "with" : "without");
+
+cleanup_winusb:
+		if (WinUSBX[SUB_API_WINUSB].hDll == NULL) {
+			usbi_err(ctx, "failed to initialize WinUSB");
+			memset(&WinUSBX[SUB_API_WINUSB], 0, sizeof(WinUSBX[SUB_API_WINUSB]));
+			FreeLibrary(hWinUSB);
+			hWinUSB = NULL;
+		}
+	} else {
+		usbi_info(ctx, "WinUSB DLL is not available");
+	}
+
+	hlibusbK = load_system_library(ctx, "libusbK");
+	if (hlibusbK != NULL) {
+		LibK_GetVersion_t pLibK_GetVersion;
+		LibK_GetProcAddress_t pLibK_GetProcAddress;
+		int sub_api = 0;
+
+		pLibK_GetVersion = (LibK_GetVersion_t)GetProcAddress(hlibusbK, "LibK_GetVersion");
+		if (pLibK_GetVersion != NULL) {
+			KLIB_VERSION LibK_Version;
+
+			pLibK_GetVersion(&LibK_Version);
+			usbi_dbg(ctx, "libusbK DLL found, version: %d.%d.%d.%d", LibK_Version.Major, LibK_Version.Minor,
+				LibK_Version.Micro, LibK_Version.Nano);
+		} else {
+			usbi_dbg(ctx, "libusbK DLL found, version unknown");
+		}
+
+		pLibK_GetProcAddress = (LibK_GetProcAddress_t)GetProcAddress(hlibusbK, "LibK_GetProcAddress");
+		if (pLibK_GetProcAddress == NULL) {
+			usbi_err(ctx, "LibK_GetProcAddress() not found in libusbK DLL");
+			goto cleanup_libusbk;
+		}
+
+		// NB: The below for loop works because the sub_api value for WinUSB
+		// is a higher value than that of libusbK and libusb0
+		for (; sub_api < SUB_API_WINUSB; sub_api++) {
+			libusbK_Set(sub_api, AbortPipe, true);
+			libusbK_Set(sub_api, ControlTransfer, true);
+			libusbK_Set(sub_api, FlushPipe, true);
+			libusbK_Set(sub_api, Free, true);
+			libusbK_Set(sub_api, GetAssociatedInterface, true);
+			libusbK_Set(sub_api, Initialize, true);
+			libusbK_Set(sub_api, ReadPipe, true);
+			libusbK_Set(sub_api, ResetPipe, true);
+			libusbK_Set(sub_api, SetCurrentAlternateSetting, true);
+			libusbK_Set(sub_api, SetPipePolicy, true);
+			libusbK_Set(sub_api, WritePipe, true);
+
+			// Optional isochronous support
+			libusbK_Set(sub_api, IsoReadPipe, false);
+			if (WinUSBX[sub_api].IsoReadPipe != NULL)
+				libusbK_Set(sub_api, IsoWritePipe, true);
+
+			// Optional device reset support
+			libusbK_Set(sub_api, ResetDevice, false);
+
+			WinUSBX[sub_api].hDll = hlibusbK;
+		}
+
+cleanup_libusbk:
+		if (sub_api < SUB_API_WINUSB) {
+			usbi_err(ctx, "failed to initialize libusbK");
+			while (sub_api >= 0) {
+				memset(&WinUSBX[sub_api], 0, sizeof(WinUSBX[sub_api]));
+				sub_api--;
+			}
+			FreeLibrary(hlibusbK);
+			hlibusbK = NULL;
+		}
+	} else {
+		usbi_info(ctx, "libusbK DLL is not available");
+	}
+
+	if ((hWinUSB == NULL) && (hlibusbK == NULL)) {
+		usbi_warn(ctx, "neither WinUSB nor libusbK DLLs were found, "
+			"you will not be able to access devices outside of enumeration");
+		return false;
+	}
+
+	return true;
+}
+
+static void winusbx_exit(void)
+{
+	bool loaded = false;
+	HMODULE hDll;
+
+	hDll = WinUSBX[SUB_API_LIBUSBK].hDll;
+	if (hDll != NULL) {
+		FreeLibrary(hDll);
+		loaded = true;
+	}
+
+	hDll = WinUSBX[SUB_API_WINUSB].hDll;
+	if (hDll != NULL) {
+		FreeLibrary(hDll);
+		loaded = true;
+	}
+
+	// Reset the WinUSBX API structures if something was loaded
+	if (loaded)
+		memset(&WinUSBX, 0, sizeof(WinUSBX));
+}
+
+// NB: open and close must ensure that they only handle interface of
+// the right API type, as these functions can be called wholesale from
+// composite_open(), with interfaces belonging to different APIs
+static int winusbx_open(int sub_api, struct libusb_device_handle *dev_handle)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	HANDLE file_handle;
+	int i;
+
+	CHECK_WINUSBX_AVAILABLE(sub_api);
+
+	// WinUSB requires a separate handle for each interface
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		if ((priv->usb_interface[i].path != NULL)
+				&& (priv->usb_interface[i].apib->id == USB_API_WINUSBX)) {
+			file_handle = windows_open(dev_handle, priv->usb_interface[i].path, GENERIC_READ | GENERIC_WRITE);
+			if (file_handle == INVALID_HANDLE_VALUE) {
+				usbi_err(HANDLE_CTX(dev_handle), "could not open device %s (interface %d): %s", priv->usb_interface[i].path, i, windows_error_str(0));
+				switch (GetLastError()) {
+				case ERROR_FILE_NOT_FOUND: // The device was disconnected
+					return LIBUSB_ERROR_NO_DEVICE;
+				case ERROR_ACCESS_DENIED:
+					return LIBUSB_ERROR_ACCESS;
+				default:
+					return LIBUSB_ERROR_IO;
+				}
+			}
+
+			handle_priv->interface_handle[i].dev_handle = file_handle;
+		}
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static void winusbx_close(int sub_api, struct libusb_device_handle *dev_handle)
+{
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	HANDLE handle;
+	int i;
+
+	if (sub_api == SUB_API_NOTSET)
+		sub_api = priv->sub_api;
+
+	if (WinUSBX[sub_api].hDll == NULL)
+		return;
+
+	if (priv->apib->id == USB_API_COMPOSITE) {
+		// If this is a composite device, just free and close all WinUSB-like
+		// interfaces directly (each is independent and not associated with another)
+		for (i = 0; i < USB_MAXINTERFACES; i++) {
+			if (priv->usb_interface[i].apib->id == USB_API_WINUSBX) {
+				handle = handle_priv->interface_handle[i].api_handle;
+				if (HANDLE_VALID(handle))
+					WinUSBX[sub_api].Free(handle);
+
+				handle = handle_priv->interface_handle[i].dev_handle;
+				if (HANDLE_VALID(handle))
+					CloseHandle(handle);
+			}
+		}
+	} else {
+		// If this is a WinUSB device, free all interfaces above interface 0,
+		// then free and close interface 0 last
+		for (i = 1; i < USB_MAXINTERFACES; i++) {
+			handle = handle_priv->interface_handle[i].api_handle;
+			if (HANDLE_VALID(handle))
+				WinUSBX[sub_api].Free(handle);
+		}
+		handle = handle_priv->interface_handle[0].api_handle;
+		if (HANDLE_VALID(handle))
+			WinUSBX[sub_api].Free(handle);
+
+		handle = handle_priv->interface_handle[0].dev_handle;
+		if (HANDLE_VALID(handle))
+			CloseHandle(handle);
+	}
+}
+
+static int winusbx_configure_endpoints(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface)
+{
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	HANDLE winusb_handle = handle_priv->interface_handle[iface].api_handle;
+	UCHAR policy;
+	ULONG timeout = 0;
+	uint8_t endpoint_address;
+	int i;
+
+	CHECK_WINUSBX_AVAILABLE(sub_api);
+
+	// With handle and endpoints set (in parent), we can setup the default pipe properties
+	// see http://download.microsoft.com/download/D/1/D/D1DD7745-426B-4CC3-A269-ABBBE427C0EF/DVC-T705_DDC08.pptx
+	for (i = -1; i < priv->usb_interface[iface].nb_endpoints; i++) {
+		endpoint_address = (i == -1) ? 0 : priv->usb_interface[iface].endpoint[i];
+		if (!WinUSBX[sub_api].SetPipePolicy(winusb_handle, endpoint_address,
+			PIPE_TRANSFER_TIMEOUT, sizeof(ULONG), &timeout))
+			usbi_dbg(HANDLE_CTX(dev_handle), "failed to set PIPE_TRANSFER_TIMEOUT for control endpoint %02X", endpoint_address);
+
+		if ((i == -1) || (sub_api == SUB_API_LIBUSB0))
+			continue; // Other policies don't apply to control endpoint or libusb0
+
+		policy = false;
+		handle_priv->interface_handle[iface].zlp[endpoint_address] = WINUSB_ZLP_UNSET;
+		if (!WinUSBX[sub_api].SetPipePolicy(winusb_handle, endpoint_address,
+			SHORT_PACKET_TERMINATE, sizeof(UCHAR), &policy))
+			usbi_dbg(HANDLE_CTX(dev_handle), "failed to disable SHORT_PACKET_TERMINATE for endpoint %02X", endpoint_address);
+
+		if (!WinUSBX[sub_api].SetPipePolicy(winusb_handle, endpoint_address,
+			IGNORE_SHORT_PACKETS, sizeof(UCHAR), &policy))
+			usbi_dbg(HANDLE_CTX(dev_handle), "failed to disable IGNORE_SHORT_PACKETS for endpoint %02X", endpoint_address);
+
+		policy = true;
+		/* ALLOW_PARTIAL_READS must be enabled due to likely libusbK bug. See:
+		   https://sourceforge.net/mailarchive/message.php?msg_id=29736015 */
+		if (!WinUSBX[sub_api].SetPipePolicy(winusb_handle, endpoint_address,
+			ALLOW_PARTIAL_READS, sizeof(UCHAR), &policy))
+			usbi_dbg(HANDLE_CTX(dev_handle), "failed to enable ALLOW_PARTIAL_READS for endpoint %02X", endpoint_address);
+
+		if (!WinUSBX[sub_api].SetPipePolicy(winusb_handle, endpoint_address,
+			AUTO_CLEAR_STALL, sizeof(UCHAR), &policy))
+			usbi_dbg(HANDLE_CTX(dev_handle), "failed to enable AUTO_CLEAR_STALL for endpoint %02X", endpoint_address);
+
+		if (sub_api == SUB_API_LIBUSBK) {
+			if (!WinUSBX[sub_api].SetPipePolicy(winusb_handle, endpoint_address,
+				ISO_ALWAYS_START_ASAP, sizeof(UCHAR), &policy))
+				usbi_dbg(HANDLE_CTX(dev_handle), "failed to enable ISO_ALWAYS_START_ASAP for endpoint %02X", endpoint_address);
+		}
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int winusbx_claim_interface(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface)
+{
+	struct libusb_context *ctx = HANDLE_CTX(dev_handle);
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	bool is_using_usbccgp = (priv->apib->id == USB_API_COMPOSITE);
+	HDEVINFO dev_info;
+	char *dev_interface_path = NULL;
+	char *dev_interface_path_guid_start;
+	char filter_path[] = "\\\\.\\libusb0-0000";
+	bool found_filter = false;
+	HANDLE file_handle, winusb_handle;
+	DWORD err, _index;
+	int r;
+
+	CHECK_WINUSBX_AVAILABLE(sub_api);
+
+	// If the device is composite, but using the default Windows composite parent driver (usbccgp)
+	// or if it's the first WinUSB-like interface, we get a handle through Initialize().
+	if ((is_using_usbccgp) || (iface == 0)) {
+		// composite device (independent interfaces) or interface 0
+		file_handle = handle_priv->interface_handle[iface].dev_handle;
+		if (!HANDLE_VALID(file_handle))
+			return LIBUSB_ERROR_NOT_FOUND;
+
+		if (!WinUSBX[sub_api].Initialize(file_handle, &winusb_handle)) {
+			handle_priv->interface_handle[iface].api_handle = INVALID_HANDLE_VALUE;
+			err = GetLastError();
+			switch (err) {
+			case ERROR_BAD_COMMAND:
+				// The device was disconnected
+				usbi_err(ctx, "could not access interface %u: %s", iface, windows_error_str(0));
+				return LIBUSB_ERROR_NO_DEVICE;
+			default:
+				// it may be that we're using the libusb0 filter driver.
+				// TODO: can we move this whole business into the K/0 DLL?
+				r = LIBUSB_SUCCESS;
+				for (_index = 0; ; _index++) {
+					safe_free(dev_interface_path);
+
+					if (found_filter)
+						break;
+
+					r = get_interface_details_filter(ctx, &dev_info, _index, filter_path, &dev_interface_path);
+					if ((r != LIBUSB_SUCCESS) || (dev_interface_path == NULL))
+						break;
+
+					// ignore GUID part
+					dev_interface_path_guid_start = strchr(dev_interface_path, '{');
+					if (dev_interface_path_guid_start == NULL)
+						continue;
+					*dev_interface_path_guid_start = '\0';
+
+					if (strncmp(dev_interface_path, priv->usb_interface[iface].path, strlen(dev_interface_path)) == 0) {
+						file_handle = windows_open(dev_handle, filter_path, GENERIC_READ | GENERIC_WRITE);
+						if (file_handle != INVALID_HANDLE_VALUE) {
+							if (WinUSBX[sub_api].Initialize(file_handle, &winusb_handle)) {
+								// Replace the existing file handle with the working one
+								CloseHandle(handle_priv->interface_handle[iface].dev_handle);
+								handle_priv->interface_handle[iface].dev_handle = file_handle;
+								found_filter = true;
+							} else {
+								usbi_err(ctx, "could not initialize filter driver for %s", filter_path);
+								CloseHandle(file_handle);
+							}
+						} else {
+							usbi_err(ctx, "could not open device %s: %s", filter_path, windows_error_str(0));
+						}
+					}
+				}
+				if (r != LIBUSB_SUCCESS)
+					return r;
+				if (!found_filter) {
+					usbi_err(ctx, "could not access interface %u: %s", iface, windows_error_str(err));
+					return LIBUSB_ERROR_ACCESS;
+				}
+			}
+		}
+		handle_priv->interface_handle[iface].api_handle = winusb_handle;
+	} else {
+		// For all other interfaces, use GetAssociatedInterface()
+		winusb_handle = handle_priv->interface_handle[0].api_handle;
+		// It is a requirement for multiple interface devices on Windows that, to you
+		// must first claim the first interface before you claim the others
+		if (!HANDLE_VALID(winusb_handle)) {
+			file_handle = handle_priv->interface_handle[0].dev_handle;
+			if (WinUSBX[sub_api].Initialize(file_handle, &winusb_handle)) {
+				handle_priv->interface_handle[0].api_handle = winusb_handle;
+				usbi_warn(ctx, "auto-claimed interface 0 (required to claim %u with WinUSB)", iface);
+			} else {
+				usbi_warn(ctx, "failed to auto-claim interface 0 (required to claim %u with WinUSB): %s", iface, windows_error_str(0));
+				return LIBUSB_ERROR_ACCESS;
+			}
+		}
+		if (!WinUSBX[sub_api].GetAssociatedInterface(winusb_handle, (UCHAR)(iface - 1),
+			&handle_priv->interface_handle[iface].api_handle)) {
+			handle_priv->interface_handle[iface].api_handle = INVALID_HANDLE_VALUE;
+			switch (GetLastError()) {
+			case ERROR_NO_MORE_ITEMS:   // invalid iface
+				return LIBUSB_ERROR_NOT_FOUND;
+			case ERROR_BAD_COMMAND:     // The device was disconnected
+				return LIBUSB_ERROR_NO_DEVICE;
+			case ERROR_ALREADY_EXISTS:  // already claimed
+				return LIBUSB_ERROR_BUSY;
+			default:
+				usbi_err(ctx, "could not claim interface %u: %s", iface, windows_error_str(0));
+				return LIBUSB_ERROR_ACCESS;
+			}
+		}
+		handle_priv->interface_handle[iface].dev_handle = handle_priv->interface_handle[0].dev_handle;
+	}
+	usbi_dbg(ctx, "claimed interface %u", iface);
+	handle_priv->active_interface = iface;
+
+	return LIBUSB_SUCCESS;
+}
+
+static int winusbx_release_interface(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface)
+{
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	HANDLE winusb_handle;
+
+	CHECK_WINUSBX_AVAILABLE(sub_api);
+
+	winusb_handle = handle_priv->interface_handle[iface].api_handle;
+	if (!HANDLE_VALID(winusb_handle))
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	WinUSBX[sub_api].Free(winusb_handle);
+	handle_priv->interface_handle[iface].api_handle = INVALID_HANDLE_VALUE;
+
+	return LIBUSB_SUCCESS;
+}
+
+/*
+ * Return the first valid interface (of the same API type), for control transfers
+ */
+static int get_valid_interface(struct libusb_device_handle *dev_handle, int api_id)
+{
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	int i;
+
+	if ((api_id < USB_API_WINUSBX) || (api_id > USB_API_HID)) {
+		usbi_dbg(HANDLE_CTX(dev_handle), "unsupported API ID");
+		return -1;
+	}
+
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+	if (HANDLE_VALID(handle_priv->interface_handle[i].dev_handle)
+			&& HANDLE_VALID(handle_priv->interface_handle[i].api_handle)
+			&& (priv->usb_interface[i].apib->id == api_id))
+		return i;
+	}
+
+	return -1;
+}
+
+/*
+* Check a specific interface is valid (of the same API type), for control transfers
+*/
+static int check_valid_interface(struct libusb_device_handle *dev_handle, unsigned short interface, int api_id)
+{
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	if (interface >= USB_MAXINTERFACES)
+		return -1;
+
+	if ((api_id < USB_API_WINUSBX) || (api_id > USB_API_HID)) {
+		usbi_dbg(HANDLE_CTX(dev_handle), "unsupported API ID");
+		return -1;
+	}
+
+	// try the requested interface
+	if (HANDLE_VALID(handle_priv->interface_handle[interface].dev_handle)
+		&& HANDLE_VALID(handle_priv->interface_handle[interface].api_handle)
+		&& (priv->usb_interface[interface].apib->id == api_id))
+		return interface;
+
+	return -1;
+}
+
+/*
+ * Lookup interface by endpoint address. -1 if not found
+ */
+static int interface_by_endpoint(struct winusb_device_priv *priv,
+	struct winusb_device_handle_priv *handle_priv, uint8_t endpoint_address)
+{
+	int i, j;
+
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		if (!HANDLE_VALID(handle_priv->interface_handle[i].api_handle))
+			continue;
+		if (priv->usb_interface[i].endpoint == NULL)
+			continue;
+		for (j = 0; j < priv->usb_interface[i].nb_endpoints; j++) {
+			if (priv->usb_interface[i].endpoint[j] == endpoint_address)
+				return i;
+		}
+	}
+
+	return -1;
+}
+
+static int winusbx_submit_control_transfer(int sub_api, struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	struct winusb_transfer_priv *transfer_priv = get_winusb_transfer_priv(itransfer);
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(transfer->dev_handle);
+	PWINUSB_SETUP_PACKET setup = (PWINUSB_SETUP_PACKET)transfer->buffer;
+	ULONG size, transferred;
+	HANDLE winusb_handle;
+	OVERLAPPED *overlapped;
+	int current_interface;
+
+	CHECK_WINUSBX_AVAILABLE(sub_api);
+
+	size = transfer->length - LIBUSB_CONTROL_SETUP_SIZE;
+
+	// Windows places upper limits on the control transfer size
+	// See: https://docs.microsoft.com/en-us/windows-hardware/drivers/usbcon/usb-bandwidth-allocation#maximum-transfer-size
+	if (size > MAX_CTRL_BUFFER_LENGTH)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	if ((setup->RequestType & 0x1F) == LIBUSB_RECIPIENT_INTERFACE)
+		current_interface = check_valid_interface(transfer->dev_handle, setup->Index & 0xff, USB_API_WINUSBX);
+	else
+		current_interface = get_valid_interface(transfer->dev_handle, USB_API_WINUSBX);
+	if (current_interface < 0) {
+		if (auto_claim(transfer, &current_interface, USB_API_WINUSBX) != LIBUSB_SUCCESS)
+			return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	usbi_dbg(ITRANSFER_CTX(itransfer), "will use interface %d", current_interface);
+
+	transfer_priv->interface_number = (uint8_t)current_interface;
+	winusb_handle = handle_priv->interface_handle[current_interface].api_handle;
+	set_transfer_priv_handle(itransfer, handle_priv->interface_handle[current_interface].dev_handle);
+	overlapped = get_transfer_priv_overlapped(itransfer);
+
+	// Sending of set configuration control requests from WinUSB creates issues, except when using libusb0.sys
+	if (sub_api != SUB_API_LIBUSB0
+			&& (LIBUSB_REQ_TYPE(setup->RequestType) == LIBUSB_REQUEST_TYPE_STANDARD)
+			&& (setup->Request == LIBUSB_REQUEST_SET_CONFIGURATION)) {
+		if (setup->Value != priv->active_config) {
+			usbi_warn(TRANSFER_CTX(transfer), "cannot set configuration other than the default one");
+			return LIBUSB_ERROR_NOT_SUPPORTED;
+		}
+		windows_force_sync_completion(itransfer, 0);
+	} else {
+		if (!WinUSBX[sub_api].ControlTransfer(winusb_handle, *setup, transfer->buffer + LIBUSB_CONTROL_SETUP_SIZE, size, &transferred, overlapped)) {
+			if (GetLastError() != ERROR_IO_PENDING) {
+				usbi_warn(TRANSFER_CTX(transfer), "ControlTransfer failed: %s", windows_error_str(0));
+				return LIBUSB_ERROR_IO;
+			}
+		} else {
+			windows_force_sync_completion(itransfer, transferred);
+		}
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int winusbx_set_interface_altsetting(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface, uint8_t altsetting)
+{
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	HANDLE winusb_handle;
+
+	CHECK_WINUSBX_AVAILABLE(sub_api);
+
+	winusb_handle = handle_priv->interface_handle[iface].api_handle;
+	if (!HANDLE_VALID(winusb_handle)) {
+		usbi_err(HANDLE_CTX(dev_handle), "interface must be claimed first");
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	if (!WinUSBX[sub_api].SetCurrentAlternateSetting(winusb_handle, altsetting)) {
+		usbi_err(HANDLE_CTX(dev_handle), "SetCurrentAlternateSetting failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_IO;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+
+static void WINAPI winusbx_native_iso_transfer_continue_stream_callback(struct libusb_transfer *transfer)
+{
+	// If this callback is invoked, this means that we attempted to set ContinueStream
+	// to TRUE when calling Read/WriteIsochPipeAsap in winusbx_do_iso_transfer.
+	// The role of this callback is to fallback to ContinueStream = FALSE if the transfer
+	// did not succeed.
+
+	struct winusb_transfer_priv *transfer_priv =
+		get_winusb_transfer_priv(LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer));
+	bool fallback = (transfer->status != LIBUSB_TRANSFER_COMPLETED);
+	int idx;
+
+	// Restore the user callback
+	transfer->callback = transfer_priv->iso_user_callback;
+
+	for (idx = 0; idx < transfer->num_iso_packets && !fallback; idx++) {
+		if (transfer->iso_packet_desc[idx].status != LIBUSB_TRANSFER_COMPLETED)
+			fallback = true;
+	}
+
+	if (!fallback) {
+		// If the transfer was successful, we restore the user callback and call it.
+		if (transfer->callback)
+			transfer->callback(transfer);
+	} else {
+		// If the transfer wasn't successful we reschedule the transfer while forcing it
+		// not to continue the stream. This might results in a 5-ms delay.
+		transfer_priv->iso_break_stream = TRUE;
+		libusb_submit_transfer(transfer);
+	}
+}
+static int winusbx_submit_iso_transfer(int sub_api, struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_transfer_priv *transfer_priv = get_winusb_transfer_priv(itransfer);
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(transfer->dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	HANDLE winusb_handle;
+	OVERLAPPED *overlapped;
+	BOOL ret;
+	int current_interface;
+
+	CHECK_WINUSBX_AVAILABLE(sub_api);
+
+	current_interface = interface_by_endpoint(priv, handle_priv, transfer->endpoint);
+	if (current_interface < 0) {
+		usbi_err(TRANSFER_CTX(transfer), "unable to match endpoint to an open interface - cancelling transfer");
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	usbi_dbg(TRANSFER_CTX(transfer), "matched endpoint %02X with interface %d", transfer->endpoint, current_interface);
+
+	transfer_priv->interface_number = (uint8_t)current_interface;
+	winusb_handle = handle_priv->interface_handle[current_interface].api_handle;
+	set_transfer_priv_handle(itransfer, handle_priv->interface_handle[current_interface].dev_handle);
+	overlapped = get_transfer_priv_overlapped(itransfer);
+
+	if ((sub_api == SUB_API_LIBUSBK) || (sub_api == SUB_API_LIBUSB0)) {
+		int i;
+		UINT offset;
+		size_t iso_ctx_size;
+		PKISO_CONTEXT iso_context;
+
+		if (WinUSBX[sub_api].IsoReadPipe == NULL) {
+			usbi_warn(TRANSFER_CTX(transfer), "libusbK DLL does not support isoch transfers");
+			return LIBUSB_ERROR_NOT_SUPPORTED;
+		}
+
+		iso_ctx_size = sizeof(KISO_CONTEXT) + (transfer->num_iso_packets * sizeof(KISO_PACKET));
+		transfer_priv->iso_context = iso_context = calloc(1, iso_ctx_size);
+		if (transfer_priv->iso_context == NULL)
+			return LIBUSB_ERROR_NO_MEM;
+
+		// start ASAP
+		iso_context->StartFrame = 0;
+		iso_context->NumberOfPackets = (SHORT)transfer->num_iso_packets;
+
+		// convert the transfer packet lengths to iso_packet offsets
+		offset = 0;
+		for (i = 0; i < transfer->num_iso_packets; i++) {
+			iso_context->IsoPackets[i].offset = offset;
+			offset += transfer->iso_packet_desc[i].length;
+		}
+
+		if (IS_XFERIN(transfer)) {
+			usbi_dbg(TRANSFER_CTX(transfer), "reading %d iso packets", transfer->num_iso_packets);
+			ret = WinUSBX[sub_api].IsoReadPipe(winusb_handle, transfer->endpoint, transfer->buffer, transfer->length, overlapped, iso_context);
+		} else {
+			usbi_dbg(TRANSFER_CTX(transfer), "writing %d iso packets", transfer->num_iso_packets);
+			ret = WinUSBX[sub_api].IsoWritePipe(winusb_handle, transfer->endpoint, transfer->buffer, transfer->length, overlapped, iso_context);
+		}
+
+		if (!ret && GetLastError() != ERROR_IO_PENDING) {
+			usbi_err(TRANSFER_CTX(transfer), "IsoReadPipe/IsoWritePipe failed: %s", windows_error_str(0));
+			return LIBUSB_ERROR_IO;
+		}
+
+		return LIBUSB_SUCCESS;
+	} else if (sub_api == SUB_API_WINUSB) {
+		WINUSB_PIPE_INFORMATION_EX pipe_info_ex = { 0 };
+		WINUSB_ISOCH_BUFFER_HANDLE buffer_handle;
+		ULONG iso_transfer_size_multiple;
+		int out_transfer_length = 0;
+		int idx;
+
+		// Depending on the version of Microsoft WinUSB, isochronous transfers may not be supported.
+		if (WinUSBX[sub_api].ReadIsochPipeAsap == NULL) {
+			usbi_warn(TRANSFER_CTX(transfer), "WinUSB DLL does not support isoch transfers");
+			return LIBUSB_ERROR_NOT_SUPPORTED;
+		}
+
+		if (sizeof(struct libusb_iso_packet_descriptor) != sizeof(USBD_ISO_PACKET_DESCRIPTOR)) {
+			usbi_err(TRANSFER_CTX(transfer), "size of WinUsb and libusb isoch packet descriptors don't match");
+			return LIBUSB_ERROR_NOT_SUPPORTED;
+		}
+
+		// Query the pipe extended information to find the pipe index corresponding to the endpoint.
+		for (idx = 0; idx < priv->usb_interface[current_interface].nb_endpoints; ++idx) {
+			ret = WinUSBX[sub_api].QueryPipeEx(winusb_handle, (UINT8)priv->usb_interface[current_interface].current_altsetting, (UCHAR)idx, &pipe_info_ex);
+			if (!ret) {
+				usbi_err(TRANSFER_CTX(transfer), "couldn't query interface settings for USB pipe with index %d. Error: %s", idx, windows_error_str(0));
+				return LIBUSB_ERROR_NOT_FOUND;
+			}
+
+			if (pipe_info_ex.PipeId == transfer->endpoint && pipe_info_ex.PipeType == UsbdPipeTypeIsochronous)
+				break;
+		}
+
+		// Make sure we found the index.
+		if (idx == priv->usb_interface[current_interface].nb_endpoints) {
+			usbi_err(TRANSFER_CTX(transfer), "couldn't find isoch endpoint 0x%02x", transfer->endpoint);
+			return LIBUSB_ERROR_NOT_FOUND;
+		}
+
+		if (IS_XFERIN(transfer)) {
+			int interval = pipe_info_ex.Interval;
+
+			// For high-speed and SuperSpeed device, the interval is 2**(bInterval-1).
+			if (transfer->dev_handle->dev->speed >= LIBUSB_SPEED_HIGH)
+				interval = (1 << (pipe_info_ex.Interval - 1));
+
+			// WinUSB only supports isoch transfers spanning a full USB frames. Later, we might be smarter about this
+			// and allocate a temporary buffer. However, this is harder than it seems as its destruction would depend on overlapped
+			// IO...
+			iso_transfer_size_multiple = (pipe_info_ex.MaximumBytesPerInterval * 8) / interval;
+			if (transfer->length % iso_transfer_size_multiple != 0) {
+				usbi_err(TRANSFER_CTX(transfer), "length of isoch buffer must be a multiple of the MaximumBytesPerInterval * 8 / Interval");
+				return LIBUSB_ERROR_INVALID_PARAM;
+			}
+		} else {
+			// If this is an OUT transfer, we make sure the isoch packets are contiguous as this isn't supported otherwise.
+			bool size_should_be_zero = false;
+
+			for (idx = 0; idx < transfer->num_iso_packets; ++idx) {
+				if ((size_should_be_zero && transfer->iso_packet_desc[idx].length != 0) ||
+					(transfer->iso_packet_desc[idx].length != pipe_info_ex.MaximumBytesPerInterval && idx + 1 < transfer->num_iso_packets && transfer->iso_packet_desc[idx + 1].length > 0)) {
+					usbi_err(TRANSFER_CTX(transfer), "isoch packets for OUT transfer with WinUSB must be contiguous in memory");
+					return LIBUSB_ERROR_INVALID_PARAM;
+				}
+
+				size_should_be_zero = (transfer->iso_packet_desc[idx].length == 0);
+				out_transfer_length += transfer->iso_packet_desc[idx].length;
+			}
+		}
+
+		if (transfer_priv->isoch_buffer_handle != NULL) {
+			if (WinUSBX[sub_api].UnregisterIsochBuffer(transfer_priv->isoch_buffer_handle)) {
+				transfer_priv->isoch_buffer_handle = NULL;
+			} else {
+				usbi_err(TRANSFER_CTX(transfer), "failed to unregister WinUSB isoch buffer: %s", windows_error_str(0));
+				return LIBUSB_ERROR_OTHER;
+			}
+		}
+
+		// Register the isoch buffer to the operating system.
+		ret = WinUSBX[sub_api].RegisterIsochBuffer(winusb_handle, transfer->endpoint, transfer->buffer, transfer->length, &buffer_handle);
+		if (!ret) {
+			usbi_err(TRANSFER_CTX(transfer), "failed to register WinUSB isoch buffer: %s", windows_error_str(0));
+			return LIBUSB_ERROR_NO_MEM;
+		}
+
+		// Important note: the WinUSB_Read/WriteIsochPipeAsap API requires a ContinueStream parameter that tells whether the isochronous
+		// stream must be continued or if the WinUSB driver can schedule the transfer at its convenience. Profiling subsequent transfers
+		// with ContinueStream = FALSE showed that 5 frames, i.e. about 5 milliseconds, were left empty between each transfer. This
+		// is critical as this greatly diminish the achievable isochronous bandwidth. We solved the problem using the following strategy:
+		// - Transfers are first scheduled with ContinueStream = TRUE and with winusbx_iso_transfer_continue_stream_callback as user callback.
+		// - If the transfer succeeds, winusbx_iso_transfer_continue_stream_callback restore the user callback and calls its.
+		// - If the transfer fails, winusbx_iso_transfer_continue_stream_callback reschedule the transfer and force ContinueStream = FALSE.
+		if (!transfer_priv->iso_break_stream) {
+			transfer_priv->iso_user_callback = transfer->callback;
+			transfer->callback = winusbx_native_iso_transfer_continue_stream_callback;
+		}
+
+		// Initiate the transfers.
+		if (IS_XFERIN(transfer))
+			ret = WinUSBX[sub_api].ReadIsochPipeAsap(buffer_handle, 0, transfer->length, !transfer_priv->iso_break_stream, transfer->num_iso_packets, (PUSBD_ISO_PACKET_DESCRIPTOR)transfer->iso_packet_desc, overlapped);
+		else
+			ret = WinUSBX[sub_api].WriteIsochPipeAsap(buffer_handle, 0, out_transfer_length, !transfer_priv->iso_break_stream, overlapped);
+
+		if (!ret && GetLastError() != ERROR_IO_PENDING) {
+			usbi_err(TRANSFER_CTX(transfer), "ReadIsochPipeAsap/WriteIsochPipeAsap failed: %s", windows_error_str(0));
+			if (!WinUSBX[sub_api].UnregisterIsochBuffer(buffer_handle))
+				usbi_warn(TRANSFER_CTX(transfer), "failed to unregister WinUSB isoch buffer: %s", windows_error_str(0));
+			return LIBUSB_ERROR_IO;
+		}
+
+		// Restore the ContinueStream parameter to TRUE.
+		transfer_priv->iso_break_stream = FALSE;
+
+		transfer_priv->isoch_buffer_handle = buffer_handle;
+
+		return LIBUSB_SUCCESS;
+	} else {
+		PRINT_UNSUPPORTED_API(winusbx_submit_iso_transfer);
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+	}
+}
+
+static int winusbx_submit_bulk_transfer(int sub_api, struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_transfer_priv *transfer_priv = get_winusb_transfer_priv(itransfer);
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(transfer->dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	HANDLE winusb_handle;
+	OVERLAPPED *overlapped;
+	BOOL ret;
+	int current_interface;
+
+	CHECK_WINUSBX_AVAILABLE(sub_api);
+
+	current_interface = interface_by_endpoint(priv, handle_priv, transfer->endpoint);
+	if (current_interface < 0) {
+		usbi_err(TRANSFER_CTX(transfer), "unable to match endpoint to an open interface - cancelling transfer");
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	usbi_dbg(TRANSFER_CTX(transfer), "matched endpoint %02X with interface %d", transfer->endpoint, current_interface);
+
+	transfer_priv->interface_number = (uint8_t)current_interface;
+	winusb_handle = handle_priv->interface_handle[current_interface].api_handle;
+	set_transfer_priv_handle(itransfer, handle_priv->interface_handle[current_interface].dev_handle);
+	overlapped = get_transfer_priv_overlapped(itransfer);
+
+	if (IS_XFERIN(transfer)) {
+		usbi_dbg(TRANSFER_CTX(transfer), "reading %d bytes", transfer->length);
+		ret = WinUSBX[sub_api].ReadPipe(winusb_handle, transfer->endpoint, transfer->buffer, transfer->length, NULL, overlapped);
+	} else {
+		// Set SHORT_PACKET_TERMINATE if ZLP requested.
+		// Changing this can be a problem with packets in flight, so only allow on the first transfer.
+		UCHAR policy = (transfer->flags & LIBUSB_TRANSFER_ADD_ZERO_PACKET) != 0;
+		uint8_t* current_zlp = &handle_priv->interface_handle[current_interface].zlp[transfer->endpoint];
+		if (*current_zlp == WINUSB_ZLP_UNSET) {
+			if (policy &&
+				!WinUSBX[sub_api].SetPipePolicy(winusb_handle, transfer->endpoint,
+				SHORT_PACKET_TERMINATE, sizeof(UCHAR), &policy)) {
+				usbi_err(TRANSFER_CTX(transfer), "failed to set SHORT_PACKET_TERMINATE for endpoint %02X", transfer->endpoint);
+				return LIBUSB_ERROR_NOT_SUPPORTED;
+			}
+			*current_zlp = policy ? WINUSB_ZLP_ON : WINUSB_ZLP_OFF;
+		} else if (policy != (*current_zlp == WINUSB_ZLP_ON)) {
+			usbi_err(TRANSFER_CTX(transfer), "cannot change ZERO_PACKET for endpoint %02X on Windows", transfer->endpoint);
+			return LIBUSB_ERROR_NOT_SUPPORTED;
+		}
+
+		usbi_dbg(TRANSFER_CTX(transfer), "writing %d bytes", transfer->length);
+		ret = WinUSBX[sub_api].WritePipe(winusb_handle, transfer->endpoint, transfer->buffer, transfer->length, NULL, overlapped);
+	}
+
+	if (!ret && GetLastError() != ERROR_IO_PENDING) {
+		usbi_err(TRANSFER_CTX(transfer), "ReadPipe/WritePipe failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_IO;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int winusbx_clear_halt(int sub_api, struct libusb_device_handle *dev_handle, unsigned char endpoint)
+{
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	HANDLE winusb_handle;
+	int current_interface;
+
+	CHECK_WINUSBX_AVAILABLE(sub_api);
+
+	current_interface = interface_by_endpoint(priv, handle_priv, endpoint);
+	if (current_interface < 0) {
+		usbi_err(HANDLE_CTX(dev_handle), "unable to match endpoint to an open interface - cannot clear");
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	usbi_dbg(HANDLE_CTX(dev_handle), "matched endpoint %02X with interface %d", endpoint, current_interface);
+	winusb_handle = handle_priv->interface_handle[current_interface].api_handle;
+
+	if (!WinUSBX[sub_api].ResetPipe(winusb_handle, endpoint)) {
+		usbi_err(HANDLE_CTX(dev_handle), "ResetPipe failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_NO_DEVICE;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int winusbx_cancel_transfer(int sub_api, struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(transfer->dev_handle);
+	struct winusb_transfer_priv *transfer_priv = get_winusb_transfer_priv(itransfer);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	int current_interface = transfer_priv->interface_number;
+	HANDLE handle;
+
+	CHECK_WINUSBX_AVAILABLE(sub_api);
+
+	usbi_dbg(TRANSFER_CTX(transfer), "will use interface %d", current_interface);
+
+	handle = handle_priv->interface_handle[current_interface].api_handle;
+	if (!WinUSBX[sub_api].AbortPipe(handle, transfer->endpoint)) {
+		usbi_err(TRANSFER_CTX(transfer), "AbortPipe failed: %s", windows_error_str(0));
+		return LIBUSB_ERROR_NO_DEVICE;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+/*
+ * from the "How to Use WinUSB to Communicate with a USB Device" Microsoft white paper
+ * (http://www.microsoft.com/whdc/connect/usb/winusb_howto.mspx):
+ * "WinUSB does not support host-initiated reset port and cycle port operations" and
+ * IOCTL_INTERNAL_USB_CYCLE_PORT is only available in kernel mode and the
+ * IOCTL_USB_HUB_CYCLE_PORT ioctl was removed from Vista => the best we can do is
+ * cycle the pipes (and even then, the control pipe can not be reset using WinUSB)
+ */
+// TODO: (post hotplug): see if we can force eject the device and redetect it (reuse hotplug?)
+static int winusbx_reset_device(int sub_api, struct libusb_device_handle *dev_handle)
+{
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	HANDLE winusb_handle;
+	int i, j;
+
+	CHECK_WINUSBX_AVAILABLE(sub_api);
+
+	// Reset any available pipe (except control)
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		winusb_handle = handle_priv->interface_handle[i].api_handle;
+		if (HANDLE_VALID(winusb_handle)) {
+			for (j = 0; j < priv->usb_interface[i].nb_endpoints; j++) {
+				usbi_dbg(HANDLE_CTX(dev_handle), "resetting ep %02X", priv->usb_interface[i].endpoint[j]);
+				if (!WinUSBX[sub_api].AbortPipe(winusb_handle, priv->usb_interface[i].endpoint[j]))
+					usbi_err(HANDLE_CTX(dev_handle), "AbortPipe (pipe address %02X) failed: %s",
+						priv->usb_interface[i].endpoint[j], windows_error_str(0));
+
+				// FlushPipe seems to fail on OUT pipes
+				if (IS_EPIN(priv->usb_interface[i].endpoint[j])
+						&& (!WinUSBX[sub_api].FlushPipe(winusb_handle, priv->usb_interface[i].endpoint[j])))
+					usbi_err(HANDLE_CTX(dev_handle), "FlushPipe (pipe address %02X) failed: %s",
+						priv->usb_interface[i].endpoint[j], windows_error_str(0));
+
+				if (!WinUSBX[sub_api].ResetPipe(winusb_handle, priv->usb_interface[i].endpoint[j]))
+					usbi_err(HANDLE_CTX(dev_handle), "ResetPipe (pipe address %02X) failed: %s",
+						priv->usb_interface[i].endpoint[j], windows_error_str(0));
+			}
+		}
+	}
+
+	// libusbK & libusb0 have the ability to issue an actual device reset
+	if ((sub_api != SUB_API_WINUSB) && (WinUSBX[sub_api].ResetDevice != NULL)) {
+		winusb_handle = handle_priv->interface_handle[0].api_handle;
+		if (HANDLE_VALID(winusb_handle))
+			WinUSBX[sub_api].ResetDevice(winusb_handle);
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static enum libusb_transfer_status winusbx_copy_transfer_data(int sub_api, struct usbi_transfer *itransfer, DWORD length)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_transfer_priv *transfer_priv = get_winusb_transfer_priv(itransfer);
+	int i;
+
+	if (transfer->type == LIBUSB_TRANSFER_TYPE_ISOCHRONOUS) {
+		// for isochronous, need to copy the individual iso packet actual_lengths and statuses
+		if ((sub_api == SUB_API_LIBUSBK) || (sub_api == SUB_API_LIBUSB0)) {
+			// iso only supported on libusbk-based backends for now
+			PKISO_CONTEXT iso_context = transfer_priv->iso_context;
+			for (i = 0; i < transfer->num_iso_packets; i++) {
+				transfer->iso_packet_desc[i].actual_length = iso_context->IsoPackets[i].actual_length;
+				// TODO translate USDB_STATUS codes http://msdn.microsoft.com/en-us/library/ff539136(VS.85).aspx to libusb_transfer_status
+				//transfer->iso_packet_desc[i].status = transfer_priv->iso_context->IsoPackets[i].status;
+			}
+		} else if (sub_api == SUB_API_WINUSB) {
+			if (IS_XFERIN(transfer)) {
+				/* Convert isochronous packet descriptor between Windows and libusb representation.
+				 * Both representation are guaranteed to have the same length in bytes.*/
+				PUSBD_ISO_PACKET_DESCRIPTOR usbd_iso_packet_desc = (PUSBD_ISO_PACKET_DESCRIPTOR)transfer->iso_packet_desc;
+				for (i = 0; i < transfer->num_iso_packets; i++) {
+					unsigned int packet_length = (i < transfer->num_iso_packets - 1) ? (usbd_iso_packet_desc[i + 1].Offset - usbd_iso_packet_desc[i].Offset) : usbd_iso_packet_desc[i].Length;
+					unsigned int actual_length = usbd_iso_packet_desc[i].Length;
+					USBD_STATUS status = usbd_iso_packet_desc[i].Status;
+
+					transfer->iso_packet_desc[i].length = packet_length;
+					transfer->iso_packet_desc[i].actual_length = actual_length;
+					transfer->iso_packet_desc[i].status = usbd_status_to_libusb_transfer_status(status);
+				}
+			} else {
+				for (i = 0; i < transfer->num_iso_packets; i++) {
+					transfer->iso_packet_desc[i].status = LIBUSB_TRANSFER_COMPLETED;
+				}
+			}
+		} else {
+			// This should only occur if backend is not set correctly or other backend isoc is partially implemented
+			PRINT_UNSUPPORTED_API(copy_transfer_data);
+			return LIBUSB_TRANSFER_ERROR;
+		}
+	}
+
+	itransfer->transferred += (int)length;
+	return LIBUSB_TRANSFER_COMPLETED;
+}
+
+/*
+ * Internal HID Support functions (from libusb-win32)
+ * Note that functions that complete data transfer synchronously must return
+ * LIBUSB_COMPLETED instead of LIBUSB_SUCCESS
+ */
+static int _hid_get_hid_descriptor(struct hid_device_priv *dev, void *data, size_t *size);
+static int _hid_get_report_descriptor(struct hid_device_priv *dev, void *data, size_t *size);
+
+static int _hid_wcslen(WCHAR *str)
+{
+	int i = 0;
+
+	while (str[i] && (str[i] != 0x409))
+		i++;
+
+	return i;
+}
+
+static int _hid_get_device_descriptor(struct hid_device_priv *hid_priv, void *data, size_t *size)
+{
+	struct libusb_device_descriptor d;
+
+	d.bLength = LIBUSB_DT_DEVICE_SIZE;
+	d.bDescriptorType = LIBUSB_DT_DEVICE;
+	d.bcdUSB = 0x0200; /* 2.00 */
+	d.bDeviceClass = 0;
+	d.bDeviceSubClass = 0;
+	d.bDeviceProtocol = 0;
+	d.bMaxPacketSize0 = 64; /* fix this! */
+	d.idVendor = (uint16_t)hid_priv->vid;
+	d.idProduct = (uint16_t)hid_priv->pid;
+	d.bcdDevice = 0x0100;
+	d.iManufacturer = hid_priv->string_index[0];
+	d.iProduct = hid_priv->string_index[1];
+	d.iSerialNumber = hid_priv->string_index[2];
+	d.bNumConfigurations = 1;
+
+	if (*size > LIBUSB_DT_DEVICE_SIZE)
+		*size = LIBUSB_DT_DEVICE_SIZE;
+	memcpy(data, &d, *size);
+
+	return LIBUSB_COMPLETED;
+}
+
+static int _hid_get_config_descriptor(struct hid_device_priv *hid_priv, void *data, size_t *size)
+{
+	char num_endpoints = 0;
+	size_t config_total_len = 0;
+	char tmp[HID_MAX_CONFIG_DESC_SIZE];
+	struct libusb_config_descriptor *cd;
+	struct libusb_interface_descriptor *id;
+	struct libusb_hid_descriptor *hd;
+	struct libusb_endpoint_descriptor *ed;
+	size_t tmp_size;
+
+	if (hid_priv->input_report_size)
+		num_endpoints++;
+	if (hid_priv->output_report_size)
+		num_endpoints++;
+
+	config_total_len = LIBUSB_DT_CONFIG_SIZE + LIBUSB_DT_INTERFACE_SIZE
+		+ LIBUSB_DT_HID_SIZE + num_endpoints * LIBUSB_DT_ENDPOINT_SIZE;
+
+	cd = (struct libusb_config_descriptor *)tmp;
+	id = (struct libusb_interface_descriptor *)(tmp + LIBUSB_DT_CONFIG_SIZE);
+	hd = (struct libusb_hid_descriptor *)(tmp + LIBUSB_DT_CONFIG_SIZE
+		+ LIBUSB_DT_INTERFACE_SIZE);
+	ed = (struct libusb_endpoint_descriptor *)(tmp + LIBUSB_DT_CONFIG_SIZE
+		+ LIBUSB_DT_INTERFACE_SIZE
+		+ LIBUSB_DT_HID_SIZE);
+
+	cd->bLength = LIBUSB_DT_CONFIG_SIZE;
+	cd->bDescriptorType = LIBUSB_DT_CONFIG;
+	cd->wTotalLength = (uint16_t)config_total_len;
+	cd->bNumInterfaces = 1;
+	cd->bConfigurationValue = 1;
+	cd->iConfiguration = 0;
+	cd->bmAttributes = 1 << 7; /* bus powered */
+	cd->MaxPower = 50;
+
+	id->bLength = LIBUSB_DT_INTERFACE_SIZE;
+	id->bDescriptorType = LIBUSB_DT_INTERFACE;
+	id->bInterfaceNumber = 0;
+	id->bAlternateSetting = 0;
+	id->bNumEndpoints = num_endpoints;
+	id->bInterfaceClass = 3;
+	id->bInterfaceSubClass = 0;
+	id->bInterfaceProtocol = 0;
+	id->iInterface = 0;
+
+	tmp_size = LIBUSB_DT_HID_SIZE;
+	_hid_get_hid_descriptor(hid_priv, hd, &tmp_size);
+
+	if (hid_priv->input_report_size) {
+		ed->bLength = LIBUSB_DT_ENDPOINT_SIZE;
+		ed->bDescriptorType = LIBUSB_DT_ENDPOINT;
+		ed->bEndpointAddress = HID_IN_EP;
+		ed->bmAttributes = 3;
+		ed->wMaxPacketSize = hid_priv->input_report_size - 1;
+		ed->bInterval = 10;
+		ed = (struct libusb_endpoint_descriptor *)((char *)ed + LIBUSB_DT_ENDPOINT_SIZE);
+	}
+
+	if (hid_priv->output_report_size) {
+		ed->bLength = LIBUSB_DT_ENDPOINT_SIZE;
+		ed->bDescriptorType = LIBUSB_DT_ENDPOINT;
+		ed->bEndpointAddress = HID_OUT_EP;
+		ed->bmAttributes = 3;
+		ed->wMaxPacketSize = hid_priv->output_report_size - 1;
+		ed->bInterval = 10;
+	}
+
+	if (*size > config_total_len)
+		*size = config_total_len;
+	memcpy(data, tmp, *size);
+
+	return LIBUSB_COMPLETED;
+}
+
+static int _hid_get_string_descriptor(struct hid_device_priv *hid_priv, int _index,
+	void *data, size_t *size, HANDLE hid_handle)
+{
+	void *tmp = NULL;
+	WCHAR string[MAX_USB_STRING_LENGTH];
+	size_t tmp_size = 0;
+	int i;
+
+	/* language ID, EN-US */
+	char string_langid[] = {0x09, 0x04};
+
+	if (_index == 0) {
+		tmp = string_langid;
+		tmp_size = sizeof(string_langid) + 2;
+	} else {
+		for (i = 0; i < 3; i++) {
+			if (_index == (hid_priv->string_index[i])) {
+				tmp = hid_priv->string[i];
+				tmp_size = (_hid_wcslen(hid_priv->string[i]) + 1) * sizeof(WCHAR);
+				break;
+			}
+		}
+
+		if (i == 3) {
+			if (!HidD_GetIndexedString(hid_handle, _index, string, sizeof(string)))
+				return LIBUSB_ERROR_INVALID_PARAM;
+			tmp = string;
+			tmp_size = (_hid_wcslen(string) + 1) * sizeof(WCHAR);
+		}
+	}
+
+	if (!tmp_size)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	if (tmp_size < *size)
+		*size = tmp_size;
+
+	// 2 byte header
+	((uint8_t *)data)[0] = (uint8_t)*size;
+	((uint8_t *)data)[1] = LIBUSB_DT_STRING;
+	memcpy((uint8_t *)data + 2, tmp, *size - 2);
+
+	return LIBUSB_COMPLETED;
+}
+
+static int _hid_get_hid_descriptor(struct hid_device_priv *hid_priv, void *data, size_t *size)
+{
+	struct libusb_hid_descriptor d;
+	uint8_t tmp[MAX_HID_DESCRIPTOR_SIZE];
+	size_t report_len = MAX_HID_DESCRIPTOR_SIZE;
+
+	_hid_get_report_descriptor(hid_priv, tmp, &report_len);
+
+	d.bLength = LIBUSB_DT_HID_SIZE;
+	d.bDescriptorType = LIBUSB_DT_HID;
+	d.bcdHID = 0x0110; /* 1.10 */
+	d.bCountryCode = 0;
+	d.bNumDescriptors = 1;
+	d.bClassDescriptorType = LIBUSB_DT_REPORT;
+	d.wClassDescriptorLength = (uint16_t)report_len;
+
+	if (*size > LIBUSB_DT_HID_SIZE)
+		*size = LIBUSB_DT_HID_SIZE;
+	memcpy(data, &d, *size);
+
+	return LIBUSB_COMPLETED;
+}
+
+static int _hid_get_report_descriptor(struct hid_device_priv *hid_priv, void *data, size_t *size)
+{
+	uint8_t d[MAX_HID_DESCRIPTOR_SIZE];
+	size_t i = 0;
+
+	/* usage page */
+	d[i++] = 0x06; d[i++] = hid_priv->usagePage & 0xFF; d[i++] = hid_priv->usagePage >> 8;
+	/* usage */
+	d[i++] = 0x09; d[i++] = (uint8_t)hid_priv->usage;
+	/* start collection (application) */
+	d[i++] = 0xA1; d[i++] = 0x01;
+	/* input report */
+	if (hid_priv->input_report_size) {
+		/* usage (vendor defined) */
+		d[i++] = 0x09; d[i++] = 0x01;
+		/* logical minimum (0) */
+		d[i++] = 0x15; d[i++] = 0x00;
+		/* logical maximum (255) */
+		d[i++] = 0x25; d[i++] = 0xFF;
+		/* report size (8 bits) */
+		d[i++] = 0x75; d[i++] = 0x08;
+		/* report count */
+		d[i++] = 0x95; d[i++] = (uint8_t)hid_priv->input_report_size - 1;
+		/* input (data, variable, absolute) */
+		d[i++] = 0x81; d[i++] = 0x00;
+	}
+	/* output report */
+	if (hid_priv->output_report_size) {
+		/* usage (vendor defined) */
+		d[i++] = 0x09; d[i++] = 0x02;
+		/* logical minimum (0) */
+		d[i++] = 0x15; d[i++] = 0x00;
+		/* logical maximum (255) */
+		d[i++] = 0x25; d[i++] = 0xFF;
+		/* report size (8 bits) */
+		d[i++] = 0x75; d[i++] = 0x08;
+		/* report count */
+		d[i++] = 0x95; d[i++] = (uint8_t)hid_priv->output_report_size - 1;
+		/* output (data, variable, absolute) */
+		d[i++] = 0x91; d[i++] = 0x00;
+	}
+	/* feature report */
+	if (hid_priv->feature_report_size) {
+		/* usage (vendor defined) */
+		d[i++] = 0x09; d[i++] = 0x03;
+		/* logical minimum (0) */
+		d[i++] = 0x15; d[i++] = 0x00;
+		/* logical maximum (255) */
+		d[i++] = 0x25; d[i++] = 0xFF;
+		/* report size (8 bits) */
+		d[i++] = 0x75; d[i++] = 0x08;
+		/* report count */
+		d[i++] = 0x95; d[i++] = (uint8_t)hid_priv->feature_report_size - 1;
+		/* feature (data, variable, absolute) */
+		d[i++] = 0xb2; d[i++] = 0x02; d[i++] = 0x01;
+	}
+
+	/* end collection */
+	d[i++] = 0xC0;
+
+	if (*size > i)
+		*size = i;
+	memcpy(data, d, *size);
+
+	return LIBUSB_COMPLETED;
+}
+
+static int _hid_get_descriptor(struct libusb_device *dev, HANDLE hid_handle, int recipient,
+	int type, int _index, void *data, size_t *size)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev);
+	UNUSED(recipient);
+
+	switch (type) {
+	case LIBUSB_DT_DEVICE:
+		usbi_dbg(DEVICE_CTX(dev), "LIBUSB_DT_DEVICE");
+		return _hid_get_device_descriptor(priv->hid, data, size);
+	case LIBUSB_DT_CONFIG:
+		usbi_dbg(DEVICE_CTX(dev), "LIBUSB_DT_CONFIG");
+		if (!_index)
+			return _hid_get_config_descriptor(priv->hid, data, size);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	case LIBUSB_DT_STRING:
+		usbi_dbg(DEVICE_CTX(dev), "LIBUSB_DT_STRING");
+		return _hid_get_string_descriptor(priv->hid, _index, data, size, hid_handle);
+	case LIBUSB_DT_HID:
+		usbi_dbg(DEVICE_CTX(dev), "LIBUSB_DT_HID");
+		if (!_index)
+			return _hid_get_hid_descriptor(priv->hid, data, size);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	case LIBUSB_DT_REPORT:
+		usbi_dbg(DEVICE_CTX(dev), "LIBUSB_DT_REPORT");
+		if (!_index)
+			return _hid_get_report_descriptor(priv->hid, data, size);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	case LIBUSB_DT_PHYSICAL:
+		usbi_dbg(DEVICE_CTX(dev), "LIBUSB_DT_PHYSICAL");
+		if (HidD_GetPhysicalDescriptor(hid_handle, data, (ULONG)*size))
+			return LIBUSB_COMPLETED;
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	usbi_warn(DEVICE_CTX(dev), "unsupported");
+	return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+static int _hid_get_report(struct libusb_device *dev, HANDLE hid_handle, int id, void *data,
+	struct winusb_transfer_priv *tp, size_t size, OVERLAPPED *overlapped, int report_type)
+{
+	DWORD ioctl_code, expected_size = (DWORD)size;
+	uint8_t *buf;
+
+	if (tp->hid_buffer != NULL)
+		usbi_err(DEVICE_CTX(dev), "program assertion failed - hid_buffer is not NULL");
+
+	if ((size == 0) || (size > MAX_HID_REPORT_SIZE)) {
+		usbi_warn(DEVICE_CTX(dev), "invalid size (%"PRIuPTR")", (uintptr_t)size);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	}
+
+	switch (report_type) {
+	case HID_REPORT_TYPE_INPUT:
+		ioctl_code = IOCTL_HID_GET_INPUT_REPORT;
+		break;
+	case HID_REPORT_TYPE_FEATURE:
+		ioctl_code = IOCTL_HID_GET_FEATURE;
+		break;
+	default:
+		usbi_warn(DEVICE_CTX(dev), "unknown HID report type %d", report_type);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	}
+
+	// Add a trailing byte to detect overflows
+	buf = calloc(1, expected_size + 1);
+	if (buf == NULL)
+		return LIBUSB_ERROR_NO_MEM;
+
+	buf[0] = (uint8_t)id; // Must be set always
+	usbi_dbg(DEVICE_CTX(dev), "report ID: 0x%02X", buf[0]);
+
+	// NB: The size returned by DeviceIoControl doesn't include report IDs when not in use (0)
+	if (!DeviceIoControl(hid_handle, ioctl_code, buf, expected_size + 1,
+		buf, expected_size + 1, NULL, overlapped)) {
+		if (GetLastError() != ERROR_IO_PENDING) {
+			usbi_err(DEVICE_CTX(dev), "failed to read HID Report: %s", windows_error_str(0));
+			free(buf);
+			return LIBUSB_ERROR_IO;
+		}
+	}
+
+	// Asynchronous wait
+	tp->hid_buffer = buf;
+	tp->hid_dest = data; // copy dest, as not necessarily the start of the transfer buffer
+	tp->hid_expected_size = expected_size;
+
+	return LIBUSB_SUCCESS;
+}
+
+static int _hid_set_report(struct libusb_device *dev, HANDLE hid_handle, int id, void *data,
+	struct winusb_transfer_priv *tp, size_t size, OVERLAPPED *overlapped, int report_type)
+{
+	DWORD ioctl_code, write_size = (DWORD)size;
+	// If an id is reported, we must allow MAX_HID_REPORT_SIZE + 1
+	size_t max_report_size = MAX_HID_REPORT_SIZE + (id ? 1 : 0);
+	uint8_t *buf;
+
+	if (tp->hid_buffer != NULL)
+		usbi_err(DEVICE_CTX(dev), "program assertion failed - hid_buffer is not NULL");
+
+	if ((size == 0) || (size > max_report_size)) {
+		usbi_warn(DEVICE_CTX(dev), "invalid size (%"PRIuPTR")", (uintptr_t)size);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	}
+
+	switch (report_type) {
+	case HID_REPORT_TYPE_OUTPUT:
+		ioctl_code = IOCTL_HID_SET_OUTPUT_REPORT;
+		break;
+	case HID_REPORT_TYPE_FEATURE:
+		ioctl_code = IOCTL_HID_SET_FEATURE;
+		break;
+	default:
+		usbi_warn(DEVICE_CTX(dev), "unknown HID report type %d", report_type);
+		return LIBUSB_ERROR_INVALID_PARAM;
+	}
+
+	usbi_dbg(DEVICE_CTX(dev), "report ID: 0x%02X", id);
+	// When report IDs are not used (i.e. when id == 0), we must add
+	// a null report ID. Otherwise, we just use original data buffer
+	if (id == 0)
+		write_size++;
+
+	buf = malloc(write_size);
+	if (buf == NULL)
+		return LIBUSB_ERROR_NO_MEM;
+
+	if (id == 0) {
+		buf[0] = 0;
+		memcpy(buf + 1, data, size);
+	} else {
+		// This seems like a waste, but if we don't duplicate the
+		// data, we'll get issues when freeing hid_buffer
+		memcpy(buf, data, size);
+		if (buf[0] != id)
+			usbi_warn(DEVICE_CTX(dev), "mismatched report ID (data is %02X, parameter is %02X)", buf[0], id);
+	}
+
+	// NB: The size returned by DeviceIoControl doesn't include report IDs when not in use (0)
+	if (!DeviceIoControl(hid_handle, ioctl_code, buf, write_size,
+		buf, write_size, NULL, overlapped)) {
+		if (GetLastError() != ERROR_IO_PENDING) {
+			usbi_err(DEVICE_CTX(dev), "failed to write HID Output Report: %s", windows_error_str(0));
+			free(buf);
+			return LIBUSB_ERROR_IO;
+		}
+	}
+
+	tp->hid_buffer = buf;
+	tp->hid_dest = NULL;
+	return LIBUSB_SUCCESS;
+}
+
+static int _hid_class_request(struct libusb_device *dev, HANDLE hid_handle, int request_type,
+	int request, int value, int _index, void *data, struct winusb_transfer_priv *tp,
+	size_t size, OVERLAPPED *overlapped)
+{
+	int report_type = (value >> 8) & 0xFF;
+	int report_id = value & 0xFF;
+
+	UNUSED(_index);
+
+	if ((LIBUSB_REQ_RECIPIENT(request_type) != LIBUSB_RECIPIENT_INTERFACE)
+			&& (LIBUSB_REQ_RECIPIENT(request_type) != LIBUSB_RECIPIENT_DEVICE))
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	if (LIBUSB_REQ_OUT(request_type) && request == HID_REQ_SET_REPORT)
+		return _hid_set_report(dev, hid_handle, report_id, data, tp, size, overlapped, report_type);
+
+	if (LIBUSB_REQ_IN(request_type) && request == HID_REQ_GET_REPORT)
+		return _hid_get_report(dev, hid_handle, report_id, data, tp, size, overlapped, report_type);
+
+	return LIBUSB_ERROR_INVALID_PARAM;
+}
+
+/*
+ * HID API functions
+ */
+static bool hid_init(struct libusb_context *ctx)
+{
+	DLL_GET_HANDLE(ctx, hid);
+
+	DLL_LOAD_FUNC(hid, HidD_GetAttributes, true);
+	DLL_LOAD_FUNC(hid, HidD_GetHidGuid, true);
+	DLL_LOAD_FUNC(hid, HidD_GetPreparsedData, true);
+	DLL_LOAD_FUNC(hid, HidD_FreePreparsedData, true);
+	DLL_LOAD_FUNC(hid, HidD_GetManufacturerString, true);
+	DLL_LOAD_FUNC(hid, HidD_GetProductString, true);
+	DLL_LOAD_FUNC(hid, HidD_GetSerialNumberString, true);
+	DLL_LOAD_FUNC(hid, HidD_GetIndexedString, true);
+	DLL_LOAD_FUNC(hid, HidP_GetCaps, true);
+	DLL_LOAD_FUNC(hid, HidD_SetNumInputBuffers, true);
+	DLL_LOAD_FUNC(hid, HidD_GetPhysicalDescriptor, true);
+	DLL_LOAD_FUNC(hid, HidD_FlushQueue, true);
+	DLL_LOAD_FUNC(hid, HidP_GetValueCaps, true);
+
+	return true;
+}
+
+static void hid_exit(void)
+{
+	DLL_FREE_HANDLE(hid);
+}
+
+// NB: open and close must ensure that they only handle interface of
+// the right API type, as these functions can be called wholesale from
+// composite_open(), with interfaces belonging to different APIs
+static int hid_open(int sub_api, struct libusb_device_handle *dev_handle)
+{
+	struct libusb_device *dev = dev_handle->dev;
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev);
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	HIDD_ATTRIBUTES hid_attributes;
+	PHIDP_PREPARSED_DATA preparsed_data = NULL;
+	HIDP_CAPS capabilities;
+	HIDP_VALUE_CAPS *value_caps;
+	HANDLE hid_handle = INVALID_HANDLE_VALUE;
+	int i, j;
+	// report IDs handling
+	ULONG size[3];
+	int nb_ids[2]; // zero and nonzero report IDs
+#if defined(ENABLE_LOGGING)
+	const char * const type[3] = {"input", "output", "feature"};
+#endif
+
+	UNUSED(sub_api);
+	CHECK_HID_AVAILABLE;
+
+	if (priv->hid == NULL) {
+		usbi_err(HANDLE_CTX(dev_handle), "program assertion failed - private HID structure is uninitialized");
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		if ((priv->usb_interface[i].path != NULL)
+				&& (priv->usb_interface[i].apib->id == USB_API_HID)) {
+			hid_handle = windows_open(dev_handle, priv->usb_interface[i].path, GENERIC_READ | GENERIC_WRITE);
+			/*
+			 * http://www.lvr.com/hidfaq.htm: Why do I receive "Access denied" when attempting to access my HID?
+			 * "Windows 2000 and later have exclusive read/write access to HIDs that are configured as a system
+			 * keyboards or mice. An application can obtain a handle to a system keyboard or mouse by not
+			 * requesting READ or WRITE access with CreateFile. Applications can then use HidD_SetFeature and
+			 * HidD_GetFeature (if the device supports Feature reports)."
+			 */
+			if (hid_handle == INVALID_HANDLE_VALUE) {
+				usbi_warn(HANDLE_CTX(dev_handle), "could not open HID device in R/W mode (keyboard or mouse?) - trying without");
+				hid_handle = windows_open(dev_handle, priv->usb_interface[i].path, 0);
+				if (hid_handle == INVALID_HANDLE_VALUE) {
+					usbi_err(HANDLE_CTX(dev_handle), "could not open device %s (interface %d): %s", priv->path, i, windows_error_str(0));
+					switch (GetLastError()) {
+					case ERROR_FILE_NOT_FOUND: // The device was disconnected
+						return LIBUSB_ERROR_NO_DEVICE;
+					case ERROR_ACCESS_DENIED:
+						return LIBUSB_ERROR_ACCESS;
+					default:
+						return LIBUSB_ERROR_IO;
+					}
+				}
+				priv->usb_interface[i].restricted_functionality = true;
+			}
+			handle_priv->interface_handle[i].api_handle = hid_handle;
+		}
+	}
+
+	hid_attributes.Size = sizeof(hid_attributes);
+	do {
+		if (!HidD_GetAttributes(hid_handle, &hid_attributes)) {
+			usbi_err(HANDLE_CTX(dev_handle), "could not gain access to HID top collection (HidD_GetAttributes)");
+			break;
+		}
+
+		priv->hid->vid = hid_attributes.VendorID;
+		priv->hid->pid = hid_attributes.ProductID;
+
+		// Set the maximum available input buffer size
+		for (i = 32; HidD_SetNumInputBuffers(hid_handle, i); i *= 2);
+		usbi_dbg(HANDLE_CTX(dev_handle), "set maximum input buffer size to %d", i / 2);
+
+		// Get the maximum input and output report size
+		if (!HidD_GetPreparsedData(hid_handle, &preparsed_data) || !preparsed_data) {
+			usbi_err(HANDLE_CTX(dev_handle), "could not read HID preparsed data (HidD_GetPreparsedData)");
+			break;
+		}
+		if (HidP_GetCaps(preparsed_data, &capabilities) != HIDP_STATUS_SUCCESS) {
+			usbi_err(HANDLE_CTX(dev_handle), "could not parse HID capabilities (HidP_GetCaps)");
+			break;
+		}
+
+		// Find out if interrupt will need report IDs
+		size[0] = capabilities.NumberInputValueCaps;
+		size[1] = capabilities.NumberOutputValueCaps;
+		size[2] = capabilities.NumberFeatureValueCaps;
+		for (j = HidP_Input; j <= HidP_Feature; j++) {
+			usbi_dbg(HANDLE_CTX(dev_handle), "%lu HID %s report value(s) found", ULONG_CAST(size[j]), type[j]);
+			priv->hid->uses_report_ids[j] = false;
+			if (size[j] > 0) {
+				value_caps = calloc(size[j], sizeof(HIDP_VALUE_CAPS));
+				if ((value_caps != NULL)
+						&& (HidP_GetValueCaps((HIDP_REPORT_TYPE)j, value_caps, &size[j], preparsed_data) == HIDP_STATUS_SUCCESS)
+						&& (size[j] >= 1)) {
+					nb_ids[0] = 0;
+					nb_ids[1] = 0;
+					for (i = 0; i < (int)size[j]; i++) {
+						usbi_dbg(HANDLE_CTX(dev_handle), "  Report ID: 0x%02X", value_caps[i].ReportID);
+						if (value_caps[i].ReportID != 0)
+							nb_ids[1]++;
+						else
+							nb_ids[0]++;
+					}
+					if (nb_ids[1] != 0) {
+						if (nb_ids[0] != 0)
+							usbi_warn(HANDLE_CTX(dev_handle), "program assertion failed - zero and nonzero report IDs used for %s",
+								type[j]);
+						priv->hid->uses_report_ids[j] = true;
+					}
+				} else {
+					usbi_warn(HANDLE_CTX(dev_handle), "  could not process %s report IDs", type[j]);
+				}
+				free(value_caps);
+			}
+		}
+
+		// Set the report sizes
+		priv->hid->input_report_size = capabilities.InputReportByteLength;
+		priv->hid->output_report_size = capabilities.OutputReportByteLength;
+		priv->hid->feature_report_size = capabilities.FeatureReportByteLength;
+
+		// Store usage and usagePage values
+		priv->hid->usage = capabilities.Usage;
+		priv->hid->usagePage = capabilities.UsagePage;
+
+		// Fetch string descriptors
+		priv->hid->string_index[0] = dev->device_descriptor.iManufacturer;
+		if (priv->hid->string_index[0] != 0)
+			HidD_GetManufacturerString(hid_handle, priv->hid->string[0], sizeof(priv->hid->string[0]));
+		else
+			priv->hid->string[0][0] = 0;
+
+		priv->hid->string_index[1] = dev->device_descriptor.iProduct;
+		if (priv->hid->string_index[1] != 0)
+			HidD_GetProductString(hid_handle, priv->hid->string[1], sizeof(priv->hid->string[1]));
+		else
+			priv->hid->string[1][0] = 0;
+
+		priv->hid->string_index[2] = dev->device_descriptor.iSerialNumber;
+		if (priv->hid->string_index[2] != 0)
+			HidD_GetSerialNumberString(hid_handle, priv->hid->string[2], sizeof(priv->hid->string[2]));
+		else
+			priv->hid->string[2][0] = 0;
+	} while (0);
+
+	if (preparsed_data)
+		HidD_FreePreparsedData(preparsed_data);
+
+	return LIBUSB_SUCCESS;
+}
+
+static void hid_close(int sub_api, struct libusb_device_handle *dev_handle)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	HANDLE file_handle;
+	int i;
+
+	UNUSED(sub_api);
+
+	if (DLL_HANDLE_NAME(hid) == NULL)
+		return;
+
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		if (priv->usb_interface[i].apib->id == USB_API_HID) {
+			file_handle = handle_priv->interface_handle[i].api_handle;
+			if (HANDLE_VALID(file_handle))
+				CloseHandle(file_handle);
+		}
+	}
+}
+
+static int hid_claim_interface(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface)
+{
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	UNUSED(sub_api);
+	CHECK_HID_AVAILABLE;
+
+	// NB: Disconnection detection is not possible in this function
+	if (priv->usb_interface[iface].path == NULL)
+		return LIBUSB_ERROR_NOT_FOUND; // invalid iface
+
+	// We use dev_handle as a flag for interface claimed
+	if (handle_priv->interface_handle[iface].dev_handle == INTERFACE_CLAIMED)
+		return LIBUSB_ERROR_BUSY; // already claimed
+
+	handle_priv->interface_handle[iface].dev_handle = INTERFACE_CLAIMED;
+
+	usbi_dbg(HANDLE_CTX(dev_handle), "claimed interface %u", iface);
+	handle_priv->active_interface = iface;
+
+	return LIBUSB_SUCCESS;
+}
+
+static int hid_release_interface(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface)
+{
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	UNUSED(sub_api);
+	CHECK_HID_AVAILABLE;
+
+	if (priv->usb_interface[iface].path == NULL)
+		return LIBUSB_ERROR_NOT_FOUND; // invalid iface
+
+	if (handle_priv->interface_handle[iface].dev_handle != INTERFACE_CLAIMED)
+		return LIBUSB_ERROR_NOT_FOUND; // invalid iface
+
+	handle_priv->interface_handle[iface].dev_handle = INVALID_HANDLE_VALUE;
+
+	return LIBUSB_SUCCESS;
+}
+
+static int hid_set_interface_altsetting(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface, uint8_t altsetting)
+{
+	UNUSED(sub_api);
+	UNUSED(iface);
+
+	CHECK_HID_AVAILABLE;
+
+	if (altsetting != 0) {
+		usbi_err(HANDLE_CTX(dev_handle), "set interface altsetting not supported for altsetting >0");
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int hid_submit_control_transfer(int sub_api, struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_transfer_priv *transfer_priv = get_winusb_transfer_priv(itransfer);
+	struct libusb_device_handle *dev_handle = transfer->dev_handle;
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	WINUSB_SETUP_PACKET *setup = (WINUSB_SETUP_PACKET *)transfer->buffer;
+	HANDLE hid_handle;
+	OVERLAPPED *overlapped;
+	int current_interface;
+	uint8_t config;
+	size_t size;
+	int r;
+
+	UNUSED(sub_api);
+	CHECK_HID_AVAILABLE;
+
+	safe_free(transfer_priv->hid_buffer);
+	transfer_priv->hid_dest = NULL;
+	size = transfer->length - LIBUSB_CONTROL_SETUP_SIZE;
+
+	if (size > MAX_CTRL_BUFFER_LENGTH)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	current_interface = get_valid_interface(dev_handle, USB_API_HID);
+	if (current_interface < 0) {
+		if (auto_claim(transfer, &current_interface, USB_API_HID) != LIBUSB_SUCCESS)
+			return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	usbi_dbg(ITRANSFER_CTX(itransfer), "will use interface %d", current_interface);
+
+	transfer_priv->interface_number = (uint8_t)current_interface;
+	hid_handle = handle_priv->interface_handle[current_interface].api_handle;
+	set_transfer_priv_handle(itransfer, hid_handle);
+	overlapped = get_transfer_priv_overlapped(itransfer);
+
+	switch (LIBUSB_REQ_TYPE(setup->RequestType)) {
+	case LIBUSB_REQUEST_TYPE_STANDARD:
+		switch (setup->Request) {
+		case LIBUSB_REQUEST_GET_DESCRIPTOR:
+			r = _hid_get_descriptor(dev_handle->dev, hid_handle, LIBUSB_REQ_RECIPIENT(setup->RequestType),
+				(setup->Value >> 8) & 0xFF, setup->Value & 0xFF, transfer->buffer + LIBUSB_CONTROL_SETUP_SIZE, &size);
+			break;
+		case LIBUSB_REQUEST_GET_CONFIGURATION:
+			r = winusb_get_configuration(dev_handle, &config);
+			if (r == LIBUSB_SUCCESS) {
+				size = 1;
+				((uint8_t *)transfer->buffer)[LIBUSB_CONTROL_SETUP_SIZE] = config;
+				r = LIBUSB_COMPLETED;
+			}
+			break;
+		case LIBUSB_REQUEST_SET_CONFIGURATION:
+			if (setup->Value == priv->active_config) {
+				r = LIBUSB_COMPLETED;
+			} else {
+				usbi_warn(TRANSFER_CTX(transfer), "cannot set configuration other than the default one");
+				r = LIBUSB_ERROR_NOT_SUPPORTED;
+			}
+			break;
+		case LIBUSB_REQUEST_GET_INTERFACE:
+			size = 1;
+			((uint8_t *)transfer->buffer)[LIBUSB_CONTROL_SETUP_SIZE] = 0;
+			r = LIBUSB_COMPLETED;
+			break;
+		case LIBUSB_REQUEST_SET_INTERFACE:
+			r = hid_set_interface_altsetting(0, dev_handle, (uint8_t)setup->Index, (uint8_t)setup->Value);
+			if (r == LIBUSB_SUCCESS)
+				r = LIBUSB_COMPLETED;
+			break;
+		default:
+			usbi_warn(TRANSFER_CTX(transfer), "unsupported HID control request");
+			return LIBUSB_ERROR_NOT_SUPPORTED;
+		}
+		break;
+	case LIBUSB_REQUEST_TYPE_CLASS:
+		r = _hid_class_request(dev_handle->dev, hid_handle, setup->RequestType, setup->Request, setup->Value,
+			setup->Index, transfer->buffer + LIBUSB_CONTROL_SETUP_SIZE, transfer_priv,
+			size, overlapped);
+		break;
+	default:
+		usbi_warn(TRANSFER_CTX(transfer), "unsupported HID control request");
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+	}
+
+	if (r < 0)
+		return r;
+
+	if (r == LIBUSB_COMPLETED) {
+		// Force request to be completed synchronously. Transferred size has been set by previous call
+		windows_force_sync_completion(itransfer, (ULONG)size);
+		r = LIBUSB_SUCCESS;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int hid_submit_bulk_transfer(int sub_api, struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_transfer_priv *transfer_priv = get_winusb_transfer_priv(itransfer);
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(transfer->dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	HANDLE hid_handle;
+	OVERLAPPED *overlapped;
+	bool direction_in;
+	BOOL ret;
+	int current_interface, length;
+
+	UNUSED(sub_api);
+	CHECK_HID_AVAILABLE;
+
+	if (IS_XFEROUT(transfer) && (transfer->flags & LIBUSB_TRANSFER_ADD_ZERO_PACKET))
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+
+	transfer_priv->hid_dest = NULL;
+	safe_free(transfer_priv->hid_buffer);
+
+	current_interface = interface_by_endpoint(priv, handle_priv, transfer->endpoint);
+	if (current_interface < 0) {
+		usbi_err(TRANSFER_CTX(transfer), "unable to match endpoint to an open interface - cancelling transfer");
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	usbi_dbg(TRANSFER_CTX(transfer), "matched endpoint %02X with interface %d", transfer->endpoint, current_interface);
+
+	transfer_priv->interface_number = (uint8_t)current_interface;
+	hid_handle = handle_priv->interface_handle[current_interface].api_handle;
+	set_transfer_priv_handle(itransfer, hid_handle);
+	overlapped = get_transfer_priv_overlapped(itransfer);
+	direction_in = IS_XFERIN(transfer);
+
+	// If report IDs are not in use, an extra prefix byte must be added
+	if (((direction_in) && (!priv->hid->uses_report_ids[0]))
+			|| ((!direction_in) && (!priv->hid->uses_report_ids[1])))
+		length = transfer->length + 1;
+	else
+		length = transfer->length;
+
+	// Add a trailing byte to detect overflows on input
+	transfer_priv->hid_buffer = calloc(1, length + 1);
+	if (transfer_priv->hid_buffer == NULL)
+		return LIBUSB_ERROR_NO_MEM;
+
+	transfer_priv->hid_expected_size = length;
+
+	if (direction_in) {
+		transfer_priv->hid_dest = transfer->buffer;
+		usbi_dbg(TRANSFER_CTX(transfer), "reading %d bytes (report ID: 0x00)", length);
+		ret = ReadFile(hid_handle, transfer_priv->hid_buffer, length + 1, NULL, overlapped);
+	} else {
+		if (!priv->hid->uses_report_ids[1])
+			memcpy(transfer_priv->hid_buffer + 1, transfer->buffer, transfer->length);
+		else
+			// We could actually do without the calloc and memcpy in this case
+			memcpy(transfer_priv->hid_buffer, transfer->buffer, transfer->length);
+
+		usbi_dbg(TRANSFER_CTX(transfer), "writing %d bytes (report ID: 0x%02X)", length, transfer_priv->hid_buffer[0]);
+		ret = WriteFile(hid_handle, transfer_priv->hid_buffer, length, NULL, overlapped);
+	}
+
+	if (!ret && GetLastError() != ERROR_IO_PENDING) {
+		usbi_err(TRANSFER_CTX(transfer), "HID transfer failed: %s", windows_error_str(0));
+		safe_free(transfer_priv->hid_buffer);
+		return LIBUSB_ERROR_IO;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int hid_reset_device(int sub_api, struct libusb_device_handle *dev_handle)
+{
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	HANDLE hid_handle;
+	int current_interface;
+
+	UNUSED(sub_api);
+	CHECK_HID_AVAILABLE;
+
+	// Flushing the queues on all interfaces is the best we can achieve
+	for (current_interface = 0; current_interface < USB_MAXINTERFACES; current_interface++) {
+		hid_handle = handle_priv->interface_handle[current_interface].api_handle;
+		if (HANDLE_VALID(hid_handle))
+			HidD_FlushQueue(hid_handle);
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static int hid_clear_halt(int sub_api, struct libusb_device_handle *dev_handle, unsigned char endpoint)
+{
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	HANDLE hid_handle;
+	int current_interface;
+
+	UNUSED(sub_api);
+	CHECK_HID_AVAILABLE;
+
+	current_interface = interface_by_endpoint(priv, handle_priv, endpoint);
+	if (current_interface < 0) {
+		usbi_err(HANDLE_CTX(dev_handle), "unable to match endpoint to an open interface - cannot clear");
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	usbi_dbg(HANDLE_CTX(dev_handle), "matched endpoint %02X with interface %d", endpoint, current_interface);
+	hid_handle = handle_priv->interface_handle[current_interface].api_handle;
+
+	// No endpoint selection with Microsoft's implementation, so we try to flush the
+	// whole interface. Should be OK for most case scenarios
+	if (!HidD_FlushQueue(hid_handle)) {
+		usbi_err(HANDLE_CTX(dev_handle), "Flushing of HID queue failed: %s", windows_error_str(0));
+		// Device was probably disconnected
+		return LIBUSB_ERROR_NO_DEVICE;
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+// This extra function is only needed for HID
+static enum libusb_transfer_status hid_copy_transfer_data(int sub_api, struct usbi_transfer *itransfer, DWORD length)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_transfer_priv *transfer_priv = get_winusb_transfer_priv(itransfer);
+	enum libusb_transfer_status r = LIBUSB_TRANSFER_COMPLETED;
+
+	UNUSED(sub_api);
+
+	if (transfer_priv->hid_buffer != NULL) {
+		// If we have a valid hid_buffer, it means the transfer was async
+		if (transfer_priv->hid_dest != NULL) { // Data readout
+			if (length > 0) {
+				// First, check for overflow
+				if ((size_t)length > transfer_priv->hid_expected_size) {
+					usbi_err(TRANSFER_CTX(transfer), "OVERFLOW!");
+					length = (DWORD)transfer_priv->hid_expected_size;
+					r = LIBUSB_TRANSFER_OVERFLOW;
+				}
+
+				if (transfer_priv->hid_buffer[0] == 0) {
+					memcpy(transfer_priv->hid_dest, transfer_priv->hid_buffer + 1, length);
+				} else {
+					memcpy(transfer_priv->hid_dest, transfer_priv->hid_buffer, length);
+				}
+			}
+			transfer_priv->hid_dest = NULL;
+		}
+		// For write, we just need to free the hid buffer
+		safe_free(transfer_priv->hid_buffer);
+	}
+
+	itransfer->transferred += (int)length;
+	return r;
+}
+
+
+/*
+ * Composite API functions
+ */
+static int composite_open(int sub_api, struct libusb_device_handle *dev_handle)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	int i, r = LIBUSB_ERROR_NOT_FOUND;
+	// SUB_API_MAX + 1 as the SUB_API_MAX pos is used to indicate availability of HID
+	bool available[SUB_API_MAX + 1];
+
+	UNUSED(sub_api);
+
+	for (i = 0; i < SUB_API_MAX + 1; i++)
+		available[i] = false;
+
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		switch (priv->usb_interface[i].apib->id) {
+		case USB_API_WINUSBX:
+			if (priv->usb_interface[i].sub_api != SUB_API_NOTSET)
+				available[priv->usb_interface[i].sub_api] = true;
+			break;
+		case USB_API_HID:
+			available[SUB_API_MAX] = true;
+			break;
+		default:
+			break;
+		}
+	}
+
+	for (i = 0; i < SUB_API_MAX; i++) { // WinUSB-like drivers
+		if (available[i]) {
+			r = usb_api_backend[USB_API_WINUSBX].open(i, dev_handle);
+			if (r != LIBUSB_SUCCESS)
+				return r;
+		}
+	}
+
+	if (available[SUB_API_MAX]) { // HID driver
+		r = hid_open(SUB_API_NOTSET, dev_handle);
+
+		// On Windows 10 version 1903 (OS Build 18362) and later Windows blocks attempts to
+		// open HID devices with a U2F usage unless running as administrator. We ignore this
+		// failure and proceed without the HID device opened.
+		if (r == LIBUSB_ERROR_ACCESS) {
+			usbi_dbg(HANDLE_CTX(dev_handle), "ignoring access denied error while opening HID interface of composite device");
+			r = LIBUSB_SUCCESS;
+		}
+	}
+
+	return r;
+}
+
+static void composite_close(int sub_api, struct libusb_device_handle *dev_handle)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	int i;
+	// SUB_API_MAX + 1 as the SUB_API_MAX pos is used to indicate availability of HID
+	bool available[SUB_API_MAX + 1];
+
+	UNUSED(sub_api);
+
+	for (i = 0; i < SUB_API_MAX + 1; i++)
+		available[i] = false;
+
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		switch (priv->usb_interface[i].apib->id) {
+		case USB_API_WINUSBX:
+			if (priv->usb_interface[i].sub_api != SUB_API_NOTSET)
+				available[priv->usb_interface[i].sub_api] = true;
+			break;
+		case USB_API_HID:
+			available[SUB_API_MAX] = true;
+			break;
+		default:
+			break;
+		}
+	}
+
+	for (i = 0; i < SUB_API_MAX; i++) { // WinUSB-like drivers
+		if (available[i])
+			usb_api_backend[USB_API_WINUSBX].close(i, dev_handle);
+	}
+
+	if (available[SUB_API_MAX]) // HID driver
+		hid_close(SUB_API_NOTSET, dev_handle);
+}
+
+static int composite_claim_interface(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	UNUSED(sub_api);
+	CHECK_SUPPORTED_API(priv->usb_interface[iface].apib, claim_interface);
+
+	return priv->usb_interface[iface].apib->
+		claim_interface(priv->usb_interface[iface].sub_api, dev_handle, iface);
+}
+
+static int composite_set_interface_altsetting(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface, uint8_t altsetting)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	UNUSED(sub_api);
+	CHECK_SUPPORTED_API(priv->usb_interface[iface].apib, set_interface_altsetting);
+
+	return priv->usb_interface[iface].apib->
+		set_interface_altsetting(priv->usb_interface[iface].sub_api, dev_handle, iface, altsetting);
+}
+
+static int composite_release_interface(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+
+	UNUSED(sub_api);
+	CHECK_SUPPORTED_API(priv->usb_interface[iface].apib, release_interface);
+
+	return priv->usb_interface[iface].apib->
+		release_interface(priv->usb_interface[iface].sub_api, dev_handle, iface);
+}
+
+static int composite_submit_control_transfer(int sub_api, struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	struct libusb_config_descriptor *conf_desc;
+	WINUSB_SETUP_PACKET *setup = (WINUSB_SETUP_PACKET *)transfer->buffer;
+	int iface, pass, r;
+
+	UNUSED(sub_api);
+
+	// Interface shouldn't matter for control, but it does in practice, with Windows'
+	// restrictions with regards to accessing HID keyboards and mice. Try to target
+	// a specific interface first, if possible.
+	switch (LIBUSB_REQ_RECIPIENT(setup->RequestType)) {
+	case LIBUSB_RECIPIENT_INTERFACE:
+		iface = setup->Index & 0xFF;
+		break;
+	case LIBUSB_RECIPIENT_ENDPOINT:
+		r = libusb_get_active_config_descriptor(transfer->dev_handle->dev, &conf_desc);
+		if (r == LIBUSB_SUCCESS) {
+			iface = get_interface_by_endpoint(conf_desc, (setup->Index & 0xFF));
+			libusb_free_config_descriptor(conf_desc);
+			break;
+		}
+		// No break if not able to determine interface
+		// Fall through
+	default:
+		iface = -1;
+		break;
+	}
+
+	// Try and target a specific interface if the control setup indicates such
+	if ((iface >= 0) && (iface < USB_MAXINTERFACES)) {
+		usbi_dbg(TRANSFER_CTX(transfer), "attempting control transfer targeted to interface %d", iface);
+		if ((priv->usb_interface[iface].path != NULL)
+				&& (priv->usb_interface[iface].apib->submit_control_transfer != NULL)) {
+			r = priv->usb_interface[iface].apib->submit_control_transfer(priv->usb_interface[iface].sub_api, itransfer);
+			if (r == LIBUSB_SUCCESS)
+				return r;
+		}
+	}
+
+	// Either not targeted to a specific interface or no luck in doing so.
+	// Try a 2 pass approach with all interfaces.
+	for (pass = 0; pass < 2; pass++) {
+		for (iface = 0; iface < USB_MAXINTERFACES; iface++) {
+			if ((priv->usb_interface[iface].path != NULL)
+					&& (priv->usb_interface[iface].apib->submit_control_transfer != NULL)) {
+				if ((pass == 0) && (priv->usb_interface[iface].restricted_functionality)) {
+					usbi_dbg(TRANSFER_CTX(transfer), "trying to skip restricted interface #%d (HID keyboard or mouse?)", iface);
+					continue;
+				}
+				usbi_dbg(TRANSFER_CTX(transfer), "using interface %d", iface);
+				r = priv->usb_interface[iface].apib->submit_control_transfer(priv->usb_interface[iface].sub_api, itransfer);
+				// If not supported on this API, it may be supported on another, so don't give up yet!!
+				if (r == LIBUSB_ERROR_NOT_SUPPORTED)
+					continue;
+				return r;
+			}
+		}
+	}
+
+	usbi_err(TRANSFER_CTX(transfer), "no libusb supported interfaces to complete request");
+	return LIBUSB_ERROR_NOT_FOUND;
+}
+
+static int composite_submit_bulk_transfer(int sub_api, struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(transfer->dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	int current_interface;
+
+	UNUSED(sub_api);
+
+	current_interface = interface_by_endpoint(priv, handle_priv, transfer->endpoint);
+	if (current_interface < 0) {
+		usbi_err(TRANSFER_CTX(transfer), "unable to match endpoint to an open interface - cancelling transfer");
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	CHECK_SUPPORTED_API(priv->usb_interface[current_interface].apib, submit_bulk_transfer);
+
+	return priv->usb_interface[current_interface].apib->
+		submit_bulk_transfer(priv->usb_interface[current_interface].sub_api, itransfer);
+}
+
+static int composite_submit_iso_transfer(int sub_api, struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(transfer->dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	int current_interface;
+
+	UNUSED(sub_api);
+
+	current_interface = interface_by_endpoint(priv, handle_priv, transfer->endpoint);
+	if (current_interface < 0) {
+		usbi_err(TRANSFER_CTX(transfer), "unable to match endpoint to an open interface - cancelling transfer");
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	CHECK_SUPPORTED_API(priv->usb_interface[current_interface].apib, submit_iso_transfer);
+
+	return priv->usb_interface[current_interface].apib->
+		submit_iso_transfer(priv->usb_interface[current_interface].sub_api, itransfer);
+}
+
+static int composite_clear_halt(int sub_api, struct libusb_device_handle *dev_handle, unsigned char endpoint)
+{
+	struct winusb_device_handle_priv *handle_priv = get_winusb_device_handle_priv(dev_handle);
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	int current_interface;
+
+	UNUSED(sub_api);
+
+	current_interface = interface_by_endpoint(priv, handle_priv, endpoint);
+	if (current_interface < 0) {
+		usbi_err(HANDLE_CTX(dev_handle), "unable to match endpoint to an open interface - cannot clear");
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	CHECK_SUPPORTED_API(priv->usb_interface[current_interface].apib, clear_halt);
+
+	return priv->usb_interface[current_interface].apib->
+		clear_halt(priv->usb_interface[current_interface].sub_api, dev_handle, endpoint);
+}
+
+static int composite_cancel_transfer(int sub_api, struct usbi_transfer *itransfer)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_transfer_priv *transfer_priv = get_winusb_transfer_priv(itransfer);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	int current_interface = transfer_priv->interface_number;
+
+	UNUSED(sub_api);
+
+	if ((current_interface < 0) || (current_interface >= USB_MAXINTERFACES)) {
+		usbi_err(TRANSFER_CTX(transfer), "program assertion failed - invalid interface_number");
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+
+	CHECK_SUPPORTED_API(priv->usb_interface[current_interface].apib, cancel_transfer);
+
+	return priv->usb_interface[current_interface].apib->
+		cancel_transfer(priv->usb_interface[current_interface].sub_api, itransfer);
+}
+
+static int composite_reset_device(int sub_api, struct libusb_device_handle *dev_handle)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev_handle->dev);
+	int i, r;
+	bool available[SUB_API_MAX];
+
+	UNUSED(sub_api);
+
+	for (i = 0; i < SUB_API_MAX; i++)
+		available[i] = false;
+
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		if ((priv->usb_interface[i].apib->id == USB_API_WINUSBX)
+				&& (priv->usb_interface[i].sub_api != SUB_API_NOTSET))
+			available[priv->usb_interface[i].sub_api] = true;
+	}
+
+	for (i = 0; i < SUB_API_MAX; i++) {
+		if (available[i]) {
+			r = usb_api_backend[USB_API_WINUSBX].reset_device(i, dev_handle);
+			if (r != LIBUSB_SUCCESS)
+				return r;
+		}
+	}
+
+	return LIBUSB_SUCCESS;
+}
+
+static enum libusb_transfer_status composite_copy_transfer_data(int sub_api, struct usbi_transfer *itransfer, DWORD length)
+{
+	struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+	struct winusb_transfer_priv *transfer_priv = get_winusb_transfer_priv(itransfer);
+	struct winusb_device_priv *priv = usbi_get_device_priv(transfer->dev_handle->dev);
+	int current_interface = transfer_priv->interface_number;
+
+	UNUSED(sub_api);
+	if (priv->usb_interface[current_interface].apib->copy_transfer_data == NULL) {
+		usbi_err(TRANSFER_CTX(transfer), "program assertion failed - no function to copy transfer data");
+		return LIBUSB_TRANSFER_ERROR;
+	}
+
+	return priv->usb_interface[current_interface].apib->
+		copy_transfer_data(priv->usb_interface[current_interface].sub_api, itransfer, length);
+}
diff --git a/src/os/windows_winusb.h b/src/os/windows_winusb.h
new file mode 100644
index 0000000..6afd5cb
--- /dev/null
+++ b/src/os/windows_winusb.h
@@ -0,0 +1,783 @@
+/*
+ * Windows backend for libusb 1.0
+ * Copyright © 2009-2012 Pete Batard <pete@akeo.ie>
+ * With contributions from Michael Plante, Orin Eman et al.
+ * Parts of this code adapted from libusb-win32-v1 by Stephan Meyer
+ * Major code testing contribution by Xiaofan Chen
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
+ */
+
+#ifndef LIBUSB_WINDOWS_WINUSB_H
+#define LIBUSB_WINDOWS_WINUSB_H
+
+#include <devioctl.h>
+#include <guiddef.h>
+
+#include "windows_common.h"
+
+#define MAX_CTRL_BUFFER_LENGTH	4096
+#define MAX_USB_STRING_LENGTH	128
+#define MAX_HID_REPORT_SIZE	1024
+#define MAX_HID_DESCRIPTOR_SIZE	256
+#define MAX_GUID_STRING_LENGTH	40
+#define MAX_PATH_LENGTH		256
+#define MAX_KEY_LENGTH		256
+#define LIST_SEPARATOR		';'
+
+// Handle code for HID interface that have been claimed ("dibs")
+#define INTERFACE_CLAIMED	((HANDLE)(intptr_t)0xD1B5)
+// Additional return code for HID operations that completed synchronously
+#define LIBUSB_COMPLETED	(LIBUSB_SUCCESS + 1)
+
+// http://msdn.microsoft.com/en-us/library/ff545978.aspx
+// http://msdn.microsoft.com/en-us/library/ff545972.aspx
+// http://msdn.microsoft.com/en-us/library/ff545982.aspx
+static const GUID GUID_DEVINTERFACE_USB_HOST_CONTROLLER = {0x3ABF6F2D, 0x71C4, 0x462A, {0x8A, 0x92, 0x1E, 0x68, 0x61, 0xE6, 0xAF, 0x27}};
+static const GUID GUID_DEVINTERFACE_USB_HUB = {0xF18A0E88, 0xC30C, 0x11D0, {0x88, 0x15, 0x00, 0xA0, 0xC9, 0x06, 0xBE, 0xD8}};
+static const GUID GUID_DEVINTERFACE_USB_DEVICE = {0xA5DCBF10, 0x6530, 0x11D2, {0x90, 0x1F, 0x00, 0xC0, 0x4F, 0xB9, 0x51, 0xED}};
+static const GUID GUID_DEVINTERFACE_LIBUSB0_FILTER = {0xF9F3FF14, 0xAE21, 0x48A0, {0x8A, 0x25, 0x80, 0x11, 0xA7, 0xA9, 0x31, 0xD9}};
+
+// The following define MUST be == sizeof(USB_DESCRIPTOR_REQUEST)
+#define USB_DESCRIPTOR_REQUEST_SIZE	12U
+
+/*
+ * Multiple USB API backend support
+ */
+#define USB_API_UNSUPPORTED	0
+#define USB_API_HUB		1
+#define USB_API_COMPOSITE	2
+#define USB_API_WINUSBX		3
+#define USB_API_HID		4
+#define USB_API_MAX		5
+
+// Sub-APIs for WinUSB-like driver APIs (WinUSB, libusbK, libusb-win32 through the libusbK DLL)
+// Must have the same values as the KUSB_DRVID enum from libusbk.h
+#define SUB_API_NOTSET		-1
+#define SUB_API_LIBUSBK		0
+#define SUB_API_LIBUSB0		1
+#define SUB_API_WINUSB		2
+#define SUB_API_MAX		3
+
+struct windows_usb_api_backend {
+	const uint8_t id;
+	const char * const designation;
+	const char * const * const driver_name_list; // Driver name, without .sys, e.g. "usbccgp"
+	const uint8_t nb_driver_names;
+	bool (*init)(struct libusb_context *ctx);
+	void (*exit)(void);
+	int (*open)(int sub_api, struct libusb_device_handle *dev_handle);
+	void (*close)(int sub_api, struct libusb_device_handle *dev_handle);
+	int (*configure_endpoints)(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface);
+	int (*claim_interface)(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface);
+	int (*set_interface_altsetting)(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface, uint8_t altsetting);
+	int (*release_interface)(int sub_api, struct libusb_device_handle *dev_handle, uint8_t iface);
+	int (*clear_halt)(int sub_api, struct libusb_device_handle *dev_handle, unsigned char endpoint);
+	int (*reset_device)(int sub_api, struct libusb_device_handle *dev_handle);
+	int (*submit_bulk_transfer)(int sub_api, struct usbi_transfer *itransfer);
+	int (*submit_iso_transfer)(int sub_api, struct usbi_transfer *itransfer);
+	int (*submit_control_transfer)(int sub_api, struct usbi_transfer *itransfer);
+	int (*cancel_transfer)(int sub_api, struct usbi_transfer *itransfer);
+	enum libusb_transfer_status (*copy_transfer_data)(int sub_api, struct usbi_transfer *itransfer, DWORD length);
+};
+
+extern const struct windows_usb_api_backend usb_api_backend[USB_API_MAX];
+
+#define PRINT_UNSUPPORTED_API(fname)				\
+	usbi_dbg(NULL, "unsupported API call for '%s' "		\
+		"(unrecognized device driver)", #fname)
+
+#define CHECK_SUPPORTED_API(apip, fname)			\
+	do {							\
+		if ((apip)->fname == NULL) {			\
+			PRINT_UNSUPPORTED_API(fname);		\
+			return LIBUSB_ERROR_NOT_SUPPORTED;	\
+		}						\
+	} while (0)
+
+/*
+ * private structures definition
+ * with inline pseudo constructors/destructors
+ */
+
+// TODO (v2+): move hid desc to libusb.h?
+struct libusb_hid_descriptor {
+	uint8_t bLength;
+	uint8_t bDescriptorType;
+	uint16_t bcdHID;
+	uint8_t bCountryCode;
+	uint8_t bNumDescriptors;
+	uint8_t bClassDescriptorType;
+	uint16_t wClassDescriptorLength;
+};
+
+#define LIBUSB_DT_HID_SIZE		9
+#define HID_MAX_CONFIG_DESC_SIZE (LIBUSB_DT_CONFIG_SIZE + LIBUSB_DT_INTERFACE_SIZE \
+	+ LIBUSB_DT_HID_SIZE + 2 * LIBUSB_DT_ENDPOINT_SIZE)
+#define HID_MAX_REPORT_SIZE		1024
+#define HID_IN_EP			0x81
+#define HID_OUT_EP			0x02
+#define LIBUSB_REQ_RECIPIENT(request_type)	((request_type) & 0x1F)
+#define LIBUSB_REQ_TYPE(request_type)		((request_type) & (0x03 << 5))
+#define LIBUSB_REQ_IN(request_type)		((request_type) & LIBUSB_ENDPOINT_IN)
+#define LIBUSB_REQ_OUT(request_type)		(!LIBUSB_REQ_IN(request_type))
+
+// The following are used for HID reports IOCTLs
+#define HID_IN_CTL_CODE(id) \
+	CTL_CODE(FILE_DEVICE_KEYBOARD, (id), METHOD_IN_DIRECT, FILE_ANY_ACCESS)
+#define HID_OUT_CTL_CODE(id) \
+	CTL_CODE(FILE_DEVICE_KEYBOARD, (id), METHOD_OUT_DIRECT, FILE_ANY_ACCESS)
+
+#define IOCTL_HID_GET_FEATURE		HID_OUT_CTL_CODE(100)
+#define IOCTL_HID_GET_INPUT_REPORT	HID_OUT_CTL_CODE(104)
+#define IOCTL_HID_SET_FEATURE		HID_IN_CTL_CODE(100)
+#define IOCTL_HID_SET_OUTPUT_REPORT	HID_IN_CTL_CODE(101)
+
+enum libusb_hid_request_type {
+	HID_REQ_GET_REPORT = 0x01,
+	HID_REQ_GET_IDLE = 0x02,
+	HID_REQ_GET_PROTOCOL = 0x03,
+	HID_REQ_SET_REPORT = 0x09,
+	HID_REQ_SET_IDLE = 0x0A,
+	HID_REQ_SET_PROTOCOL = 0x0B
+};
+
+enum libusb_hid_report_type {
+	HID_REPORT_TYPE_INPUT = 0x01,
+	HID_REPORT_TYPE_OUTPUT = 0x02,
+	HID_REPORT_TYPE_FEATURE = 0x03
+};
+
+struct hid_device_priv {
+	uint16_t vid;
+	uint16_t pid;
+	uint8_t config;
+	uint8_t nb_interfaces;
+	bool uses_report_ids[3]; // input, ouptput, feature
+	uint16_t input_report_size;
+	uint16_t output_report_size;
+	uint16_t feature_report_size;
+	uint16_t usage;
+	uint16_t usagePage;
+	WCHAR string[3][MAX_USB_STRING_LENGTH];
+	uint8_t string_index[3]; // man, prod, ser
+};
+
+static inline struct winusb_device_priv *winusb_device_priv_init(struct libusb_device *dev)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev);
+	int i;
+
+	priv->apib = &usb_api_backend[USB_API_UNSUPPORTED];
+	priv->sub_api = SUB_API_NOTSET;
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		priv->usb_interface[i].apib = &usb_api_backend[USB_API_UNSUPPORTED];
+		priv->usb_interface[i].sub_api = SUB_API_NOTSET;
+	}
+
+	return priv;
+}
+
+static inline void winusb_device_priv_release(struct libusb_device *dev)
+{
+	struct winusb_device_priv *priv = usbi_get_device_priv(dev);
+	int i;
+
+	free(priv->dev_id);
+	free(priv->path);
+	if ((dev->device_descriptor.bNumConfigurations > 0) && (priv->config_descriptor != NULL)) {
+		for (i = 0; i < dev->device_descriptor.bNumConfigurations; i++) {
+			if (priv->config_descriptor[i] == NULL)
+				continue;
+			free((UCHAR *)priv->config_descriptor[i] - USB_DESCRIPTOR_REQUEST_SIZE);
+		}
+	}
+	free(priv->config_descriptor);
+	free(priv->hid);
+	for (i = 0; i < USB_MAXINTERFACES; i++) {
+		free(priv->usb_interface[i].path);
+		free(priv->usb_interface[i].endpoint);
+	}
+}
+
+// used to match a device driver (including filter drivers) against a supported API
+struct driver_lookup {
+	char list[MAX_KEY_LENGTH + 1]; // REG_MULTI_SZ list of services (driver) names
+	const DWORD reg_prop;          // SPDRP registry key to use to retrieve list
+	const char *designation;       // internal designation (for debug output)
+};
+
+/*
+ * Windows DDK API definitions. Most of it copied from MinGW's includes
+ */
+typedef DWORD DEVNODE, DEVINST;
+typedef DEVNODE *PDEVNODE, *PDEVINST;
+typedef DWORD RETURN_TYPE;
+typedef RETURN_TYPE CONFIGRET;
+
+#define CR_SUCCESS	0x00000000
+
+/* Cfgmgr32 dependencies */
+DLL_DECLARE_HANDLE(Cfgmgr32);
+DLL_DECLARE_FUNC(WINAPI, CONFIGRET, CM_Get_Parent, (PDEVINST, DEVINST, ULONG));
+DLL_DECLARE_FUNC(WINAPI, CONFIGRET, CM_Get_Child, (PDEVINST, DEVINST, ULONG));
+
+/* AdvAPI32 dependencies */
+DLL_DECLARE_HANDLE(AdvAPI32);
+DLL_DECLARE_FUNC_PREFIXED(WINAPI, LONG, p, RegQueryValueExA, (HKEY, LPCSTR, LPDWORD, LPDWORD, LPBYTE, LPDWORD));
+DLL_DECLARE_FUNC_PREFIXED(WINAPI, LONG, p, RegCloseKey, (HKEY));
+
+/* SetupAPI dependencies */
+DLL_DECLARE_HANDLE(SetupAPI);
+DLL_DECLARE_FUNC_PREFIXED(WINAPI, HDEVINFO, p, SetupDiGetClassDevsA, (LPCGUID, PCSTR, HWND, DWORD));
+DLL_DECLARE_FUNC_PREFIXED(WINAPI, BOOL, p, SetupDiEnumDeviceInfo, (HDEVINFO, DWORD, PSP_DEVINFO_DATA));
+DLL_DECLARE_FUNC_PREFIXED(WINAPI, BOOL, p, SetupDiEnumDeviceInterfaces, (HDEVINFO, PSP_DEVINFO_DATA,
+			LPCGUID, DWORD, PSP_DEVICE_INTERFACE_DATA));
+DLL_DECLARE_FUNC_PREFIXED(WINAPI, BOOL, p, SetupDiGetDeviceInstanceIdA, (HDEVINFO, PSP_DEVINFO_DATA,
+			PCSTR, DWORD, PDWORD));
+DLL_DECLARE_FUNC_PREFIXED(WINAPI, BOOL, p, SetupDiGetDeviceInterfaceDetailA, (HDEVINFO, PSP_DEVICE_INTERFACE_DATA,
+			PSP_DEVICE_INTERFACE_DETAIL_DATA_A, DWORD, PDWORD, PSP_DEVINFO_DATA));
+DLL_DECLARE_FUNC_PREFIXED(WINAPI, BOOL, p, SetupDiGetDeviceRegistryPropertyA, (HDEVINFO,
+			PSP_DEVINFO_DATA, DWORD, PDWORD, PBYTE, DWORD, PDWORD));
+DLL_DECLARE_FUNC_PREFIXED(WINAPI, BOOL, p, SetupDiDestroyDeviceInfoList, (HDEVINFO));
+DLL_DECLARE_FUNC_PREFIXED(WINAPI, HKEY, p, SetupDiOpenDevRegKey, (HDEVINFO, PSP_DEVINFO_DATA, DWORD, DWORD, DWORD, REGSAM));
+DLL_DECLARE_FUNC_PREFIXED(WINAPI, HKEY, p, SetupDiOpenDeviceInterfaceRegKey, (HDEVINFO, PSP_DEVICE_INTERFACE_DATA, DWORD, DWORD));
+
+#define FILE_DEVICE_USB	FILE_DEVICE_UNKNOWN
+
+#define USB_GET_NODE_INFORMATION			258
+#define USB_GET_DESCRIPTOR_FROM_NODE_CONNECTION		260
+#define USB_GET_NODE_CONNECTION_INFORMATION_EX		274
+#define USB_GET_NODE_CONNECTION_INFORMATION_EX_V2	279
+
+#define USB_CTL_CODE(id) \
+	CTL_CODE(FILE_DEVICE_USB, (id), METHOD_BUFFERED, FILE_ANY_ACCESS)
+
+#define IOCTL_USB_GET_NODE_INFORMATION \
+	USB_CTL_CODE(USB_GET_NODE_INFORMATION)
+
+#define IOCTL_USB_GET_DESCRIPTOR_FROM_NODE_CONNECTION \
+	USB_CTL_CODE(USB_GET_DESCRIPTOR_FROM_NODE_CONNECTION)
+
+#define IOCTL_USB_GET_NODE_CONNECTION_INFORMATION_EX \
+	USB_CTL_CODE(USB_GET_NODE_CONNECTION_INFORMATION_EX)
+
+#define IOCTL_USB_GET_NODE_CONNECTION_INFORMATION_EX_V2 \
+	USB_CTL_CODE(USB_GET_NODE_CONNECTION_INFORMATION_EX_V2)
+
+typedef enum _USB_CONNECTION_STATUS {
+	NoDeviceConnected,
+	DeviceConnected,
+	DeviceFailedEnumeration,
+	DeviceGeneralFailure,
+	DeviceCausedOvercurrent,
+	DeviceNotEnoughPower,
+	DeviceNotEnoughBandwidth,
+	DeviceHubNestedTooDeeply,
+	DeviceInLegacyHub,
+	DeviceEnumerating,
+	DeviceReset
+} USB_CONNECTION_STATUS;
+
+typedef enum _USB_DEVICE_SPEED {
+	UsbLowSpeed = 0,
+	UsbFullSpeed,
+	UsbHighSpeed,
+	UsbSuperSpeed,
+	UsbSuperSpeedPlus	// Not in Microsoft headers
+} USB_DEVICE_SPEED;
+
+typedef enum _USB_HUB_NODE {
+	UsbHub,
+	UsbMIParent
+} USB_HUB_NODE;
+
+#if defined(_MSC_VER)
+// disable /W4 MSVC warnings that are benign
+#pragma warning(push)
+#pragma warning(disable:4214)  // bit field types other than int
+#endif
+
+// Most of the structures below need to be packed
+#include <pshpack1.h>
+
+typedef struct _USB_HUB_DESCRIPTOR {
+	UCHAR bDescriptorLength;
+	UCHAR bDescriptorType;
+	UCHAR bNumberOfPorts;
+	USHORT wHubCharacteristics;
+	UCHAR bPowerOnToPowerGood;
+	UCHAR bHubControlCurrent;
+	UCHAR bRemoveAndPowerMask[64];
+} USB_HUB_DESCRIPTOR, *PUSB_HUB_DESCRIPTOR;
+
+typedef struct _USB_HUB_INFORMATION {
+	USB_HUB_DESCRIPTOR HubDescriptor;
+	BOOLEAN HubIsBusPowered;
+} USB_HUB_INFORMATION, *PUSB_HUB_INFORMATION;
+
+typedef struct _USB_NODE_INFORMATION {
+	USB_HUB_NODE NodeType;
+	union {
+		USB_HUB_INFORMATION HubInformation;
+//		USB_MI_PARENT_INFORMATION MiParentInformation;
+	} u;
+} USB_NODE_INFORMATION, *PUSB_NODE_INFORMATION;
+
+typedef struct _USB_DESCRIPTOR_REQUEST {
+	ULONG ConnectionIndex;
+	struct {
+		UCHAR bmRequest;
+		UCHAR bRequest;
+		USHORT wValue;
+		USHORT wIndex;
+		USHORT wLength;
+	} SetupPacket;
+//	UCHAR Data[0];
+} USB_DESCRIPTOR_REQUEST, *PUSB_DESCRIPTOR_REQUEST;
+
+typedef struct _USB_CONFIGURATION_DESCRIPTOR_SHORT {
+	USB_DESCRIPTOR_REQUEST req;
+	USB_CONFIGURATION_DESCRIPTOR desc;
+} USB_CONFIGURATION_DESCRIPTOR_SHORT;
+
+typedef struct USB_INTERFACE_DESCRIPTOR {
+	UCHAR bLength;
+	UCHAR bDescriptorType;
+	UCHAR bInterfaceNumber;
+	UCHAR bAlternateSetting;
+	UCHAR bNumEndpoints;
+	UCHAR bInterfaceClass;
+	UCHAR bInterfaceSubClass;
+	UCHAR bInterfaceProtocol;
+	UCHAR iInterface;
+} USB_INTERFACE_DESCRIPTOR, *PUSB_INTERFACE_DESCRIPTOR;
+
+typedef struct _USB_NODE_CONNECTION_INFORMATION_EX {
+	ULONG ConnectionIndex;
+	USB_DEVICE_DESCRIPTOR DeviceDescriptor;
+	UCHAR CurrentConfigurationValue;
+	UCHAR Speed;
+	BOOLEAN DeviceIsHub;
+	USHORT DeviceAddress;
+	ULONG NumberOfOpenPipes;
+	USB_CONNECTION_STATUS ConnectionStatus;
+//	USB_PIPE_INFO PipeList[0];
+} USB_NODE_CONNECTION_INFORMATION_EX, *PUSB_NODE_CONNECTION_INFORMATION_EX;
+
+typedef union _USB_PROTOCOLS {
+	ULONG ul;
+	struct {
+		ULONG Usb110:1;
+		ULONG Usb200:1;
+		ULONG Usb300:1;
+		ULONG ReservedMBZ:29;
+	};
+} USB_PROTOCOLS, *PUSB_PROTOCOLS;
+
+typedef union _USB_NODE_CONNECTION_INFORMATION_EX_V2_FLAGS {
+	ULONG ul;
+	struct {
+		ULONG DeviceIsOperatingAtSuperSpeedOrHigher:1;
+		ULONG DeviceIsSuperSpeedCapableOrHigher:1;
+		ULONG DeviceIsOperatingAtSuperSpeedPlusOrHigher:1;
+		ULONG DeviceIsSuperSpeedPlusCapableOrHigher:1;
+		ULONG ReservedMBZ:28;
+	};
+} USB_NODE_CONNECTION_INFORMATION_EX_V2_FLAGS, *PUSB_NODE_CONNECTION_INFORMATION_EX_V2_FLAGS;
+
+typedef struct _USB_NODE_CONNECTION_INFORMATION_EX_V2 {
+	ULONG ConnectionIndex;
+	ULONG Length;
+	USB_PROTOCOLS SupportedUsbProtocols;
+	USB_NODE_CONNECTION_INFORMATION_EX_V2_FLAGS Flags;
+} USB_NODE_CONNECTION_INFORMATION_EX_V2, *PUSB_NODE_CONNECTION_INFORMATION_EX_V2;
+
+#include <poppack.h>
+
+#if defined(_MSC_VER)
+// Restore original warnings
+#pragma warning(pop)
+#endif
+
+/* winusb.dll interface */
+
+/* pipe policies */
+#define SHORT_PACKET_TERMINATE	0x01
+#define AUTO_CLEAR_STALL	0x02
+#define PIPE_TRANSFER_TIMEOUT	0x03
+#define IGNORE_SHORT_PACKETS	0x04
+#define ALLOW_PARTIAL_READS	0x05
+#define AUTO_FLUSH		0x06
+#define RAW_IO			0x07
+#define MAXIMUM_TRANSFER_SIZE	0x08
+/* libusbK */
+#define ISO_ALWAYS_START_ASAP	0x21
+
+typedef struct _USBD_ISO_PACKET_DESCRIPTOR {
+	ULONG Offset;
+	ULONG Length;
+	USBD_STATUS Status;
+} USBD_ISO_PACKET_DESCRIPTOR, *PUSBD_ISO_PACKET_DESCRIPTOR;
+
+typedef enum _USBD_PIPE_TYPE {
+	UsbdPipeTypeControl,
+	UsbdPipeTypeIsochronous,
+	UsbdPipeTypeBulk,
+	UsbdPipeTypeInterrupt
+} USBD_PIPE_TYPE;
+
+typedef struct {
+	USBD_PIPE_TYPE PipeType;
+	UCHAR PipeId;
+	USHORT MaximumPacketSize;
+	UCHAR Interval;
+	ULONG MaximumBytesPerInterval;
+} WINUSB_PIPE_INFORMATION_EX, *PWINUSB_PIPE_INFORMATION_EX;
+
+#include <pshpack1.h>
+
+typedef struct _WINUSB_SETUP_PACKET {
+	UCHAR RequestType;
+	UCHAR Request;
+	USHORT Value;
+	USHORT Index;
+	USHORT Length;
+} WINUSB_SETUP_PACKET, *PWINUSB_SETUP_PACKET;
+
+#include <poppack.h>
+
+typedef PVOID WINUSB_INTERFACE_HANDLE, *PWINUSB_INTERFACE_HANDLE;
+typedef PVOID WINUSB_ISOCH_BUFFER_HANDLE, *PWINUSB_ISOCH_BUFFER_HANDLE;
+
+typedef BOOL (WINAPI *WinUsb_AbortPipe_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle,
+	UCHAR PipeID
+);
+typedef BOOL (WINAPI *WinUsb_ControlTransfer_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle,
+	WINUSB_SETUP_PACKET SetupPacket,
+	PUCHAR Buffer,
+	ULONG BufferLength,
+	PULONG LengthTransferred,
+	LPOVERLAPPED Overlapped
+);
+typedef BOOL (WINAPI *WinUsb_FlushPipe_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle,
+	UCHAR PipeID
+);
+typedef BOOL (WINAPI *WinUsb_Free_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle
+);
+typedef BOOL (WINAPI *WinUsb_GetAssociatedInterface_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle,
+	UCHAR AssociatedInterfaceIndex,
+	PWINUSB_INTERFACE_HANDLE AssociatedInterfaceHandle
+);
+typedef BOOL (WINAPI *WinUsb_Initialize_t)(
+	HANDLE DeviceHandle,
+	PWINUSB_INTERFACE_HANDLE InterfaceHandle
+);
+typedef BOOL (WINAPI *WinUsb_QueryPipeEx_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle,
+	UCHAR AlternateInterfaceHandle,
+	UCHAR PipeIndex,
+	PWINUSB_PIPE_INFORMATION_EX PipeInformationEx
+);
+typedef BOOL (WINAPI *WinUsb_ReadIsochPipeAsap_t)(
+	PWINUSB_ISOCH_BUFFER_HANDLE BufferHandle,
+	ULONG Offset,
+	ULONG Length,
+	BOOL ContinueStream,
+	ULONG NumberOfPackets,
+	PUSBD_ISO_PACKET_DESCRIPTOR IsoPacketDescriptors,
+	LPOVERLAPPED Overlapped
+);
+typedef BOOL (WINAPI *WinUsb_ReadPipe_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle,
+	UCHAR PipeID,
+	PUCHAR Buffer,
+	ULONG BufferLength,
+	PULONG LengthTransferred,
+	LPOVERLAPPED Overlapped
+);
+typedef BOOL (WINAPI *WinUsb_RegisterIsochBuffer_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle,
+	UCHAR PipeID,
+	PVOID Buffer,
+	ULONG BufferLength,
+	PWINUSB_ISOCH_BUFFER_HANDLE BufferHandle
+);
+typedef BOOL (WINAPI *WinUsb_ResetPipe_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle,
+	UCHAR PipeID
+);
+typedef BOOL (WINAPI *WinUsb_SetCurrentAlternateSetting_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle,
+	UCHAR AlternateSetting
+);
+typedef BOOL (WINAPI *WinUsb_SetPipePolicy_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle,
+	UCHAR PipeID,
+	ULONG PolicyType,
+	ULONG ValueLength,
+	PVOID Value
+);
+typedef BOOL (WINAPI *WinUsb_UnregisterIsochBuffer_t)(
+	WINUSB_ISOCH_BUFFER_HANDLE BufferHandle
+);
+typedef BOOL (WINAPI *WinUsb_WriteIsochPipeAsap_t)(
+	WINUSB_ISOCH_BUFFER_HANDLE BufferHandle,
+	ULONG Offset,
+	ULONG Length,
+	BOOL ContinueStream,
+	LPOVERLAPPED Overlapped
+);
+typedef BOOL (WINAPI *WinUsb_WritePipe_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle,
+	UCHAR PipeID,
+	PUCHAR Buffer,
+	ULONG BufferLength,
+	PULONG LengthTransferred,
+	LPOVERLAPPED Overlapped
+);
+
+/* /!\ These must match the ones from the official libusbk.h */
+typedef enum _KUSB_FNID {
+	KUSB_FNID_Init,
+	KUSB_FNID_Free,
+	KUSB_FNID_ClaimInterface,
+	KUSB_FNID_ReleaseInterface,
+	KUSB_FNID_SetAltInterface,
+	KUSB_FNID_GetAltInterface,
+	KUSB_FNID_GetDescriptor,
+	KUSB_FNID_ControlTransfer,
+	KUSB_FNID_SetPowerPolicy,
+	KUSB_FNID_GetPowerPolicy,
+	KUSB_FNID_SetConfiguration,
+	KUSB_FNID_GetConfiguration,
+	KUSB_FNID_ResetDevice,
+	KUSB_FNID_Initialize,
+	KUSB_FNID_SelectInterface,
+	KUSB_FNID_GetAssociatedInterface,
+	KUSB_FNID_Clone,
+	KUSB_FNID_QueryInterfaceSettings,
+	KUSB_FNID_QueryDeviceInformation,
+	KUSB_FNID_SetCurrentAlternateSetting,
+	KUSB_FNID_GetCurrentAlternateSetting,
+	KUSB_FNID_QueryPipe,
+	KUSB_FNID_SetPipePolicy,
+	KUSB_FNID_GetPipePolicy,
+	KUSB_FNID_ReadPipe,
+	KUSB_FNID_WritePipe,
+	KUSB_FNID_ResetPipe,
+	KUSB_FNID_AbortPipe,
+	KUSB_FNID_FlushPipe,
+	KUSB_FNID_IsoReadPipe,
+	KUSB_FNID_IsoWritePipe,
+	KUSB_FNID_GetCurrentFrameNumber,
+	KUSB_FNID_GetOverlappedResult,
+	KUSB_FNID_GetProperty,
+	KUSB_FNID_COUNT,
+} KUSB_FNID;
+
+typedef struct _KLIB_VERSION {
+	INT Major;
+	INT Minor;
+	INT Micro;
+	INT Nano;
+} KLIB_VERSION, *PKLIB_VERSION;
+
+typedef BOOL (WINAPI *LibK_GetProcAddress_t)(
+	PVOID ProcAddress,
+	INT DriverID,
+	INT FunctionID
+);
+
+typedef VOID (WINAPI *LibK_GetVersion_t)(
+	PKLIB_VERSION Version
+);
+
+typedef BOOL (WINAPI *LibK_ResetDevice_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle
+);
+
+//KISO_PACKET is equivalent of libusb_iso_packet_descriptor except uses absolute "offset" field instead of sequential Lengths
+typedef struct _KISO_PACKET {
+	UINT offset;
+	USHORT actual_length; //changed from libusbk_shared.h "Length" for clarity
+	USHORT status;
+} KISO_PACKET, *PKISO_PACKET;
+
+typedef enum _KISO_FLAG {
+	KISO_FLAG_NONE = 0,
+	KISO_FLAG_SET_START_FRAME = 0x00000001,
+} KISO_FLAG;
+
+//KISO_CONTEXT is the conceptual equivalent of libusb_transfer except is isochronous-specific and must match libusbk's version
+typedef struct _KISO_CONTEXT {
+	KISO_FLAG Flags;
+	UINT StartFrame;
+	SHORT ErrorCount;
+	SHORT NumberOfPackets;
+	UINT UrbHdrStatus;
+	KISO_PACKET IsoPackets[0];
+} KISO_CONTEXT, *PKISO_CONTEXT;
+
+typedef BOOL(WINAPI *LibK_IsoReadPipe_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle,
+	UCHAR PipeID,
+	PUCHAR Buffer,
+	ULONG BufferLength,
+	LPOVERLAPPED Overlapped,
+	PKISO_CONTEXT IsoContext
+);
+
+typedef BOOL(WINAPI *LibK_IsoWritePipe_t)(
+	WINUSB_INTERFACE_HANDLE InterfaceHandle,
+	UCHAR PipeID,
+	PUCHAR Buffer,
+	ULONG BufferLength,
+	LPOVERLAPPED Overlapped,
+	PKISO_CONTEXT IsoContext
+);
+
+struct winusb_interface {
+	HMODULE hDll;
+	WinUsb_AbortPipe_t AbortPipe;
+	WinUsb_ControlTransfer_t ControlTransfer;
+	WinUsb_FlushPipe_t FlushPipe;
+	WinUsb_Free_t Free;
+	WinUsb_GetAssociatedInterface_t GetAssociatedInterface;
+	WinUsb_Initialize_t Initialize;
+	WinUsb_ReadPipe_t ReadPipe;
+	WinUsb_ResetPipe_t ResetPipe;
+	WinUsb_SetCurrentAlternateSetting_t SetCurrentAlternateSetting;
+	WinUsb_SetPipePolicy_t SetPipePolicy;
+	WinUsb_WritePipe_t WritePipe;
+	union {
+		struct {
+			// Isochoronous functions for libusbK sub api:
+			LibK_IsoReadPipe_t IsoReadPipe;
+			LibK_IsoWritePipe_t IsoWritePipe;
+			// Reset device function for libusbK sub api:
+			LibK_ResetDevice_t ResetDevice;
+		};
+		struct {
+			// Isochronous functions for WinUSB sub api:
+			WinUsb_QueryPipeEx_t QueryPipeEx;
+			WinUsb_ReadIsochPipeAsap_t ReadIsochPipeAsap;
+			WinUsb_RegisterIsochBuffer_t RegisterIsochBuffer;
+			WinUsb_UnregisterIsochBuffer_t UnregisterIsochBuffer;
+			WinUsb_WriteIsochPipeAsap_t WriteIsochPipeAsap;
+		};
+	};
+};
+
+/* hid.dll interface */
+
+#define HIDP_STATUS_SUCCESS	0x110000
+typedef void * PHIDP_PREPARSED_DATA;
+
+#include <pshpack1.h>
+
+typedef struct _HIDD_ATTIRBUTES {
+	ULONG Size;
+	USHORT VendorID;
+	USHORT ProductID;
+	USHORT VersionNumber;
+} HIDD_ATTRIBUTES, *PHIDD_ATTRIBUTES;
+
+#include <poppack.h>
+
+typedef USHORT USAGE;
+typedef struct _HIDP_CAPS {
+	USAGE Usage;
+	USAGE UsagePage;
+	USHORT InputReportByteLength;
+	USHORT OutputReportByteLength;
+	USHORT FeatureReportByteLength;
+	USHORT Reserved[17];
+	USHORT NumberLinkCollectionNodes;
+	USHORT NumberInputButtonCaps;
+	USHORT NumberInputValueCaps;
+	USHORT NumberInputDataIndices;
+	USHORT NumberOutputButtonCaps;
+	USHORT NumberOutputValueCaps;
+	USHORT NumberOutputDataIndices;
+	USHORT NumberFeatureButtonCaps;
+	USHORT NumberFeatureValueCaps;
+	USHORT NumberFeatureDataIndices;
+} HIDP_CAPS, *PHIDP_CAPS;
+
+typedef enum _HIDP_REPORT_TYPE {
+	HidP_Input,
+	HidP_Output,
+	HidP_Feature
+} HIDP_REPORT_TYPE;
+
+typedef struct _HIDP_VALUE_CAPS {
+	USAGE UsagePage;
+	UCHAR ReportID;
+	BOOLEAN IsAlias;
+	USHORT BitField;
+	USHORT LinkCollection;
+	USAGE LinkUsage;
+	USAGE LinkUsagePage;
+	BOOLEAN IsRange;
+	BOOLEAN IsStringRange;
+	BOOLEAN IsDesignatorRange;
+	BOOLEAN IsAbsolute;
+	BOOLEAN HasNull;
+	UCHAR Reserved;
+	USHORT BitSize;
+	USHORT ReportCount;
+	USHORT Reserved2[5];
+	ULONG UnitsExp;
+	ULONG Units;
+	LONG LogicalMin, LogicalMax;
+	LONG PhysicalMin, PhysicalMax;
+	union {
+		struct {
+			USAGE UsageMin, UsageMax;
+			USHORT StringMin, StringMax;
+			USHORT DesignatorMin, DesignatorMax;
+			USHORT DataIndexMin, DataIndexMax;
+		} Range;
+		struct {
+			USAGE Usage, Reserved1;
+			USHORT StringIndex, Reserved2;
+			USHORT DesignatorIndex, Reserved3;
+			USHORT DataIndex, Reserved4;
+		} NotRange;
+	} u;
+} HIDP_VALUE_CAPS, *PHIDP_VALUE_CAPS;
+
+DLL_DECLARE_HANDLE(hid);
+DLL_DECLARE_FUNC(WINAPI, VOID, HidD_GetHidGuid, (LPGUID));
+DLL_DECLARE_FUNC(WINAPI, BOOL, HidD_GetAttributes, (HANDLE, PHIDD_ATTRIBUTES));
+DLL_DECLARE_FUNC(WINAPI, BOOL, HidD_GetPreparsedData, (HANDLE, PHIDP_PREPARSED_DATA *));
+DLL_DECLARE_FUNC(WINAPI, BOOL, HidD_FreePreparsedData, (PHIDP_PREPARSED_DATA));
+DLL_DECLARE_FUNC(WINAPI, BOOL, HidD_GetManufacturerString, (HANDLE, PVOID, ULONG));
+DLL_DECLARE_FUNC(WINAPI, BOOL, HidD_GetProductString, (HANDLE, PVOID, ULONG));
+DLL_DECLARE_FUNC(WINAPI, BOOL, HidD_GetSerialNumberString, (HANDLE, PVOID, ULONG));
+DLL_DECLARE_FUNC(WINAPI, BOOL, HidD_GetIndexedString, (HANDLE, ULONG, PVOID, ULONG));
+DLL_DECLARE_FUNC(WINAPI, LONG, HidP_GetCaps, (PHIDP_PREPARSED_DATA, PHIDP_CAPS));
+DLL_DECLARE_FUNC(WINAPI, BOOL, HidD_SetNumInputBuffers, (HANDLE, ULONG));
+DLL_DECLARE_FUNC(WINAPI, BOOL, HidD_GetPhysicalDescriptor, (HANDLE, PVOID, ULONG));
+DLL_DECLARE_FUNC(WINAPI, BOOL, HidD_FlushQueue, (HANDLE));
+DLL_DECLARE_FUNC(WINAPI, BOOL, HidP_GetValueCaps, (HIDP_REPORT_TYPE, PHIDP_VALUE_CAPS, PULONG, PHIDP_PREPARSED_DATA));
+
+#endif