Import libusb 1.0.9-rc3 into third_party

third_party/libusb/libusb/core.c

Index: third_party/libusb/libusb/core.c
diff --git a/third_party/libusb/libusb/core.c b/third_party/libusb/libusb/core.c
new file mode 100644
index 0000000000000000000000000000000000000000..a91c77b968635ca8233b17c89b3b2607c52c5001
--- /dev/null
+++ b/third_party/libusb/libusb/core.c
@@ -0,0 +1,1781 @@
+/*
+ * Core functions for libusb
+ * Copyright (C) 2007-2008 Daniel Drake <dsd@gentoo.org>
+ * Copyright (c) 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
+ */
+
+#include <config.h>
+
+#include <errno.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+
+#include "libusbi.h"
+
+#if defined(OS_LINUX)
+const struct usbi_os_backend * const usbi_backend = &linux_usbfs_backend;
+#elif defined(OS_DARWIN)
+const struct usbi_os_backend * const usbi_backend = &darwin_backend;
+#elif defined(OS_WINDOWS)
+const struct usbi_os_backend * const usbi_backend = &windows_backend;
+#else
+#error "Unsupported OS"
+#endif
+
+struct libusb_context *usbi_default_context = NULL;
+static int default_context_refcnt = 0;
+static usbi_mutex_static_t default_context_lock = USBI_MUTEX_INITIALIZER;
+
+/**
+ * \mainpage libusb-1.0 API Reference
+ *
+ * \section intro Introduction
+ *
+ * libusb is an open source library that allows you to communicate with USB
+ * devices from userspace. For more info, see the
+ * <a href="http://libusb.sourceforge.net">libusb homepage</a>.
+ *
+ * This documentation is aimed at application developers wishing to
+ * communicate with USB peripherals from their own software. After reviewing
+ * this documentation, feedback and questions can be sent to the
+ * <a href="http://sourceforge.net/mail/?group_id=1674">libusb-devel mailing
+ * list</a>.
+ *
+ * This documentation assumes knowledge of how to operate USB devices from
+ * a software standpoint (descriptors, configurations, interfaces, endpoints,
+ * control/bulk/interrupt/isochronous transfers, etc). Full information
+ * can be found in the <a href="http://www.usb.org/developers/docs/">USB 2.0
+ * Specification</a> which is available for free download. You can probably
+ * find less verbose introductions by searching the web.
+ *
+ * \section features Library features
+ *
+ * - All transfer types supported (control/bulk/interrupt/isochronous)
+ * - 2 transfer interfaces:
+ *    -# Synchronous (simple)
+ *    -# Asynchronous (more complicated, but more powerful)
+ * - Thread safe (although the asynchronous interface means that you
+ *   usually won't need to thread)
+ * - Lightweight with lean API
+ * - Compatible with libusb-0.1 through the libusb-compat-0.1 translation layer
+ *
+ * \section gettingstarted Getting Started
+ *
+ * To begin reading the API documentation, start with the Modules page which
+ * links to the different categories of libusb's functionality.
+ *
+ * One decision you will have to make is whether to use the synchronous
+ * or the asynchronous data transfer interface. The \ref io documentation
+ * provides some insight into this topic.
+ *
+ * Some example programs can be found in the libusb source distribution under
+ * the "examples" subdirectory. The libusb homepage includes a list of
+ * real-life project examples which use libusb.
+ *
+ * \section errorhandling Error handling
+ *
+ * libusb functions typically return 0 on success or a negative error code
+ * on failure. These negative error codes relate to LIBUSB_ERROR constants
+ * which are listed on the \ref misc "miscellaneous" documentation page.
+ *
+ * \section msglog Debug message logging
+ *
+ * libusb does not log any messages by default. Your application is therefore
+ * free to close stdout/stderr and those descriptors may be reused without
+ * worry.
+ *
+ * The libusb_set_debug() function can be used to enable stdout/stderr logging
+ * of certain messages. Under standard configuration, libusb doesn't really
+ * log much at all, so you are advised to use this function to enable all
+ * error/warning/informational messages. It will help you debug problems with
+ * your software.
+ *
+ * The logged messages are unstructured. There is no one-to-one correspondence
+ * between messages being logged and success or failure return codes from
+ * libusb functions. There is no format to the messages, so you should not
+ * try to capture or parse them. They are not and will not be localized.
+ * These messages are not suitable for being passed to your application user;
+ * instead, you should interpret the error codes returned from libusb functions
+ * and provide appropriate notification to the user. The messages are simply
+ * there to aid you as a programmer, and if you're confused because you're
+ * getting a strange error code from a libusb function, enabling message
+ * logging may give you a suitable explanation.
+ *
+ * The LIBUSB_DEBUG environment variable can be used to enable message logging
+ * at run-time. This environment variable should be set to a number, which is
+ * interpreted the same as the libusb_set_debug() parameter. When this
+ * environment variable is set, the message logging verbosity level is fixed
+ * and libusb_set_debug() effectively does nothing.
+ *
+ * libusb can be compiled without any logging functions, useful for embedded
+ * systems. In this case, libusb_set_debug() and the LIBUSB_DEBUG environment
+ * variable have no effects.
+ *
+ * libusb can also be compiled with verbose debugging messages. When the
+ * library is compiled in this way, all messages of all verbosities are always
+ * logged.  libusb_set_debug() and the LIBUSB_DEBUG environment variable have
+ * no effects.
+ *
+ * \section remarks Other remarks
+ *
+ * libusb does have imperfections. The \ref caveats "caveats" page attempts
+ * to document these.
+ */
+
+/**
+ * \page caveats Caveats
+ *
+ * \section devresets Device resets
+ *
+ * The libusb_reset_device() function allows you to reset a device. If your
+ * program has to call such a function, it should obviously be aware that
+ * the reset will cause device state to change (e.g. register values may be
+ * reset).
+ *
+ * The problem is that any other program could reset the device your program
+ * is working with, at any time. libusb does not offer a mechanism to inform
+ * you when this has happened, so if someone else resets your device it will
+ * not be clear to your own program why the device state has changed.
+ *
+ * Ultimately, this is a limitation of writing drivers in userspace.
+ * Separation from the USB stack in the underlying kernel makes it difficult
+ * for the operating system to deliver such notifications to your program.
+ * The Linux kernel USB stack allows such reset notifications to be delivered
+ * to in-kernel USB drivers, but it is not clear how such notifications could
+ * be delivered to second-class drivers that live in userspace.
+ *
+ * \section blockonly Blocking-only functionality
+ *
+ * The functionality listed below is only available through synchronous,
+ * blocking functions. There are no asynchronous/non-blocking alternatives,
+ * and no clear ways of implementing these.
+ *
+ * - Configuration activation (libusb_set_configuration())
+ * - Interface/alternate setting activation (libusb_set_interface_alt_setting())
+ * - Releasing of interfaces (libusb_release_interface())
+ * - Clearing of halt/stall condition (libusb_clear_halt())
+ * - Device resets (libusb_reset_device())
+ *
+ * \section nohotplug No hotplugging
+ *
+ * libusb-1.0 lacks functionality for providing notifications of when devices
+ * are added or removed. This functionality is planned to be implemented
+ * for libusb-1.1.
+ *
+ * That said, there is basic disconnection handling for open device handles:
+ *  - If there are ongoing transfers, libusb's handle_events loop will detect
+ *    disconnections and complete ongoing transfers with the
+ *    LIBUSB_TRANSFER_NO_DEVICE status code.
+ *  - Many functions such as libusb_set_configuration() return the special
+ *    LIBUSB_ERROR_NO_DEVICE error code when the device has been disconnected.
+ *
+ * \section configsel Configuration selection and handling
+ *
+ * When libusb presents a device handle to an application, there is a chance
+ * that the corresponding device may be in unconfigured state. For devices
+ * with multiple configurations, there is also a chance that the configuration
+ * currently selected is not the one that the application wants to use.
+ *
+ * The obvious solution is to add a call to libusb_set_configuration() early
+ * on during your device initialization routines, but there are caveats to
+ * be aware of:
+ * -# If the device is already in the desired configuration, calling
+ *    libusb_set_configuration() using the same configuration value will cause
+ *    a lightweight device reset. This may not be desirable behaviour.
+ * -# libusb will be unable to change configuration if the device is in
+ *    another configuration and other programs or drivers have claimed
+ *    interfaces under that configuration.
+ * -# In the case where the desired configuration is already active, libusb
+ *    may not even be able to perform a lightweight device reset. For example,
+ *    take my USB keyboard with fingerprint reader: I'm interested in driving
+ *    the fingerprint reader interface through libusb, but the kernel's
+ *    USB-HID driver will almost always have claimed the keyboard interface.
+ *    Because the kernel has claimed an interface, it is not even possible to
+ *    perform the lightweight device reset, so libusb_set_configuration() will
+ *    fail. (Luckily the device in question only has a single configuration.)
+ *
+ * One solution to some of the above problems is to consider the currently
+ * active configuration. If the configuration we want is already active, then
+ * we don't have to select any configuration:
+\code
+cfg = libusb_get_configuration(dev);
+if (cfg != desired)
+	libusb_set_configuration(dev, desired);
+\endcode
+ *
+ * This is probably suitable for most scenarios, but is inherently racy:
+ * another application or driver may change the selected configuration
+ * <em>after</em> the libusb_get_configuration() call.
+ *
+ * Even in cases where libusb_set_configuration() succeeds, consider that other
+ * applications or drivers may change configuration after your application
+ * calls libusb_set_configuration().
+ *
+ * One possible way to lock your device into a specific configuration is as
+ * follows:
+ * -# Set the desired configuration (or use the logic above to realise that
+ *    it is already in the desired configuration)
+ * -# Claim the interface that you wish to use
+ * -# Check that the currently active configuration is the one that you want
+ *    to use.
+ *
+ * The above method works because once an interface is claimed, no application
+ * or driver is able to select another configuration.
+ *
+ * \section earlycomp Early transfer completion
+ *
+ * NOTE: This section is currently Linux-centric. I am not sure if any of these
+ * considerations apply to Darwin or other platforms.
+ *
+ * When a transfer completes early (i.e. when less data is received/sent in
+ * any one packet than the transfer buffer allows for) then libusb is designed
+ * to terminate the transfer immediately, not transferring or receiving any
+ * more data unless other transfers have been queued by the user.
+ *
+ * On legacy platforms, libusb is unable to do this in all situations. After
+ * the incomplete packet occurs, "surplus" data may be transferred. Prior to
+ * libusb v1.0.2, this information was lost (and for device-to-host transfers,
+ * the corresponding data was discarded). As of libusb v1.0.3, this information
+ * is kept (the data length of the transfer is updated) and, for device-to-host
+ * transfers, any surplus data was added to the buffer. Still, this is not
+ * a nice solution because it loses the information about the end of the short
+ * packet, and the user probably wanted that surplus data to arrive in the next
+ * logical transfer.
+ *
+ * A previous workaround was to only ever submit transfers of size 16kb or
+ * less.
+ *
+ * As of libusb v1.0.4 and Linux v2.6.32, this is fixed. A technical
+ * explanation of this issue follows.
+ *
+ * When you ask libusb to submit a bulk transfer larger than 16kb in size,
+ * libusb breaks it up into a number of smaller subtransfers. This is because
+ * the usbfs kernel interface only accepts transfers of up to 16kb in size.
+ * The subtransfers are submitted all at once so that the kernel can queue
+ * them at the hardware level, therefore maximizing bus throughput.
+ *
+ * On legacy platforms, this caused problems when transfers completed early.
+ * Upon this event, the kernel would terminate all further packets in that
+ * subtransfer (but not any following ones). libusb would note this event and
+ * immediately cancel any following subtransfers that had been queued,
+ * but often libusb was not fast enough, and the following subtransfers had
+ * started before libusb got around to cancelling them.
+ *
+ * Thanks to an API extension to usbfs, this is fixed with recent kernel and
+ * libusb releases. The solution was to allow libusb to communicate to the
+ * kernel where boundaries occur between logical libusb-level transfers. When
+ * a short transfer (or other error) occurs, the kernel will cancel all the
+ * subtransfers until the boundary without allowing those transfers to start.
+ */
+
+/**
+ * \page contexts Contexts
+ *
+ * It is possible that libusb may be used simultaneously from two independent
+ * libraries linked into the same executable. For example, if your application
+ * has a plugin-like system which allows the user to dynamically load a range
+ * of modules into your program, it is feasible that two independently
+ * developed modules may both use libusb.
+ *
+ * libusb is written to allow for these multiple user scenarios. The two
+ * "instances" of libusb will not interfere: libusb_set_debug() calls
+ * from one user will not affect the same settings for other users, other
+ * users can continue using libusb after one of them calls libusb_exit(), etc.
+ *
+ * This is made possible through libusb's <em>context</em> concept. When you
+ * call libusb_init(), you are (optionally) given a context. You can then pass
+ * this context pointer back into future libusb functions.
+ *
+ * In order to keep things simple for more simplistic applications, it is
+ * legal to pass NULL to all functions requiring a context pointer (as long as
+ * you're sure no other code will attempt to use libusb from the same process).
+ * When you pass NULL, the default context will be used. The default context
+ * is created the first time a process calls libusb_init() when no other
+ * context is alive. Contexts are destroyed during libusb_exit().
+ *
+ * The default context is reference-counted and can be shared. That means that
+ * if libusb_init(NULL) is called twice within the same process, the two
+ * users end up sharing the same context. The deinitialization and freeing of
+ * the default context will only happen when the last user calls libusb_exit().
+ * In other words, the default context is created and initialized when its
+ * reference count goes from 0 to 1, and is deinitialized and destroyed when
+ * its reference count goes from 1 to 0.
+ *
+ * You may be wondering why only a subset of libusb functions require a
+ * context pointer in their function definition. Internally, libusb stores
+ * context pointers in other objects (e.g. libusb_device instances) and hence
+ * can infer the context from those objects.
+ */
+
+/**
+ * @defgroup lib Library initialization/deinitialization
+ * This page details how to initialize and deinitialize libusb. Initialization
+ * must be performed before using any libusb functionality, and similarly you
+ * must not call any libusb functions after deinitialization.
+ */
+
+/**
+ * @defgroup dev Device handling and enumeration
+ * The functionality documented below is designed to help with the following
+ * operations:
+ * - Enumerating the USB devices currently attached to the system
+ * - Choosing a device to operate from your software
+ * - Opening and closing the chosen device
+ *
+ * \section nutshell In a nutshell...
+ *
+ * The description below really makes things sound more complicated than they
+ * actually are. The following sequence of function calls will be suitable
+ * for almost all scenarios and does not require you to have such a deep
+ * understanding of the resource management issues:
+ * \code
+// discover devices
+libusb_device **list;
+libusb_device *found = NULL;
+ssize_t cnt = libusb_get_device_list(NULL, &list);
+ssize_t i = 0;
+int err = 0;
+if (cnt < 0)
+	error();
+
+for (i = 0; i < cnt; i++) {
+	libusb_device *device = list[i];
+	if (is_interesting(device)) {
+		found = device;
+		break;
+	}
+}
+
+if (found) {
+	libusb_device_handle *handle;
+
+	err = libusb_open(found, &handle);
+	if (err)
+		error();
+	// etc
+}
+
+libusb_free_device_list(list, 1);
+\endcode
+ *
+ * The two important points:
+ * - You asked libusb_free_device_list() to unreference the devices (2nd
+ *   parameter)
+ * - You opened the device before freeing the list and unreferencing the
+ *   devices
+ *
+ * If you ended up with a handle, you can now proceed to perform I/O on the
+ * device.
+ *
+ * \section devshandles Devices and device handles
+ * libusb has a concept of a USB device, represented by the
+ * \ref libusb_device opaque type. A device represents a USB device that
+ * is currently or was previously connected to the system. Using a reference
+ * to a device, you can determine certain information about the device (e.g.
+ * you can read the descriptor data).
+ *
+ * The libusb_get_device_list() function can be used to obtain a list of
+ * devices currently connected to the system. This is known as device
+ * discovery.
+ *
+ * Just because you have a reference to a device does not mean it is
+ * necessarily usable. The device may have been unplugged, you may not have
+ * permission to operate such device, or another program or driver may be
+ * using the device.
+ *
+ * When you've found a device that you'd like to operate, you must ask
+ * libusb to open the device using the libusb_open() function. Assuming
+ * success, libusb then returns you a <em>device handle</em>
+ * (a \ref libusb_device_handle pointer). All "real" I/O operations then
+ * operate on the handle rather than the original device pointer.
+ *
+ * \section devref Device discovery and reference counting
+ *
+ * Device discovery (i.e. calling libusb_get_device_list()) returns a
+ * freshly-allocated list of devices. The list itself must be freed when
+ * you are done with it. libusb also needs to know when it is OK to free
+ * the contents of the list - the devices themselves.
+ *
+ * To handle these issues, libusb provides you with two separate items:
+ * - A function to free the list itself
+ * - A reference counting system for the devices inside
+ *
+ * New devices presented by the libusb_get_device_list() function all have a
+ * reference count of 1. You can increase and decrease reference count using
+ * libusb_ref_device() and libusb_unref_device(). A device is destroyed when
+ * its reference count reaches 0.
+ *
+ * With the above information in mind, the process of opening a device can
+ * be viewed as follows:
+ * -# Discover devices using libusb_get_device_list().
+ * -# Choose the device that you want to operate, and call libusb_open().
+ * -# Unref all devices in the discovered device list.
+ * -# Free the discovered device list.
+ *
+ * The order is important - you must not unreference the device before
+ * attempting to open it, because unreferencing it may destroy the device.
+ *
+ * For convenience, the libusb_free_device_list() function includes a
+ * parameter to optionally unreference all the devices in the list before
+ * freeing the list itself. This combines steps 3 and 4 above.
+ *
+ * As an implementation detail, libusb_open() actually adds a reference to
+ * the device in question. This is because the device remains available
+ * through the handle via libusb_get_device(). The reference is deleted during
+ * libusb_close().
+ */
+
+/** @defgroup misc Miscellaneous */
+
+/* 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. */
+#define DISCOVERED_DEVICES_SIZE_STEP 8
+
+static struct discovered_devs *discovered_devs_alloc(void)
+{
+	struct discovered_devs *ret =
+		malloc(sizeof(*ret) + (sizeof(void *) * DISCOVERED_DEVICES_SIZE_STEP));
+
+	if (ret) {
+		ret->len = 0;
+		ret->capacity = DISCOVERED_DEVICES_SIZE_STEP;
+	}
+	return ret;
+}
+
+/* append a device to the discovered devices collection. may realloc itself,
+ * returning new discdevs. returns NULL on realloc failure. */
+struct discovered_devs *discovered_devs_append(
+	struct discovered_devs *discdevs, struct libusb_device *dev)
+{
+	size_t len = discdevs->len;
+	size_t capacity;
+
+	/* if there is space, just append the device */
+	if (len < discdevs->capacity) {
+		discdevs->devices[len] = libusb_ref_device(dev);
+		discdevs->len++;
+		return discdevs;
+	}
+
+	/* exceeded capacity, need to grow */
+	usbi_dbg("need to increase capacity");
+	capacity = discdevs->capacity + DISCOVERED_DEVICES_SIZE_STEP;
+	discdevs = realloc(discdevs,
+		sizeof(*discdevs) + (sizeof(void *) * capacity));
+	if (discdevs) {
+		discdevs->capacity = capacity;
+		discdevs->devices[len] = libusb_ref_device(dev);
+		discdevs->len++;
+	}
+
+	return discdevs;
+}
+
+static void discovered_devs_free(struct discovered_devs *discdevs)
+{
+	size_t i;
+
+	for (i = 0; i < discdevs->len; i++)
+		libusb_unref_device(discdevs->devices[i]);
+
+	free(discdevs);
+}
+
+/* Allocate a new device with a specific session ID. The returned device has
+ * a reference count of 1. */
+struct libusb_device *usbi_alloc_device(struct libusb_context *ctx,
+	unsigned long session_id)
+{
+	size_t priv_size = usbi_backend->device_priv_size;
+	struct libusb_device *dev = calloc(1, sizeof(*dev) + priv_size);
+	int r;
+
+	if (!dev)
+		return NULL;
+
+	r = usbi_mutex_init(&dev->lock, NULL);
+	if (r) {
+		free(dev);
+		return NULL;
+	}
+
+	dev->ctx = ctx;
+	dev->refcnt = 1;
+	dev->session_data = session_id;
+	dev->speed = LIBUSB_SPEED_UNKNOWN;
+	memset(&dev->os_priv, 0, priv_size);
+
+	usbi_mutex_lock(&ctx->usb_devs_lock);
+	list_add(&dev->list, &ctx->usb_devs);
+	usbi_mutex_unlock(&ctx->usb_devs_lock);
+	return dev;
+}
+
+/* Perform some final sanity checks on a newly discovered device. If this
+ * function fails (negative return code), the device should not be added
+ * to the discovered device list. */
+int usbi_sanitize_device(struct libusb_device *dev)
+{
+	int r;
+	unsigned char raw_desc[DEVICE_DESC_LENGTH];
+	uint8_t num_configurations;
+	int host_endian;
+
+	r = usbi_backend->get_device_descriptor(dev, raw_desc, &host_endian);
+	if (r < 0)
+		return r;
+
+	num_configurations = raw_desc[DEVICE_DESC_LENGTH - 1];
+	if (num_configurations > USB_MAXCONFIG) {
+		usbi_err(DEVICE_CTX(dev), "too many configurations");
+		return LIBUSB_ERROR_IO;
+	} else if (0 == num_configurations)
+		usbi_dbg("zero configurations, maybe an unauthorized device");
+
+	dev->num_configurations = num_configurations;
+	return 0;
+}
+
+/* Examine libusb's internal list of known devices, looking for one with
+ * a specific session ID. Returns the matching device if it was found, and
+ * NULL otherwise. */
+struct libusb_device *usbi_get_device_by_session_id(struct libusb_context *ctx,
+	unsigned long session_id)
+{
+	struct libusb_device *dev;
+	struct libusb_device *ret = NULL;
+
+	usbi_mutex_lock(&ctx->usb_devs_lock);
+	list_for_each_entry(dev, &ctx->usb_devs, list, struct libusb_device)
+		if (dev->session_data == session_id) {
+			ret = dev;
+			break;
+		}
+	usbi_mutex_unlock(&ctx->usb_devs_lock);
+
+	return ret;
+}
+
+/** @ingroup dev
+ * Returns a list of USB devices currently attached to the system. This is
+ * your entry point into finding a USB device to operate.
+ *
+ * You are expected to unreference all the devices when you are done with
+ * them, and then free the list with libusb_free_device_list(). Note that
+ * libusb_free_device_list() can unref all the devices for you. Be careful
+ * not to unreference a device you are about to open until after you have
+ * opened it.
+ *
+ * This return value of this function indicates the number of devices in
+ * the resultant list. The list is actually one element larger, as it is
+ * NULL-terminated.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \param list output location for a list of devices. Must be later freed with
+ * libusb_free_device_list().
+ * \returns The number of devices in the outputted list, or any
+ * \ref libusb_error according to errors encountered by the backend.
+ */
+ssize_t API_EXPORTED libusb_get_device_list(libusb_context *ctx,
+	libusb_device ***list)
+{
+	struct discovered_devs *discdevs = discovered_devs_alloc();
+	struct libusb_device **ret;
+	int r = 0;
+	ssize_t i, len;
+	USBI_GET_CONTEXT(ctx);
+	usbi_dbg("");
+
+	if (!discdevs)
+		return LIBUSB_ERROR_NO_MEM;
+
+	r = usbi_backend->get_device_list(ctx, &discdevs);
+	if (r < 0) {
+		len = r;
+		goto out;
+	}
+
+	/* convert discovered_devs into a list */
+	len = discdevs->len;
+	ret = malloc(sizeof(void *) * (len + 1));
+	if (!ret) {
+		len = LIBUSB_ERROR_NO_MEM;
+		goto out;
+	}
+
+	ret[len] = NULL;
+	for (i = 0; i < len; i++) {
+		struct libusb_device *dev = discdevs->devices[i];
+		ret[i] = libusb_ref_device(dev);
+	}
+	*list = ret;
+
+out:
+	discovered_devs_free(discdevs);
+	return len;
+}
+
+/** \ingroup dev
+ * Frees a list of devices previously discovered using
+ * libusb_get_device_list(). If the unref_devices parameter is set, the
+ * reference count of each device in the list is decremented by 1.
+ * \param list the list to free
+ * \param unref_devices whether to unref the devices in the list
+ */
+void API_EXPORTED libusb_free_device_list(libusb_device **list,
+	int unref_devices)
+{
+	if (!list)
+		return;
+
+	if (unref_devices) {
+		int i = 0;
+		struct libusb_device *dev;
+
+		while ((dev = list[i++]) != NULL)
+			libusb_unref_device(dev);
+	}
+	free(list);
+}
+
+/** \ingroup dev
+ * Get the number of the bus that a device is connected to.
+ * \param dev a device
+ * \returns the bus number
+ */
+uint8_t API_EXPORTED libusb_get_bus_number(libusb_device *dev)
+{
+	return dev->bus_number;
+}
+
+/** \ingroup dev
+ * Get the address of the device on the bus it is connected to.
+ * \param dev a device
+ * \returns the device address
+ */
+uint8_t API_EXPORTED libusb_get_device_address(libusb_device *dev)
+{
+	return dev->device_address;
+}
+
+/** \ingroup dev
+ * Get the negotiated connection speed for a device.
+ * \param dev a device
+ * \returns a \ref libusb_speed code, where LIBUSB_SPEED_UNKNOWN means that
+ * the OS doesn't know or doesn't support returning the negotiated speed.
+ */
+int API_EXPORTED libusb_get_device_speed(libusb_device *dev)
+{
+	return dev->speed;
+}
+
+static const struct libusb_endpoint_descriptor *find_endpoint(
+	struct libusb_config_descriptor *config, unsigned char endpoint)
+{
+	int iface_idx;
+	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)
+					return ep;
+			}
+		}
+	}
+	return NULL;
+}
+
+/** \ingroup dev
+ * Convenience function to retrieve the wMaxPacketSize value for a particular
+ * endpoint in the active device configuration.
+ *
+ * This function was originally intended to be of assistance when setting up
+ * isochronous transfers, but a design mistake resulted in this function
+ * instead. It simply returns the wMaxPacketSize value without considering
+ * its contents. If you're dealing with isochronous transfers, you probably
+ * want libusb_get_max_iso_packet_size() instead.
+ *
+ * \param dev a device
+ * \param endpoint address of the endpoint in question
+ * \returns the wMaxPacketSize value
+ * \returns LIBUSB_ERROR_NOT_FOUND if the endpoint does not exist
+ * \returns LIBUSB_ERROR_OTHER on other failure
+ */
+int API_EXPORTED libusb_get_max_packet_size(libusb_device *dev,
+	unsigned char endpoint)
+{
+	struct libusb_config_descriptor *config;
+	const struct libusb_endpoint_descriptor *ep;
+	int r;
+
+	r = libusb_get_active_config_descriptor(dev, &config);
+	if (r < 0) {
+		usbi_err(DEVICE_CTX(dev),
+			"could not retrieve active config descriptor");
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	ep = find_endpoint(config, endpoint);
+	if (!ep)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	r = ep->wMaxPacketSize;
+	libusb_free_config_descriptor(config);
+	return r;
+}
+
+/** \ingroup dev
+ * Calculate the maximum packet size which a specific endpoint is capable is
+ * sending or receiving in the duration of 1 microframe
+ *
+ * Only the active configution is examined. The calculation is based on the
+ * wMaxPacketSize field in the endpoint descriptor as described in section
+ * 9.6.6 in the USB 2.0 specifications.
+ *
+ * If acting on an isochronous or interrupt endpoint, this function will
+ * multiply the value found in bits 0:10 by the number of transactions per
+ * microframe (determined by bits 11:12). Otherwise, this function just
+ * returns the numeric value found in bits 0:10.
+ *
+ * This function is useful for setting up isochronous transfers, for example
+ * you might pass the return value from this function to
+ * libusb_set_iso_packet_lengths() in order to set the length field of every
+ * isochronous packet in a transfer.
+ *
+ * Since v1.0.3.
+ *
+ * \param dev a device
+ * \param endpoint address of the endpoint in question
+ * \returns the maximum packet size which can be sent/received on this endpoint
+ * \returns LIBUSB_ERROR_NOT_FOUND if the endpoint does not exist
+ * \returns LIBUSB_ERROR_OTHER on other failure
+ */
+int API_EXPORTED libusb_get_max_iso_packet_size(libusb_device *dev,
+	unsigned char endpoint)
+{
+	struct libusb_config_descriptor *config;
+	const struct libusb_endpoint_descriptor *ep;
+	enum libusb_transfer_type ep_type;
+	uint16_t val;
+	int r;
+
+	r = libusb_get_active_config_descriptor(dev, &config);
+	if (r < 0) {
+		usbi_err(DEVICE_CTX(dev),
+			"could not retrieve active config descriptor");
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	ep = find_endpoint(config, endpoint);
+	if (!ep)
+		return LIBUSB_ERROR_NOT_FOUND;
+
+	val = ep->wMaxPacketSize;
+	ep_type = ep->bmAttributes & 0x3;
+	libusb_free_config_descriptor(config);
+
+	r = val & 0x07ff;
+	if (ep_type == LIBUSB_TRANSFER_TYPE_ISOCHRONOUS
+			|| ep_type == LIBUSB_TRANSFER_TYPE_INTERRUPT)
+		r *= (1 + ((val >> 11) & 3));
+	return r;
+}
+
+/** \ingroup dev
+ * Increment the reference count of a device.
+ * \param dev the device to reference
+ * \returns the same device
+ */
+DEFAULT_VISIBILITY
+libusb_device * LIBUSB_CALL libusb_ref_device(libusb_device *dev)
+{
+	usbi_mutex_lock(&dev->lock);
+	dev->refcnt++;
+	usbi_mutex_unlock(&dev->lock);
+	return dev;
+}
+
+/** \ingroup dev
+ * Decrement the reference count of a device. If the decrement operation
+ * causes the reference count to reach zero, the device shall be destroyed.
+ * \param dev the device to unreference
+ */
+void API_EXPORTED libusb_unref_device(libusb_device *dev)
+{
+	int refcnt;
+
+	if (!dev)
+		return;
+
+	usbi_mutex_lock(&dev->lock);
+	refcnt = --dev->refcnt;
+	usbi_mutex_unlock(&dev->lock);
+
+	if (refcnt == 0) {
+		usbi_dbg("destroy device %d.%d", dev->bus_number, dev->device_address);
+
+		if (usbi_backend->destroy_device)
+			usbi_backend->destroy_device(dev);
+
+		usbi_mutex_lock(&dev->ctx->usb_devs_lock);
+		list_del(&dev->list);
+		usbi_mutex_unlock(&dev->ctx->usb_devs_lock);
+
+		usbi_mutex_destroy(&dev->lock);
+		free(dev);
+	}
+}
+
+/*
+ * Interrupt the iteration of the event handling thread, so that it picks
+ * up the new fd.
+ */
+void usbi_fd_notification(struct libusb_context *ctx)
+{
+	unsigned char dummy = 1;
+	ssize_t r;
+
+	if (ctx == NULL)
+		return;
+
+	/* record that we are messing with poll fds */
+	usbi_mutex_lock(&ctx->pollfd_modify_lock);
+	ctx->pollfd_modify++;
+	usbi_mutex_unlock(&ctx->pollfd_modify_lock);
+
+	/* write some data on control pipe to interrupt event handlers */
+	r = usbi_write(ctx->ctrl_pipe[1], &dummy, sizeof(dummy));
+	if (r <= 0) {
+		usbi_warn(ctx, "internal signalling write failed");
+		usbi_mutex_lock(&ctx->pollfd_modify_lock);
+		ctx->pollfd_modify--;
+		usbi_mutex_unlock(&ctx->pollfd_modify_lock);
+		return;
+	}
+
+	/* take event handling lock */
+	libusb_lock_events(ctx);
+
+	/* read the dummy data */
+	r = usbi_read(ctx->ctrl_pipe[0], &dummy, sizeof(dummy));
+	if (r <= 0)
+		usbi_warn(ctx, "internal signalling read failed");
+
+	/* we're done with modifying poll fds */
+	usbi_mutex_lock(&ctx->pollfd_modify_lock);
+	ctx->pollfd_modify--;
+	usbi_mutex_unlock(&ctx->pollfd_modify_lock);
+
+	/* Release event handling lock and wake up event waiters */
+	libusb_unlock_events(ctx);
+}
+
+/** \ingroup dev
+ * Open a device and obtain a device handle. A handle allows you to perform
+ * I/O on the device in question.
+ *
+ * Internally, this function adds a reference to the device and makes it
+ * available to you through libusb_get_device(). This reference is removed
+ * during libusb_close().
+ *
+ * This is a non-blocking function; no requests are sent over the bus.
+ *
+ * \param dev the device to open
+ * \param handle output location for the returned device handle pointer. Only
+ * populated when the return code is 0.
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NO_MEM on memory allocation failure
+ * \returns LIBUSB_ERROR_ACCESS if the user has insufficient permissions
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+int API_EXPORTED libusb_open(libusb_device *dev,
+	libusb_device_handle **handle)
+{
+	struct libusb_context *ctx = DEVICE_CTX(dev);
+	struct libusb_device_handle *_handle;
+	size_t priv_size = usbi_backend->device_handle_priv_size;
+	int r;
+	usbi_dbg("open %d.%d", dev->bus_number, dev->device_address);
+
+	_handle = malloc(sizeof(*_handle) + priv_size);
+	if (!_handle)
+		return LIBUSB_ERROR_NO_MEM;
+
+	r = usbi_mutex_init(&_handle->lock, NULL);
+	if (r) {
+		free(_handle);
+		return LIBUSB_ERROR_OTHER;
+	}
+
+	_handle->dev = libusb_ref_device(dev);
+	_handle->claimed_interfaces = 0;
+	memset(&_handle->os_priv, 0, priv_size);
+
+	r = usbi_backend->open(_handle);
+	if (r < 0) {
+		usbi_dbg("open %d.%d returns %d", dev->bus_number, dev->device_address, r);
+		libusb_unref_device(dev);
+		usbi_mutex_destroy(&_handle->lock);
+		free(_handle);
+		return r;
+	}
+
+	usbi_mutex_lock(&ctx->open_devs_lock);
+	list_add(&_handle->list, &ctx->open_devs);
+	usbi_mutex_unlock(&ctx->open_devs_lock);
+	*handle = _handle;
+
+	/* At this point, we want to interrupt any existing event handlers so
+	 * that they realise the addition of the new device's poll fd. One
+	 * example when this is desirable is if the user is running a separate
+	 * dedicated libusb events handling thread, which is running with a long
+	 * or infinite timeout. We want to interrupt that iteration of the loop,
+	 * so that it picks up the new fd, and then continues. */
+	usbi_fd_notification(ctx);
+
+	return 0;
+}
+
+/** \ingroup dev
+ * Convenience function for finding a device with a particular
+ * <tt>idVendor</tt>/<tt>idProduct</tt> combination. This function is intended
+ * for those scenarios where you are using libusb to knock up a quick test
+ * application - it allows you to avoid calling libusb_get_device_list() and
+ * worrying about traversing/freeing the list.
+ *
+ * This function has limitations and is hence not intended for use in real
+ * applications: if multiple devices have the same IDs it will only
+ * give you the first one, etc.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \param vendor_id the idVendor value to search for
+ * \param product_id the idProduct value to search for
+ * \returns a handle for the first found device, or NULL on error or if the
+ * device could not be found. */
+DEFAULT_VISIBILITY
+libusb_device_handle * LIBUSB_CALL libusb_open_device_with_vid_pid(
+	libusb_context *ctx, uint16_t vendor_id, uint16_t product_id)
+{
+	struct libusb_device **devs;
+	struct libusb_device *found = NULL;
+	struct libusb_device *dev;
+	struct libusb_device_handle *handle = NULL;
+	size_t i = 0;
+	int r;
+
+	if (libusb_get_device_list(ctx, &devs) < 0)
+		return NULL;
+
+	while ((dev = devs[i++]) != NULL) {
+		struct libusb_device_descriptor desc;
+		r = libusb_get_device_descriptor(dev, &desc);
+		if (r < 0)
+			goto out;
+		if (desc.idVendor == vendor_id && desc.idProduct == product_id) {
+			found = dev;
+			break;
+		}
+	}
+
+	if (found) {
+		r = libusb_open(found, &handle);
+		if (r < 0)
+			handle = NULL;
+	}
+
+out:
+	libusb_free_device_list(devs, 1);
+	return handle;
+}
+
+static void do_close(struct libusb_context *ctx,
+	struct libusb_device_handle *dev_handle)
+{
+	struct usbi_transfer *itransfer;
+	struct usbi_transfer *tmp;
+
+	libusb_lock_events(ctx);
+
+	/* remove any transfers in flight that are for this device */
+	usbi_mutex_lock(&ctx->flying_transfers_lock);
+
+	/* safe iteration because transfers may be being deleted */
+	list_for_each_entry_safe(itransfer, tmp, &ctx->flying_transfers, list, struct usbi_transfer) {
+		struct libusb_transfer *transfer =
+		        USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
+
+		if (transfer->dev_handle != dev_handle)
+			continue;
+
+		if (!(itransfer->flags & USBI_TRANSFER_DEVICE_DISAPPEARED)) {
+			usbi_err(ctx, "Device handle closed while transfer was still being processed, but the device is still connected as far as we know");
+
+			if (itransfer->flags & USBI_TRANSFER_CANCELLING)
+				usbi_warn(ctx, "A cancellation for an in-flight transfer hasn't completed but closing the device handle");
+			else
+				usbi_err(ctx, "A cancellation hasn't even been scheduled on the transfer for which the device is closing");
+		}
+
+		/* remove from the list of in-flight transfers and make sure
+		 * we don't accidentally use the device handle in the future
+		 * (or that such accesses will be easily caught and identified as a crash)
+		 */
+		usbi_mutex_lock(&itransfer->lock);
+		list_del(&itransfer->list);
+		transfer->dev_handle = NULL;
+		usbi_mutex_unlock(&itransfer->lock);
+
+		/* it is up to the user to free up the actual transfer struct.  this is
+		 * just making sure that we don't attempt to process the transfer after
+		 * the device handle is invalid
+		 */
+		usbi_dbg("Removed transfer %p from the in-flight list because device handle %p closed",
+			 transfer, dev_handle);
+	}
+	usbi_mutex_unlock(&ctx->flying_transfers_lock);
+
+	libusb_unlock_events(ctx);
+
+	usbi_mutex_lock(&ctx->open_devs_lock);
+	list_del(&dev_handle->list);
+	usbi_mutex_unlock(&ctx->open_devs_lock);
+
+	usbi_backend->close(dev_handle);
+	libusb_unref_device(dev_handle->dev);
+	usbi_mutex_destroy(&dev_handle->lock);
+	free(dev_handle);
+}
+
+/** \ingroup dev
+ * Close a device handle. Should be called on all open handles before your
+ * application exits.
+ *
+ * Internally, this function destroys the reference that was added by
+ * libusb_open() on the given device.
+ *
+ * This is a non-blocking function; no requests are sent over the bus.
+ *
+ * \param dev_handle the handle to close
+ */
+void API_EXPORTED libusb_close(libusb_device_handle *dev_handle)
+{
+	struct libusb_context *ctx;
+	unsigned char dummy = 1;
+	ssize_t r;
+
+	if (!dev_handle)
+		return;
+	usbi_dbg("");
+
+	ctx = HANDLE_CTX(dev_handle);
+
+	/* Similarly to libusb_open(), we want to interrupt all event handlers
+	 * at this point. More importantly, we want to perform the actual close of
+	 * the device while holding the event handling lock (preventing any other
+	 * thread from doing event handling) because we will be removing a file
+	 * descriptor from the polling loop. */
+
+	/* record that we are messing with poll fds */
+	usbi_mutex_lock(&ctx->pollfd_modify_lock);
+	ctx->pollfd_modify++;
+	usbi_mutex_unlock(&ctx->pollfd_modify_lock);
+
+	/* write some data on control pipe to interrupt event handlers */
+	r = usbi_write(ctx->ctrl_pipe[1], &dummy, sizeof(dummy));
+	if (r <= 0) {
+		usbi_warn(ctx, "internal signalling write failed, closing anyway");
+		do_close(ctx, dev_handle);
+		usbi_mutex_lock(&ctx->pollfd_modify_lock);
+		ctx->pollfd_modify--;
+		usbi_mutex_unlock(&ctx->pollfd_modify_lock);
+		return;
+	}
+
+	/* take event handling lock */
+	libusb_lock_events(ctx);
+
+	/* read the dummy data */
+	r = usbi_read(ctx->ctrl_pipe[0], &dummy, sizeof(dummy));
+	if (r <= 0)
+		usbi_warn(ctx, "internal signalling read failed, closing anyway");
+
+	/* Close the device */
+	do_close(ctx, dev_handle);
+
+	/* we're done with modifying poll fds */
+	usbi_mutex_lock(&ctx->pollfd_modify_lock);
+	ctx->pollfd_modify--;
+	usbi_mutex_unlock(&ctx->pollfd_modify_lock);
+
+	/* Release event handling lock and wake up event waiters */
+	libusb_unlock_events(ctx);
+}
+
+/** \ingroup dev
+ * Get the underlying device for a handle. This function does not modify
+ * the reference count of the returned device, so do not feel compelled to
+ * unreference it when you are done.
+ * \param dev_handle a device handle
+ * \returns the underlying device
+ */
+DEFAULT_VISIBILITY
+libusb_device * LIBUSB_CALL libusb_get_device(libusb_device_handle *dev_handle)
+{
+	return dev_handle->dev;
+}
+
+/** \ingroup dev
+ * Determine the bConfigurationValue of the currently active configuration.
+ *
+ * You could formulate your own control request to obtain this information,
+ * but this function has the advantage that it may be able to retrieve the
+ * information from operating system caches (no I/O involved).
+ *
+ * If the OS does not cache this information, then this function will block
+ * while a control transfer is submitted to retrieve the information.
+ *
+ * This function will return a value of 0 in the <tt>config</tt> output
+ * parameter if the device is in unconfigured state.
+ *
+ * \param dev a device handle
+ * \param config output location for the bConfigurationValue of the active
+ * configuration (only valid for return code 0)
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+int API_EXPORTED libusb_get_configuration(libusb_device_handle *dev,
+	int *config)
+{
+	int r = LIBUSB_ERROR_NOT_SUPPORTED;
+
+	usbi_dbg("");
+	if (usbi_backend->get_configuration)
+		r = usbi_backend->get_configuration(dev, config);
+
+	if (r == LIBUSB_ERROR_NOT_SUPPORTED) {
+		uint8_t tmp = 0;
+		usbi_dbg("falling back to control message");
+		r = libusb_control_transfer(dev, LIBUSB_ENDPOINT_IN,
+			LIBUSB_REQUEST_GET_CONFIGURATION, 0, 0, &tmp, 1, 1000);
+		if (r == 0) {
+			usbi_err(HANDLE_CTX(dev), "zero bytes returned in ctrl transfer?");
+			r = LIBUSB_ERROR_IO;
+		} else if (r == 1) {
+			r = 0;
+			*config = tmp;
+		} else {
+			usbi_dbg("control failed, error %d", r);
+		}
+	}
+
+	if (r == 0)
+		usbi_dbg("active config %d", *config);
+
+	return r;
+}
+
+/** \ingroup dev
+ * Set the active configuration for a device.
+ *
+ * The operating system may or may not have already set an active
+ * configuration on the device. It is up to your application to ensure the
+ * correct configuration is selected before you attempt to claim interfaces
+ * and perform other operations.
+ *
+ * If you call this function on a device already configured with the selected
+ * configuration, then this function will act as a lightweight device reset:
+ * it will issue a SET_CONFIGURATION request using the current configuration,
+ * causing most USB-related device state to be reset (altsetting reset to zero,
+ * endpoint halts cleared, toggles reset).
+ *
+ * You cannot change/reset configuration if your application has claimed
+ * interfaces - you should free them with libusb_release_interface() first.
+ * You cannot change/reset configuration if other applications or drivers have
+ * claimed interfaces.
+ *
+ * A configuration value of -1 will put the device in unconfigured state.
+ * The USB specifications state that a configuration value of 0 does this,
+ * however buggy devices exist which actually have a configuration 0.
+ *
+ * You should always use this function rather than formulating your own
+ * SET_CONFIGURATION control request. This is because the underlying operating
+ * system needs to know when such changes happen.
+ *
+ * This is a blocking function.
+ *
+ * \param dev a device handle
+ * \param configuration the bConfigurationValue of the configuration you
+ * wish to activate, or -1 if you wish to put the device in unconfigured state
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the requested configuration does not exist
+ * \returns LIBUSB_ERROR_BUSY if interfaces are currently claimed
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+int API_EXPORTED libusb_set_configuration(libusb_device_handle *dev,
+	int configuration)
+{
+	usbi_dbg("configuration %d", configuration);
+	return usbi_backend->set_configuration(dev, configuration);
+}
+
+/** \ingroup dev
+ * Claim an interface on a given device handle. You must claim the interface
+ * you wish to use before you can perform I/O on any of its endpoints.
+ *
+ * It is legal to attempt to claim an already-claimed interface, in which
+ * case libusb just returns 0 without doing anything.
+ *
+ * Claiming of interfaces is a purely logical operation; it does not cause
+ * any requests to be sent over the bus. Interface claiming is used to
+ * instruct the underlying operating system that your application wishes
+ * to take ownership of the interface.
+ *
+ * This is a non-blocking function.
+ *
+ * \param dev a device handle
+ * \param interface_number the <tt>bInterfaceNumber</tt> of the interface you
+ * wish to claim
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the requested interface does not exist
+ * \returns LIBUSB_ERROR_BUSY if another program or driver has claimed the
+ * interface
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns a LIBUSB_ERROR code on other failure
+ */
+int API_EXPORTED libusb_claim_interface(libusb_device_handle *dev,
+	int interface_number)
+{
+	int r = 0;
+
+	usbi_dbg("interface %d", interface_number);
+	if (interface_number >= USB_MAXINTERFACES)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	usbi_mutex_lock(&dev->lock);
+	if (dev->claimed_interfaces & (1 << interface_number))
+		goto out;
+
+	r = usbi_backend->claim_interface(dev, interface_number);
+	if (r == 0)
+		dev->claimed_interfaces |= 1 << interface_number;
+
+out:
+	usbi_mutex_unlock(&dev->lock);
+	return r;
+}
+
+/** \ingroup dev
+ * Release an interface previously claimed with libusb_claim_interface(). You
+ * should release all claimed interfaces before closing a device handle.
+ *
+ * This is a blocking function. A SET_INTERFACE control request will be sent
+ * to the device, resetting interface state to the first alternate setting.
+ *
+ * \param dev a device handle
+ * \param interface_number the <tt>bInterfaceNumber</tt> of the
+ * previously-claimed interface
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the interface was not claimed
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+int API_EXPORTED libusb_release_interface(libusb_device_handle *dev,
+	int interface_number)
+{
+	int r;
+
+	usbi_dbg("interface %d", interface_number);
+	if (interface_number >= USB_MAXINTERFACES)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	usbi_mutex_lock(&dev->lock);
+	if (!(dev->claimed_interfaces & (1 << interface_number))) {
+		r = LIBUSB_ERROR_NOT_FOUND;
+		goto out;
+	}
+
+	r = usbi_backend->release_interface(dev, interface_number);
+	if (r == 0)
+		dev->claimed_interfaces &= ~(1 << interface_number);
+
+out:
+	usbi_mutex_unlock(&dev->lock);
+	return r;
+}
+
+/** \ingroup dev
+ * Activate an alternate setting for an interface. The interface must have
+ * been previously claimed with libusb_claim_interface().
+ *
+ * You should always use this function rather than formulating your own
+ * SET_INTERFACE control request. This is because the underlying operating
+ * system needs to know when such changes happen.
+ *
+ * This is a blocking function.
+ *
+ * \param dev a device handle
+ * \param interface_number the <tt>bInterfaceNumber</tt> of the
+ * previously-claimed interface
+ * \param alternate_setting the <tt>bAlternateSetting</tt> of the alternate
+ * setting to activate
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the interface was not claimed, or the
+ * requested alternate setting does not exist
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+int API_EXPORTED libusb_set_interface_alt_setting(libusb_device_handle *dev,
+	int interface_number, int alternate_setting)
+{
+	usbi_dbg("interface %d altsetting %d",
+		interface_number, alternate_setting);
+	if (interface_number >= USB_MAXINTERFACES)
+		return LIBUSB_ERROR_INVALID_PARAM;
+
+	usbi_mutex_lock(&dev->lock);
+	if (!(dev->claimed_interfaces & (1 << interface_number))) {
+		usbi_mutex_unlock(&dev->lock);
+		return LIBUSB_ERROR_NOT_FOUND;
+	}
+	usbi_mutex_unlock(&dev->lock);
+
+	return usbi_backend->set_interface_altsetting(dev, interface_number,
+		alternate_setting);
+}
+
+/** \ingroup dev
+ * Clear the halt/stall condition for an endpoint. Endpoints with halt status
+ * are unable to receive or transmit data until the halt condition is stalled.
+ *
+ * You should cancel all pending transfers before attempting to clear the halt
+ * condition.
+ *
+ * This is a blocking function.
+ *
+ * \param dev a device handle
+ * \param endpoint the endpoint to clear halt status
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if the endpoint does not exist
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+int API_EXPORTED libusb_clear_halt(libusb_device_handle *dev,
+	unsigned char endpoint)
+{
+	usbi_dbg("endpoint %x", endpoint);
+	return usbi_backend->clear_halt(dev, endpoint);
+}
+
+/** \ingroup dev
+ * Perform a USB port reset to reinitialize a device. The system will attempt
+ * to restore the previous configuration and alternate settings after the
+ * reset has completed.
+ *
+ * If the reset fails, the descriptors change, or the previous state cannot be
+ * restored, the device will appear to be disconnected and reconnected. This
+ * means that the device handle is no longer valid (you should close it) and
+ * rediscover the device. A return code of LIBUSB_ERROR_NOT_FOUND indicates
+ * when this is the case.
+ *
+ * This is a blocking function which usually incurs a noticeable delay.
+ *
+ * \param dev a handle of the device to reset
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if re-enumeration is required, or if the
+ * device has been disconnected
+ * \returns another LIBUSB_ERROR code on other failure
+ */
+int API_EXPORTED libusb_reset_device(libusb_device_handle *dev)
+{
+	usbi_dbg("");
+	return usbi_backend->reset_device(dev);
+}
+
+/** \ingroup dev
+ * Determine if a kernel driver is active on an interface. If a kernel driver
+ * is active, you cannot claim the interface, and libusb will be unable to
+ * perform I/O.
+ *
+ * This functionality is not available on Windows.
+ *
+ * \param dev a device handle
+ * \param interface_number the interface to check
+ * \returns 0 if no kernel driver is active
+ * \returns 1 if a kernel driver is active
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns LIBUSB_ERROR_NOT_SUPPORTED on platforms where the functionality
+ * is not available
+ * \returns another LIBUSB_ERROR code on other failure
+ * \see libusb_detach_kernel_driver()
+ */
+int API_EXPORTED libusb_kernel_driver_active(libusb_device_handle *dev,
+	int interface_number)
+{
+	usbi_dbg("interface %d", interface_number);
+	if (usbi_backend->kernel_driver_active)
+		return usbi_backend->kernel_driver_active(dev, interface_number);
+	else
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+/** \ingroup dev
+ * Detach a kernel driver from an interface. If successful, you will then be
+ * able to claim the interface and perform I/O.
+ *
+ * This functionality is not available on Darwin or Windows.
+ *
+ * \param dev a device handle
+ * \param interface_number the interface to detach the driver from
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if no kernel driver was active
+ * \returns LIBUSB_ERROR_INVALID_PARAM if the interface does not exist
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns LIBUSB_ERROR_NOT_SUPPORTED on platforms where the functionality
+ * is not available
+ * \returns another LIBUSB_ERROR code on other failure
+ * \see libusb_kernel_driver_active()
+ */
+int API_EXPORTED libusb_detach_kernel_driver(libusb_device_handle *dev,
+	int interface_number)
+{
+	usbi_dbg("interface %d", interface_number);
+	if (usbi_backend->detach_kernel_driver)
+		return usbi_backend->detach_kernel_driver(dev, interface_number);
+	else
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+/** \ingroup dev
+ * Re-attach an interface's kernel driver, which was previously detached
+ * using libusb_detach_kernel_driver(). This call is only effective on
+ * Linux and returns LIBUSB_ERROR_NOT_SUPPORTED on all other platforms.
+ *
+ * This functionality is not available on Darwin or Windows.
+ *
+ * \param dev a device handle
+ * \param interface_number the interface to attach the driver from
+ * \returns 0 on success
+ * \returns LIBUSB_ERROR_NOT_FOUND if no kernel driver was active
+ * \returns LIBUSB_ERROR_INVALID_PARAM if the interface does not exist
+ * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
+ * \returns LIBUSB_ERROR_NOT_SUPPORTED on platforms where the functionality
+ * is not available
+ * \returns LIBUSB_ERROR_BUSY if the driver cannot be attached because the
+ * interface is claimed by a program or driver
+ * \returns another LIBUSB_ERROR code on other failure
+ * \see libusb_kernel_driver_active()
+ */
+int API_EXPORTED libusb_attach_kernel_driver(libusb_device_handle *dev,
+	int interface_number)
+{
+	usbi_dbg("interface %d", interface_number);
+	if (usbi_backend->attach_kernel_driver)
+		return usbi_backend->attach_kernel_driver(dev, interface_number);
+	else
+		return LIBUSB_ERROR_NOT_SUPPORTED;
+}
+
+/** \ingroup lib
+ * Set message verbosity.
+ *  - Level 0: no messages ever printed by the library (default)
+ *  - Level 1: error messages are printed to stderr
+ *  - Level 2: warning and error messages are printed to stderr
+ *  - Level 3: informational messages are printed to stdout, warning and error
+ *    messages are printed to stderr
+ *
+ * The default level is 0, which means no messages are ever printed. If you
+ * choose to increase the message verbosity level, ensure that your
+ * application does not close the stdout/stderr file descriptors.
+ *
+ * You are advised to set level 3. libusb is conservative with its message
+ * logging and most of the time, will only log messages that explain error
+ * conditions and other oddities. This will help you debug your software.
+ *
+ * If the LIBUSB_DEBUG environment variable was set when libusb was
+ * initialized, this function does nothing: the message verbosity is fixed
+ * to the value in the environment variable.
+ *
+ * If libusb was compiled without any message logging, this function does
+ * nothing: you'll never get any messages.
+ *
+ * If libusb was compiled with verbose debug message logging, this function
+ * does nothing: you'll always get messages from all levels.
+ *
+ * \param ctx the context to operate on, or NULL for the default context
+ * \param level debug level to set
+ */
+void API_EXPORTED libusb_set_debug(libusb_context *ctx, int level)
+{
+	USBI_GET_CONTEXT(ctx);
+	if (!ctx->debug_fixed)
+		ctx->debug = level;
+}
+
+/** \ingroup lib
+ * Initialize libusb. This function must be called before calling any other
+ * libusb function.
+ *
+ * If you do not provide an output location for a context pointer, a default
+ * context will be created. If there was already a default context, it will
+ * be reused (and nothing will be initialized/reinitialized).
+ *
+ * \param context Optional output location for context pointer.
+ * Only valid on return code 0.
+ * \returns 0 on success, or a LIBUSB_ERROR code on failure
+ * \see contexts
+ */
+int API_EXPORTED libusb_init(libusb_context **context)
+{
+	char *dbg = getenv("LIBUSB_DEBUG");
+	struct libusb_context *ctx;
+	int r;
+
+	usbi_mutex_static_lock(&default_context_lock);
+	if (!context && usbi_default_context) {
+		r = 0;
+		usbi_dbg("reusing default context");
+		default_context_refcnt++;
+		usbi_mutex_static_unlock(&default_context_lock);
+		return 0;
+	}
+
+	ctx = malloc(sizeof(*ctx));
+	if (!ctx) {
+		r = LIBUSB_ERROR_NO_MEM;
+		goto err_unlock;
+	}
+	memset(ctx, 0, sizeof(*ctx));
+
+	if (dbg) {
+		ctx->debug = atoi(dbg);
+		if (ctx->debug)
+			ctx->debug_fixed = 1;
+	}
+
+	usbi_dbg("");
+
+	if (usbi_backend->init) {
+		r = usbi_backend->init(ctx);
+		if (r)
+			goto err_free_ctx;
+	}
+
+	usbi_mutex_init(&ctx->usb_devs_lock, NULL);
+	usbi_mutex_init(&ctx->open_devs_lock, NULL);
+	list_init(&ctx->usb_devs);
+	list_init(&ctx->open_devs);
+
+	r = usbi_io_init(ctx);
+	if (r < 0) {
+		if (usbi_backend->exit)
+			usbi_backend->exit();
+		goto err_destroy_mutex;
+	}
+
+	if (context) {
+		*context = ctx;
+	} else if (!usbi_default_context) {
+		usbi_dbg("created default context");
+		usbi_default_context = ctx;
+		default_context_refcnt++;
+	}
+	usbi_mutex_static_unlock(&default_context_lock);
+
+	return 0;
+
+err_destroy_mutex:
+	usbi_mutex_destroy(&ctx->open_devs_lock);
+	usbi_mutex_destroy(&ctx->usb_devs_lock);
+err_free_ctx:
+	free(ctx);
+err_unlock:
+	usbi_mutex_static_unlock(&default_context_lock);
+	return r;
+}
+
+/** \ingroup lib
+ * Deinitialize libusb. Should be called after closing all open devices and
+ * before your application terminates.
+ * \param ctx the context to deinitialize, or NULL for the default context
+ */
+void API_EXPORTED libusb_exit(struct libusb_context *ctx)
+{
+	usbi_dbg("");
+	USBI_GET_CONTEXT(ctx);
+
+	/* if working with default context, only actually do the deinitialization
+	 * if we're the last user */
+	if (ctx == usbi_default_context) {
+		usbi_mutex_static_lock(&default_context_lock);
+		if (--default_context_refcnt > 0) {
+			usbi_dbg("not destroying default context");
+			usbi_mutex_static_unlock(&default_context_lock);
+			return;
+		}
+		usbi_dbg("destroying default context");
+		usbi_default_context = NULL;
+		usbi_mutex_static_unlock(&default_context_lock);
+	}
+
+	/* a little sanity check. doesn't bother with open_devs locking because
+	 * unless there is an application bug, nobody will be accessing this. */
+	if (!list_empty(&ctx->open_devs))
+		usbi_warn(ctx, "application left some devices open");
+
+	usbi_io_exit(ctx);
+	if (usbi_backend->exit)
+		usbi_backend->exit();
+
+	usbi_mutex_destroy(&ctx->open_devs_lock);
+	usbi_mutex_destroy(&ctx->usb_devs_lock);
+	free(ctx);
+}
+
+/** \ingroup misc
+ * Check if the running library has a given capability.
+ *
+ * \param capability the \ref libusb_capability to check for
+ * \returns 1 if the running library has the capability, 0 otherwise
+ */
+int API_EXPORTED libusb_has_capability(uint32_t capability)
+{
+	switch (capability) {
+	case LIBUSB_CAN_GET_DEVICE_SPEED:
+		return 1;
+	default:
+		break;
+	}
+	return 0;
+}
+
+void usbi_log_v(struct libusb_context *ctx, enum usbi_log_level level,
+	const char *function, const char *format, va_list args)
+{
+	FILE *stream = stdout;
+	const char *prefix;
+
+#ifndef ENABLE_DEBUG_LOGGING
+	USBI_GET_CONTEXT(ctx);
+	if (!ctx->debug)
+		return;
+	if (level == LOG_LEVEL_WARNING && ctx->debug < 2)
+		return;
+	if (level == LOG_LEVEL_INFO && ctx->debug < 3)
+		return;
+#endif
+
+	switch (level) {
+	case LOG_LEVEL_INFO:
+		prefix = "info";
+		break;
+	case LOG_LEVEL_WARNING:
+		stream = stderr;
+		prefix = "warning";
+		break;
+	case LOG_LEVEL_ERROR:
+		stream = stderr;
+		prefix = "error";
+		break;
+	case LOG_LEVEL_DEBUG:
+		stream = stderr;
+		prefix = "debug";
+		break;
+	default:
+		stream = stderr;
+		prefix = "unknown";
+		break;
+	}
+
+	fprintf(stream, "libusb:%s [%s] ", prefix, function);
+
+	vfprintf(stream, format, args);
+
+	fprintf(stream, "\n");
+}
+
+void usbi_log(struct libusb_context *ctx, enum usbi_log_level level,
+	const char *function, const char *format, ...)
+{
+	va_list args;
+
+	va_start (args, format);
+	usbi_log_v(ctx, level, function, format, args);
+	va_end (args);
+}
+
+/** \ingroup misc
+ * Returns a constant NULL-terminated string with the ASCII name of a libusb
+ * error code. The caller must not free() the returned string.
+ *
+ * \param error_code The \ref libusb_error code to return the name of.
+ * \returns The error name, or the string **UNKNOWN** if the value of
+ * error_code is not a known error code.
+ */
+DEFAULT_VISIBILITY const char * LIBUSB_CALL libusb_error_name(int error_code)
+{
+	enum libusb_error error = error_code;
+	switch (error) {
+	case LIBUSB_SUCCESS:
+		return "LIBUSB_SUCCESS";
+	case LIBUSB_ERROR_IO:
+		return "LIBUSB_ERROR_IO";
+	case LIBUSB_ERROR_INVALID_PARAM:
+		return "LIBUSB_ERROR_INVALID_PARAM";
+	case LIBUSB_ERROR_ACCESS:
+		return "LIBUSB_ERROR_ACCESS";
+	case LIBUSB_ERROR_NO_DEVICE:
+		return "LIBUSB_ERROR_NO_DEVICE";
+	case LIBUSB_ERROR_NOT_FOUND:
+		return "LIBUSB_ERROR_NOT_FOUND";
+	case LIBUSB_ERROR_BUSY:
+		return "LIBUSB_ERROR_BUSY";
+	case LIBUSB_ERROR_TIMEOUT:
+		return "LIBUSB_ERROR_TIMEOUT";
+	case LIBUSB_ERROR_OVERFLOW:
+		return "LIBUSB_ERROR_OVERFLOW";
+	case LIBUSB_ERROR_PIPE:
+		return "LIBUSB_ERROR_PIPE";
+	case LIBUSB_ERROR_INTERRUPTED:
+		return "LIBUSB_ERROR_INTERRUPTED";
+	case LIBUSB_ERROR_NO_MEM:
+		return "LIBUSB_ERROR_NO_MEM";
+	case LIBUSB_ERROR_NOT_SUPPORTED:
+		return "LIBUSB_ERROR_NOT_SUPPORTED";
+	case LIBUSB_ERROR_OTHER:
+		return "LIBUSB_ERROR_OTHER";
+	}
+	return "**UNKNOWN**";
+}