Working project

1 files changed, 1483 insertions, 0 deletions

diff --git a/hardware/src/libusb/libusbi.h b/hardware/src/libusb/libusbi.h
new file mode 100644
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+++ b/hardware/src/libusb/libusbi.h
@@ -0,0 +1,1483 @@
+/*
+ * Internal header for libusb
+ * Copyright © 2007-2009 Daniel Drake <dsd@gentoo.org>
+ * Copyright © 2001 Johannes Erdfelt <johannes@erdfelt.com>
+ * Copyright © 2019 Nathan Hjelm <hjelmn@cs.umm.edu>
+ * Copyright © 2019-2020 Google LLC. All rights reserved.
+ * 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 LIBUSBI_H
+#define LIBUSBI_H
+
+#include "config.h"
+
+#include <assert.h>
+#include <inttypes.h>
+#include <stdarg.h>
+#include <stddef.h>
+#include <stdlib.h>
+#ifdef HAVE_SYS_TIME_H
+#include <sys/time.h>
+#endif
+
+#include "libusb.h"
+
+/* Not all C standard library headers define static_assert in assert.h
+ * Additionally, Visual Studio treats static_assert as a keyword.
+ */
+#if !defined(__cplusplus) && !defined(static_assert) && !defined(_MSC_VER)
+#define static_assert(cond, msg) _Static_assert(cond, msg)
+#endif
+
+#ifdef NDEBUG
+#define ASSERT_EQ(expression, value)	(void)expression
+#define ASSERT_NE(expression, value)	(void)expression
+#else
+#define ASSERT_EQ(expression, value)	assert(expression == value)
+#define ASSERT_NE(expression, value)	assert(expression != value)
+#endif
+
+#define container_of(ptr, type, member) \
+	((type *)((uintptr_t)(ptr) - (uintptr_t)offsetof(type, member)))
+
+#ifndef ARRAYSIZE
+#define ARRAYSIZE(array) (sizeof(array) / sizeof(array[0]))
+#endif
+
+#ifndef CLAMP
+#define CLAMP(val, min, max) \
+	((val) < (min) ? (min) : ((val) > (max) ? (max) : (val)))
+#endif
+
+#ifndef MIN
+#define MIN(a, b)	((a) < (b) ? (a) : (b))
+#endif
+
+#ifndef MAX
+#define MAX(a, b)	((a) > (b) ? (a) : (b))
+#endif
+
+/* The following is used to silence warnings for unused variables */
+#if defined(UNREFERENCED_PARAMETER)
+#define UNUSED(var)	UNREFERENCED_PARAMETER(var)
+#else
+#define UNUSED(var)	do { (void)(var); } while(0)
+#endif
+
+/* Macro to align a value up to the next multiple of the size of a pointer */
+#define PTR_ALIGN(v) \
+	(((v) + (sizeof(void *) - 1)) & ~(sizeof(void *) - 1))
+
+/* Atomic operations
+ *
+ * Useful for reference counting or when accessing a value without a lock
+ *
+ * The following atomic operations are defined:
+ *   usbi_atomic_load() - Atomically read a variable's value
+ *   usbi_atomic_store() - Atomically write a new value value to a variable
+ *   usbi_atomic_inc() - Atomically increment a variable's value and return the new value
+ *   usbi_atomic_dec() - Atomically decrement a variable's value and return the new value
+ *
+ * All of these operations are ordered with each other, thus the effects of
+ * any one operation is guaranteed to be seen by any other operation.
+ */
+#ifdef _MSC_VER
+typedef volatile LONG usbi_atomic_t;
+#define usbi_atomic_load(a)	(*(a))
+#define usbi_atomic_store(a, v)	(*(a)) = (v)
+#define usbi_atomic_inc(a)	InterlockedIncrement((a))
+#define usbi_atomic_dec(a)	InterlockedDecrement((a))
+#else
+#include <stdatomic.h>
+typedef atomic_long usbi_atomic_t;
+#define usbi_atomic_load(a)	atomic_load((a))
+#define usbi_atomic_store(a, v)	atomic_store((a), (v))
+#define usbi_atomic_inc(a)	(atomic_fetch_add((a), 1) + 1)
+#define usbi_atomic_dec(a)	(atomic_fetch_add((a), -1) - 1)
+#endif
+
+/* Internal abstractions for event handling and thread synchronization */
+#if defined(PLATFORM_POSIX)
+#include "os/events_posix.h"
+#include "os/threads_posix.h"
+#elif defined(PLATFORM_WINDOWS)
+#include "os/events_windows.h"
+#include "os/threads_windows.h"
+#endif
+
+/* Inside the libusb code, mark all public functions as follows:
+ *   return_type API_EXPORTED function_name(params) { ... }
+ * But if the function returns a pointer, mark it as follows:
+ *   DEFAULT_VISIBILITY return_type * LIBUSB_CALL function_name(params) { ... }
+ * In the libusb public header, mark all declarations as:
+ *   return_type LIBUSB_CALL function_name(params);
+ */
+#define API_EXPORTED LIBUSB_CALL DEFAULT_VISIBILITY
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#define USB_MAXENDPOINTS	32
+#define USB_MAXINTERFACES	32
+#define USB_MAXCONFIG		8
+
+/* Backend specific capabilities */
+#define USBI_CAP_HAS_HID_ACCESS			0x00010000
+#define USBI_CAP_SUPPORTS_DETACH_KERNEL_DRIVER	0x00020000
+
+/* Maximum number of bytes in a log line */
+#define USBI_MAX_LOG_LEN	1024
+/* Terminator for log lines */
+#define USBI_LOG_LINE_END	"\n"
+
+struct list_head {
+	struct list_head *prev, *next;
+};
+
+/* Get an entry from the list
+ *  ptr - the address of this list_head element in "type"
+ *  type - the data type that contains "member"
+ *  member - the list_head element in "type"
+ */
+#define list_entry(ptr, type, member) \
+	container_of(ptr, type, member)
+
+#define list_first_entry(ptr, type, member) \
+	list_entry((ptr)->next, type, member)
+
+#define list_next_entry(ptr, type, member) \
+	list_entry((ptr)->member.next, type, member)
+
+/* Get each entry from a list
+ *  pos - A structure pointer has a "member" element
+ *  head - list head
+ *  member - the list_head element in "pos"
+ *  type - the type of the first parameter
+ */
+#define list_for_each_entry(pos, head, member, type)			\
+	for (pos = list_first_entry(head, type, member);		\
+		 &pos->member != (head);				\
+		 pos = list_next_entry(pos, type, member))
+
+#define list_for_each_entry_safe(pos, n, head, member, type)		\
+	for (pos = list_first_entry(head, type, member),		\
+		 n = list_next_entry(pos, type, member);		\
+		 &pos->member != (head);				\
+		 pos = n, n = list_next_entry(n, type, member))
+
+/* Helper macros to iterate over a list. The structure pointed
+ * to by "pos" must have a list_head member named "list".
+ */
+#define for_each_helper(pos, head, type) \
+	list_for_each_entry(pos, head, list, type)
+
+#define for_each_safe_helper(pos, n, head, type) \
+	list_for_each_entry_safe(pos, n, head, list, type)
+
+#define list_empty(entry) ((entry)->next == (entry))
+
+static inline void list_init(struct list_head *entry)
+{
+	entry->prev = entry->next = entry;
+}
+
+static inline void list_add(struct list_head *entry, struct list_head *head)
+{
+	entry->next = head->next;
+	entry->prev = head;
+
+	head->next->prev = entry;
+	head->next = entry;
+}
+
+static inline void list_add_tail(struct list_head *entry,
+	struct list_head *head)
+{
+	entry->next = head;
+	entry->prev = head->prev;
+
+	head->prev->next = entry;
+	head->prev = entry;
+}
+
+static inline void list_del(struct list_head *entry)
+{
+	entry->next->prev = entry->prev;
+	entry->prev->next = entry->next;
+	entry->next = entry->prev = NULL;
+}
+
+static inline void list_cut(struct list_head *list, struct list_head *head)
+{
+	if (list_empty(head)) {
+		list_init(list);
+		return;
+	}
+
+	list->next = head->next;
+	list->next->prev = list;
+	list->prev = head->prev;
+	list->prev->next = list;
+
+	list_init(head);
+}
+
+static inline void list_splice_front(struct list_head *list, struct list_head *head)
+{
+	list->next->prev = head;
+	list->prev->next = head->next;
+	head->next->prev = list->prev;
+	head->next = list->next;
+}
+
+static inline void *usbi_reallocf(void *ptr, size_t size)
+{
+	void *ret = realloc(ptr, size);
+
+	if (!ret)
+		free(ptr);
+	return ret;
+}
+
+#if !defined(USEC_PER_SEC)
+#define USEC_PER_SEC	1000000L
+#endif
+
+#if !defined(NSEC_PER_SEC)
+#define NSEC_PER_SEC	1000000000L
+#endif
+
+#define TIMEVAL_IS_VALID(tv)						\
+	((tv)->tv_sec >= 0 &&						\
+	 (tv)->tv_usec >= 0 && (tv)->tv_usec < USEC_PER_SEC)
+
+#define TIMESPEC_IS_SET(ts)	((ts)->tv_sec || (ts)->tv_nsec)
+#define TIMESPEC_CLEAR(ts)	(ts)->tv_sec = (ts)->tv_nsec = 0
+#define TIMESPEC_CMP(a, b, CMP)						\
+	(((a)->tv_sec == (b)->tv_sec)					\
+	 ? ((a)->tv_nsec CMP (b)->tv_nsec)				\
+	 : ((a)->tv_sec CMP (b)->tv_sec))
+#define TIMESPEC_SUB(a, b, result)					\
+	do {								\
+		(result)->tv_sec = (a)->tv_sec - (b)->tv_sec;		\
+		(result)->tv_nsec = (a)->tv_nsec - (b)->tv_nsec;	\
+		if ((result)->tv_nsec < 0L) {				\
+			--(result)->tv_sec;				\
+			(result)->tv_nsec += NSEC_PER_SEC;		\
+		}							\
+	} while (0)
+
+#if defined(PLATFORM_WINDOWS)
+#define TIMEVAL_TV_SEC_TYPE	long
+#else
+#define TIMEVAL_TV_SEC_TYPE	time_t
+#endif
+
+/* Some platforms don't have this define */
+#ifndef TIMESPEC_TO_TIMEVAL
+#define TIMESPEC_TO_TIMEVAL(tv, ts)					\
+	do {								\
+		(tv)->tv_sec = (TIMEVAL_TV_SEC_TYPE) (ts)->tv_sec;	\
+		(tv)->tv_usec = (ts)->tv_nsec / 1000L;			\
+	} while (0)
+#endif
+
+#ifdef ENABLE_LOGGING
+
+#if defined(_MSC_VER) && (_MSC_VER < 1900)
+#include <stdio.h>
+#define snprintf usbi_snprintf
+#define vsnprintf usbi_vsnprintf
+int usbi_snprintf(char *dst, size_t size, const char *format, ...);
+int usbi_vsnprintf(char *dst, size_t size, const char *format, va_list args);
+#define LIBUSB_PRINTF_WIN32
+#endif /* defined(_MSC_VER) && (_MSC_VER < 1900) */
+
+void usbi_log(struct libusb_context *ctx, enum libusb_log_level level,
+	const char *function, const char *format, ...) PRINTF_FORMAT(4, 5);
+
+#define _usbi_log(ctx, level, ...) usbi_log(ctx, level, __func__, __VA_ARGS__)
+
+#define usbi_err(ctx, ...)	_usbi_log(ctx, LIBUSB_LOG_LEVEL_ERROR, __VA_ARGS__)
+#define usbi_warn(ctx, ...)	_usbi_log(ctx, LIBUSB_LOG_LEVEL_WARNING, __VA_ARGS__)
+#define usbi_info(ctx, ...)	_usbi_log(ctx, LIBUSB_LOG_LEVEL_INFO, __VA_ARGS__)
+#define usbi_dbg(ctx ,...)      	_usbi_log(ctx, LIBUSB_LOG_LEVEL_DEBUG, __VA_ARGS__)
+
+#else /* ENABLE_LOGGING */
+
+#define usbi_err(ctx, ...)	UNUSED(ctx)
+#define usbi_warn(ctx, ...)	UNUSED(ctx)
+#define usbi_info(ctx, ...)	UNUSED(ctx)
+#define usbi_dbg(ctx, ...)	do {} while (0)
+
+#endif /* ENABLE_LOGGING */
+
+#define DEVICE_CTX(dev)		((dev)->ctx)
+#define HANDLE_CTX(handle)	(DEVICE_CTX((handle)->dev))
+#define TRANSFER_CTX(transfer)	(HANDLE_CTX((transfer)->dev_handle))
+#define ITRANSFER_CTX(itransfer) \
+	(TRANSFER_CTX(USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)))
+
+#define IS_EPIN(ep)		(0 != ((ep) & LIBUSB_ENDPOINT_IN))
+#define IS_EPOUT(ep)		(!IS_EPIN(ep))
+#define IS_XFERIN(xfer)		(0 != ((xfer)->endpoint & LIBUSB_ENDPOINT_IN))
+#define IS_XFEROUT(xfer)	(!IS_XFERIN(xfer))
+
+struct libusb_context {
+#if defined(ENABLE_LOGGING) && !defined(ENABLE_DEBUG_LOGGING)
+	enum libusb_log_level debug;
+	int debug_fixed;
+	libusb_log_cb log_handler;
+#endif
+
+	/* used for signalling occurrence of an internal event. */
+	usbi_event_t event;
+
+#ifdef HAVE_OS_TIMER
+	/* used for timeout handling, if supported by OS.
+	 * this timer is maintained to trigger on the next pending timeout */
+	usbi_timer_t timer;
+#endif
+
+	struct list_head usb_devs;
+	usbi_mutex_t usb_devs_lock;
+
+	/* A list of open handles. Backends are free to traverse this if required.
+	 */
+	struct list_head open_devs;
+	usbi_mutex_t open_devs_lock;
+
+	/* A list of registered hotplug callbacks */
+	struct list_head hotplug_cbs;
+	libusb_hotplug_callback_handle next_hotplug_cb_handle;
+	usbi_mutex_t hotplug_cbs_lock;
+
+	/* A flag to indicate that the context is ready for hotplug notifications */
+	usbi_atomic_t hotplug_ready;
+
+	/* this is a list of in-flight transfer handles, sorted by timeout
+	 * expiration. URBs to timeout the soonest are placed at the beginning of
+	 * the list, URBs that will time out later are placed after, and urbs with
+	 * infinite timeout are always placed at the very end. */
+	struct list_head flying_transfers;
+	/* Note paths taking both this and usbi_transfer->lock must always
+	 * take this lock first */
+	usbi_mutex_t flying_transfers_lock;
+
+#if !defined(PLATFORM_WINDOWS)
+	/* user callbacks for pollfd changes */
+	libusb_pollfd_added_cb fd_added_cb;
+	libusb_pollfd_removed_cb fd_removed_cb;
+	void *fd_cb_user_data;
+#endif
+
+	/* ensures that only one thread is handling events at any one time */
+	usbi_mutex_t events_lock;
+
+	/* used to see if there is an active thread doing event handling */
+	int event_handler_active;
+
+	/* A thread-local storage key to track which thread is performing event
+	 * handling */
+	usbi_tls_key_t event_handling_key;
+
+	/* used to wait for event completion in threads other than the one that is
+	 * event handling */
+	usbi_mutex_t event_waiters_lock;
+	usbi_cond_t event_waiters_cond;
+
+	/* A lock to protect internal context event data. */
+	usbi_mutex_t event_data_lock;
+
+	/* A bitmask of flags that are set to indicate specific events that need to
+	 * be handled. Protected by event_data_lock. */
+	unsigned int event_flags;
+
+	/* A counter that is set when we want to interrupt and prevent event handling,
+	 * in order to safely close a device. Protected by event_data_lock. */
+	unsigned int device_close;
+
+	/* A list of currently active event sources. Protected by event_data_lock. */
+	struct list_head event_sources;
+
+	/* A list of event sources that have been removed since the last time
+	 * event sources were waited on. Protected by event_data_lock. */
+	struct list_head removed_event_sources;
+
+	/* A pointer and count to platform-specific data used for monitoring event
+	 * sources. Only accessed during event handling. */
+	void *event_data;
+	unsigned int event_data_cnt;
+
+	/* A list of pending hotplug messages. Protected by event_data_lock. */
+	struct list_head hotplug_msgs;
+
+	/* A list of pending completed transfers. Protected by event_data_lock. */
+	struct list_head completed_transfers;
+
+	struct list_head list;
+};
+
+extern struct libusb_context *usbi_default_context;
+
+extern struct list_head active_contexts_list;
+extern usbi_mutex_static_t active_contexts_lock;
+
+static inline struct libusb_context *usbi_get_context(struct libusb_context *ctx)
+{
+	return ctx ? ctx : usbi_default_context;
+}
+
+enum usbi_event_flags {
+	/* The list of event sources has been modified */
+	USBI_EVENT_EVENT_SOURCES_MODIFIED = 1U << 0,
+
+	/* The user has interrupted the event handler */
+	USBI_EVENT_USER_INTERRUPT = 1U << 1,
+
+	/* A hotplug callback deregistration is pending */
+	USBI_EVENT_HOTPLUG_CB_DEREGISTERED = 1U << 2,
+
+	/* One or more hotplug messages are pending */
+	USBI_EVENT_HOTPLUG_MSG_PENDING = 1U << 3,
+
+	/* One or more completed transfers are pending */
+	USBI_EVENT_TRANSFER_COMPLETED = 1U << 4,
+
+	/* A device is in the process of being closed */
+	USBI_EVENT_DEVICE_CLOSE = 1U << 5,
+};
+
+/* Macros for managing event handling state */
+static inline int usbi_handling_events(struct libusb_context *ctx)
+{
+	return usbi_tls_key_get(ctx->event_handling_key) != NULL;
+}
+
+static inline void usbi_start_event_handling(struct libusb_context *ctx)
+{
+	usbi_tls_key_set(ctx->event_handling_key, ctx);
+}
+
+static inline void usbi_end_event_handling(struct libusb_context *ctx)
+{
+	usbi_tls_key_set(ctx->event_handling_key, NULL);
+}
+
+struct libusb_device {
+	usbi_atomic_t refcnt;
+
+	struct libusb_context *ctx;
+	struct libusb_device *parent_dev;
+
+	uint8_t bus_number;
+	uint8_t port_number;
+	uint8_t device_address;
+	enum libusb_speed speed;
+
+	struct list_head list;
+	unsigned long session_data;
+
+	struct libusb_device_descriptor device_descriptor;
+	usbi_atomic_t attached;
+};
+
+struct libusb_device_handle {
+	/* lock protects claimed_interfaces */
+	usbi_mutex_t lock;
+	unsigned long claimed_interfaces;
+
+	struct list_head list;
+	struct libusb_device *dev;
+	int auto_detach_kernel_driver;
+};
+
+/* Function called by backend during device initialization to convert
+ * multi-byte fields in the device descriptor to host-endian format.
+ */
+static inline void usbi_localize_device_descriptor(struct libusb_device_descriptor *desc)
+{
+	desc->bcdUSB = libusb_le16_to_cpu(desc->bcdUSB);
+	desc->idVendor = libusb_le16_to_cpu(desc->idVendor);
+	desc->idProduct = libusb_le16_to_cpu(desc->idProduct);
+	desc->bcdDevice = libusb_le16_to_cpu(desc->bcdDevice);
+}
+
+#ifdef HAVE_CLOCK_GETTIME
+static inline void usbi_get_monotonic_time(struct timespec *tp)
+{
+	ASSERT_EQ(clock_gettime(CLOCK_MONOTONIC, tp), 0);
+}
+static inline void usbi_get_real_time(struct timespec *tp)
+{
+	ASSERT_EQ(clock_gettime(CLOCK_REALTIME, tp), 0);
+}
+#else
+/* If the platform doesn't provide the clock_gettime() function, the backend
+ * must provide its own clock implementations.  Two clock functions are
+ * required:
+ *
+ *   usbi_get_monotonic_time(): returns the time since an unspecified starting
+ *                              point (usually boot) that is monotonically
+ *                              increasing.
+ *   usbi_get_real_time(): returns the time since system epoch.
+ */
+void usbi_get_monotonic_time(struct timespec *tp);
+void usbi_get_real_time(struct timespec *tp);
+#endif
+
+/* in-memory transfer layout:
+ *
+ * 1. os private data
+ * 2. struct usbi_transfer
+ * 3. struct libusb_transfer (which includes iso packets) [variable size]
+ *
+ * from a libusb_transfer, you can get the usbi_transfer by rewinding the
+ * appropriate number of bytes.
+ */
+
+struct usbi_transfer {
+	int num_iso_packets;
+	struct list_head list;
+	struct list_head completed_list;
+	struct timespec timeout;
+	int transferred;
+	uint32_t stream_id;
+	uint32_t state_flags;   /* Protected by usbi_transfer->lock */
+	uint32_t timeout_flags; /* Protected by the flying_stransfers_lock */
+
+	/* this lock is held during libusb_submit_transfer() and
+	 * libusb_cancel_transfer() (allowing the OS backend to prevent duplicate
+	 * cancellation, submission-during-cancellation, etc). the OS backend
+	 * should also take this lock in the handle_events path, to prevent the user
+	 * cancelling the transfer from another thread while you are processing
+	 * its completion (presumably there would be races within your OS backend
+	 * if this were possible).
+	 * Note paths taking both this and the flying_transfers_lock must
+	 * always take the flying_transfers_lock first */
+	usbi_mutex_t lock;
+
+	void *priv;
+};
+
+enum usbi_transfer_state_flags {
+	/* Transfer successfully submitted by backend */
+	USBI_TRANSFER_IN_FLIGHT = 1U << 0,
+
+	/* Cancellation was requested via libusb_cancel_transfer() */
+	USBI_TRANSFER_CANCELLING = 1U << 1,
+
+	/* Operation on the transfer failed because the device disappeared */
+	USBI_TRANSFER_DEVICE_DISAPPEARED = 1U << 2,
+};
+
+enum usbi_transfer_timeout_flags {
+	/* Set by backend submit_transfer() if the OS handles timeout */
+	USBI_TRANSFER_OS_HANDLES_TIMEOUT = 1U << 0,
+
+	/* The transfer timeout has been handled */
+	USBI_TRANSFER_TIMEOUT_HANDLED = 1U << 1,
+
+	/* The transfer timeout was successfully processed */
+	USBI_TRANSFER_TIMED_OUT = 1U << 2,
+};
+
+#define USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)	\
+	((struct libusb_transfer *)			\
+	 ((unsigned char *)(itransfer)			\
+	  + PTR_ALIGN(sizeof(struct usbi_transfer))))
+#define LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer)	\
+	((struct usbi_transfer *)			\
+	 ((unsigned char *)(transfer)			\
+	  - PTR_ALIGN(sizeof(struct usbi_transfer))))
+
+#ifdef _MSC_VER
+#pragma pack(push, 1)
+#endif
+
+/* All standard descriptors have these 2 fields in common */
+struct usbi_descriptor_header {
+	uint8_t  bLength;
+	uint8_t  bDescriptorType;
+} LIBUSB_PACKED;
+
+struct usbi_device_descriptor {
+	uint8_t  bLength;
+	uint8_t  bDescriptorType;
+	uint16_t bcdUSB;
+	uint8_t  bDeviceClass;
+	uint8_t  bDeviceSubClass;
+	uint8_t  bDeviceProtocol;
+	uint8_t  bMaxPacketSize0;
+	uint16_t idVendor;
+	uint16_t idProduct;
+	uint16_t bcdDevice;
+	uint8_t  iManufacturer;
+	uint8_t  iProduct;
+	uint8_t  iSerialNumber;
+	uint8_t  bNumConfigurations;
+} LIBUSB_PACKED;
+
+struct usbi_configuration_descriptor {
+	uint8_t  bLength;
+	uint8_t  bDescriptorType;
+	uint16_t wTotalLength;
+	uint8_t  bNumInterfaces;
+	uint8_t  bConfigurationValue;
+	uint8_t  iConfiguration;
+	uint8_t  bmAttributes;
+	uint8_t  bMaxPower;
+} LIBUSB_PACKED;
+
+struct usbi_interface_descriptor {
+	uint8_t  bLength;
+	uint8_t  bDescriptorType;
+	uint8_t  bInterfaceNumber;
+	uint8_t  bAlternateSetting;
+	uint8_t  bNumEndpoints;
+	uint8_t  bInterfaceClass;
+	uint8_t  bInterfaceSubClass;
+	uint8_t  bInterfaceProtocol;
+	uint8_t  iInterface;
+} LIBUSB_PACKED;
+
+struct usbi_string_descriptor {
+	uint8_t  bLength;
+	uint8_t  bDescriptorType;
+	uint16_t wData[ZERO_SIZED_ARRAY];
+} LIBUSB_PACKED;
+
+struct usbi_bos_descriptor {
+	uint8_t  bLength;
+	uint8_t  bDescriptorType;
+	uint16_t wTotalLength;
+	uint8_t  bNumDeviceCaps;
+} LIBUSB_PACKED;
+
+#ifdef _MSC_VER
+#pragma pack(pop)
+#endif
+
+union usbi_config_desc_buf {
+        struct usbi_configuration_descriptor desc;
+        uint8_t buf[LIBUSB_DT_CONFIG_SIZE];
+        uint16_t align;         /* Force 2-byte alignment */
+};
+
+union usbi_string_desc_buf {
+        struct usbi_string_descriptor desc;
+        uint8_t buf[255];       /* Some devices choke on size > 255 */
+        uint16_t align;         /* Force 2-byte alignment */
+};
+
+union usbi_bos_desc_buf {
+        struct usbi_bos_descriptor desc;
+        uint8_t buf[LIBUSB_DT_BOS_SIZE];
+        uint16_t align;         /* Force 2-byte alignment */
+};
+
+enum usbi_hotplug_flags {
+	/* This callback is interested in device arrivals */
+	USBI_HOTPLUG_DEVICE_ARRIVED = LIBUSB_HOTPLUG_EVENT_DEVICE_ARRIVED,
+
+	/* This callback is interested in device removals */
+	USBI_HOTPLUG_DEVICE_LEFT = LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT,
+
+	/* IMPORTANT: The values for the below entries must start *after*
+	 * the highest value of the above entries!!!
+	 */
+
+	/* The vendor_id field is valid for matching */
+	USBI_HOTPLUG_VENDOR_ID_VALID = (1U << 3),
+
+	/* The product_id field is valid for matching */
+	USBI_HOTPLUG_PRODUCT_ID_VALID = (1U << 4),
+
+	/* The dev_class field is valid for matching */
+	USBI_HOTPLUG_DEV_CLASS_VALID = (1U << 5),
+
+	/* This callback has been unregistered and needs to be freed */
+	USBI_HOTPLUG_NEEDS_FREE = (1U << 6),
+};
+
+struct usbi_hotplug_callback {
+	/* Flags that control how this callback behaves */
+	uint8_t flags;
+
+	/* Vendor ID to match (if flags says this is valid) */
+	uint16_t vendor_id;
+
+	/* Product ID to match (if flags says this is valid) */
+	uint16_t product_id;
+
+	/* Device class to match (if flags says this is valid) */
+	uint8_t dev_class;
+
+	/* Callback function to invoke for matching event/device */
+	libusb_hotplug_callback_fn cb;
+
+	/* Handle for this callback (used to match on deregister) */
+	libusb_hotplug_callback_handle handle;
+
+	/* User data that will be passed to the callback function */
+	void *user_data;
+
+	/* List this callback is registered in (ctx->hotplug_cbs) */
+	struct list_head list;
+};
+
+struct usbi_hotplug_message {
+	/* The hotplug event that occurred */
+	libusb_hotplug_event event;
+
+	/* The device for which this hotplug event occurred */
+	struct libusb_device *device;
+
+	/* List this message is contained in (ctx->hotplug_msgs) */
+	struct list_head list;
+};
+
+/* shared data and functions */
+
+void usbi_hotplug_init(struct libusb_context *ctx);
+void usbi_hotplug_exit(struct libusb_context *ctx);
+void usbi_hotplug_notification(struct libusb_context *ctx, struct libusb_device *dev,
+	libusb_hotplug_event event);
+void usbi_hotplug_process(struct libusb_context *ctx, struct list_head *hotplug_msgs);
+
+int usbi_io_init(struct libusb_context *ctx);
+void usbi_io_exit(struct libusb_context *ctx);
+
+struct libusb_device *usbi_alloc_device(struct libusb_context *ctx,
+	unsigned long session_id);
+struct libusb_device *usbi_get_device_by_session_id(struct libusb_context *ctx,
+	unsigned long session_id);
+int usbi_sanitize_device(struct libusb_device *dev);
+void usbi_handle_disconnect(struct libusb_device_handle *dev_handle);
+
+int usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
+	enum libusb_transfer_status status);
+int usbi_handle_transfer_cancellation(struct usbi_transfer *itransfer);
+void usbi_signal_transfer_completion(struct usbi_transfer *itransfer);
+
+void usbi_connect_device(struct libusb_device *dev);
+void usbi_disconnect_device(struct libusb_device *dev);
+
+struct usbi_event_source {
+	struct usbi_event_source_data {
+		usbi_os_handle_t os_handle;
+		short poll_events;
+	} data;
+	struct list_head list;
+};
+
+int usbi_add_event_source(struct libusb_context *ctx, usbi_os_handle_t os_handle,
+	short poll_events);
+void usbi_remove_event_source(struct libusb_context *ctx, usbi_os_handle_t os_handle);
+
+struct usbi_option {
+  int is_set;
+  union {
+    int ival;
+  } arg;
+};
+
+/* OS event abstraction */
+
+int usbi_create_event(usbi_event_t *event);
+void usbi_destroy_event(usbi_event_t *event);
+void usbi_signal_event(usbi_event_t *event);
+void usbi_clear_event(usbi_event_t *event);
+
+#ifdef HAVE_OS_TIMER
+int usbi_create_timer(usbi_timer_t *timer);
+void usbi_destroy_timer(usbi_timer_t *timer);
+int usbi_arm_timer(usbi_timer_t *timer, const struct timespec *timeout);
+int usbi_disarm_timer(usbi_timer_t *timer);
+#endif
+
+static inline int usbi_using_timer(struct libusb_context *ctx)
+{
+#ifdef HAVE_OS_TIMER
+	return usbi_timer_valid(&ctx->timer);
+#else
+	UNUSED(ctx);
+	return 0;
+#endif
+}
+
+struct usbi_reported_events {
+	union {
+		struct {
+			unsigned int event_triggered:1;
+#ifdef HAVE_OS_TIMER
+			unsigned int timer_triggered:1;
+#endif
+		};
+		unsigned int event_bits;
+	};
+	void *event_data;
+	unsigned int event_data_count;
+	unsigned int num_ready;
+};
+
+int usbi_alloc_event_data(struct libusb_context *ctx);
+int usbi_wait_for_events(struct libusb_context *ctx,
+	struct usbi_reported_events *reported_events, int timeout_ms);
+
+/* accessor functions for structure private data */
+
+static inline void *usbi_get_context_priv(struct libusb_context *ctx)
+{
+	return (unsigned char *)ctx + PTR_ALIGN(sizeof(*ctx));
+}
+
+static inline void *usbi_get_device_priv(struct libusb_device *dev)
+{
+	return (unsigned char *)dev + PTR_ALIGN(sizeof(*dev));
+}
+
+static inline void *usbi_get_device_handle_priv(struct libusb_device_handle *dev_handle)
+{
+	return (unsigned char *)dev_handle + PTR_ALIGN(sizeof(*dev_handle));
+}
+
+static inline void *usbi_get_transfer_priv(struct usbi_transfer *itransfer)
+{
+	return itransfer->priv;
+}
+
+/* device discovery */
+
+/* we traverse usbfs without knowing how many devices we are going to find.
+ * so we create this discovered_devs model which is similar to a linked-list
+ * which grows when required. it can be freed once discovery has completed,
+ * eliminating the need for a list node in the libusb_device structure
+ * itself. */
+struct discovered_devs {
+	size_t len;
+	size_t capacity;
+	struct libusb_device *devices[ZERO_SIZED_ARRAY];
+};
+
+struct discovered_devs *discovered_devs_append(
+	struct discovered_devs *discdevs, struct libusb_device *dev);
+
+/* OS abstraction */
+
+/* This is the interface that OS backends need to implement.
+ * All fields are mandatory, except ones explicitly noted as optional. */
+struct usbi_os_backend {
+	/* A human-readable name for your backend, e.g. "Linux usbfs" */
+	const char *name;
+
+	/* Binary mask for backend specific capabilities */
+	uint32_t caps;
+
+	/* Perform initialization of your backend. You might use this function
+	 * to determine specific capabilities of the system, allocate required
+	 * data structures for later, etc.
+	 *
+	 * This function is called when a libusb user initializes the library
+	 * prior to use. Mutual exclusion with other init and exit calls is
+	 * guaranteed when this function is called.
+	 *
+	 * Return 0 on success, or a LIBUSB_ERROR code on failure.
+	 */
+	int (*init)(struct libusb_context *ctx);
+
+	/* Deinitialization. Optional. This function should destroy anything
+	 * that was set up by init.
+	 *
+	 * This function is called when the user deinitializes the library.
+	 * Mutual exclusion with other init and exit calls is guaranteed when
+	 * this function is called.
+	 */
+	void (*exit)(struct libusb_context *ctx);
+
+	/* Set a backend-specific option. Optional.
+	 *
+	 * This function is called when the user calls libusb_set_option() and
+	 * the option is not handled by the core library.
+	 *
+	 * Return 0 on success, or a LIBUSB_ERROR code on failure.
+	 */
+	int (*set_option)(struct libusb_context *ctx, enum libusb_option option,
+		va_list args);
+
+	/* Enumerate all the USB devices on the system, returning them in a list
+	 * of discovered devices.
+	 *
+	 * Your implementation should enumerate all devices on the system,
+	 * regardless of whether they have been seen before or not.
+	 *
+	 * When you have found a device, compute a session ID for it. The session
+	 * ID should uniquely represent that particular device for that particular
+	 * connection session since boot (i.e. if you disconnect and reconnect a
+	 * device immediately after, it should be assigned a different session ID).
+	 * If your OS cannot provide a unique session ID as described above,
+	 * presenting a session ID of (bus_number << 8 | device_address) should
+	 * be sufficient. Bus numbers and device addresses wrap and get reused,
+	 * but that is an unlikely case.
+	 *
+	 * After computing a session ID for a device, call
+	 * usbi_get_device_by_session_id(). This function checks if libusb already
+	 * knows about the device, and if so, it provides you with a reference
+	 * to a libusb_device structure for it.
+	 *
+	 * If usbi_get_device_by_session_id() returns NULL, it is time to allocate
+	 * a new device structure for the device. Call usbi_alloc_device() to
+	 * obtain a new libusb_device structure with reference count 1. Populate
+	 * the bus_number and device_address attributes of the new device, and
+	 * perform any other internal backend initialization you need to do. At
+	 * this point, you should be ready to provide device descriptors and so
+	 * on through the get_*_descriptor functions. Finally, call
+	 * usbi_sanitize_device() to perform some final sanity checks on the
+	 * device. Assuming all of the above succeeded, we can now continue.
+	 * If any of the above failed, remember to unreference the device that
+	 * was returned by usbi_alloc_device().
+	 *
+	 * At this stage we have a populated libusb_device structure (either one
+	 * that was found earlier, or one that we have just allocated and
+	 * populated). This can now be added to the discovered devices list
+	 * using discovered_devs_append(). Note that discovered_devs_append()
+	 * may reallocate the list, returning a new location for it, and also
+	 * note that reallocation can fail. Your backend should handle these
+	 * error conditions appropriately.
+	 *
+	 * This function should not generate any bus I/O and should not block.
+	 * If I/O is required (e.g. reading the active configuration value), it is
+	 * OK to ignore these suggestions :)
+	 *
+	 * This function is executed when the user wishes to retrieve a list
+	 * of USB devices connected to the system.
+	 *
+	 * If the backend has hotplug support, this function is not used!
+	 *
+	 * Return 0 on success, or a LIBUSB_ERROR code on failure.
+	 */
+	int (*get_device_list)(struct libusb_context *ctx,
+		struct discovered_devs **discdevs);
+
+	/* Apps which were written before hotplug support, may listen for
+	 * hotplug events on their own and call libusb_get_device_list on
+	 * device addition. In this case libusb_get_device_list will likely
+	 * return a list without the new device in there, as the hotplug
+	 * event thread will still be busy enumerating the device, which may
+	 * take a while, or may not even have seen the event yet.
+	 *
+	 * To avoid this libusb_get_device_list will call this optional
+	 * function for backends with hotplug support before copying
+	 * ctx->usb_devs to the user. In this function the backend should
+	 * ensure any pending hotplug events are fully processed before
+	 * returning.
+	 *
+	 * Optional, should be implemented by backends with hotplug support.
+	 */
+	void (*hotplug_poll)(void);
+
+	/* Wrap a platform-specific device handle for I/O and other USB
+	 * operations. The device handle is preallocated for you.
+	 *
+	 * Your backend should allocate any internal resources required for I/O
+	 * and other operations so that those operations can happen (hopefully)
+	 * without hiccup. This is also a good place to inform libusb that it
+	 * should monitor certain file descriptors related to this device -
+	 * see the usbi_add_event_source() function.
+	 *
+	 * Your backend should also initialize the device structure
+	 * (dev_handle->dev), which is NULL at the beginning of the call.
+	 *
+	 * This function should not generate any bus I/O and should not block.
+	 *
+	 * This function is called when the user attempts to wrap an existing
+	 * platform-specific device handle for a device.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_ACCESS if the user has insufficient permissions
+	 * - another LIBUSB_ERROR code on other failure
+	 *
+	 * Do not worry about freeing the handle on failed open, the upper layers
+	 * do this for you.
+	 */
+	int (*wrap_sys_device)(struct libusb_context *ctx,
+		struct libusb_device_handle *dev_handle, intptr_t sys_dev);
+
+	/* Open a device for I/O and other USB operations. The device handle
+	 * is preallocated for you, you can retrieve the device in question
+	 * through handle->dev.
+	 *
+	 * Your backend should allocate any internal resources required for I/O
+	 * and other operations so that those operations can happen (hopefully)
+	 * without hiccup. This is also a good place to inform libusb that it
+	 * should monitor certain file descriptors related to this device -
+	 * see the usbi_add_event_source() function.
+	 *
+	 * This function should not generate any bus I/O and should not block.
+	 *
+	 * This function is called when the user attempts to obtain a device
+	 * handle for a device.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_ACCESS if the user has insufficient permissions
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since
+	 *   discovery
+	 * - another LIBUSB_ERROR code on other failure
+	 *
+	 * Do not worry about freeing the handle on failed open, the upper layers
+	 * do this for you.
+	 */
+	int (*open)(struct libusb_device_handle *dev_handle);
+
+	/* Close a device such that the handle cannot be used again. Your backend
+	 * should destroy any resources that were allocated in the open path.
+	 * This may also be a good place to call usbi_remove_event_source() to
+	 * inform libusb of any event sources associated with this device that
+	 * should no longer be monitored.
+	 *
+	 * This function is called when the user closes a device handle.
+	 */
+	void (*close)(struct libusb_device_handle *dev_handle);
+
+	/* Get the ACTIVE configuration descriptor for a device.
+	 *
+	 * The descriptor should be retrieved from memory, NOT via bus I/O to the
+	 * device. This means that you may have to cache it in a private structure
+	 * during get_device_list enumeration. You may also have to keep track
+	 * of which configuration is active when the user changes it.
+	 *
+	 * This function is expected to write len bytes of data into buffer, which
+	 * is guaranteed to be big enough. If you can only do a partial write,
+	 * return an error code.
+	 *
+	 * This function is expected to return the descriptor in bus-endian format
+	 * (LE).
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if the device is in unconfigured state
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*get_active_config_descriptor)(struct libusb_device *device,
+		void *buffer, size_t len);
+
+	/* Get a specific configuration descriptor for a device.
+	 *
+	 * The descriptor should be retrieved from memory, NOT via bus I/O to the
+	 * device. This means that you may have to cache it in a private structure
+	 * during get_device_list enumeration.
+	 *
+	 * The requested descriptor is expressed as a zero-based index (i.e. 0
+	 * indicates that we are requesting the first descriptor). The index does
+	 * not (necessarily) equal the bConfigurationValue of the configuration
+	 * being requested.
+	 *
+	 * This function is expected to write len bytes of data into buffer, which
+	 * is guaranteed to be big enough. If you can only do a partial write,
+	 * return an error code.
+	 *
+	 * This function is expected to return the descriptor in bus-endian format
+	 * (LE).
+	 *
+	 * Return the length read on success or a LIBUSB_ERROR code on failure.
+	 */
+	int (*get_config_descriptor)(struct libusb_device *device,
+		uint8_t config_index, void *buffer, size_t len);
+
+	/* Like get_config_descriptor but then by bConfigurationValue instead
+	 * of by index.
+	 *
+	 * Optional, if not present the core will call get_config_descriptor
+	 * for all configs until it finds the desired bConfigurationValue.
+	 *
+	 * Returns a pointer to the raw-descriptor in *buffer, this memory
+	 * is valid as long as device is valid.
+	 *
+	 * Returns the length of the returned raw-descriptor on success,
+	 * or a LIBUSB_ERROR code on failure.
+	 */
+	int (*get_config_descriptor_by_value)(struct libusb_device *device,
+		uint8_t bConfigurationValue, void **buffer);
+
+	/* Get the bConfigurationValue for the active configuration for a device.
+	 * Optional. This should only be implemented if you can retrieve it from
+	 * cache (don't generate I/O).
+	 *
+	 * If you cannot retrieve this from cache, either do not implement this
+	 * function, or return LIBUSB_ERROR_NOT_SUPPORTED. This will cause
+	 * libusb to retrieve the information through a standard control transfer.
+	 *
+	 * This function must be non-blocking.
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - LIBUSB_ERROR_NOT_SUPPORTED if the value cannot be retrieved without
+	 *   blocking
+	 * - another LIBUSB_ERROR code on other failure.
+	 */
+	int (*get_configuration)(struct libusb_device_handle *dev_handle, uint8_t *config);
+
+	/* Set the active configuration for a device.
+	 *
+	 * A configuration value of -1 should put the device in unconfigured state.
+	 *
+	 * This function can block.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if the configuration does not exist
+	 * - LIBUSB_ERROR_BUSY if interfaces are currently claimed (and hence
+	 *   configuration cannot be changed)
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure.
+	 */
+	int (*set_configuration)(struct libusb_device_handle *dev_handle, int config);
+
+	/* Claim an interface. When claimed, the application can then perform
+	 * I/O to an interface's endpoints.
+	 *
+	 * This function should not generate any bus I/O and should not block.
+	 * Interface claiming is a logical operation that simply ensures that
+	 * no other drivers/applications are using the interface, and after
+	 * claiming, no other drivers/applications can use the interface because
+	 * we now "own" it.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if the interface does not exist
+	 * - LIBUSB_ERROR_BUSY if the interface is in use by another driver/app
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*claim_interface)(struct libusb_device_handle *dev_handle, uint8_t interface_number);
+
+	/* Release a previously claimed interface.
+	 *
+	 * This function should also generate a SET_INTERFACE control request,
+	 * resetting the alternate setting of that interface to 0. It's OK for
+	 * this function to block as a result.
+	 *
+	 * You will only ever be asked to release an interface which was
+	 * successfully claimed earlier.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*release_interface)(struct libusb_device_handle *dev_handle, uint8_t interface_number);
+
+	/* Set the alternate setting for an interface.
+	 *
+	 * You will only ever be asked to set the alternate setting for an
+	 * interface which was successfully claimed earlier.
+	 *
+	 * It's OK for this function to block.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if the alternate setting does not exist
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*set_interface_altsetting)(struct libusb_device_handle *dev_handle,
+		uint8_t interface_number, uint8_t altsetting);
+
+	/* Clear a halt/stall condition on an endpoint.
+	 *
+	 * It's OK for this function to block.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if the endpoint does not exist
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*clear_halt)(struct libusb_device_handle *dev_handle,
+		unsigned char endpoint);
+
+	/* Perform a USB port reset to reinitialize a device. Optional.
+	 *
+	 * If possible, the device handle should still be usable after the reset
+	 * completes, assuming that the device descriptors did not change during
+	 * reset and all previous interface state can be restored.
+	 *
+	 * If something changes, or you cannot easily locate/verify the reset
+	 * device, return LIBUSB_ERROR_NOT_FOUND. This prompts the application
+	 * to close the old handle and re-enumerate the device.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if re-enumeration is required, or if the device
+	 *   has been disconnected since it was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*reset_device)(struct libusb_device_handle *dev_handle);
+
+	/* Alloc num_streams usb3 bulk streams on the passed in endpoints */
+	int (*alloc_streams)(struct libusb_device_handle *dev_handle,
+		uint32_t num_streams, unsigned char *endpoints, int num_endpoints);
+
+	/* Free usb3 bulk streams allocated with alloc_streams */
+	int (*free_streams)(struct libusb_device_handle *dev_handle,
+		unsigned char *endpoints, int num_endpoints);
+
+	/* Allocate persistent DMA memory for the given device, suitable for
+	 * zerocopy. May return NULL on failure. Optional to implement.
+	 */
+	void *(*dev_mem_alloc)(struct libusb_device_handle *handle, size_t len);
+
+	/* Free memory allocated by dev_mem_alloc. */
+	int (*dev_mem_free)(struct libusb_device_handle *handle, void *buffer,
+		size_t len);
+
+	/* Determine if a kernel driver is active on an interface. Optional.
+	 *
+	 * The presence of a kernel driver on an interface indicates that any
+	 * calls to claim_interface would fail with the LIBUSB_ERROR_BUSY code.
+	 *
+	 * Return:
+	 * - 0 if no driver is active
+	 * - 1 if a driver is active
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*kernel_driver_active)(struct libusb_device_handle *dev_handle,
+		uint8_t interface_number);
+
+	/* Detach a kernel driver from an interface. Optional.
+	 *
+	 * After detaching a kernel driver, the interface should be available
+	 * for claim.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if no kernel driver was active
+	 * - LIBUSB_ERROR_INVALID_PARAM if the interface does not exist
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*detach_kernel_driver)(struct libusb_device_handle *dev_handle,
+		uint8_t interface_number);
+
+	/* Attach a kernel driver to an interface. Optional.
+	 *
+	 * Reattach a kernel driver to the device.
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NOT_FOUND if no kernel driver was active
+	 * - LIBUSB_ERROR_INVALID_PARAM if the interface does not exist
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
+	 *   was opened
+	 * - LIBUSB_ERROR_BUSY if a program or driver has claimed the interface,
+	 *   preventing reattachment
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*attach_kernel_driver)(struct libusb_device_handle *dev_handle,
+		uint8_t interface_number);
+
+	/* Destroy a device. Optional.
+	 *
+	 * This function is called when the last reference to a device is
+	 * destroyed. It should free any resources allocated in the get_device_list
+	 * path.
+	 */
+	void (*destroy_device)(struct libusb_device *dev);
+
+	/* Submit a transfer. Your implementation should take the transfer,
+	 * morph it into whatever form your platform requires, and submit it
+	 * asynchronously.
+	 *
+	 * This function must not block.
+	 *
+	 * This function gets called with the flying_transfers_lock locked!
+	 *
+	 * Return:
+	 * - 0 on success
+	 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+	 * - another LIBUSB_ERROR code on other failure
+	 */
+	int (*submit_transfer)(struct usbi_transfer *itransfer);
+
+	/* Cancel a previously submitted transfer.
+	 *
+	 * This function must not block. The transfer cancellation must complete
+	 * later, resulting in a call to usbi_handle_transfer_cancellation()
+	 * from the context of handle_events.
+	 */
+	int (*cancel_transfer)(struct usbi_transfer *itransfer);
+
+	/* Clear a transfer as if it has completed or cancelled, but do not
+	 * report any completion/cancellation to the library. You should free
+	 * all private data from the transfer as if you were just about to report
+	 * completion or cancellation.
+	 *
+	 * This function might seem a bit out of place. It is used when libusb
+	 * detects a disconnected device - it calls this function for all pending
+	 * transfers before reporting completion (with the disconnect code) to
+	 * the user. Maybe we can improve upon this internal interface in future.
+	 */
+	void (*clear_transfer_priv)(struct usbi_transfer *itransfer);
+
+	/* Handle any pending events on event sources. Optional.
+	 *
+	 * Provide this function when event sources directly indicate device
+	 * or transfer activity. If your backend does not have such event sources,
+	 * implement the handle_transfer_completion function below.
+	 *
+	 * This involves monitoring any active transfers and processing their
+	 * completion or cancellation.
+	 *
+	 * The function is passed a pointer that represents platform-specific
+	 * data for monitoring event sources (size count). This data is to be
+	 * (re)allocated as necessary when event sources are modified.
+	 * The num_ready parameter indicates the number of event sources that
+	 * have reported events. This should be enough information for you to
+	 * determine which actions need to be taken on the currently active
+	 * transfers.
+	 *
+	 * For any cancelled transfers, call usbi_handle_transfer_cancellation().
+	 * For completed transfers, call usbi_handle_transfer_completion().
+	 * For control/bulk/interrupt transfers, populate the "transferred"
+	 * element of the appropriate usbi_transfer structure before calling the
+	 * above functions. For isochronous transfers, populate the status and
+	 * transferred fields of the iso packet descriptors of the transfer.
+	 *
+	 * This function should also be able to detect disconnection of the
+	 * device, reporting that situation with usbi_handle_disconnect().
+	 *
+	 * When processing an event related to a transfer, you probably want to
+	 * take usbi_transfer.lock to prevent races. See the documentation for
+	 * the usbi_transfer structure.
+	 *
+	 * Return 0 on success, or a LIBUSB_ERROR code on failure.
+	 */
+	int (*handle_events)(struct libusb_context *ctx,
+		void *event_data, unsigned int count, unsigned int num_ready);
+
+	/* Handle transfer completion. Optional.
+	 *
+	 * Provide this function when there are no event sources available that
+	 * directly indicate device or transfer activity. If your backend does
+	 * have such event sources, implement the handle_events function above.
+	 *
+	 * Your backend must tell the library when a transfer has completed by
+	 * calling usbi_signal_transfer_completion(). You should store any private
+	 * information about the transfer and its completion status in the transfer's
+	 * private backend data.
+	 *
+	 * During event handling, this function will be called on each transfer for
+	 * which usbi_signal_transfer_completion() was called.
+	 *
+	 * For any cancelled transfers, call usbi_handle_transfer_cancellation().
+	 * For completed transfers, call usbi_handle_transfer_completion().
+	 * For control/bulk/interrupt transfers, populate the "transferred"
+	 * element of the appropriate usbi_transfer structure before calling the
+	 * above functions. For isochronous transfers, populate the status and
+	 * transferred fields of the iso packet descriptors of the transfer.
+	 *
+	 * Return 0 on success, or a LIBUSB_ERROR code on failure.
+	 */
+	int (*handle_transfer_completion)(struct usbi_transfer *itransfer);
+
+	/* Number of bytes to reserve for per-context private backend data.
+	 * This private data area is accessible by calling
+	 * usbi_get_context_priv() on the libusb_context instance.
+	 */
+	size_t context_priv_size;
+
+	/* Number of bytes to reserve for per-device private backend data.
+	 * This private data area is accessible by calling
+	 * usbi_get_device_priv() on the libusb_device instance.
+	 */
+	size_t device_priv_size;
+
+	/* Number of bytes to reserve for per-handle private backend data.
+	 * This private data area is accessible by calling
+	 * usbi_get_device_handle_priv() on the libusb_device_handle instance.
+	 */
+	size_t device_handle_priv_size;
+
+	/* Number of bytes to reserve for per-transfer private backend data.
+	 * This private data area is accessible by calling
+	 * usbi_get_transfer_priv() on the usbi_transfer instance.
+	 */
+	size_t transfer_priv_size;
+};
+
+extern const struct usbi_os_backend usbi_backend;
+
+#define for_each_context(c) \
+	for_each_helper(c, &active_contexts_list, struct libusb_context)
+
+#define for_each_device(ctx, d) \
+	for_each_helper(d, &(ctx)->usb_devs, struct libusb_device)
+
+#define for_each_device_safe(ctx, d, n) \
+	for_each_safe_helper(d, n, &(ctx)->usb_devs, struct libusb_device)
+
+#define for_each_open_device(ctx, h) \
+	for_each_helper(h, &(ctx)->open_devs, struct libusb_device_handle)
+
+#define __for_each_transfer(list, t) \
+	for_each_helper(t, (list), struct usbi_transfer)
+
+#define for_each_transfer(ctx, t) \
+	__for_each_transfer(&(ctx)->flying_transfers, t)
+
+#define __for_each_transfer_safe(list, t, n) \
+	for_each_safe_helper(t, n, (list), struct usbi_transfer)
+
+#define for_each_transfer_safe(ctx, t, n) \
+	__for_each_transfer_safe(&(ctx)->flying_transfers, t, n)
+
+#define __for_each_completed_transfer_safe(list, t, n) \
+	list_for_each_entry_safe(t, n, (list), completed_list, struct usbi_transfer)
+
+#define for_each_event_source(ctx, e) \
+	for_each_helper(e, &(ctx)->event_sources, struct usbi_event_source)
+
+#define for_each_removed_event_source(ctx, e) \
+	for_each_helper(e, &(ctx)->removed_event_sources, struct usbi_event_source)
+
+#define for_each_removed_event_source_safe(ctx, e, n) \
+	for_each_safe_helper(e, n, &(ctx)->removed_event_sources, struct usbi_event_source)
+
+#define for_each_hotplug_cb(ctx, c) \
+	for_each_helper(c, &(ctx)->hotplug_cbs, struct usbi_hotplug_callback)
+
+#define for_each_hotplug_cb_safe(ctx, c, n) \
+	for_each_safe_helper(c, n, &(ctx)->hotplug_cbs, struct usbi_hotplug_callback)
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif