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 /* -*- Mode: C; indent-tabs-mode:t ; c-basic-offset:8 -*- */ /* * I/O functions for libusb * Copyright © 2007-2009 Daniel Drake * Copyright © 2001 Johannes Erdfelt * Copyright © 2019 Nathan Hjelm * Copyright © 2019 Google LLC. All rights reserved. * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ #include "libusbi.h" /** * \page libusb_io Synchronous and asynchronous device I/O * * \section io_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 libusb_syncio * - \ref libusb_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 libusb-0.1 before, this I/O style will seem familiar 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(dev_handle, LIBUSB_ENDPOINT_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 tying 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 libusb_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 libusb_asyncio "asynchronous I/O API" documentation pages. */ /** * \page libusb_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 libusb_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 libusb_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: * -# Allocation: allocate a libusb_transfer * -# Filling: populate the libusb_transfer instance with information * about the transfer you wish to perform * -# Submission: ask libusb to submit the transfer * -# Completion handling: examine transfer results in the * libusb_transfer structure * -# Deallocation: 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. * * Important Note: The user-specified callback is called from an event * handling context. It is therefore important that no calls are made into * libusb that will attempt to perform any event handling. Examples of such * functions are any listed in the \ref libusb_syncio "synchronous API" and any of * the blocking functions that retrieve \ref libusb_desc "USB descriptors". * * \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. * * \attention * 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 asyncpartial Partial data transfer resulting from cancellation * * As noted above, some of the data may have been transferred at the time a * transfer is cancelled. It is helpful to see how this is possible if you * consider a bulk transfer to an endpoint with a packet size of 64 bytes. * Supposing you submit a 512-byte transfer to this endpoint, the operating * system will divide this transfer up into 8 separate 64-byte frames that the * host controller will schedule for the device to transfer data. If this * transfer is cancelled while the device is transferring data, a subset of * these frames may be descheduled from the host controller before the device * has the opportunity to finish transferring data to the host. * * What your application should do with a partial data transfer is a policy * decision; there is no single answer that satisfies the needs of every * application. The data that was successfully transferred should be * considered entirely valid, but your application must decide what to do with * the remaining data that was not transferred. Some possible actions to take * are: * - Resubmit another transfer for the remaining data, possibly with a shorter * timeout * - Discard the partially transferred data and report an error * * \section asynctimeout Timeouts * * When a transfer times out, libusb internally notes this and attempts to * cancel the transfer. As noted in \ref asyncpartial "above", it is possible * that some of the data may actually have been transferred. Your application * should always check how much data was actually transferred once the * transfer completes and act accordingly. * * \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 libusb_packetoverflow page for discussion. * * \section asyncctrl Considerations for control transfers * * The libusb_transfer 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 plus 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 length was 12, then you * should expect an actual_length of 4 to indicate that the data was * transferred in entirety. * * 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 asynclimits Transfer length limitations * * Some operating systems may impose limits on the length of the transfer data * buffer or, in the case of isochronous transfers, the length of individual * isochronous packets. Such limits can be difficult for libusb to detect, so * in most cases the library will simply try and submit the transfer as set up * by you. If the transfer fails to submit because it is too large, * libusb_submit_transfer() will return * \ref libusb_error::LIBUSB_ERROR_INVALID_PARAM "LIBUSB_ERROR_INVALID_PARAM". * * The following are known limits for control transfer lengths. Note that this * length includes the 8-byte setup packet. * - Linux (4,096 bytes) * - Windows (4,096 bytes) * * \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 * * 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. * * \note * All event handling is performed by whichever thread calls the * libusb_handle_events() function. libusb does not invoke any callbacks * outside of this context. Consequently, any callbacks will be run on the * thread that calls the libusb_handle_events() function. * * When to call the libusb_handle_events() function depends on which model * your application decides to use. The 2 different approaches: * * -# Repeatedly call libusb_handle_events() in blocking mode from a dedicated * thread. * -# Integrate libusb with your application's main event loop. libusb * exposes a set of file descriptors which allow you to do this. * * The first approach has the big advantage that it will also work on Windows * were libusb' poll API for select / poll integration is not available. So * if you want to support Windows and use the async API, you must use this * approach, see the \ref eventthread "Using an event handling thread" section * below for details. * * If you prefer a single threaded approach with a single central event loop, * see the \ref libusb_poll "polling and timing" section for how to integrate libusb * into your application's main event loop. * * \section eventthread Using an event handling thread * * Lets begin with stating the obvious: If you're going to use a separate * thread for libusb event handling, your callback functions MUST be * thread-safe. * * Other then that doing event handling from a separate thread, is mostly * simple. You can use an event thread function as follows: \code void *event_thread_func(void *ctx) { while (event_thread_run) libusb_handle_events(ctx); return NULL; } \endcode * * There is one caveat though, stopping this thread requires setting the * event_thread_run variable to 0, and after that libusb_handle_events() needs * to return control to event_thread_func. But unless some event happens, * libusb_handle_events() will not return. * * There are 2 different ways of dealing with this, depending on if your * application uses libusb' \ref libusb_hotplug "hotplug" support or not. * * Applications which do not use hotplug support, should not start the event * thread until after their first call to libusb_open(), and should stop the * thread when closing the last open device as follows: \code void my_close_handle(libusb_device_handle *dev_handle) { if (open_devs == 1) event_thread_run = 0; libusb_close(dev_handle); // This wakes up libusb_handle_events() if (open_devs == 1) pthread_join(event_thread); open_devs--; } \endcode * * Applications using hotplug support should start the thread at program init, * after having successfully called libusb_hotplug_register_callback(), and * should stop the thread at program exit as follows: \code void my_libusb_exit(void) { event_thread_run = 0; libusb_hotplug_deregister_callback(ctx, hotplug_cb_handle); // This wakes up libusb_handle_events() pthread_join(event_thread); libusb_exit(ctx); } \endcode */ /** * @defgroup libusb_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 libusb_asyncio "asynchronous API". If you are only using the simpler * \ref libusb_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. * * 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. * * On some platforms a timerfd is used, so the timeout handling is just another * fd, on other platforms this requires that libusb is called into at or after * the timeout to handle it. 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, see \ref polltime details. * * 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 libusb_pollmain The more advanced option * * \note This functionality is currently only available on Unix-like platforms. * On Windows, libusb_get_pollfds() simply returns NULL. Applications which * want to support Windows are advised to use an \ref eventthread * "event handling thread" instead. * * 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, &zero_tv); if (time has elapsed to or beyond the libusb timeout) libusb_handle_events_timeout(ctx, &zero_tv); // 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, &zero_tv); // 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 any future platforms supported by libusb which may have time-based * event requirements). 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 libusb_mtasync */ /** \page libusb_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 libusb_asyncio "asynchronous interface" but it is important to note that the * \ref libusb_syncio "synchronous interface" is implemented on top of the * asynchronous 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] __attribute__ ((aligned (2))); 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, &zero_tv); } printf("completed!"); // other code here } \endcode * * Here we are serializing 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, myfunc() * will only realise that the transfer has completed on the next iteration of * the loop, up to 120 seconds later. 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 its variants, and all the * synchronous I/O functions - libusb hides this headache from you. * * \section Using libusb_handle_events() from multiple threads * * Even when only using libusb_handle_events() and synchronous I/O functions, * you can still have a race condition. You might be tempted to solve the * above with libusb_handle_events() like so: * \code libusb_submit_transfer(transfer); while (!completed) { libusb_handle_events(ctx); } printf("completed!"); \endcode * * This however has a race between the checking of completed and * libusb_handle_events() acquiring the events lock, so another thread * could have completed the transfer, resulting in this thread hanging * until either a timeout or another event occurs. See also commit * 6696512aade99bb15d6792af90ae329af270eba6 which fixes this in the * synchronous API implementation of libusb. * * Fixing this race requires checking the variable completed only after * taking the event lock, which defeats the concept of just calling * libusb_handle_events() without worrying about locking. This is why * libusb-1.0.9 introduces the new libusb_handle_events_timeout_completed() * and libusb_handle_events_completed() functions, which handles doing the * completion check for you after they have acquired the lock: * \code libusb_submit_transfer(transfer); while (!completed) { libusb_handle_events_completed(ctx, &completed); } printf("completed!"); \endcode * * This nicely fixes the race in our example. Note that if all you want to * do is submit a single transfer and wait for its completion, then using * one of the synchronous I/O functions is much easier. * * \note * The completed variable must be modified while holding the event lock, * otherwise a race condition can still exist. It is simplest to do so from * within the transfer callback as shown above. * * \section eventlock The events lock * * 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. * * 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, &zero_tv); } 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 event waiters 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 reacquires 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 event 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 event 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 occurring. 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); usbi_mutex_init(&ctx->events_lock); usbi_mutex_init(&ctx->event_waiters_lock); usbi_cond_init(&ctx->event_waiters_cond); usbi_mutex_init(&ctx->event_data_lock); usbi_tls_key_create(&ctx->event_handling_key); list_init(&ctx->flying_transfers); list_init(&ctx->event_sources); list_init(&ctx->removed_event_sources); list_init(&ctx->hotplug_msgs); list_init(&ctx->completed_transfers); r = usbi_create_event(&ctx->event); if (r < 0) goto err; r = usbi_add_event_source(ctx, USBI_EVENT_OS_HANDLE(&ctx->event), USBI_EVENT_POLL_EVENTS); if (r < 0) goto err_destroy_event; #ifdef HAVE_OS_TIMER r = usbi_create_timer(&ctx->timer); if (r == 0) { usbi_dbg(ctx, "using timer for timeouts"); r = usbi_add_event_source(ctx, USBI_TIMER_OS_HANDLE(&ctx->timer), USBI_TIMER_POLL_EVENTS); if (r < 0) goto err_destroy_timer; } else { usbi_dbg(ctx, "timer not available for timeouts"); } #endif return 0; #ifdef HAVE_OS_TIMER err_destroy_timer: usbi_destroy_timer(&ctx->timer); usbi_remove_event_source(ctx, USBI_EVENT_OS_HANDLE(&ctx->event)); #endif err_destroy_event: usbi_destroy_event(&ctx->event); err: usbi_mutex_destroy(&ctx->flying_transfers_lock); usbi_mutex_destroy(&ctx->events_lock); usbi_mutex_destroy(&ctx->event_waiters_lock); usbi_cond_destroy(&ctx->event_waiters_cond); usbi_mutex_destroy(&ctx->event_data_lock); usbi_tls_key_delete(ctx->event_handling_key); return r; } static void cleanup_removed_event_sources(struct libusb_context *ctx) { struct usbi_event_source *ievent_source, *tmp; for_each_removed_event_source_safe(ctx, ievent_source, tmp) { list_del(&ievent_source->list); free(ievent_source); } } void usbi_io_exit(struct libusb_context *ctx) { #ifdef HAVE_OS_TIMER if (usbi_using_timer(ctx)) { usbi_remove_event_source(ctx, USBI_TIMER_OS_HANDLE(&ctx->timer)); usbi_destroy_timer(&ctx->timer); } #endif usbi_remove_event_source(ctx, USBI_EVENT_OS_HANDLE(&ctx->event)); usbi_destroy_event(&ctx->event); usbi_mutex_destroy(&ctx->flying_transfers_lock); usbi_mutex_destroy(&ctx->events_lock); usbi_mutex_destroy(&ctx->event_waiters_lock); usbi_cond_destroy(&ctx->event_waiters_cond); usbi_mutex_destroy(&ctx->event_data_lock); usbi_tls_key_delete(ctx->event_handling_key); cleanup_removed_event_sources(ctx); free(ctx->event_data); } static void calculate_timeout(struct usbi_transfer *itransfer) { unsigned int timeout = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)->timeout; if (!timeout) { TIMESPEC_CLEAR(&itransfer->timeout); return; } usbi_get_monotonic_time(&itransfer->timeout); itransfer->timeout.tv_sec += timeout / 1000U; itransfer->timeout.tv_nsec += (timeout % 1000U) * 1000000L; if (itransfer->timeout.tv_nsec >= NSEC_PER_SEC) { ++itransfer->timeout.tv_sec; itransfer->timeout.tv_nsec -= NSEC_PER_SEC; } } /** \ingroup libusb_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. Must be non-negative. * \returns a newly allocated transfer, or NULL on error */ DEFAULT_VISIBILITY struct libusb_transfer * LIBUSB_CALL libusb_alloc_transfer( int iso_packets) { size_t priv_size; size_t alloc_size; unsigned char *ptr; struct usbi_transfer *itransfer; struct libusb_transfer *transfer; assert(iso_packets >= 0); if (iso_packets < 0) return NULL; priv_size = PTR_ALIGN(usbi_backend.transfer_priv_size); alloc_size = priv_size + sizeof(struct usbi_transfer) + sizeof(struct libusb_transfer) + (sizeof(struct libusb_iso_packet_descriptor) * (size_t)iso_packets); ptr = calloc(1, alloc_size); if (!ptr) return NULL; itransfer = (struct usbi_transfer *)(ptr + priv_size); itransfer->num_iso_packets = iso_packets; itransfer->priv = ptr; usbi_mutex_init(&itransfer->lock); transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer); return transfer; } /** \ingroup libusb_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; size_t priv_size; unsigned char *ptr; if (!transfer) return; usbi_dbg(TRANSFER_CTX(transfer), "transfer %p", transfer); if (transfer->flags & LIBUSB_TRANSFER_FREE_BUFFER) free(transfer->buffer); itransfer = LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer); usbi_mutex_destroy(&itransfer->lock); priv_size = PTR_ALIGN(usbi_backend.transfer_priv_size); ptr = (unsigned char *)itransfer - priv_size; assert(ptr == itransfer->priv); free(ptr); } /* iterates through the flying transfers, and rearms the timer based on the * next upcoming timeout. * must be called with flying_list locked. * returns 0 on success or a LIBUSB_ERROR code on failure. */ #ifdef HAVE_OS_TIMER static int arm_timer_for_next_timeout(struct libusb_context *ctx) { struct usbi_transfer *itransfer; if (!usbi_using_timer(ctx)) return 0; for_each_transfer(ctx, itransfer) { struct timespec *cur_ts = &itransfer->timeout; /* if we've reached transfers of infinite timeout, then we have no * arming to do */ if (!TIMESPEC_IS_SET(cur_ts)) break; /* act on first transfer that has not already been handled */ if (!(itransfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT))) { usbi_dbg(ctx, "next timeout originally %ums", USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)->timeout); return usbi_arm_timer(&ctx->timer, cur_ts); } } usbi_dbg(ctx, "no timeouts, disarming timer"); return usbi_disarm_timer(&ctx->timer); } #else static inline int arm_timer_for_next_timeout(struct libusb_context *ctx) { UNUSED(ctx); return 0; } #endif /* add a transfer to the (timeout-sorted) active transfers list. * This function will return non 0 if fails to update the timer, * in which case the transfer is *not* on the flying_transfers list. */ static int add_to_flying_list(struct usbi_transfer *itransfer) { struct usbi_transfer *cur; struct timespec *timeout = &itransfer->timeout; struct libusb_context *ctx = ITRANSFER_CTX(itransfer); int r = 0; int first = 1; calculate_timeout(itransfer); /* if we have no other flying transfers, start the list with this one */ if (list_empty(&ctx->flying_transfers)) { list_add(&itransfer->list, &ctx->flying_transfers); goto out; } /* if we have infinite timeout, append to end of list */ if (!TIMESPEC_IS_SET(timeout)) { list_add_tail(&itransfer->list, &ctx->flying_transfers); /* first is irrelevant in this case */ goto out; } /* otherwise, find appropriate place in list */ for_each_transfer(ctx, cur) { /* find first timeout that occurs after the transfer in question */ struct timespec *cur_ts = &cur->timeout; if (!TIMESPEC_IS_SET(cur_ts) || TIMESPEC_CMP(cur_ts, timeout, >)) { list_add_tail(&itransfer->list, &cur->list); goto out; } first = 0; } /* first is 0 at this stage (list not empty) */ /* otherwise we need to be inserted at the end */ list_add_tail(&itransfer->list, &ctx->flying_transfers); out: #ifdef HAVE_OS_TIMER if (first && usbi_using_timer(ctx) && TIMESPEC_IS_SET(timeout)) { /* if this transfer has the lowest timeout of all active transfers, * rearm the timer with this transfer's timeout */ usbi_dbg(ctx, "arm timer for timeout in %ums (first in line)", USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)->timeout); r = usbi_arm_timer(&ctx->timer, timeout); } #else UNUSED(first); #endif if (r) list_del(&itransfer->list); return r; } /* remove a transfer from the active transfers list. * This function will *always* remove the transfer from the * flying_transfers list. It will return a LIBUSB_ERROR code * if it fails to update the timer for the next timeout. */ static int remove_from_flying_list(struct usbi_transfer *itransfer) { struct libusb_context *ctx = ITRANSFER_CTX(itransfer); int rearm_timer; int r = 0; usbi_mutex_lock(&ctx->flying_transfers_lock); rearm_timer = (TIMESPEC_IS_SET(&itransfer->timeout) && list_first_entry(&ctx->flying_transfers, struct usbi_transfer, list) == itransfer); list_del(&itransfer->list); if (rearm_timer) r = arm_timer_for_next_timeout(ctx); usbi_mutex_unlock(&ctx->flying_transfers_lock); return r; } /** \ingroup libusb_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 LIBUSB_ERROR_NOT_SUPPORTED if the transfer flags are not supported * by the operating system. * \returns LIBUSB_ERROR_INVALID_PARAM if the transfer size is larger than * the operating system and/or hardware can support (see \ref asynclimits) * \returns another LIBUSB_ERROR code on other failure */ int API_EXPORTED libusb_submit_transfer(struct libusb_transfer *transfer) { struct usbi_transfer *itransfer = LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer); struct libusb_context *ctx = TRANSFER_CTX(transfer); int r; usbi_dbg(ctx, "transfer %p", transfer); /* * Important note on locking, this function takes / releases locks * in the following order: * take flying_transfers_lock * take itransfer->lock * clear transfer * add to flying_transfers list * release flying_transfers_lock * submit transfer * release itransfer->lock * if submit failed: * take flying_transfers_lock * remove from flying_transfers list * release flying_transfers_lock * * Note that it takes locks in the order a-b and then releases them * in the same order a-b. This is somewhat unusual but not wrong, * release order is not important as long as *all* locks are released * before re-acquiring any locks. * * This means that the ordering of first releasing itransfer->lock * and then re-acquiring the flying_transfers_list on error is * important and must not be changed! * * This is done this way because when we take both locks we must always * take flying_transfers_lock first to avoid ab-ba style deadlocks with * the timeout handling and usbi_handle_disconnect paths. * * And we cannot release itransfer->lock before the submission is * complete otherwise timeout handling for transfers with short * timeouts may run before submission. */ usbi_mutex_lock(&ctx->flying_transfers_lock); usbi_mutex_lock(&itransfer->lock); if (itransfer->state_flags & USBI_TRANSFER_IN_FLIGHT) { usbi_mutex_unlock(&ctx->flying_transfers_lock); usbi_mutex_unlock(&itransfer->lock); return LIBUSB_ERROR_BUSY; } itransfer->transferred = 0; itransfer->state_flags = 0; itransfer->timeout_flags = 0; r = add_to_flying_list(itransfer); if (r) { usbi_mutex_unlock(&ctx->flying_transfers_lock); usbi_mutex_unlock(&itransfer->lock); return r; } /* * We must release the flying transfers lock here, because with * some backends the submit_transfer method is synchronous. */ usbi_mutex_unlock(&ctx->flying_transfers_lock); r = usbi_backend.submit_transfer(itransfer); if (r == LIBUSB_SUCCESS) { itransfer->state_flags |= USBI_TRANSFER_IN_FLIGHT; /* keep a reference to this device */ libusb_ref_device(transfer->dev_handle->dev); } usbi_mutex_unlock(&itransfer->lock); if (r != LIBUSB_SUCCESS) remove_from_flying_list(itransfer); return r; } /** \ingroup libusb_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 not in progress, * already complete, or already 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); struct libusb_context *ctx = ITRANSFER_CTX(itransfer); int r; usbi_dbg(ctx, "transfer %p", transfer ); usbi_mutex_lock(&itransfer->lock); if (!(itransfer->state_flags & USBI_TRANSFER_IN_FLIGHT) || (itransfer->state_flags & USBI_TRANSFER_CANCELLING)) { r = LIBUSB_ERROR_NOT_FOUND; goto out; } r = usbi_backend.cancel_transfer(itransfer); if (r < 0) { if (r != LIBUSB_ERROR_NOT_FOUND && r != LIBUSB_ERROR_NO_DEVICE) usbi_err(ctx, "cancel transfer failed error %d", r); else usbi_dbg(ctx, "cancel transfer failed error %d", r); if (r == LIBUSB_ERROR_NO_DEVICE) itransfer->state_flags |= USBI_TRANSFER_DEVICE_DISAPPEARED; } itransfer->state_flags |= USBI_TRANSFER_CANCELLING; out: usbi_mutex_unlock(&itransfer->lock); return r; } /** \ingroup libusb_asyncio * Set a transfers bulk stream id. Note users are advised to use * libusb_fill_bulk_stream_transfer() instead of calling this function * directly. * * Since version 1.0.19, \ref LIBUSB_API_VERSION >= 0x01000103 * * \param transfer the transfer to set the stream id for * \param stream_id the stream id to set * \see libusb_alloc_streams() */ void API_EXPORTED libusb_transfer_set_stream_id( struct libusb_transfer *transfer, uint32_t stream_id) { struct usbi_transfer *itransfer = LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer); itransfer->stream_id = stream_id; } /** \ingroup libusb_asyncio * Get a transfers bulk stream id. * * Since version 1.0.19, \ref LIBUSB_API_VERSION >= 0x01000103 * * \param transfer the transfer to get the stream id for * \returns the stream id for the transfer */ uint32_t API_EXPORTED libusb_transfer_get_stream_id( struct libusb_transfer *transfer) { struct usbi_transfer *itransfer = LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer); return itransfer->stream_id; } /* 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_device_handle *dev_handle = transfer->dev_handle; struct libusb_context *ctx = ITRANSFER_CTX(itransfer); uint8_t flags; int r; r = remove_from_flying_list(itransfer); if (r < 0) usbi_err(ctx, "failed to set timer for next timeout"); usbi_mutex_lock(&itransfer->lock); itransfer->state_flags &= ~USBI_TRANSFER_IN_FLIGHT; usbi_mutex_unlock(&itransfer->lock); 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(ctx, "interpreting short transfer as error"); status = LIBUSB_TRANSFER_ERROR; } } flags = transfer->flags; transfer->status = status; transfer->actual_length = itransfer->transferred; usbi_dbg(ctx, "transfer %p has callback %p", transfer, transfer->callback); 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); libusb_unref_device(dev_handle->dev); return r; } /* 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 *itransfer) { struct libusb_context *ctx = ITRANSFER_CTX(itransfer); uint8_t timed_out; usbi_mutex_lock(&ctx->flying_transfers_lock); timed_out = itransfer->timeout_flags & USBI_TRANSFER_TIMED_OUT; usbi_mutex_unlock(&ctx->flying_transfers_lock); /* if the URB was cancelled due to timeout, report timeout to the user */ if (timed_out) { usbi_dbg(ctx, "detected timeout cancellation"); return usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_TIMED_OUT); } /* otherwise its a normal async cancel */ return usbi_handle_transfer_completion(itransfer, LIBUSB_TRANSFER_CANCELLED); } /* Add a completed transfer to the completed_transfers list of the * context and signal the event. The backend's handle_transfer_completion() * function will be called the next time an event handler runs. */ void usbi_signal_transfer_completion(struct usbi_transfer *itransfer) { libusb_device_handle *dev_handle = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer)->dev_handle; if (dev_handle) { struct libusb_context *ctx = HANDLE_CTX(dev_handle); unsigned int event_flags; usbi_mutex_lock(&ctx->event_data_lock); event_flags = ctx->event_flags; ctx->event_flags |= USBI_EVENT_TRANSFER_COMPLETED; list_add_tail(&itransfer->completed_list, &ctx->completed_transfers); if (!event_flags) usbi_signal_event(&ctx->event); usbi_mutex_unlock(&ctx->event_data_lock); } } /** \ingroup libusb_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) * \ref libusb_mtasync */ int API_EXPORTED libusb_try_lock_events(libusb_context *ctx) { int r; unsigned int ru; ctx = usbi_get_context(ctx); /* is someone else waiting to close a device? if so, don't let this thread * start event handling */ usbi_mutex_lock(&ctx->event_data_lock); ru = ctx->device_close; usbi_mutex_unlock(&ctx->event_data_lock); if (ru) { usbi_dbg(ctx, "someone else is closing a device"); return 1; } r = usbi_mutex_trylock(&ctx->events_lock); if (!r) return 1; ctx->event_handler_active = 1; return 0; } /** \ingroup libusb_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 * \ref libusb_mtasync */ void API_EXPORTED libusb_lock_events(libusb_context *ctx) { ctx = usbi_get_context(ctx); usbi_mutex_lock(&ctx->events_lock); ctx->event_handler_active = 1; } /** \ingroup libusb_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 * \ref libusb_mtasync */ void API_EXPORTED libusb_unlock_events(libusb_context *ctx) { 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->device_close)? */ usbi_mutex_lock(&ctx->event_waiters_lock); usbi_cond_broadcast(&ctx->event_waiters_cond); usbi_mutex_unlock(&ctx->event_waiters_lock); } /** \ingroup libusb_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 libusb_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 * \ref fullstory "Multi-threaded I/O: the full story" */ int API_EXPORTED libusb_event_handling_ok(libusb_context *ctx) { unsigned int r; ctx = usbi_get_context(ctx); /* is someone else waiting to close a device? if so, don't let this thread * continue event handling */ usbi_mutex_lock(&ctx->event_data_lock); r = ctx->device_close; usbi_mutex_unlock(&ctx->event_data_lock); if (r) { usbi_dbg(ctx, "someone else is closing a device"); return 0; } return 1; } /** \ingroup libusb_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 * \ref libusb_mtasync */ int API_EXPORTED libusb_event_handler_active(libusb_context *ctx) { unsigned int r; ctx = usbi_get_context(ctx); /* is someone else waiting to close a device? if so, don't let this thread * start event handling -- indicate that event handling is happening */ usbi_mutex_lock(&ctx->event_data_lock); r = ctx->device_close; usbi_mutex_unlock(&ctx->event_data_lock); if (r) { usbi_dbg(ctx, "someone else is closing a device"); return 1; } return ctx->event_handler_active; } /** \ingroup libusb_poll * Interrupt any active thread that is handling events. This is mainly useful * for interrupting a dedicated event handling thread when an application * wishes to call libusb_exit(). * * Since version 1.0.21, \ref LIBUSB_API_VERSION >= 0x01000105 * * \param ctx the context to operate on, or NULL for the default context * \ref libusb_mtasync */ void API_EXPORTED libusb_interrupt_event_handler(libusb_context *ctx) { unsigned int event_flags; usbi_dbg(ctx, " "); ctx = usbi_get_context(ctx); usbi_mutex_lock(&ctx->event_data_lock); event_flags = ctx->event_flags; ctx->event_flags |= USBI_EVENT_USER_INTERRUPT; if (!event_flags) usbi_signal_event(&ctx->event); usbi_mutex_unlock(&ctx->event_data_lock); } /** \ingroup libusb_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, * and may potentially be handling events from 2 threads simultaneously. * 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 * \ref libusb_mtasync */ void API_EXPORTED libusb_lock_event_waiters(libusb_context *ctx) { ctx = usbi_get_context(ctx); usbi_mutex_lock(&ctx->event_waiters_lock); } /** \ingroup libusb_poll * Release the event waiters lock. * \param ctx the context to operate on, or NULL for the default context * \ref libusb_mtasync */ void API_EXPORTED libusb_unlock_event_waiters(libusb_context *ctx) { ctx = usbi_get_context(ctx); usbi_mutex_unlock(&ctx->event_waiters_lock); } /** \ingroup libusb_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 after * 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 * \returns LIBUSB_ERROR_INVALID_PARAM if timeval is invalid * \ref libusb_mtasync */ int API_EXPORTED libusb_wait_for_event(libusb_context *ctx, struct timeval *tv) { int r; ctx = usbi_get_context(ctx); if (!tv) { usbi_cond_wait(&ctx->event_waiters_cond, &ctx->event_waiters_lock); return 0; } if (!TIMEVAL_IS_VALID(tv)) return LIBUSB_ERROR_INVALID_PARAM; r = usbi_cond_timedwait(&ctx->event_waiters_cond, &ctx->event_waiters_lock, tv); if (r < 0) return r == LIBUSB_ERROR_TIMEOUT; return 0; } static void handle_timeout(struct usbi_transfer *itransfer) { struct libusb_transfer *transfer = USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer); int r; itransfer->timeout_flags |= USBI_TRANSFER_TIMEOUT_HANDLED; r = libusb_cancel_transfer(transfer); if (r == LIBUSB_SUCCESS) itransfer->timeout_flags |= USBI_TRANSFER_TIMED_OUT; else usbi_warn(TRANSFER_CTX(transfer), "async cancel failed %d", r); } static void handle_timeouts_locked(struct libusb_context *ctx) { struct timespec systime; struct usbi_transfer *itransfer; if (list_empty(&ctx->flying_transfers)) return; /* get current time */ usbi_get_monotonic_time(&systime); /* iterate through flying transfers list, finding all transfers that * have expired timeouts */ for_each_transfer(ctx, itransfer) { struct timespec *cur_ts = &itransfer->timeout; /* if we've reached transfers of infinite timeout, we're all done */ if (!TIMESPEC_IS_SET(cur_ts)) return; /* ignore timeouts we've already handled */ if (itransfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT)) continue; /* if transfer has non-expired timeout, nothing more to do */ if (TIMESPEC_CMP(cur_ts, &systime, >)) return; /* otherwise, we've got an expired timeout to handle */ handle_timeout(itransfer); } } static void handle_timeouts(struct libusb_context *ctx) { ctx = usbi_get_context(ctx); usbi_mutex_lock(&ctx->flying_transfers_lock); handle_timeouts_locked(ctx); usbi_mutex_unlock(&ctx->flying_transfers_lock); } static int handle_event_trigger(struct libusb_context *ctx) { struct list_head hotplug_msgs; int hotplug_event = 0; int r = 0; usbi_dbg(ctx, "event triggered"); list_init(&hotplug_msgs); /* take the the event data lock while processing events */ usbi_mutex_lock(&ctx->event_data_lock); /* check if someone modified the event sources */ if (ctx->event_flags & USBI_EVENT_EVENT_SOURCES_MODIFIED) usbi_dbg(ctx, "someone updated the event sources"); if (ctx->event_flags & USBI_EVENT_USER_INTERRUPT) { usbi_dbg(ctx, "someone purposefully interrupted"); ctx->event_flags &= ~USBI_EVENT_USER_INTERRUPT; } if (ctx->event_flags & USBI_EVENT_HOTPLUG_CB_DEREGISTERED) { usbi_dbg(ctx, "someone unregistered a hotplug cb"); ctx->event_flags &= ~USBI_EVENT_HOTPLUG_CB_DEREGISTERED; hotplug_event = 1; } /* check if someone is closing a device */ if (ctx->event_flags & USBI_EVENT_DEVICE_CLOSE) usbi_dbg(ctx, "someone is closing a device"); /* check for any pending hotplug messages */ if (ctx->event_flags & USBI_EVENT_HOTPLUG_MSG_PENDING) { usbi_dbg(ctx, "hotplug message received"); ctx->event_flags &= ~USBI_EVENT_HOTPLUG_MSG_PENDING; hotplug_event = 1; assert(!list_empty(&ctx->hotplug_msgs)); list_cut(&hotplug_msgs, &ctx->hotplug_msgs); } /* complete any pending transfers */ if (ctx->event_flags & USBI_EVENT_TRANSFER_COMPLETED) { struct usbi_transfer *itransfer, *tmp; struct list_head completed_transfers; assert(!list_empty(&ctx->completed_transfers)); list_cut(&completed_transfers, &ctx->completed_transfers); usbi_mutex_unlock(&ctx->event_data_lock); __for_each_completed_transfer_safe(&completed_transfers, itransfer, tmp) { list_del(&itransfer->completed_list); r = usbi_backend.handle_transfer_completion(itransfer); if (r) { usbi_err(ctx, "backend handle_transfer_completion failed with error %d", r); break; } } usbi_mutex_lock(&ctx->event_data_lock); if (!list_empty(&completed_transfers)) { /* an error occurred, put the remaining transfers back on the list */ list_splice_front(&completed_transfers, &ctx->completed_transfers); } else if (list_empty(&ctx->completed_transfers)) { ctx->event_flags &= ~USBI_EVENT_TRANSFER_COMPLETED; } } /* if no further pending events, clear the event */ if (!ctx->event_flags) usbi_clear_event(&ctx->event); usbi_mutex_unlock(&ctx->event_data_lock); /* process the hotplug events, if any */ if (hotplug_event) usbi_hotplug_process(ctx, &hotplug_msgs); return r; } #ifdef HAVE_OS_TIMER static int handle_timer_trigger(struct libusb_context *ctx) { int r; usbi_mutex_lock(&ctx->flying_transfers_lock); /* process the timeout that just happened */ handle_timeouts_locked(ctx); /* arm for next timeout */ r = arm_timer_for_next_timeout(ctx); 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) { struct usbi_reported_events reported_events; int r, timeout_ms; /* prevent attempts to recursively handle events (e.g. calling into * libusb_handle_events() from within a hotplug or transfer callback) */ if (usbi_handling_events(ctx)) return LIBUSB_ERROR_BUSY; /* only reallocate the event source data when the list of event sources has * been modified since the last handle_events(), otherwise reuse them to * save the additional overhead */ usbi_mutex_lock(&ctx->event_data_lock); if (ctx->event_flags & USBI_EVENT_EVENT_SOURCES_MODIFIED) { usbi_dbg(ctx, "event sources modified, reallocating event data"); /* free anything removed since we last ran */ cleanup_removed_event_sources(ctx); r = usbi_alloc_event_data(ctx); if (r) { usbi_mutex_unlock(&ctx->event_data_lock); return r; } /* reset the flag now that we have the updated list */ ctx->event_flags &= ~USBI_EVENT_EVENT_SOURCES_MODIFIED; /* if no further pending events, clear the event so that we do * not immediately return from the wait function */ if (!ctx->event_flags) usbi_clear_event(&ctx->event); } usbi_mutex_unlock(&ctx->event_data_lock); timeout_ms = (int)(tv->tv_sec * 1000) + (tv->tv_usec / 1000); /* round up to next millisecond */ if (tv->tv_usec % 1000) timeout_ms++; reported_events.event_bits = 0; usbi_start_event_handling(ctx); r = usbi_wait_for_events(ctx, &reported_events, timeout_ms); if (r != LIBUSB_SUCCESS) { if (r == LIBUSB_ERROR_TIMEOUT) { handle_timeouts(ctx); r = LIBUSB_SUCCESS; } goto done; } if (reported_events.event_triggered) { r = handle_event_trigger(ctx); if (r) { /* return error code */ goto done; } } #ifdef HAVE_OS_TIMER if (reported_events.timer_triggered) { r = handle_timer_trigger(ctx); if (r) { /* return error code */ goto done; } } #endif if (!reported_events.num_ready) goto done; r = usbi_backend.handle_events(ctx, reported_events.event_data, reported_events.event_data_count, reported_events.num_ready); if (r) usbi_err(ctx, "backend handle_events failed with error %d", r); done: usbi_end_event_handling(ctx); 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 libusb_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. * * If the parameter completed is not NULL then after obtaining the event * handling lock this function will return immediately if the integer * pointed to is not 0. This allows for race free waiting for the completion * of a specific transfer. * * \param ctx the context to operate on, or NULL for the default context * \param tv the maximum time to block waiting for events, or an all zero * timeval struct for non-blocking mode * \param completed pointer to completion integer to check, or NULL * \returns 0 on success * \returns LIBUSB_ERROR_INVALID_PARAM if timeval is invalid * \returns another LIBUSB_ERROR code on other failure * \ref libusb_mtasync */ int API_EXPORTED libusb_handle_events_timeout_completed(libusb_context *ctx, struct timeval *tv, int *completed) { int r; struct timeval poll_timeout; if (!TIMEVAL_IS_VALID(tv)) return LIBUSB_ERROR_INVALID_PARAM; ctx = usbi_get_context(ctx); r = get_next_timeout(ctx, tv, &poll_timeout); if (r) { /* timeout already expired */ handle_timeouts(ctx); return 0; } retry: if (libusb_try_lock_events(ctx) == 0) { if (completed == NULL || !*completed) { /* we obtained the event lock: do our own event handling */ usbi_dbg(ctx, "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 thread events that * notify event completion. */ libusb_lock_event_waiters(ctx); if (completed && *completed) goto already_done; 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(ctx, "event handler was active but went away, retrying"); goto retry; } usbi_dbg(ctx, "another thread is doing event handling"); r = libusb_wait_for_event(ctx, &poll_timeout); already_done: libusb_unlock_event_waiters(ctx); if (r < 0) return r; else if (r == 1) handle_timeouts(ctx); return 0; } /** \ingroup libusb_poll * Handle any pending events * * Like libusb_handle_events_timeout_completed(), but without the completed * parameter, calling this function is equivalent to calling * libusb_handle_events_timeout_completed() with a NULL completed parameter. * * This function is kept primarily for backwards compatibility. * All new code should call libusb_handle_events_completed() or * libusb_handle_events_timeout_completed() to avoid race conditions. * * \param ctx the context to operate on, or NULL for the default context * \param tv the maximum time to block waiting for events, or an all zero * timeval struct for non-blocking mode * \returns 0 on success, or a LIBUSB_ERROR code on failure */ int API_EXPORTED libusb_handle_events_timeout(libusb_context *ctx, struct timeval *tv) { return libusb_handle_events_timeout_completed(ctx, tv, NULL); } /** \ingroup libusb_poll * Handle any pending events in blocking mode. There is currently a timeout * hard-coded 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_completed() * instead. * * This function is kept primarily for backwards compatibility. * All new code should call libusb_handle_events_completed() or * libusb_handle_events_timeout_completed() to avoid race conditions. * * \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_completed(ctx, &tv, NULL); } /** \ingroup libusb_poll * Handle any pending events in blocking mode. * * Like libusb_handle_events(), with the addition of a completed parameter * to allow for race free waiting for the completion of a specific transfer. * * See libusb_handle_events_timeout_completed() for details on the completed * parameter. * * \param ctx the context to operate on, or NULL for the default context * \param completed pointer to completion integer to check, or NULL * \returns 0 on success, or a LIBUSB_ERROR code on failure * \ref libusb_mtasync */ int API_EXPORTED libusb_handle_events_completed(libusb_context *ctx, int *completed) { struct timeval tv; tv.tv_sec = 60; tv.tv_usec = 0; return libusb_handle_events_timeout_completed(ctx, &tv, completed); } /** \ingroup libusb_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 * \returns LIBUSB_ERROR_INVALID_PARAM if timeval is invalid * \returns another LIBUSB_ERROR code on other failure * \ref libusb_mtasync */ int API_EXPORTED libusb_handle_events_locked(libusb_context *ctx, struct timeval *tv) { int r; struct timeval poll_timeout; if (!TIMEVAL_IS_VALID(tv)) return LIBUSB_ERROR_INVALID_PARAM; ctx = usbi_get_context(ctx); r = get_next_timeout(ctx, tv, &poll_timeout); if (r) { /* timeout already expired */ handle_timeouts(ctx); return 0; } return handle_events(ctx, &poll_timeout); } /** \ingroup libusb_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 libusb_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. * \ref libusb_pollmain "Polling libusb file descriptors for event handling" */ int API_EXPORTED libusb_pollfds_handle_timeouts(libusb_context *ctx) { ctx = usbi_get_context(ctx); return usbi_using_timer(ctx); } /** \ingroup libusb_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) { struct usbi_transfer *itransfer; struct timespec systime; struct timespec next_timeout = { 0, 0 }; ctx = usbi_get_context(ctx); if (usbi_using_timer(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(ctx, "no URBs, no timeout!"); return 0; } /* find next transfer which hasn't already been processed as timed out */ for_each_transfer(ctx, itransfer) { if (itransfer->timeout_flags & (USBI_TRANSFER_TIMEOUT_HANDLED | USBI_TRANSFER_OS_HANDLES_TIMEOUT)) continue; /* if we've reached transfers of infinite timeout, we're done looking */ if (!TIMESPEC_IS_SET(&itransfer->timeout)) break; next_timeout = itransfer->timeout; break; } usbi_mutex_unlock(&ctx->flying_transfers_lock); if (!TIMESPEC_IS_SET(&next_timeout)) { usbi_dbg(ctx, "no URB with timeout or all handled by OS; no timeout!"); return 0; } usbi_get_monotonic_time(&systime); if (!TIMESPEC_CMP(&systime, &next_timeout, <)) { usbi_dbg(ctx, "first timeout already expired"); timerclear(tv); } else { TIMESPEC_SUB(&next_timeout, &systime, &next_timeout); TIMESPEC_TO_TIMEVAL(tv, &next_timeout); usbi_dbg(ctx, "next timeout in %ld.%06lds", (long)tv->tv_sec, (long)tv->tv_usec); } return 1; } /** \ingroup libusb_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) { #if !defined(PLATFORM_WINDOWS) ctx = usbi_get_context(ctx); ctx->fd_added_cb = added_cb; ctx->fd_removed_cb = removed_cb; ctx->fd_cb_user_data = user_data; #else usbi_err(ctx, "external polling of libusb's internal event sources " \ "is not yet supported on Windows"); UNUSED(added_cb); UNUSED(removed_cb); UNUSED(user_data); #endif } /* * Interrupt the iteration of the event handling thread, so that it picks * up the event source change. Callers of this function must hold the event_data_lock. */ static void usbi_event_source_notification(struct libusb_context *ctx) { unsigned int event_flags; /* Record that there is a new poll fd. * Only signal an event if there are no prior pending events. */ event_flags = ctx->event_flags; ctx->event_flags |= USBI_EVENT_EVENT_SOURCES_MODIFIED; if (!event_flags) usbi_signal_event(&ctx->event); } /* Add an event source to the list of event sources to be monitored. * poll_events should be specified as a bitmask of events passed to poll(), e.g. * POLLIN and/or POLLOUT. */ int usbi_add_event_source(struct libusb_context *ctx, usbi_os_handle_t os_handle, short poll_events) { struct usbi_event_source *ievent_source = malloc(sizeof(*ievent_source)); if (!ievent_source) return LIBUSB_ERROR_NO_MEM; usbi_dbg(ctx, "add " USBI_OS_HANDLE_FORMAT_STRING " events %d", os_handle, poll_events); ievent_source->data.os_handle = os_handle; ievent_source->data.poll_events = poll_events; usbi_mutex_lock(&ctx->event_data_lock); list_add_tail(&ievent_source->list, &ctx->event_sources); usbi_event_source_notification(ctx); usbi_mutex_unlock(&ctx->event_data_lock); #if !defined(PLATFORM_WINDOWS) if (ctx->fd_added_cb) ctx->fd_added_cb(os_handle, poll_events, ctx->fd_cb_user_data); #endif return 0; } /* Remove an event source from the list of event sources to be monitored. */ void usbi_remove_event_source(struct libusb_context *ctx, usbi_os_handle_t os_handle) { struct usbi_event_source *ievent_source; int found = 0; usbi_dbg(ctx, "remove " USBI_OS_HANDLE_FORMAT_STRING, os_handle); usbi_mutex_lock(&ctx->event_data_lock); for_each_event_source(ctx, ievent_source) { if (ievent_source->data.os_handle == os_handle) { found = 1; break; } } if (!found) { usbi_dbg(ctx, "couldn't find " USBI_OS_HANDLE_FORMAT_STRING " to remove", os_handle); usbi_mutex_unlock(&ctx->event_data_lock); return; } list_del(&ievent_source->list); list_add_tail(&ievent_source->list, &ctx->removed_event_sources); usbi_event_source_notification(ctx); usbi_mutex_unlock(&ctx->event_data_lock); #if !defined(PLATFORM_WINDOWS) if (ctx->fd_removed_cb) ctx->fd_removed_cb(os_handle, ctx->fd_cb_user_data); #endif } /** \ingroup libusb_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 libusb_free_pollfds() * 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) { #if !defined(PLATFORM_WINDOWS) struct libusb_pollfd **ret = NULL; struct usbi_event_source *ievent_source; size_t i; static_assert(sizeof(struct usbi_event_source_data) == sizeof(struct libusb_pollfd), "mismatch between usbi_event_source_data and libusb_pollfd sizes"); ctx = usbi_get_context(ctx); usbi_mutex_lock(&ctx->event_data_lock); i = 0; for_each_event_source(ctx, ievent_source) i++; ret = calloc(i + 1, sizeof(struct libusb_pollfd *)); if (!ret) goto out; i = 0; for_each_event_source(ctx, ievent_source) ret[i++] = (struct libusb_pollfd *)ievent_source; out: usbi_mutex_unlock(&ctx->event_data_lock); return (const struct libusb_pollfd **)ret; #else usbi_err(ctx, "external polling of libusb's internal event sources " \ "is not yet supported on Windows"); return NULL; #endif } /** \ingroup libusb_poll * Free a list of libusb_pollfd structures. This should be called for all * pollfd lists allocated with libusb_get_pollfds(). * * Since version 1.0.20, \ref LIBUSB_API_VERSION >= 0x01000104 * * It is legal to call this function with a NULL pollfd list. In this case, * the function will simply do nothing. * * \param pollfds the list of libusb_pollfd structures to free */ void API_EXPORTED libusb_free_pollfds(const struct libusb_pollfd **pollfds) { #if !defined(PLATFORM_WINDOWS) free((void *)pollfds); #else UNUSED(pollfds); #endif } /* Backends may call this from handle_events to report disconnection of a * device. This function ensures transfers get cancelled appropriately. * Callers of this function must hold the events_lock. */ void usbi_handle_disconnect(struct libusb_device_handle *dev_handle) { struct libusb_context *ctx = HANDLE_CTX(dev_handle); struct usbi_transfer *cur; struct usbi_transfer *to_cancel; usbi_dbg(ctx, "device %d.%d", dev_handle->dev->bus_number, dev_handle->dev->device_address); /* terminate all pending transfers with the LIBUSB_TRANSFER_NO_DEVICE * status code. * * when we find a transfer for this device on the list, there are two * possible scenarios: * 1. the transfer is currently in-flight, in which case we terminate the * transfer here * 2. the transfer has been added to the flying transfer list by * libusb_submit_transfer, has failed to submit and * libusb_submit_transfer is waiting for us to release the * flying_transfers_lock to remove it, so we ignore it */ while (1) { to_cancel = NULL; usbi_mutex_lock(&ctx->flying_transfers_lock); for_each_transfer(ctx, cur) { if (USBI_TRANSFER_TO_LIBUSB_TRANSFER(cur)->dev_handle == dev_handle) { usbi_mutex_lock(&cur->lock); if (cur->state_flags & USBI_TRANSFER_IN_FLIGHT) to_cancel = cur; usbi_mutex_unlock(&cur->lock); if (to_cancel) break; } } usbi_mutex_unlock(&ctx->flying_transfers_lock); if (!to_cancel) break; usbi_dbg(ctx, "cancelling transfer %p from disconnect", USBI_TRANSFER_TO_LIBUSB_TRANSFER(to_cancel)); usbi_mutex_lock(&to_cancel->lock); usbi_backend.clear_transfer_priv(to_cancel); usbi_mutex_unlock(&to_cancel->lock); usbi_handle_transfer_completion(to_cancel, LIBUSB_TRANSFER_NO_DEVICE); } }