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-/*
- * I/O functions for libusb
- * Copyright (C) 2007-2009 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 <signal.h>
-#include <stdint.h>
-#include <stdlib.h>
-#include <string.h>
-#include <time.h>
-
-#ifdef HAVE_SYS_TIME_H
-#include <sys/time.h>
-#endif
-
-#ifdef USBI_TIMERFD_AVAILABLE
-#include <sys/timerfd.h>
-#endif
-
-#include "libusbi.h"
-
-/**
- * \page io Synchronous and asynchronous device I/O
- *
- * \section intro Introduction
- *
- * If you're using libusb in your application, you're probably wanting to
- * perform I/O with devices - you want to perform USB data transfers.
- *
- * libusb offers two separate interfaces for device I/O. This page aims to
- * introduce the two in order to help you decide which one is more suitable
- * for your application. You can also choose to use both interfaces in your
- * application by considering each transfer on a case-by-case basis.
- *
- * Once you have read through the following discussion, you should consult the
- * detailed API documentation pages for the details:
- * - \ref syncio
- * - \ref asyncio
- *
- * \section theory Transfers at a logical level
- *
- * At a logical level, USB transfers typically happen in two parts. For
- * example, when reading data from a endpoint:
- * -# A request for data is sent to the device
- * -# Some time later, the incoming data is received by the host
- *
- * or when writing data to an endpoint:
- *
- * -# The data is sent to the device
- * -# Some time later, the host receives acknowledgement from the device that
- *    the data has been transferred.
- *
- * There may be an indefinite delay between the two steps. Consider a
- * fictional USB input device with a button that the user can press. In order
- * to determine when the button is pressed, you would likely submit a request
- * to read data on a bulk or interrupt endpoint and wait for data to arrive.
- * Data will arrive when the button is pressed by the user, which is
- * potentially hours later.
- *
- * libusb offers both a synchronous and an asynchronous interface to performing
- * USB transfers. The main difference is that the synchronous interface
- * combines both steps indicated above into a single function call, whereas
- * the asynchronous interface separates them.
- *
- * \section sync The synchronous interface
- *
- * The synchronous I/O interface allows you to perform a USB transfer with
- * a single function call. When the function call returns, the transfer has
- * completed and you can parse the results.
- *
- * If you have used the libusb-0.1 before, this I/O style will seem familar to
- * you. libusb-0.1 only offered a synchronous interface.
- *
- * In our input device example, to read button presses you might write code
- * in the following style:
-\code
-unsigned char data[4];
-int actual_length,
-int r = libusb_bulk_transfer(handle, EP_IN, data, sizeof(data), &actual_length, 0);
-if (r == 0 && actual_length == sizeof(data)) {
-	// results of the transaction can now be found in the data buffer
-	// parse them here and report button press
-} else {
-	error();
-}
-\endcode
- *
- * The main advantage of this model is simplicity: you did everything with
- * a single simple function call.
- *
- * However, this interface has its limitations. Your application will sleep
- * inside libusb_bulk_transfer() until the transaction has completed. If it
- * takes the user 3 hours to press the button, your application will be
- * sleeping for that long. Execution will be tied up inside the library -
- * the entire thread will be useless for that duration.
- *
- * Another issue is that by tieing up the thread with that single transaction
- * there is no possibility of performing I/O with multiple endpoints and/or
- * multiple devices simultaneously, unless you resort to creating one thread
- * per transaction.
- *
- * Additionally, there is no opportunity to cancel the transfer after the
- * request has been submitted.
- *
- * For details on how to use the synchronous API, see the
- * \ref syncio "synchronous I/O API documentation" pages.
- *
- * \section async The asynchronous interface
- *
- * Asynchronous I/O is the most significant new feature in libusb-1.0.
- * Although it is a more complex interface, it solves all the issues detailed
- * above.
- *
- * Instead of providing which functions that block until the I/O has complete,
- * libusb's asynchronous interface presents non-blocking functions which
- * begin a transfer and then return immediately. Your application passes a
- * callback function pointer to this non-blocking function, which libusb will
- * call with the results of the transaction when it has completed.
- *
- * Transfers which have been submitted through the non-blocking functions
- * can be cancelled with a separate function call.
- *
- * The non-blocking nature of this interface allows you to be simultaneously
- * performing I/O to multiple endpoints on multiple devices, without having
- * to use threads.
- *
- * This added flexibility does come with some complications though:
- * - In the interest of being a lightweight library, libusb does not create
- * threads and can only operate when your application is calling into it. Your
- * application must call into libusb from it's main loop when events are ready
- * to be handled, or you must use some other scheme to allow libusb to
- * undertake whatever work needs to be done.
- * - libusb also needs to be called into at certain fixed points in time in
- * order to accurately handle transfer timeouts.
- * - Memory handling becomes more complex. You cannot use stack memory unless
- * the function with that stack is guaranteed not to return until the transfer
- * callback has finished executing.
- * - You generally lose some linearity from your code flow because submitting
- * the transfer request is done in a separate function from where the transfer
- * results are handled. This becomes particularly obvious when you want to
- * submit a second transfer based on the results of an earlier transfer.
- *
- * Internally, libusb's synchronous interface is expressed in terms of function
- * calls to the asynchronous interface.
- *
- * For details on how to use the asynchronous API, see the
- * \ref asyncio "asynchronous I/O API" documentation pages.
- */
-
-
-/**
- * \page packetoverflow Packets and overflows
- *
- * \section packets Packet abstraction
- *
- * The USB specifications describe how data is transmitted in packets, with
- * constraints on packet size defined by endpoint descriptors. The host must
- * not send data payloads larger than the endpoint's maximum packet size.
- *
- * libusb and the underlying OS abstract out the packet concept, allowing you
- * to request transfers of any size. Internally, the request will be divided
- * up into correctly-sized packets. You do not have to be concerned with
- * packet sizes, but there is one exception when considering overflows.
- *
- * \section overflow Bulk/interrupt transfer overflows
- *
- * When requesting data on a bulk endpoint, libusb requires you to supply a
- * buffer and the maximum number of bytes of data that libusb can put in that
- * buffer. However, the size of the buffer is not communicated to the device -
- * the device is just asked to send any amount of data.
- *
- * There is no problem if the device sends an amount of data that is less than
- * or equal to the buffer size. libusb reports this condition to you through
- * the \ref libusb_transfer::actual_length "libusb_transfer.actual_length"
- * field.
- *
- * Problems may occur if the device attempts to send more data than can fit in
- * the buffer. libusb reports LIBUSB_TRANSFER_OVERFLOW for this condition but
- * other behaviour is largely undefined: actual_length may or may not be
- * accurate, the chunk of data that can fit in the buffer (before overflow)
- * may or may not have been transferred.
- *
- * Overflows are nasty, but can be avoided. Even though you were told to
- * ignore packets above, think about the lower level details: each transfer is
- * split into packets (typically small, with a maximum size of 512 bytes).
- * Overflows can only happen if the final packet in an incoming data transfer
- * is smaller than the actual packet that the device wants to transfer.
- * Therefore, you will never see an overflow if your transfer buffer size is a
- * multiple of the endpoint's packet size: the final packet will either
- * fill up completely or will be only partially filled.
- */
-
-/**
- * @defgroup asyncio Asynchronous device I/O
- *
- * This page details libusb's asynchronous (non-blocking) API for USB device
- * I/O. This interface is very powerful but is also quite complex - you will
- * need to read this page carefully to understand the necessary considerations
- * and issues surrounding use of this interface. Simplistic applications
- * may wish to consider the \ref syncio "synchronous I/O API" instead.
- *
- * The asynchronous interface is built around the idea of separating transfer
- * submission and handling of transfer completion (the synchronous model
- * combines both of these into one). There may be a long delay between
- * submission and completion, however the asynchronous submission function
- * is non-blocking so will return control to your application during that
- * potentially long delay.
- *
- * \section asyncabstraction Transfer abstraction
- *
- * For the asynchronous I/O, libusb implements the concept of a generic
- * transfer entity for all types of I/O (control, bulk, interrupt,
- * isochronous). The generic transfer object must be treated slightly
- * differently depending on which type of I/O you are performing with it.
- *
- * This is represented by the public libusb_transfer structure type.
- *
- * \section asynctrf Asynchronous transfers
- *
- * We can view asynchronous I/O as a 5 step process:
- * -# <b>Allocation</b>: allocate a libusb_transfer
- * -# <b>Filling</b>: populate the libusb_transfer instance with information
- *    about the transfer you wish to perform
- * -# <b>Submission</b>: ask libusb to submit the transfer
- * -# <b>Completion handling</b>: examine transfer results in the
- *    libusb_transfer structure
- * -# <b>Deallocation</b>: clean up resources
- *
- *
- * \subsection asyncalloc Allocation
- *
- * This step involves allocating memory for a USB transfer. This is the
- * generic transfer object mentioned above. At this stage, the transfer
- * is "blank" with no details about what type of I/O it will be used for.
- *
- * Allocation is done with the libusb_alloc_transfer() function. You must use
- * this function rather than allocating your own transfers.
- *
- * \subsection asyncfill Filling
- *
- * This step is where you take a previously allocated transfer and fill it
- * with information to determine the message type and direction, data buffer,
- * callback function, etc.
- *
- * You can either fill the required fields yourself or you can use the
- * helper functions: libusb_fill_control_transfer(), libusb_fill_bulk_transfer()
- * and libusb_fill_interrupt_transfer().
- *
- * \subsection asyncsubmit Submission
- *
- * When you have allocated a transfer and filled it, you can submit it using
- * libusb_submit_transfer(). This function returns immediately but can be
- * regarded as firing off the I/O request in the background.
- *
- * \subsection asynccomplete Completion handling
- *
- * After a transfer has been submitted, one of four things can happen to it:
- *
- * - The transfer completes (i.e. some data was transferred)
- * - The transfer has a timeout and the timeout expires before all data is
- * transferred
- * - The transfer fails due to an error
- * - The transfer is cancelled
- *
- * Each of these will cause the user-specified transfer callback function to
- * be invoked. It is up to the callback function to determine which of the
- * above actually happened and to act accordingly.
- *
- * The user-specified callback is passed a pointer to the libusb_transfer
- * structure which was used to setup and submit the transfer. At completion
- * time, libusb has populated this structure with results of the transfer:
- * success or failure reason, number of bytes of data transferred, etc. See
- * the libusb_transfer structure documentation for more information.
- *
- * \subsection Deallocation
- *
- * When a transfer has completed (i.e. the callback function has been invoked),
- * you are advised to free the transfer (unless you wish to resubmit it, see
- * below). Transfers are deallocated with libusb_free_transfer().
- *
- * It is undefined behaviour to free a transfer which has not completed.
- *
- * \section asyncresubmit Resubmission
- *
- * You may be wondering why allocation, filling, and submission are all
- * separated above where they could reasonably be combined into a single
- * operation.
- *
- * The reason for separation is to allow you to resubmit transfers without
- * having to allocate new ones every time. This is especially useful for
- * common situations dealing with interrupt endpoints - you allocate one
- * transfer, fill and submit it, and when it returns with results you just
- * resubmit it for the next interrupt.
- *
- * \section asynccancel Cancellation
- *
- * Another advantage of using the asynchronous interface is that you have
- * the ability to cancel transfers which have not yet completed. This is
- * done by calling the libusb_cancel_transfer() function.
- *
- * libusb_cancel_transfer() is asynchronous/non-blocking in itself. When the
- * cancellation actually completes, the transfer's callback function will
- * be invoked, and the callback function should check the transfer status to
- * determine that it was cancelled.
- *
- * Freeing the transfer after it has been cancelled but before cancellation
- * has completed will result in undefined behaviour.
- *
- * When a transfer is cancelled, some of the data may have been transferred.
- * libusb will communicate this to you in the transfer callback. Do not assume
- * that no data was transferred.
- *
- * \section bulk_overflows Overflows on device-to-host bulk/interrupt endpoints
- *
- * If your device does not have predictable transfer sizes (or it misbehaves),
- * your application may submit a request for data on an IN endpoint which is
- * smaller than the data that the device wishes to send. In some circumstances
- * this will cause an overflow, which is a nasty condition to deal with. See
- * the \ref packetoverflow page for discussion.
- *
- * \section asyncctrl Considerations for control transfers
- *
- * The <tt>libusb_transfer</tt> structure is generic and hence does not
- * include specific fields for the control-specific setup packet structure.
- *
- * In order to perform a control transfer, you must place the 8-byte setup
- * packet at the start of the data buffer. To simplify this, you could
- * cast the buffer pointer to type struct libusb_control_setup, or you can
- * use the helper function libusb_fill_control_setup().
- *
- * The wLength field placed in the setup packet must be the length you would
- * expect to be sent in the setup packet: the length of the payload that
- * follows (or the expected maximum number of bytes to receive). However,
- * the length field of the libusb_transfer object must be the length of
- * the data buffer - i.e. it should be wLength <em>plus</em> the size of
- * the setup packet (LIBUSB_CONTROL_SETUP_SIZE).
- *
- * If you use the helper functions, this is simplified for you:
- * -# Allocate a buffer of size LIBUSB_CONTROL_SETUP_SIZE plus the size of the
- * data you are sending/requesting.
- * -# Call libusb_fill_control_setup() on the data buffer, using the transfer
- * request size as the wLength value (i.e. do not include the extra space you
- * allocated for the control setup).
- * -# If this is a host-to-device transfer, place the data to be transferred
- * in the data buffer, starting at offset LIBUSB_CONTROL_SETUP_SIZE.
- * -# Call libusb_fill_control_transfer() to associate the data buffer with
- * the transfer (and to set the remaining details such as callback and timeout).
- *   - Note that there is no parameter to set the length field of the transfer.
- *     The length is automatically inferred from the wLength field of the setup
- *     packet.
- * -# Submit the transfer.
- *
- * The multi-byte control setup fields (wValue, wIndex and wLength) must
- * be given in little-endian byte order (the endianness of the USB bus).
- * Endianness conversion is transparently handled by
- * libusb_fill_control_setup() which is documented to accept host-endian
- * values.
- *
- * Further considerations are needed when handling transfer completion in
- * your callback function:
- * - As you might expect, the setup packet will still be sitting at the start
- * of the data buffer.
- * - If this was a device-to-host transfer, the received data will be sitting
- * at offset LIBUSB_CONTROL_SETUP_SIZE into the buffer.
- * - The actual_length field of the transfer structure is relative to the
- * wLength of the setup packet, rather than the size of the data buffer. So,
- * if your wLength was 4, your transfer's <tt>length</tt> was 12, then you
- * should expect an <tt>actual_length</tt> of 4 to indicate that the data was
- * transferred in entirity.
- *
- * To simplify parsing of setup packets and obtaining the data from the
- * correct offset, you may wish to use the libusb_control_transfer_get_data()
- * and libusb_control_transfer_get_setup() functions within your transfer
- * callback.
- *
- * Even though control endpoints do not halt, a completed control transfer
- * may have a LIBUSB_TRANSFER_STALL status code. This indicates the control
- * request was not supported.
- *
- * \section asyncintr Considerations for interrupt transfers
- *
- * All interrupt transfers are performed using the polling interval presented
- * by the bInterval value of the endpoint descriptor.
- *
- * \section asynciso Considerations for isochronous transfers
- *
- * Isochronous transfers are more complicated than transfers to
- * non-isochronous endpoints.
- *
- * To perform I/O to an isochronous endpoint, allocate the transfer by calling
- * libusb_alloc_transfer() with an appropriate number of isochronous packets.
- *
- * During filling, set \ref libusb_transfer::type "type" to
- * \ref libusb_transfer_type::LIBUSB_TRANSFER_TYPE_ISOCHRONOUS
- * "LIBUSB_TRANSFER_TYPE_ISOCHRONOUS", and set
- * \ref libusb_transfer::num_iso_packets "num_iso_packets" to a value less than
- * or equal to the number of packets you requested during allocation.
- * libusb_alloc_transfer() does not set either of these fields for you, given
- * that you might not even use the transfer on an isochronous endpoint.
- *
- * Next, populate the length field for the first num_iso_packets entries in
- * the \ref libusb_transfer::iso_packet_desc "iso_packet_desc" array. Section
- * 5.6.3 of the USB2 specifications describe how the maximum isochronous
- * packet length is determined by the wMaxPacketSize field in the endpoint
- * descriptor.
- * Two functions can help you here:
- *
- * - libusb_get_max_iso_packet_size() is an easy way to determine the max
- *   packet size for an isochronous endpoint. Note that the maximum packet
- *   size is actually the maximum number of bytes that can be transmitted in
- *   a single microframe, therefore this function multiplies the maximum number
- *   of bytes per transaction by the number of transaction opportunities per
- *   microframe.
- * - libusb_set_iso_packet_lengths() assigns the same length to all packets
- *   within a transfer, which is usually what you want.
- *
- * For outgoing transfers, you'll obviously fill the buffer and populate the
- * packet descriptors in hope that all the data gets transferred. For incoming
- * transfers, you must ensure the buffer has sufficient capacity for
- * the situation where all packets transfer the full amount of requested data.
- *
- * Completion handling requires some extra consideration. The
- * \ref libusb_transfer::actual_length "actual_length" field of the transfer
- * is meaningless and should not be examined; instead you must refer to the
- * \ref libusb_iso_packet_descriptor::actual_length "actual_length" field of
- * each individual packet.
- *
- * The \ref libusb_transfer::status "status" field of the transfer is also a
- * little misleading:
- *  - If the packets were submitted and the isochronous data microframes
- *    completed normally, status will have value
- *    \ref libusb_transfer_status::LIBUSB_TRANSFER_COMPLETED
- *    "LIBUSB_TRANSFER_COMPLETED". Note that bus errors and software-incurred
- *    delays are not counted as transfer errors; the transfer.status field may
- *    indicate COMPLETED even if some or all of the packets failed. Refer to
- *    the \ref libusb_iso_packet_descriptor::status "status" field of each
- *    individual packet to determine packet failures.
- *  - The status field will have value
- *    \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR
- *    "LIBUSB_TRANSFER_ERROR" only when serious errors were encountered.
- *  - Other transfer status codes occur with normal behaviour.
- *
- * The data for each packet will be found at an offset into the buffer that
- * can be calculated as if each prior packet completed in full. The
- * libusb_get_iso_packet_buffer() and libusb_get_iso_packet_buffer_simple()
- * functions may help you here.
- *
- * \section asyncmem Memory caveats
- *
- * In most circumstances, it is not safe to use stack memory for transfer
- * buffers. This is because the function that fired off the asynchronous
- * transfer may return before libusb has finished using the buffer, and when
- * the function returns it's stack gets destroyed. This is true for both
- * host-to-device and device-to-host transfers.
- *
- * The only case in which it is safe to use stack memory is where you can
- * guarantee that the function owning the stack space for the buffer does not
- * return until after the transfer's callback function has completed. In every
- * other case, you need to use heap memory instead.
- *
- * \section asyncflags Fine control
- *
- * Through using this asynchronous interface, you may find yourself repeating
- * a few simple operations many times. You can apply a bitwise OR of certain
- * flags to a transfer to simplify certain things:
- * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_SHORT_NOT_OK
- *   "LIBUSB_TRANSFER_SHORT_NOT_OK" results in transfers which transferred
- *   less than the requested amount of data being marked with status
- *   \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR "LIBUSB_TRANSFER_ERROR"
- *   (they would normally be regarded as COMPLETED)
- * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
- *   "LIBUSB_TRANSFER_FREE_BUFFER" allows you to ask libusb to free the transfer
- *   buffer when freeing the transfer.
- * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_TRANSFER
- *   "LIBUSB_TRANSFER_FREE_TRANSFER" causes libusb to automatically free the
- *   transfer after the transfer callback returns.
- *
- * \section asyncevent Event handling
- *
- * In accordance of the aim of being a lightweight library, libusb does not
- * create threads internally. This means that libusb code does not execute
- * at any time other than when your application is calling a libusb function.
- * However, an asynchronous model requires that libusb perform work at various
- * points in time - namely processing the results of previously-submitted
- * transfers and invoking the user-supplied callback function.
- *
- * This gives rise to the libusb_handle_events() function which your
- * application must call into when libusb has work do to. This gives libusb
- * the opportunity to reap pending transfers, invoke callbacks, etc.
- *
- * The first issue to discuss here is how your application can figure out
- * when libusb has work to do. In fact, there are two naive options which
- * do not actually require your application to know this:
- * -# Periodically call libusb_handle_events() in non-blocking mode at fixed
- *    short intervals from your main loop
- * -# Repeatedly call libusb_handle_events() in blocking mode from a dedicated
- *    thread.
- *
- * The first option is plainly not very nice, and will cause unnecessary
- * CPU wakeups leading to increased power usage and decreased battery life.
- * The second option is not very nice either, but may be the nicest option
- * available to you if the "proper" approach can not be applied to your
- * application (read on...).
- *
- * The recommended option is to integrate libusb with your application main
- * event loop. libusb exposes a set of file descriptors which allow you to do
- * this. Your main loop is probably already calling poll() or select() or a
- * variant on a set of file descriptors for other event sources (e.g. keyboard
- * button presses, mouse movements, network sockets, etc). You then add
- * libusb's file descriptors to your poll()/select() calls, and when activity
- * is detected on such descriptors you know it is time to call
- * libusb_handle_events().
- *
- * There is one final event handling complication. libusb supports
- * asynchronous transfers which time out after a specified time period, and
- * this requires that libusb is called into at or after the timeout so that
- * the timeout can be handled. So, in addition to considering libusb's file
- * descriptors in your main event loop, you must also consider that libusb
- * sometimes needs to be called into at fixed points in time even when there
- * is no file descriptor activity.
- *
- * For the details on retrieving the set of file descriptors and determining
- * the next timeout, see the \ref poll "polling and timing" API documentation.
- */
-
-/**
- * @defgroup poll Polling and timing
- *
- * This page documents libusb's functions for polling events and timing.
- * These functions are only necessary for users of the
- * \ref asyncio "asynchronous API". If you are only using the simpler
- * \ref syncio "synchronous API" then you do not need to ever call these
- * functions.
- *
- * The justification for the functionality described here has already been
- * discussed in the \ref asyncevent "event handling" section of the
- * asynchronous API documentation. In summary, libusb does not create internal
- * threads for event processing and hence relies on your application calling
- * into libusb at certain points in time so that pending events can be handled.
- * In order to know precisely when libusb needs to be called into, libusb
- * offers you a set of pollable file descriptors and information about when
- * the next timeout expires.
- *
- * If you are using the asynchronous I/O API, you must take one of the two
- * following options, otherwise your I/O will not complete.
- *
- * \section pollsimple The simple option
- *
- * If your application revolves solely around libusb and does not need to
- * handle other event sources, you can have a program structure as follows:
-\code
-// initialize libusb
-// find and open device
-// maybe fire off some initial async I/O
-
-while (user_has_not_requested_exit)
-	libusb_handle_events(ctx);
-
-// clean up and exit
-\endcode
- *
- * With such a simple main loop, you do not have to worry about managing
- * sets of file descriptors or handling timeouts. libusb_handle_events() will
- * handle those details internally.
- *
- * \section pollmain The more advanced option
- *
- * \note This functionality is currently only available on Unix-like platforms.
- * On Windows, libusb_get_pollfds() simply returns NULL. Exposing event sources
- * on Windows will require some further thought and design.
- *
- * In more advanced applications, you will already have a main loop which
- * is monitoring other event sources: network sockets, X11 events, mouse
- * movements, etc. Through exposing a set of file descriptors, libusb is
- * designed to cleanly integrate into such main loops.
- *
- * In addition to polling file descriptors for the other event sources, you
- * take a set of file descriptors from libusb and monitor those too. When you
- * detect activity on libusb's file descriptors, you call
- * libusb_handle_events_timeout() in non-blocking mode.
- *
- * What's more, libusb may also need to handle events at specific moments in
- * time. No file descriptor activity is generated at these times, so your
- * own application needs to be continually aware of when the next one of these
- * moments occurs (through calling libusb_get_next_timeout()), and then it
- * needs to call libusb_handle_events_timeout() in non-blocking mode when
- * these moments occur. This means that you need to adjust your
- * poll()/select() timeout accordingly.
- *
- * libusb provides you with a set of file descriptors to poll and expects you
- * to poll all of them, treating them as a single entity. The meaning of each
- * file descriptor in the set is an internal implementation detail,
- * platform-dependent and may vary from release to release. Don't try and
- * interpret the meaning of the file descriptors, just do as libusb indicates,
- * polling all of them at once.
- *
- * In pseudo-code, you want something that looks like:
-\code
-// initialise libusb
-
-libusb_get_pollfds(ctx)
-while (user has not requested application exit) {
-	libusb_get_next_timeout(ctx);
-	poll(on libusb file descriptors plus any other event sources of interest,
-		using a timeout no larger than the value libusb just suggested)
-	if (poll() indicated activity on libusb file descriptors)
-		libusb_handle_events_timeout(ctx, 0);
-	if (time has elapsed to or beyond the libusb timeout)
-		libusb_handle_events_timeout(ctx, 0);
-	// handle events from other sources here
-}
-
-// clean up and exit
-\endcode
- *
- * \subsection polltime Notes on time-based events
- *
- * The above complication with having to track time and call into libusb at
- * specific moments is a bit of a headache. For maximum compatibility, you do
- * need to write your main loop as above, but you may decide that you can
- * restrict the supported platforms of your application and get away with
- * a more simplistic scheme.
- *
- * These time-based event complications are \b not required on the following
- * platforms:
- *  - Darwin
- *  - Linux, provided that the following version requirements are satisfied:
- *   - Linux v2.6.27 or newer, compiled with timerfd support
- *   - glibc v2.9 or newer
- *   - libusb v1.0.5 or newer
- *
- * Under these configurations, libusb_get_next_timeout() will \em always return
- * 0, so your main loop can be simplified to:
-\code
-// initialise libusb
-
-libusb_get_pollfds(ctx)
-while (user has not requested application exit) {
-	poll(on libusb file descriptors plus any other event sources of interest,
-		using any timeout that you like)
-	if (poll() indicated activity on libusb file descriptors)
-		libusb_handle_events_timeout(ctx, 0);
-	// handle events from other sources here
-}
-
-// clean up and exit
-\endcode
- *
- * Do remember that if you simplify your main loop to the above, you will
- * lose compatibility with some platforms (including legacy Linux platforms,
- * and <em>any future platforms supported by libusb which may have time-based
- * event requirements</em>). The resultant problems will likely appear as
- * strange bugs in your application.
- *
- * You can use the libusb_pollfds_handle_timeouts() function to do a runtime
- * check to see if it is safe to ignore the time-based event complications.
- * If your application has taken the shortcut of ignoring libusb's next timeout
- * in your main loop, then you are advised to check the return value of
- * libusb_pollfds_handle_timeouts() during application startup, and to abort
- * if the platform does suffer from these timing complications.
- *
- * \subsection fdsetchange Changes in the file descriptor set
- *
- * The set of file descriptors that libusb uses as event sources may change
- * during the life of your application. Rather than having to repeatedly
- * call libusb_get_pollfds(), you can set up notification functions for when
- * the file descriptor set changes using libusb_set_pollfd_notifiers().
- *
- * \subsection mtissues Multi-threaded considerations
- *
- * Unfortunately, the situation is complicated further when multiple threads
- * come into play. If two threads are monitoring the same file descriptors,
- * the fact that only one thread will be woken up when an event occurs causes
- * some headaches.
- *
- * The events lock, event waiters lock, and libusb_handle_events_locked()
- * entities are added to solve these problems. You do not need to be concerned
- * with these entities otherwise.
- *
- * See the extra documentation: \ref mtasync
- */
-
-/** \page mtasync Multi-threaded applications and asynchronous I/O
- *
- * libusb is a thread-safe library, but extra considerations must be applied
- * to applications which interact with libusb from multiple threads.
- *
- * The underlying issue that must be addressed is that all libusb I/O
- * revolves around monitoring file descriptors through the poll()/select()
- * system calls. This is directly exposed at the
- * \ref asyncio "asynchronous interface" but it is important to note that the
- * \ref syncio "synchronous interface" is implemented on top of the
- * asynchonrous interface, therefore the same considerations apply.
- *
- * The issue is that if two or more threads are concurrently calling poll()
- * or select() on libusb's file descriptors then only one of those threads
- * will be woken up when an event arrives. The others will be completely
- * oblivious that anything has happened.
- *
- * Consider the following pseudo-code, which submits an asynchronous transfer
- * then waits for its completion. This style is one way you could implement a
- * synchronous interface on top of the asynchronous interface (and libusb
- * does something similar, albeit more advanced due to the complications
- * explained on this page).
- *
-\code
-void cb(struct libusb_transfer *transfer)
-{
-	int *completed = transfer->user_data;
-	*completed = 1;
-}
-
-void myfunc() {
-	struct libusb_transfer *transfer;
-	unsigned char buffer[LIBUSB_CONTROL_SETUP_SIZE];
-	int completed = 0;
-
-	transfer = libusb_alloc_transfer(0);
-	libusb_fill_control_setup(buffer,
-		LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_OUT, 0x04, 0x01, 0, 0);
-	libusb_fill_control_transfer(transfer, dev, buffer, cb, &completed, 1000);
-	libusb_submit_transfer(transfer);
-
-	while (!completed) {
-		poll(libusb file descriptors, 120*1000);
-		if (poll indicates activity)
-			libusb_handle_events_timeout(ctx, 0);
-	}
-	printf("completed!");
-	// other code here
-}
-\endcode
- *
- * Here we are <em>serializing</em> completion of an asynchronous event
- * against a condition - the condition being completion of a specific transfer.
- * The poll() loop has a long timeout to minimize CPU usage during situations
- * when nothing is happening (it could reasonably be unlimited).
- *
- * If this is the only thread that is polling libusb's file descriptors, there
- * is no problem: there is no danger that another thread will swallow up the
- * event that we are interested in. On the other hand, if there is another
- * thread polling the same descriptors, there is a chance that it will receive
- * the event that we were interested in. In this situation, <tt>myfunc()</tt>
- * will only realise that the transfer has completed on the next iteration of
- * the loop, <em>up to 120 seconds later.</em> Clearly a two-minute delay is
- * undesirable, and don't even think about using short timeouts to circumvent
- * this issue!
- *
- * The solution here is to ensure that no two threads are ever polling the
- * file descriptors at the same time. A naive implementation of this would
- * impact the capabilities of the library, so libusb offers the scheme
- * documented below to ensure no loss of functionality.
- *
- * Before we go any further, it is worth mentioning that all libusb-wrapped
- * event handling procedures fully adhere to the scheme documented below.
- * This includes libusb_handle_events() and all the synchronous I/O functions -
- * libusb hides this headache from you. You do not need to worry about any
- * of these issues if you stick to that level.
- *
- * The problem is when we consider the fact that libusb exposes file
- * descriptors to allow for you to integrate asynchronous USB I/O into
- * existing main loops, effectively allowing you to do some work behind
- * libusb's back. If you do take libusb's file descriptors and pass them to
- * poll()/select() yourself, you need to be aware of the associated issues.
- *
- * \section eventlock The events lock
- *
- * The first concept to be introduced is the events lock. The events lock
- * is used to serialize threads that want to handle events, such that only
- * one thread is handling events at any one time.
- *
- * You must take the events lock before polling libusb file descriptors,
- * using libusb_lock_events(). You must release the lock as soon as you have
- * aborted your poll()/select() loop, using libusb_unlock_events().
- *
- * \section threadwait Letting other threads do the work for you
- *
- * Although the events lock is a critical part of the solution, it is not
- * enough on it's own. You might wonder if the following is sufficient...
-\code
-	libusb_lock_events(ctx);
-	while (!completed) {
-		poll(libusb file descriptors, 120*1000);
-		if (poll indicates activity)
-			libusb_handle_events_timeout(ctx, 0);
-	}
-	libusb_unlock_events(ctx);
-\endcode
- * ...and the answer is that it is not. This is because the transfer in the
- * code shown above may take a long time (say 30 seconds) to complete, and
- * the lock is not released until the transfer is completed.
- *
- * Another thread with similar code that wants to do event handling may be
- * working with a transfer that completes after a few milliseconds. Despite
- * having such a quick completion time, the other thread cannot check that
- * status of its transfer until the code above has finished (30 seconds later)
- * due to contention on the lock.
- *
- * To solve this, libusb offers you a mechanism to determine when another
- * thread is handling events. It also offers a mechanism to block your thread
- * until the event handling thread has completed an event (and this mechanism
- * does not involve polling of file descriptors).
- *
- * After determining that another thread is currently handling events, you
- * obtain the <em>event waiters</em> lock using libusb_lock_event_waiters().
- * You then re-check that some other thread is still handling events, and if
- * so, you call libusb_wait_for_event().
- *
- * libusb_wait_for_event() puts your application to sleep until an event
- * occurs, or until a thread releases the events lock. When either of these
- * things happen, your thread is woken up, and should re-check the condition
- * it was waiting on. It should also re-check that another thread is handling
- * events, and if not, it should start handling events itself.
- *
- * This looks like the following, as pseudo-code:
-\code
-retry:
-if (libusb_try_lock_events(ctx) == 0) {
-	// we obtained the event lock: do our own event handling
-	while (!completed) {
-		if (!libusb_event_handling_ok(ctx)) {
-			libusb_unlock_events(ctx);
-			goto retry;
-		}
-		poll(libusb file descriptors, 120*1000);
-		if (poll indicates activity)
-			libusb_handle_events_locked(ctx, 0);
-	}
-	libusb_unlock_events(ctx);
-} else {
-	// another thread is doing event handling. wait for it to signal us that
-	// an event has completed
-	libusb_lock_event_waiters(ctx);
-
-	while (!completed) {
-		// now that we have the event waiters lock, double check that another
-		// thread is still handling events for us. (it may have ceased handling
-		// events in the time it took us to reach this point)
-		if (!libusb_event_handler_active(ctx)) {
-			// whoever was handling events is no longer doing so, try again
-			libusb_unlock_event_waiters(ctx);
-			goto retry;
-		}
-
-		libusb_wait_for_event(ctx, NULL);
-	}
-	libusb_unlock_event_waiters(ctx);
-}
-printf("completed!\n");
-\endcode
- *
- * A naive look at the above code may suggest that this can only support
- * one event waiter (hence a total of 2 competing threads, the other doing
- * event handling), because the event waiter seems to have taken the event
- * waiters lock while waiting for an event. However, the system does support
- * multiple event waiters, because libusb_wait_for_event() actually drops
- * the lock while waiting, and reaquires it before continuing.
- *
- * We have now implemented code which can dynamically handle situations where
- * nobody is handling events (so we should do it ourselves), and it can also
- * handle situations where another thread is doing event handling (so we can
- * piggyback onto them). It is also equipped to handle a combination of
- * the two, for example, another thread is doing event handling, but for
- * whatever reason it stops doing so before our condition is met, so we take
- * over the event handling.
- *
- * Four functions were introduced in the above pseudo-code. Their importance
- * should be apparent from the code shown above.
- * -# libusb_try_lock_events() is a non-blocking function which attempts
- *    to acquire the events lock but returns a failure code if it is contended.
- * -# libusb_event_handling_ok() checks that libusb is still happy for your
- *    thread to be performing event handling. Sometimes, libusb needs to
- *    interrupt the event handler, and this is how you can check if you have
- *    been interrupted. If this function returns 0, the correct behaviour is
- *    for you to give up the event handling lock, and then to repeat the cycle.
- *    The following libusb_try_lock_events() will fail, so you will become an
- *    events waiter. For more information on this, read \ref fullstory below.
- * -# libusb_handle_events_locked() is a variant of
- *    libusb_handle_events_timeout() that you can call while holding the
- *    events lock. libusb_handle_events_timeout() itself implements similar
- *    logic to the above, so be sure not to call it when you are
- *    "working behind libusb's back", as is the case here.
- * -# libusb_event_handler_active() determines if someone is currently
- *    holding the events lock
- *
- * You might be wondering why there is no function to wake up all threads
- * blocked on libusb_wait_for_event(). This is because libusb can do this
- * internally: it will wake up all such threads when someone calls
- * libusb_unlock_events() or when a transfer completes (at the point after its
- * callback has returned).
- *
- * \subsection fullstory The full story
- *
- * The above explanation should be enough to get you going, but if you're
- * really thinking through the issues then you may be left with some more
- * questions regarding libusb's internals. If you're curious, read on, and if
- * not, skip to the next section to avoid confusing yourself!
- *
- * The immediate question that may spring to mind is: what if one thread
- * modifies the set of file descriptors that need to be polled while another
- * thread is doing event handling?
- *
- * There are 2 situations in which this may happen.
- * -# libusb_open() will add another file descriptor to the poll set,
- *    therefore it is desirable to interrupt the event handler so that it
- *    restarts, picking up the new descriptor.
- * -# libusb_close() will remove a file descriptor from the poll set. There
- *    are all kinds of race conditions that could arise here, so it is
- *    important that nobody is doing event handling at this time.
- *
- * libusb handles these issues internally, so application developers do not
- * have to stop their event handlers while opening/closing devices. Here's how
- * it works, focusing on the libusb_close() situation first:
- *
- * -# During initialization, libusb opens an internal pipe, and it adds the read
- *    end of this pipe to the set of file descriptors to be polled.
- * -# During libusb_close(), libusb writes some dummy data on this control pipe.
- *    This immediately interrupts the event handler. libusb also records
- *    internally that it is trying to interrupt event handlers for this
- *    high-priority event.
- * -# At this point, some of the functions described above start behaving
- *    differently:
- *   - libusb_event_handling_ok() starts returning 1, indicating that it is NOT
- *     OK for event handling to continue.
- *   - libusb_try_lock_events() starts returning 1, indicating that another
- *     thread holds the event handling lock, even if the lock is uncontended.
- *   - libusb_event_handler_active() starts returning 1, indicating that
- *     another thread is doing event handling, even if that is not true.
- * -# The above changes in behaviour result in the event handler stopping and
- *    giving up the events lock very quickly, giving the high-priority
- *    libusb_close() operation a "free ride" to acquire the events lock. All
- *    threads that are competing to do event handling become event waiters.
- * -# With the events lock held inside libusb_close(), libusb can safely remove
- *    a file descriptor from the poll set, in the safety of knowledge that
- *    nobody is polling those descriptors or trying to access the poll set.
- * -# After obtaining the events lock, the close operation completes very
- *    quickly (usually a matter of milliseconds) and then immediately releases
- *    the events lock.
- * -# At the same time, the behaviour of libusb_event_handling_ok() and friends
- *    reverts to the original, documented behaviour.
- * -# The release of the events lock causes the threads that are waiting for
- *    events to be woken up and to start competing to become event handlers
- *    again. One of them will succeed; it will then re-obtain the list of poll
- *    descriptors, and USB I/O will then continue as normal.
- *
- * libusb_open() is similar, and is actually a more simplistic case. Upon a
- * call to libusb_open():
- *
- * -# The device is opened and a file descriptor is added to the poll set.
- * -# libusb sends some dummy data on the control pipe, and records that it
- *    is trying to modify the poll descriptor set.
- * -# The event handler is interrupted, and the same behaviour change as for
- *    libusb_close() takes effect, causing all event handling threads to become
- *    event waiters.
- * -# The libusb_open() implementation takes its free ride to the events lock.
- * -# Happy that it has successfully paused the events handler, libusb_open()
- *    releases the events lock.
- * -# The event waiter threads are all woken up and compete to become event
- *    handlers again. The one that succeeds will obtain the list of poll
- *    descriptors again, which will include the addition of the new device.
- *
- * \subsection concl Closing remarks
- *
- * The above may seem a little complicated, but hopefully I have made it clear
- * why such complications are necessary. Also, do not forget that this only
- * applies to applications that take libusb's file descriptors and integrate
- * them into their own polling loops.
- *
- * You may decide that it is OK for your multi-threaded application to ignore
- * some of the rules and locks detailed above, because you don't think that
- * two threads can ever be polling the descriptors at the same time. If that
- * is the case, then that's good news for you because you don't have to worry.
- * But be careful here; remember that the synchronous I/O functions do event
- * handling internally. If you have one thread doing event handling in a loop
- * (without implementing the rules and locking semantics documented above)
- * and another trying to send a synchronous USB transfer, you will end up with
- * two threads monitoring the same descriptors, and the above-described
- * undesirable behaviour occuring. The solution is for your polling thread to
- * play by the rules; the synchronous I/O functions do so, and this will result
- * in them getting along in perfect harmony.
- *
- * If you do have a dedicated thread doing event handling, it is perfectly
- * legal for it to take the event handling lock for long periods of time. Any
- * synchronous I/O functions you call from other threads will transparently
- * fall back to the "event waiters" mechanism detailed above. The only
- * consideration that your event handling thread must apply is the one related
- * to libusb_event_handling_ok(): you must call this before every poll(), and
- * give up the events lock if instructed.
- */
-
-int usbi_io_init(struct libusb_context *ctx)
-{
-	int r;
-
-	usbi_mutex_init(&ctx->flying_transfers_lock, NULL);
-	usbi_mutex_init(&ctx->pollfds_lock, NULL);
-	usbi_mutex_init(&ctx->pollfd_modify_lock, NULL);
-	usbi_mutex_init(&ctx->events_lock, NULL);
-	usbi_mutex_init(&ctx->event_waiters_lock, NULL);
-	usbi_cond_init(&ctx->event_waiters_cond, NULL);
-	list_init(&ctx->flying_transfers);
-	list_init(&ctx->pollfds);
-
-	/* FIXME should use an eventfd on kernels that support it */
-	r = usbi_pipe(ctx->ctrl_pipe);
-	if (r < 0) {
-		r = LIBUSB_ERROR_OTHER;
-		goto err;
-	}
-
-	r = usbi_add_pollfd(ctx, ctx->ctrl_pipe[0], POLLIN);
-	if (r < 0)
-		goto err_close_pipe;
-
-#ifdef USBI_TIMERFD_AVAILABLE
-	ctx->timerfd = timerfd_create(usbi_backend->get_timerfd_clockid(),
-		TFD_NONBLOCK);
-	if (ctx->timerfd >= 0) {
-		usbi_dbg("using timerfd for timeouts");
-		r = usbi_add_pollfd(ctx, ctx->timerfd, POLLIN);
-		if (r < 0) {
-			usbi_remove_pollfd(ctx, ctx->ctrl_pipe[0]);
-			close(ctx->timerfd);
-			goto err_close_pipe;
-		}
-	} else {
-		usbi_dbg("timerfd not available (code %d error %d)", ctx->timerfd, errno);
-		ctx->timerfd = -1;
-	}
-#endif
-
-	return 0;
-
-err_close_pipe:
-	usbi_close(ctx->ctrl_pipe[0]);
-	usbi_close(ctx->ctrl_pipe[1]);
-err:
-	usbi_mutex_destroy(&ctx->flying_transfers_lock);
-	usbi_mutex_destroy(&ctx->pollfds_lock);
-	usbi_mutex_destroy(&ctx->pollfd_modify_lock);
-	usbi_mutex_destroy(&ctx->events_lock);
-	usbi_mutex_destroy(&ctx->event_waiters_lock);
-	usbi_cond_destroy(&ctx->event_waiters_cond);
-	return r;
-}
-
-void usbi_io_exit(struct libusb_context *ctx)
-{
-	usbi_remove_pollfd(ctx, ctx->ctrl_pipe[0]);
-	usbi_close(ctx->ctrl_pipe[0]);
-	usbi_close(ctx->ctrl_pipe[1]);
-#ifdef USBI_TIMERFD_AVAILABLE
-	if (usbi_using_timerfd(ctx)) {
-		usbi_remove_pollfd(ctx, ctx->timerfd);
-		close(ctx->timerfd);
-	}
-#endif
-	usbi_mutex_destroy(&ctx->flying_transfers_lock);
-	usbi_mutex_destroy(&ctx->pollfds_lock);
-	usbi_mutex_destroy(&ctx->pollfd_modify_lock);
-	usbi_mutex_destroy(&ctx->events_lock);
-	usbi_mutex_destroy(&ctx->event_waiters_lock);
-	usbi_cond_destroy(&ctx->event_waiters_cond);
-}
-
-static int calculate_timeout(struct usbi_transfer *transfer)
-{
-	int r;
-	struct timespec current_time;
-	unsigned int timeout =
-		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout;
-
-	if (!timeout)
-		return 0;
-
-	r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, &current_time);
-	if (r < 0) {
-		usbi_err(ITRANSFER_CTX(transfer),
-			"failed to read monotonic clock, errno=%d", errno);
-		return r;
-	}
-
-	current_time.tv_sec += timeout / 1000;
-	current_time.tv_nsec += (timeout % 1000) * 1000000;
-
-	if (current_time.tv_nsec > 1000000000) {
-		current_time.tv_nsec -= 1000000000;
-		current_time.tv_sec++;
-	}
-
-	TIMESPEC_TO_TIMEVAL(&transfer->timeout, &current_time);
-	return 0;
-}
-
-/* add a transfer to the (timeout-sorted) active transfers list.
- * returns 1 if the transfer has a timeout and it is the timeout next to
- * expire */
-static int add_to_flying_list(struct usbi_transfer *transfer)
-{
-	struct usbi_transfer *cur;
-	struct timeval *timeout = &transfer->timeout;
-	struct libusb_context *ctx = ITRANSFER_CTX(transfer);
-	int r = 0;
-	int first = 1;
-
-	usbi_mutex_lock(&ctx->flying_transfers_lock);
-
-	/* if we have no other flying transfers, start the list with this one */
-	if (list_empty(&ctx->flying_transfers)) {
-		list_add(&transfer->list, &ctx->flying_transfers);
-		if (timerisset(timeout))
-			r = 1;
-		goto out;
-	}
-
-	/* if we have infinite timeout, append to end of list */
-	if (!timerisset(timeout)) {
-		list_add_tail(&transfer->list, &ctx->flying_transfers);
-		goto out;
-	}
-
-	/* otherwise, find appropriate place in list */
-	list_for_each_entry(cur, &ctx->flying_transfers, list, struct usbi_transfer) {
-		/* find first timeout that occurs after the transfer in question */
-		struct timeval *cur_tv = &cur->timeout;
-
-		if (!timerisset(cur_tv) || (cur_tv->tv_sec > timeout->tv_sec) ||
-				(cur_tv->tv_sec == timeout->tv_sec &&
-					cur_tv->tv_usec > timeout->tv_usec)) {
-			list_add_tail(&transfer->list, &cur->list);
-			r = first;
-			goto out;
-		}
-		first = 0;
-	}
-
-	/* otherwise we need to be inserted at the end */
-	list_add_tail(&transfer->list, &ctx->flying_transfers);
-out:
-	usbi_mutex_unlock(&ctx->flying_transfers_lock);
-	return r;
-}
-
-/** \ingroup asyncio
- * Allocate a libusb transfer with a specified number of isochronous packet
- * descriptors. The returned transfer is pre-initialized for you. When the new
- * transfer is no longer needed, it should be freed with
- * libusb_free_transfer().
- *
- * Transfers intended for non-isochronous endpoints (e.g. control, bulk,
- * interrupt) should specify an iso_packets count of zero.
- *
- * For transfers intended for isochronous endpoints, specify an appropriate
- * number of packet descriptors to be allocated as part of the transfer.
- * The returned transfer is not specially initialized for isochronous I/O;
- * you are still required to set the
- * \ref libusb_transfer::num_iso_packets "num_iso_packets" and
- * \ref libusb_transfer::type "type" fields accordingly.
- *
- * It is safe to allocate a transfer with some isochronous packets and then
- * use it on a non-isochronous endpoint. If you do this, ensure that at time
- * of submission, num_iso_packets is 0 and that type is set appropriately.
- *
- * \param iso_packets number of isochronous packet descriptors to allocate
- * \returns a newly allocated transfer, or NULL on error
- */
-DEFAULT_VISIBILITY
-struct libusb_transfer * LIBUSB_CALL libusb_alloc_transfer(
-	int iso_packets)
-{
-	size_t os_alloc_size = usbi_backend->transfer_priv_size
-		+ (usbi_backend->add_iso_packet_size * iso_packets);
-	size_t alloc_size = sizeof(struct usbi_transfer)
-		+ sizeof(struct libusb_transfer)
-		+ (sizeof(struct libusb_iso_packet_descriptor) * iso_packets)
-		+ os_alloc_size;
-	struct usbi_transfer *itransfer = malloc(alloc_size);
-	if (!itransfer)
-		return NULL;
-
-	memset(itransfer, 0, alloc_size);
-	itransfer->num_iso_packets = iso_packets;
-	usbi_mutex_init(&itransfer->lock, NULL);
-	return __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
-}
-
-/** \ingroup asyncio
- * Free a transfer structure. This should be called for all transfers
- * allocated with libusb_alloc_transfer().
- *
- * If the \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
- * "LIBUSB_TRANSFER_FREE_BUFFER" flag is set and the transfer buffer is
- * non-NULL, this function will also free the transfer buffer using the
- * standard system memory allocator (e.g. free()).
- *
- * It is legal to call this function with a NULL transfer. In this case,
- * the function will simply return safely.
- *
- * It is not legal to free an active transfer (one which has been submitted
- * and has not yet completed).
- *
- * \param transfer the transfer to free
- */
-void API_EXPORTED libusb_free_transfer(struct libusb_transfer *transfer)
-{
-	struct usbi_transfer *itransfer;
-	if (!transfer)
-		return;
-
-	if (transfer->flags & LIBUSB_TRANSFER_FREE_BUFFER && transfer->buffer)
-		free(transfer->buffer);
-
-	itransfer = __LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
-	usbi_mutex_destroy(&itransfer->lock);
-	free(itransfer);
-}
-
-/** \ingroup asyncio
- * Submit a transfer. This function will fire off the USB transfer and then
- * return immediately.
- *
- * \param transfer the transfer to submit
- * \returns 0 on success
- * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
- * \returns LIBUSB_ERROR_BUSY if the transfer has already been submitted.
- * \returns another LIBUSB_ERROR code on other failure
- */
-int API_EXPORTED libusb_submit_transfer(struct libusb_transfer *transfer)
-{
-	struct libusb_context *ctx = TRANSFER_CTX(transfer);
-	struct usbi_transfer *itransfer =
-		__LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
-	int r;
-	int first;
-
-	usbi_mutex_lock(&itransfer->lock);
-	itransfer->transferred = 0;
-	itransfer->flags = 0;
-	r = calculate_timeout(itransfer);
-	if (r < 0) {
-		r = LIBUSB_ERROR_OTHER;
-		goto out;
-	}
-
-	first = add_to_flying_list(itransfer);
-	r = usbi_backend->submit_transfer(itransfer);
-	if (r) {
-		usbi_mutex_lock(&ctx->flying_transfers_lock);
-		list_del(&itransfer->list);
-		usbi_mutex_unlock(&ctx->flying_transfers_lock);
-	}
-#ifdef USBI_TIMERFD_AVAILABLE
-	else if (first && usbi_using_timerfd(ctx)) {
-		/* if this transfer has the lowest timeout of all active transfers,
-		 * rearm the timerfd with this transfer's timeout */
-		const struct itimerspec it = { {0, 0},
-			{ itransfer->timeout.tv_sec, itransfer->timeout.tv_usec * 1000 } };
-		usbi_dbg("arm timerfd for timeout in %dms (first in line)", transfer->timeout);
-		r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
-		if (r < 0)
-			r = LIBUSB_ERROR_OTHER;
-	}
-#endif
-
-out:
-	usbi_mutex_unlock(&itransfer->lock);
-	return r;
-}
-
-/** \ingroup asyncio
- * Asynchronously cancel a previously submitted transfer.
- * This function returns immediately, but this does not indicate cancellation
- * is complete. Your callback function will be invoked at some later time
- * with a transfer status of
- * \ref libusb_transfer_status::LIBUSB_TRANSFER_CANCELLED
- * "LIBUSB_TRANSFER_CANCELLED."
- *
- * \param transfer the transfer to cancel
- * \returns 0 on success
- * \returns LIBUSB_ERROR_NOT_FOUND if the transfer is already complete or
- * cancelled.
- * \returns a LIBUSB_ERROR code on failure
- */
-int API_EXPORTED libusb_cancel_transfer(struct libusb_transfer *transfer)
-{
-	struct usbi_transfer *itransfer =
-		__LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
-	int r;
-
-	usbi_dbg("");
-	usbi_mutex_lock(&itransfer->lock);
-	r = usbi_backend->cancel_transfer(itransfer);
-	if (r < 0)
-		usbi_err(TRANSFER_CTX(transfer),
-			"cancel transfer failed error %d", r);
-	usbi_mutex_unlock(&itransfer->lock);
-	return r;
-}
-
-#ifdef USBI_TIMERFD_AVAILABLE
-static int disarm_timerfd(struct libusb_context *ctx)
-{
-	const struct itimerspec disarm_timer = { { 0, 0 }, { 0, 0 } };
-	int r;
-
-	usbi_dbg("");
-	r = timerfd_settime(ctx->timerfd, 0, &disarm_timer, NULL);
-	if (r < 0)
-		return LIBUSB_ERROR_OTHER;
-	else
-		return 0;
-}
-
-/* iterates through the flying transfers, and rearms the timerfd based on the
- * next upcoming timeout.
- * must be called with flying_list locked.
- * returns 0 if there was no timeout to arm, 1 if the next timeout was armed,
- * or a LIBUSB_ERROR code on failure.
- */
-static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
-{
-	struct usbi_transfer *transfer;
-
-	list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
-		struct timeval *cur_tv = &transfer->timeout;
-
-		/* if we've reached transfers of infinite timeout, then we have no
-		 * arming to do */
-		if (!timerisset(cur_tv))
-			return 0;
-
-		/* act on first transfer that is not already cancelled */
-		if (!(transfer->flags & USBI_TRANSFER_TIMED_OUT)) {
-			int r;
-			const struct itimerspec it = { {0, 0},
-				{ cur_tv->tv_sec, cur_tv->tv_usec * 1000 } };
-			usbi_dbg("next timeout originally %dms", __USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout);
-			r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
-			if (r < 0)
-				return LIBUSB_ERROR_OTHER;
-			return 1;
-		}
-	}
-
-	return 0;
-}
-#else
-static int disarm_timerfd(struct libusb_context *ctx)
-{
-	return 0;
-}
-static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
-{
-	return 0;
-}
-#endif
-
-/* Handle completion of a transfer (completion might be an error condition).
- * This will invoke the user-supplied callback function, which may end up
- * freeing the transfer. Therefore you cannot use the transfer structure
- * after calling this function, and you should free all backend-specific
- * data before calling it.
- * Do not call this function with the usbi_transfer lock held. User-specified
- * callback functions may attempt to directly resubmit the transfer, which
- * will attempt to take the lock. */
-int usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
-	enum libusb_transfer_status status)
-{
-	struct libusb_transfer *transfer =
-		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
-	struct libusb_context *ctx = TRANSFER_CTX(transfer);
-	uint8_t flags;
-	int r;
-
-	/* FIXME: could be more intelligent with the timerfd here. we don't need
-	 * to disarm the timerfd if there was no timer running, and we only need
-	 * to rearm the timerfd if the transfer that expired was the one with
-	 * the shortest timeout. */
-
-	usbi_mutex_lock(&ctx->flying_transfers_lock);
-	list_del(&itransfer->list);
-	r = arm_timerfd_for_next_timeout(ctx);
-	usbi_mutex_unlock(&ctx->flying_transfers_lock);
-
-	if (r < 0) {
-		return r;
-	} else if (r == 0) {
-		r = disarm_timerfd(ctx);
-		if (r < 0)
-			return r;
-	}
-
-	if (status == LIBUSB_TRANSFER_COMPLETED
-			&& transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) {
-		int rqlen = transfer->length;
-		if (transfer->type == LIBUSB_TRANSFER_TYPE_CONTROL)
-			rqlen -= LIBUSB_CONTROL_SETUP_SIZE;
-		if (rqlen != itransfer->transferred) {
-			usbi_dbg("interpreting short transfer as error");
-			status = LIBUSB_TRANSFER_ERROR;
-		}
-	}
-
-	flags = transfer->flags;
-	transfer->status = status;
-	transfer->actual_length = itransfer->transferred;
-	if (transfer->callback)
-		transfer->callback(transfer);
-	/* transfer might have been freed by the above call, do not use from
-	 * this point. */
-	if (flags & LIBUSB_TRANSFER_FREE_TRANSFER)
-		libusb_free_transfer(transfer);
-	usbi_mutex_lock(&ctx->event_waiters_lock);
-	usbi_cond_broadcast(&ctx->event_waiters_cond);
-	usbi_mutex_unlock(&ctx->event_waiters_lock);
-	return 0;
-}
-
-/* Similar to usbi_handle_transfer_completion() but exclusively for transfers
- * that were asynchronously cancelled. The same concerns w.r.t. freeing of
- * transfers exist here.
- * Do not call this function with the usbi_transfer lock held. User-specified
- * callback functions may attempt to directly resubmit the transfer, which
- * will attempt to take the lock. */
-int usbi_handle_transfer_cancellation(struct usbi_transfer *transfer)
-{
-	/* if the URB was cancelled due to timeout, report timeout to the user */
-	if (transfer->flags & USBI_TRANSFER_TIMED_OUT) {
-		usbi_dbg("detected timeout cancellation");
-		return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_TIMED_OUT);
-	}
-
-	/* otherwise its a normal async cancel */
-	return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_CANCELLED);
-}
-
-/** \ingroup poll
- * Attempt to acquire the event handling lock. This lock is used to ensure that
- * only one thread is monitoring libusb event sources at any one time.
- *
- * You only need to use this lock if you are developing an application
- * which calls poll() or select() on libusb's file descriptors directly.
- * If you stick to libusb's event handling loop functions (e.g.
- * libusb_handle_events()) then you do not need to be concerned with this
- * locking.
- *
- * While holding this lock, you are trusted to actually be handling events.
- * If you are no longer handling events, you must call libusb_unlock_events()
- * as soon as possible.
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \returns 0 if the lock was obtained successfully
- * \returns 1 if the lock was not obtained (i.e. another thread holds the lock)
- * \see \ref mtasync
- */
-int API_EXPORTED libusb_try_lock_events(libusb_context *ctx)
-{
-	int r;
-	USBI_GET_CONTEXT(ctx);
-
-	/* is someone else waiting to modify poll fds? if so, don't let this thread
-	 * start event handling */
-	usbi_mutex_lock(&ctx->pollfd_modify_lock);
-	r = ctx->pollfd_modify;
-	usbi_mutex_unlock(&ctx->pollfd_modify_lock);
-	if (r) {
-		usbi_dbg("someone else is modifying poll fds");
-		return 1;
-	}
-
-	r = usbi_mutex_trylock(&ctx->events_lock);
-	if (r)
-		return 1;
-
-	ctx->event_handler_active = 1;
-	return 0;
-}
-
-/** \ingroup poll
- * Acquire the event handling lock, blocking until successful acquisition if
- * it is contended. This lock is used to ensure that only one thread is
- * monitoring libusb event sources at any one time.
- *
- * You only need to use this lock if you are developing an application
- * which calls poll() or select() on libusb's file descriptors directly.
- * If you stick to libusb's event handling loop functions (e.g.
- * libusb_handle_events()) then you do not need to be concerned with this
- * locking.
- *
- * While holding this lock, you are trusted to actually be handling events.
- * If you are no longer handling events, you must call libusb_unlock_events()
- * as soon as possible.
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \see \ref mtasync
- */
-void API_EXPORTED libusb_lock_events(libusb_context *ctx)
-{
-	USBI_GET_CONTEXT(ctx);
-	usbi_mutex_lock(&ctx->events_lock);
-	ctx->event_handler_active = 1;
-}
-
-/** \ingroup poll
- * Release the lock previously acquired with libusb_try_lock_events() or
- * libusb_lock_events(). Releasing this lock will wake up any threads blocked
- * on libusb_wait_for_event().
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \see \ref mtasync
- */
-void API_EXPORTED libusb_unlock_events(libusb_context *ctx)
-{
-	USBI_GET_CONTEXT(ctx);
-	ctx->event_handler_active = 0;
-	usbi_mutex_unlock(&ctx->events_lock);
-
-	/* FIXME: perhaps we should be a bit more efficient by not broadcasting
-	 * the availability of the events lock when we are modifying pollfds
-	 * (check ctx->pollfd_modify)? */
-	usbi_mutex_lock(&ctx->event_waiters_lock);
-	usbi_cond_broadcast(&ctx->event_waiters_cond);
-	usbi_mutex_unlock(&ctx->event_waiters_lock);
-}
-
-/** \ingroup poll
- * Determine if it is still OK for this thread to be doing event handling.
- *
- * Sometimes, libusb needs to temporarily pause all event handlers, and this
- * is the function you should use before polling file descriptors to see if
- * this is the case.
- *
- * If this function instructs your thread to give up the events lock, you
- * should just continue the usual logic that is documented in \ref mtasync.
- * On the next iteration, your thread will fail to obtain the events lock,
- * and will hence become an event waiter.
- *
- * This function should be called while the events lock is held: you don't
- * need to worry about the results of this function if your thread is not
- * the current event handler.
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \returns 1 if event handling can start or continue
- * \returns 0 if this thread must give up the events lock
- * \see \ref fullstory "Multi-threaded I/O: the full story"
- */
-int API_EXPORTED libusb_event_handling_ok(libusb_context *ctx)
-{
-	int r;
-	USBI_GET_CONTEXT(ctx);
-
-	/* is someone else waiting to modify poll fds? if so, don't let this thread
-	 * continue event handling */
-	usbi_mutex_lock(&ctx->pollfd_modify_lock);
-	r = ctx->pollfd_modify;
-	usbi_mutex_unlock(&ctx->pollfd_modify_lock);
-	if (r) {
-		usbi_dbg("someone else is modifying poll fds");
-		return 0;
-	}
-
-	return 1;
-}
-
-
-/** \ingroup poll
- * Determine if an active thread is handling events (i.e. if anyone is holding
- * the event handling lock).
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \returns 1 if a thread is handling events
- * \returns 0 if there are no threads currently handling events
- * \see \ref mtasync
- */
-int API_EXPORTED libusb_event_handler_active(libusb_context *ctx)
-{
-	int r;
-	USBI_GET_CONTEXT(ctx);
-
-	/* is someone else waiting to modify poll fds? if so, don't let this thread
-	 * start event handling -- indicate that event handling is happening */
-	usbi_mutex_lock(&ctx->pollfd_modify_lock);
-	r = ctx->pollfd_modify;
-	usbi_mutex_unlock(&ctx->pollfd_modify_lock);
-	if (r) {
-		usbi_dbg("someone else is modifying poll fds");
-		return 1;
-	}
-
-	return ctx->event_handler_active;
-}
-
-/** \ingroup poll
- * Acquire the event waiters lock. This lock is designed to be obtained under
- * the situation where you want to be aware when events are completed, but
- * some other thread is event handling so calling libusb_handle_events() is not
- * allowed.
- *
- * You then obtain this lock, re-check that another thread is still handling
- * events, then call libusb_wait_for_event().
- *
- * You only need to use this lock if you are developing an application
- * which calls poll() or select() on libusb's file descriptors directly,
- * <b>and</b> may potentially be handling events from 2 threads simultaenously.
- * If you stick to libusb's event handling loop functions (e.g.
- * libusb_handle_events()) then you do not need to be concerned with this
- * locking.
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \see \ref mtasync
- */
-void API_EXPORTED libusb_lock_event_waiters(libusb_context *ctx)
-{
-	USBI_GET_CONTEXT(ctx);
-	usbi_mutex_lock(&ctx->event_waiters_lock);
-}
-
-/** \ingroup poll
- * Release the event waiters lock.
- * \param ctx the context to operate on, or NULL for the default context
- * \see \ref mtasync
- */
-void API_EXPORTED libusb_unlock_event_waiters(libusb_context *ctx)
-{
-	USBI_GET_CONTEXT(ctx);
-	usbi_mutex_unlock(&ctx->event_waiters_lock);
-}
-
-/** \ingroup poll
- * Wait for another thread to signal completion of an event. Must be called
- * with the event waiters lock held, see libusb_lock_event_waiters().
- *
- * This function will block until any of the following conditions are met:
- * -# The timeout expires
- * -# A transfer completes
- * -# A thread releases the event handling lock through libusb_unlock_events()
- *
- * Condition 1 is obvious. Condition 2 unblocks your thread <em>after</em>
- * the callback for the transfer has completed. Condition 3 is important
- * because it means that the thread that was previously handling events is no
- * longer doing so, so if any events are to complete, another thread needs to
- * step up and start event handling.
- *
- * This function releases the event waiters lock before putting your thread
- * to sleep, and reacquires the lock as it is being woken up.
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \param tv maximum timeout for this blocking function. A NULL value
- * indicates unlimited timeout.
- * \returns 0 after a transfer completes or another thread stops event handling
- * \returns 1 if the timeout expired
- * \see \ref mtasync
- */
-int API_EXPORTED libusb_wait_for_event(libusb_context *ctx, struct timeval *tv)
-{
-	struct timespec timeout;
-	int r;
-
-	USBI_GET_CONTEXT(ctx);
-	if (tv == NULL) {
-		usbi_cond_wait(&ctx->event_waiters_cond, &ctx->event_waiters_lock);
-		return 0;
-	}
-
-	r = usbi_backend->clock_gettime(USBI_CLOCK_REALTIME, &timeout);
-	if (r < 0) {
-		usbi_err(ctx, "failed to read realtime clock, error %d", errno);
-		return LIBUSB_ERROR_OTHER;
-	}
-
-	timeout.tv_sec += tv->tv_sec;
-	timeout.tv_nsec += tv->tv_usec * 1000;
-	if (timeout.tv_nsec > 1000000000) {
-		timeout.tv_nsec -= 1000000000;
-		timeout.tv_sec++;
-	}
-
-	r = usbi_cond_timedwait(&ctx->event_waiters_cond,
-		&ctx->event_waiters_lock, &timeout);
-	return (r == ETIMEDOUT);
-}
-
-static void handle_timeout(struct usbi_transfer *itransfer)
-{
-	struct libusb_transfer *transfer =
-		__USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
-	int r;
-
-	itransfer->flags |= USBI_TRANSFER_TIMED_OUT;
-	r = libusb_cancel_transfer(transfer);
-	if (r < 0)
-		usbi_warn(TRANSFER_CTX(transfer),
-			"async cancel failed %d errno=%d", r, errno);
-}
-
-#ifdef USBI_OS_HANDLES_TIMEOUT
-static int handle_timeouts_locked(struct libusb_context *ctx)
-{
-	return 0;
-}
-static int handle_timeouts(struct libusb_context *ctx)
-{
-	return 0;
-}
-#else
-static int handle_timeouts_locked(struct libusb_context *ctx)
-{
-	int r;
-	struct timespec systime_ts;
-	struct timeval systime;
-	struct usbi_transfer *transfer;
-
-	if (list_empty(&ctx->flying_transfers))
-		return 0;
-
-	/* get current time */
-	r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, &systime_ts);
-	if (r < 0)
-		return r;
-
-	TIMESPEC_TO_TIMEVAL(&systime, &systime_ts);
-
-	/* iterate through flying transfers list, finding all transfers that
-	 * have expired timeouts */
-	list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
-		struct timeval *cur_tv = &transfer->timeout;
-
-		/* if we've reached transfers of infinite timeout, we're all done */
-		if (!timerisset(cur_tv))
-			return 0;
-
-		/* ignore timeouts we've already handled */
-		if (transfer->flags & USBI_TRANSFER_TIMED_OUT)
-			continue;
-
-		/* if transfer has non-expired timeout, nothing more to do */
-		if ((cur_tv->tv_sec > systime.tv_sec) ||
-				(cur_tv->tv_sec == systime.tv_sec &&
-					cur_tv->tv_usec > systime.tv_usec))
-			return 0;
-
-		/* otherwise, we've got an expired timeout to handle */
-		handle_timeout(transfer);
-	}
-	return 0;
-}
-
-static int handle_timeouts(struct libusb_context *ctx)
-{
-	int r;
-	USBI_GET_CONTEXT(ctx);
-	usbi_mutex_lock(&ctx->flying_transfers_lock);
-	r = handle_timeouts_locked(ctx);
-	usbi_mutex_unlock(&ctx->flying_transfers_lock);
-	return r;
-}
-#endif
-
-#ifdef USBI_TIMERFD_AVAILABLE
-static int handle_timerfd_trigger(struct libusb_context *ctx)
-{
-	int r;
-
-	r = disarm_timerfd(ctx);
-	if (r < 0)
-		return r;
-
-	usbi_mutex_lock(&ctx->flying_transfers_lock);
-
-	/* process the timeout that just happened */
-	r = handle_timeouts_locked(ctx);
-	if (r < 0)
-		goto out;
-
-	/* arm for next timeout*/
-	r = arm_timerfd_for_next_timeout(ctx);
-
-out:
-	usbi_mutex_unlock(&ctx->flying_transfers_lock);
-	return r;
-}
-#endif
-
-/* do the actual event handling. assumes that no other thread is concurrently
- * doing the same thing. */
-static int handle_events(struct libusb_context *ctx, struct timeval *tv)
-{
-	int r;
-	struct usbi_pollfd *ipollfd;
-	nfds_t nfds = 0;
-	struct pollfd *fds;
-	int i = -1;
-	int timeout_ms;
-
-	usbi_mutex_lock(&ctx->pollfds_lock);
-	list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
-		nfds++;
-
-	/* TODO: malloc when number of fd's changes, not on every poll */
-	fds = malloc(sizeof(*fds) * nfds);
-	if (!fds) {
-		usbi_mutex_unlock(&ctx->pollfds_lock);
-		return LIBUSB_ERROR_NO_MEM;
-	}
-
-	list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd) {
-		struct libusb_pollfd *pollfd = &ipollfd->pollfd;
-		int fd = pollfd->fd;
-		i++;
-		fds[i].fd = fd;
-		fds[i].events = pollfd->events;
-		fds[i].revents = 0;
-	}
-	usbi_mutex_unlock(&ctx->pollfds_lock);
-
-	timeout_ms = (tv->tv_sec * 1000) + (tv->tv_usec / 1000);
-
-	/* round up to next millisecond */
-	if (tv->tv_usec % 1000)
-		timeout_ms++;
-
-	usbi_dbg("poll() %d fds with timeout in %dms", nfds, timeout_ms);
-	r = usbi_poll(fds, nfds, timeout_ms);
-	usbi_dbg("poll() returned %d", r);
-	if (r == 0) {
-		free(fds);
-		return handle_timeouts(ctx);
-	} else if (r == -1 && errno == EINTR) {
-		free(fds);
-		return LIBUSB_ERROR_INTERRUPTED;
-	} else if (r < 0) {
-		free(fds);
-		usbi_err(ctx, "poll failed %d err=%d\n", r, errno);
-		return LIBUSB_ERROR_IO;
-	}
-
-	/* fd[0] is always the ctrl pipe */
-	if (fds[0].revents) {
-		/* another thread wanted to interrupt event handling, and it succeeded!
-		 * handle any other events that cropped up at the same time, and
-		 * simply return */
-		usbi_dbg("caught a fish on the control pipe");
-
-		if (r == 1) {
-			r = 0;
-			goto handled;
-		} else {
-			/* prevent OS backend from trying to handle events on ctrl pipe */
-			fds[0].revents = 0;
-			r--;
-		}
-	}
-
-#ifdef USBI_TIMERFD_AVAILABLE
-	/* on timerfd configurations, fds[1] is the timerfd */
-	if (usbi_using_timerfd(ctx) && fds[1].revents) {
-		/* timerfd indicates that a timeout has expired */
-		int ret;
-		usbi_dbg("timerfd triggered");
-
-		ret = handle_timerfd_trigger(ctx);
-		if (ret < 0) {
-			/* return error code */
-			r = ret;
-			goto handled;
-		} else if (r == 1) {
-			/* no more active file descriptors, nothing more to do */
-			r = 0;
-			goto handled;
-		} else {
-			/* more events pending...
-			 * prevent OS backend from trying to handle events on timerfd */
-			fds[1].revents = 0;
-			r--;
-		}
-	}
-#endif
-
-	r = usbi_backend->handle_events(ctx, fds, nfds, r);
-	if (r)
-		usbi_err(ctx, "backend handle_events failed with error %d", r);
-
-handled:
-	free(fds);
-	return r;
-}
-
-/* returns the smallest of:
- *  1. timeout of next URB
- *  2. user-supplied timeout
- * returns 1 if there is an already-expired timeout, otherwise returns 0
- * and populates out
- */
-static int get_next_timeout(libusb_context *ctx, struct timeval *tv,
-	struct timeval *out)
-{
-	struct timeval timeout;
-	int r = libusb_get_next_timeout(ctx, &timeout);
-	if (r) {
-		/* timeout already expired? */
-		if (!timerisset(&timeout))
-			return 1;
-
-		/* choose the smallest of next URB timeout or user specified timeout */
-		if (timercmp(&timeout, tv, <))
-			*out = timeout;
-		else
-			*out = *tv;
-	} else {
-		*out = *tv;
-	}
-	return 0;
-}
-
-/** \ingroup poll
- * Handle any pending events.
- *
- * libusb determines "pending events" by checking if any timeouts have expired
- * and by checking the set of file descriptors for activity.
- *
- * If a zero timeval is passed, this function will handle any already-pending
- * events and then immediately return in non-blocking style.
- *
- * If a non-zero timeval is passed and no events are currently pending, this
- * function will block waiting for events to handle up until the specified
- * timeout. If an event arrives or a signal is raised, this function will
- * return early.
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \param tv the maximum time to block waiting for events, or zero for
- * non-blocking mode
- * \returns 0 on success, or a LIBUSB_ERROR code on failure
- */
-int API_EXPORTED libusb_handle_events_timeout_check(libusb_context *ctx,
-	struct timeval *tv, int *completed)
-{
-	int r;
-	struct timeval poll_timeout;
-
-	USBI_GET_CONTEXT(ctx);
-	r = get_next_timeout(ctx, tv, &poll_timeout);
-	if (r) {
-		/* timeout already expired */
-		return handle_timeouts(ctx);
-	}
-
-retry:
-	if (libusb_try_lock_events(ctx) == 0) {
-		r = 0;
-		if (completed == NULL || !*completed) {
-			/* we obtained the event lock: do our own event handling */
-			usbi_dbg("doing our own event handling");
-			r = handle_events(ctx, &poll_timeout);
-		}
-		libusb_unlock_events(ctx);
-		return r;
-	}
-
-	/* another thread is doing event handling. wait for pthread events that
-	 * notify event completion. */
-	libusb_lock_event_waiters(ctx);
-
-	if (completed == NULL || !*completed) {
-		if (!libusb_event_handler_active(ctx)) {
-			/* we hit a race: whoever was event handling earlier finished in the
-			 * time it took us to reach this point. try the cycle again. */
-			libusb_unlock_event_waiters(ctx);
-			usbi_dbg("event handler was active but went away, retrying");
-			goto retry;
-		}
-
-		usbi_dbg("another thread is doing event handling, wait for notification");
-		r = libusb_wait_for_event(ctx, &poll_timeout);
-	}
-	libusb_unlock_event_waiters(ctx);
-
-	if (r < 0)
-		return r;
-	else if (r == 1)
-		return handle_timeouts(ctx);
-	else
-		return 0;
-}
-
-int API_EXPORTED libusb_handle_events_timeout(libusb_context *ctx,
-	struct timeval *tv)
-{
-	return libusb_handle_events_timeout_check(ctx, tv, NULL);
-}
-
-int API_EXPORTED libusb_handle_events_check(libusb_context *ctx,
-	int *completed)
-{
-	struct timeval tv;
-	tv.tv_sec = 60;
-	tv.tv_usec = 0;
-	return libusb_handle_events_timeout_check(ctx, &tv, completed);
-}
-
-/** \ingroup poll
- * Handle any pending events in blocking mode. There is currently a timeout
- * hardcoded at 60 seconds but we plan to make it unlimited in future. For
- * finer control over whether this function is blocking or non-blocking, or
- * for control over the timeout, use libusb_handle_events_timeout() instead.
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \returns 0 on success, or a LIBUSB_ERROR code on failure
- */
-int API_EXPORTED libusb_handle_events(libusb_context *ctx)
-{
-	struct timeval tv;
-	tv.tv_sec = 60;
-	tv.tv_usec = 0;
-	return libusb_handle_events_timeout_check(ctx, &tv, NULL);
-}
-
-/** \ingroup poll
- * Handle any pending events by polling file descriptors, without checking if
- * any other threads are already doing so. Must be called with the event lock
- * held, see libusb_lock_events().
- *
- * This function is designed to be called under the situation where you have
- * taken the event lock and are calling poll()/select() directly on libusb's
- * file descriptors (as opposed to using libusb_handle_events() or similar).
- * You detect events on libusb's descriptors, so you then call this function
- * with a zero timeout value (while still holding the event lock).
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \param tv the maximum time to block waiting for events, or zero for
- * non-blocking mode
- * \returns 0 on success, or a LIBUSB_ERROR code on failure
- * \see \ref mtasync
- */
-int API_EXPORTED libusb_handle_events_locked(libusb_context *ctx,
-	struct timeval *tv)
-{
-	int r;
-	struct timeval poll_timeout;
-
-	USBI_GET_CONTEXT(ctx);
-	r = get_next_timeout(ctx, tv, &poll_timeout);
-	if (r) {
-		/* timeout already expired */
-		return handle_timeouts(ctx);
-	}
-
-	return handle_events(ctx, &poll_timeout);
-}
-
-/** \ingroup poll
- * Determines whether your application must apply special timing considerations
- * when monitoring libusb's file descriptors.
- *
- * This function is only useful for applications which retrieve and poll
- * libusb's file descriptors in their own main loop (\ref pollmain).
- *
- * Ordinarily, libusb's event handler needs to be called into at specific
- * moments in time (in addition to times when there is activity on the file
- * descriptor set). The usual approach is to use libusb_get_next_timeout()
- * to learn about when the next timeout occurs, and to adjust your
- * poll()/select() timeout accordingly so that you can make a call into the
- * library at that time.
- *
- * Some platforms supported by libusb do not come with this baggage - any
- * events relevant to timing will be represented by activity on the file
- * descriptor set, and libusb_get_next_timeout() will always return 0.
- * This function allows you to detect whether you are running on such a
- * platform.
- *
- * Since v1.0.5.
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \returns 0 if you must call into libusb at times determined by
- * libusb_get_next_timeout(), or 1 if all timeout events are handled internally
- * or through regular activity on the file descriptors.
- * \see \ref pollmain "Polling libusb file descriptors for event handling"
- */
-int API_EXPORTED libusb_pollfds_handle_timeouts(libusb_context *ctx)
-{
-#if defined(USBI_OS_HANDLES_TIMEOUT)
-	return 1;
-#elif defined(USBI_TIMERFD_AVAILABLE)
-	USBI_GET_CONTEXT(ctx);
-	return usbi_using_timerfd(ctx);
-#else
-	return 0;
-#endif
-}
-
-/** \ingroup poll
- * Determine the next internal timeout that libusb needs to handle. You only
- * need to use this function if you are calling poll() or select() or similar
- * on libusb's file descriptors yourself - you do not need to use it if you
- * are calling libusb_handle_events() or a variant directly.
- *
- * You should call this function in your main loop in order to determine how
- * long to wait for select() or poll() to return results. libusb needs to be
- * called into at this timeout, so you should use it as an upper bound on
- * your select() or poll() call.
- *
- * When the timeout has expired, call into libusb_handle_events_timeout()
- * (perhaps in non-blocking mode) so that libusb can handle the timeout.
- *
- * This function may return 1 (success) and an all-zero timeval. If this is
- * the case, it indicates that libusb has a timeout that has already expired
- * so you should call libusb_handle_events_timeout() or similar immediately.
- * A return code of 0 indicates that there are no pending timeouts.
- *
- * On some platforms, this function will always returns 0 (no pending
- * timeouts). See \ref polltime.
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \param tv output location for a relative time against the current
- * clock in which libusb must be called into in order to process timeout events
- * \returns 0 if there are no pending timeouts, 1 if a timeout was returned,
- * or LIBUSB_ERROR_OTHER on failure
- */
-int API_EXPORTED libusb_get_next_timeout(libusb_context *ctx,
-	struct timeval *tv)
-{
-#ifndef USBI_OS_HANDLES_TIMEOUT
-	struct usbi_transfer *transfer;
-	struct timespec cur_ts;
-	struct timeval cur_tv;
-	struct timeval *next_timeout;
-	int r;
-	int found = 0;
-
-	USBI_GET_CONTEXT(ctx);
-	if (usbi_using_timerfd(ctx))
-		return 0;
-
-	usbi_mutex_lock(&ctx->flying_transfers_lock);
-	if (list_empty(&ctx->flying_transfers)) {
-		usbi_mutex_unlock(&ctx->flying_transfers_lock);
-		usbi_dbg("no URBs, no timeout!");
-		return 0;
-	}
-
-	/* find next transfer which hasn't already been processed as timed out */
-	list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
-		if (!(transfer->flags & USBI_TRANSFER_TIMED_OUT)) {
-			found = 1;
-			break;
-		}
-	}
-	usbi_mutex_unlock(&ctx->flying_transfers_lock);
-
-	if (!found) {
-		usbi_dbg("all URBs have already been processed for timeouts");
-		return 0;
-	}
-
-	next_timeout = &transfer->timeout;
-
-	/* no timeout for next transfer */
-	if (!timerisset(next_timeout)) {
-		usbi_dbg("no URBs with timeouts, no timeout!");
-		return 0;
-	}
-
-	r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, &cur_ts);
-	if (r < 0) {
-		usbi_err(ctx, "failed to read monotonic clock, errno=%d", errno);
-		return LIBUSB_ERROR_OTHER;
-	}
-	TIMESPEC_TO_TIMEVAL(&cur_tv, &cur_ts);
-
-	if (!timercmp(&cur_tv, next_timeout, <)) {
-		usbi_dbg("first timeout already expired");
-		timerclear(tv);
-	} else {
-		timersub(next_timeout, &cur_tv, tv);
-		usbi_dbg("next timeout in %d.%06ds", tv->tv_sec, tv->tv_usec);
-	}
-
-	return 1;
-#else
-	return 0;
-#endif
-}
-
-/** \ingroup poll
- * Register notification functions for file descriptor additions/removals.
- * These functions will be invoked for every new or removed file descriptor
- * that libusb uses as an event source.
- *
- * To remove notifiers, pass NULL values for the function pointers.
- *
- * Note that file descriptors may have been added even before you register
- * these notifiers (e.g. at libusb_init() time).
- *
- * Additionally, note that the removal notifier may be called during
- * libusb_exit() (e.g. when it is closing file descriptors that were opened
- * and added to the poll set at libusb_init() time). If you don't want this,
- * remove the notifiers immediately before calling libusb_exit().
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \param added_cb pointer to function for addition notifications
- * \param removed_cb pointer to function for removal notifications
- * \param user_data User data to be passed back to callbacks (useful for
- * passing context information)
- */
-void API_EXPORTED libusb_set_pollfd_notifiers(libusb_context *ctx,
-	libusb_pollfd_added_cb added_cb, libusb_pollfd_removed_cb removed_cb,
-	void *user_data)
-{
-	USBI_GET_CONTEXT(ctx);
-	ctx->fd_added_cb = added_cb;
-	ctx->fd_removed_cb = removed_cb;
-	ctx->fd_cb_user_data = user_data;
-}
-
-/* Add a file descriptor to the list of file descriptors to be monitored.
- * events should be specified as a bitmask of events passed to poll(), e.g.
- * POLLIN and/or POLLOUT. */
-int usbi_add_pollfd(struct libusb_context *ctx, int fd, short events)
-{
-	struct usbi_pollfd *ipollfd = malloc(sizeof(*ipollfd));
-	if (!ipollfd)
-		return LIBUSB_ERROR_NO_MEM;
-
-	usbi_dbg("add fd %d events %d", fd, events);
-	ipollfd->pollfd.fd = fd;
-	ipollfd->pollfd.events = events;
-	usbi_mutex_lock(&ctx->pollfds_lock);
-	list_add_tail(&ipollfd->list, &ctx->pollfds);
-	usbi_mutex_unlock(&ctx->pollfds_lock);
-
-	if (ctx->fd_added_cb)
-		ctx->fd_added_cb(fd, events, ctx->fd_cb_user_data);
-	return 0;
-}
-
-/* Remove a file descriptor from the list of file descriptors to be polled. */
-void usbi_remove_pollfd(struct libusb_context *ctx, int fd)
-{
-	struct usbi_pollfd *ipollfd;
-	int found = 0;
-
-	usbi_dbg("remove fd %d", fd);
-	usbi_mutex_lock(&ctx->pollfds_lock);
-	list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
-		if (ipollfd->pollfd.fd == fd) {
-			found = 1;
-			break;
-		}
-
-	if (!found) {
-		usbi_dbg("couldn't find fd %d to remove", fd);
-		usbi_mutex_unlock(&ctx->pollfds_lock);
-		return;
-	}
-
-	list_del(&ipollfd->list);
-	usbi_mutex_unlock(&ctx->pollfds_lock);
-	free(ipollfd);
-	if (ctx->fd_removed_cb)
-		ctx->fd_removed_cb(fd, ctx->fd_cb_user_data);
-}
-
-/** \ingroup poll
- * Retrieve a list of file descriptors that should be polled by your main loop
- * as libusb event sources.
- *
- * The returned list is NULL-terminated and should be freed with free() when
- * done. The actual list contents must not be touched.
- *
- * As file descriptors are a Unix-specific concept, this function is not
- * available on Windows and will always return NULL.
- *
- * \param ctx the context to operate on, or NULL for the default context
- * \returns a NULL-terminated list of libusb_pollfd structures
- * \returns NULL on error
- * \returns NULL on platforms where the functionality is not available
- */
-DEFAULT_VISIBILITY
-const struct libusb_pollfd ** LIBUSB_CALL libusb_get_pollfds(
-	libusb_context *ctx)
-{
-#ifndef OS_WINDOWS
-	struct libusb_pollfd **ret = NULL;
-	struct usbi_pollfd *ipollfd;
-	size_t i = 0;
-	size_t cnt = 0;
-	USBI_GET_CONTEXT(ctx);
-
-	usbi_mutex_lock(&ctx->pollfds_lock);
-	list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
-		cnt++;
-
-	ret = calloc(cnt + 1, sizeof(struct libusb_pollfd *));
-	if (!ret)
-		goto out;
-
-	list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
-		ret[i++] = (struct libusb_pollfd *) ipollfd;
-	ret[cnt] = NULL;
-
-out:
-	usbi_mutex_unlock(&ctx->pollfds_lock);
-	return (const struct libusb_pollfd **) ret;
-#else
-	return NULL;
-#endif
-}
-
-/* Backends call this from handle_events to report disconnection of a device.
- * The transfers get cancelled appropriately.
- */
-void usbi_handle_disconnect(struct libusb_device_handle *handle)
-{
-	struct usbi_transfer *cur;
-	struct usbi_transfer *to_cancel;
-
-	usbi_dbg("device %d.%d",
-		handle->dev->bus_number, handle->dev->device_address);
-
-	/* terminate all pending transfers with the LIBUSB_TRANSFER_NO_DEVICE
-	 * status code.
-	 *
-	 * this is a bit tricky because:
-	 * 1. we can't do transfer completion while holding flying_transfers_lock
-	 * 2. the transfers list can change underneath us - if we were to build a
-	 *    list of transfers to complete (while holding look), the situation
-	 *    might be different by the time we come to free them
-	 *
-	 * so we resort to a loop-based approach as below
-	 * FIXME: is this still potentially racy?
-	 */
-
-	while (1) {
-		usbi_mutex_lock(&HANDLE_CTX(handle)->flying_transfers_lock);
-		to_cancel = NULL;
-		list_for_each_entry(cur, &HANDLE_CTX(handle)->flying_transfers, list, struct usbi_transfer)
-			if (__USBI_TRANSFER_TO_LIBUSB_TRANSFER(cur)->dev_handle == handle) {
-				to_cancel = cur;
-				break;
-			}
-		usbi_mutex_unlock(&HANDLE_CTX(handle)->flying_transfers_lock);
-
-		if (!to_cancel)
-			break;
-
-		usbi_backend->clear_transfer_priv(to_cancel);
-		usbi_handle_transfer_completion(to_cancel, LIBUSB_TRANSFER_NO_DEVICE);
-	}
-
-}