Initial

1 files changed, 904 insertions, 0 deletions

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),
+};