1 /* -*- Mode: C; indent-tabs-mode:t ; c-basic-offset:8 -*- */
3 * I/O functions for libusbx
4 * Copyright © 2007-2009 Daniel Drake <dsd@gentoo.org>
5 * Copyright © 2001 Johannes Erdfelt <johannes@erdfelt.com>
7 * This library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; either
10 * version 2.1 of the License, or (at your option) any later version.
12 * This library is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with this library; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
31 #ifdef HAVE_SYS_TIME_H
34 #ifdef USBI_TIMERFD_AVAILABLE
35 #include <sys/timerfd.h>
42 * \page io Synchronous and asynchronous device I/O
44 * \section intro Introduction
46 * If you're using libusbx in your application, you're probably wanting to
47 * perform I/O with devices - you want to perform USB data transfers.
49 * libusbx offers two separate interfaces for device I/O. This page aims to
50 * introduce the two in order to help you decide which one is more suitable
51 * for your application. You can also choose to use both interfaces in your
52 * application by considering each transfer on a case-by-case basis.
54 * Once you have read through the following discussion, you should consult the
55 * detailed API documentation pages for the details:
59 * \section theory Transfers at a logical level
61 * At a logical level, USB transfers typically happen in two parts. For
62 * example, when reading data from a endpoint:
63 * -# A request for data is sent to the device
64 * -# Some time later, the incoming data is received by the host
66 * or when writing data to an endpoint:
68 * -# The data is sent to the device
69 * -# Some time later, the host receives acknowledgement from the device that
70 * the data has been transferred.
72 * There may be an indefinite delay between the two steps. Consider a
73 * fictional USB input device with a button that the user can press. In order
74 * to determine when the button is pressed, you would likely submit a request
75 * to read data on a bulk or interrupt endpoint and wait for data to arrive.
76 * Data will arrive when the button is pressed by the user, which is
77 * potentially hours later.
79 * libusbx offers both a synchronous and an asynchronous interface to performing
80 * USB transfers. The main difference is that the synchronous interface
81 * combines both steps indicated above into a single function call, whereas
82 * the asynchronous interface separates them.
84 * \section sync The synchronous interface
86 * The synchronous I/O interface allows you to perform a USB transfer with
87 * a single function call. When the function call returns, the transfer has
88 * completed and you can parse the results.
90 * If you have used the libusb-0.1 before, this I/O style will seem familar to
91 * you. libusb-0.1 only offered a synchronous interface.
93 * In our input device example, to read button presses you might write code
94 * in the following style:
96 unsigned char data[4];
98 int r = libusb_bulk_transfer(handle, LIBUSB_ENDPOINT_IN, data, sizeof(data), &actual_length, 0);
99 if (r == 0 && actual_length == sizeof(data)) {
100 // results of the transaction can now be found in the data buffer
101 // parse them here and report button press
107 * The main advantage of this model is simplicity: you did everything with
108 * a single simple function call.
110 * However, this interface has its limitations. Your application will sleep
111 * inside libusb_bulk_transfer() until the transaction has completed. If it
112 * takes the user 3 hours to press the button, your application will be
113 * sleeping for that long. Execution will be tied up inside the library -
114 * the entire thread will be useless for that duration.
116 * Another issue is that by tieing up the thread with that single transaction
117 * there is no possibility of performing I/O with multiple endpoints and/or
118 * multiple devices simultaneously, unless you resort to creating one thread
121 * Additionally, there is no opportunity to cancel the transfer after the
122 * request has been submitted.
124 * For details on how to use the synchronous API, see the
125 * \ref syncio "synchronous I/O API documentation" pages.
127 * \section async The asynchronous interface
129 * Asynchronous I/O is the most significant new feature in libusb-1.0.
130 * Although it is a more complex interface, it solves all the issues detailed
133 * Instead of providing which functions that block until the I/O has complete,
134 * libusbx's asynchronous interface presents non-blocking functions which
135 * begin a transfer and then return immediately. Your application passes a
136 * callback function pointer to this non-blocking function, which libusbx will
137 * call with the results of the transaction when it has completed.
139 * Transfers which have been submitted through the non-blocking functions
140 * can be cancelled with a separate function call.
142 * The non-blocking nature of this interface allows you to be simultaneously
143 * performing I/O to multiple endpoints on multiple devices, without having
146 * This added flexibility does come with some complications though:
147 * - In the interest of being a lightweight library, libusbx does not create
148 * threads and can only operate when your application is calling into it. Your
149 * application must call into libusbx from it's main loop when events are ready
150 * to be handled, or you must use some other scheme to allow libusbx to
151 * undertake whatever work needs to be done.
152 * - libusbx also needs to be called into at certain fixed points in time in
153 * order to accurately handle transfer timeouts.
154 * - Memory handling becomes more complex. You cannot use stack memory unless
155 * the function with that stack is guaranteed not to return until the transfer
156 * callback has finished executing.
157 * - You generally lose some linearity from your code flow because submitting
158 * the transfer request is done in a separate function from where the transfer
159 * results are handled. This becomes particularly obvious when you want to
160 * submit a second transfer based on the results of an earlier transfer.
162 * Internally, libusbx's synchronous interface is expressed in terms of function
163 * calls to the asynchronous interface.
165 * For details on how to use the asynchronous API, see the
166 * \ref asyncio "asynchronous I/O API" documentation pages.
171 * \page packetoverflow Packets and overflows
173 * \section packets Packet abstraction
175 * The USB specifications describe how data is transmitted in packets, with
176 * constraints on packet size defined by endpoint descriptors. The host must
177 * not send data payloads larger than the endpoint's maximum packet size.
179 * libusbx and the underlying OS abstract out the packet concept, allowing you
180 * to request transfers of any size. Internally, the request will be divided
181 * up into correctly-sized packets. You do not have to be concerned with
182 * packet sizes, but there is one exception when considering overflows.
184 * \section overflow Bulk/interrupt transfer overflows
186 * When requesting data on a bulk endpoint, libusbx requires you to supply a
187 * buffer and the maximum number of bytes of data that libusbx can put in that
188 * buffer. However, the size of the buffer is not communicated to the device -
189 * the device is just asked to send any amount of data.
191 * There is no problem if the device sends an amount of data that is less than
192 * or equal to the buffer size. libusbx reports this condition to you through
193 * the \ref libusb_transfer::actual_length "libusb_transfer.actual_length"
196 * Problems may occur if the device attempts to send more data than can fit in
197 * the buffer. libusbx reports LIBUSB_TRANSFER_OVERFLOW for this condition but
198 * other behaviour is largely undefined: actual_length may or may not be
199 * accurate, the chunk of data that can fit in the buffer (before overflow)
200 * may or may not have been transferred.
202 * Overflows are nasty, but can be avoided. Even though you were told to
203 * ignore packets above, think about the lower level details: each transfer is
204 * split into packets (typically small, with a maximum size of 512 bytes).
205 * Overflows can only happen if the final packet in an incoming data transfer
206 * is smaller than the actual packet that the device wants to transfer.
207 * Therefore, you will never see an overflow if your transfer buffer size is a
208 * multiple of the endpoint's packet size: the final packet will either
209 * fill up completely or will be only partially filled.
213 * @defgroup asyncio Asynchronous device I/O
215 * This page details libusbx's asynchronous (non-blocking) API for USB device
216 * I/O. This interface is very powerful but is also quite complex - you will
217 * need to read this page carefully to understand the necessary considerations
218 * and issues surrounding use of this interface. Simplistic applications
219 * may wish to consider the \ref syncio "synchronous I/O API" instead.
221 * The asynchronous interface is built around the idea of separating transfer
222 * submission and handling of transfer completion (the synchronous model
223 * combines both of these into one). There may be a long delay between
224 * submission and completion, however the asynchronous submission function
225 * is non-blocking so will return control to your application during that
226 * potentially long delay.
228 * \section asyncabstraction Transfer abstraction
230 * For the asynchronous I/O, libusbx implements the concept of a generic
231 * transfer entity for all types of I/O (control, bulk, interrupt,
232 * isochronous). The generic transfer object must be treated slightly
233 * differently depending on which type of I/O you are performing with it.
235 * This is represented by the public libusb_transfer structure type.
237 * \section asynctrf Asynchronous transfers
239 * We can view asynchronous I/O as a 5 step process:
240 * -# <b>Allocation</b>: allocate a libusb_transfer
241 * -# <b>Filling</b>: populate the libusb_transfer instance with information
242 * about the transfer you wish to perform
243 * -# <b>Submission</b>: ask libusbx to submit the transfer
244 * -# <b>Completion handling</b>: examine transfer results in the
245 * libusb_transfer structure
246 * -# <b>Deallocation</b>: clean up resources
249 * \subsection asyncalloc Allocation
251 * This step involves allocating memory for a USB transfer. This is the
252 * generic transfer object mentioned above. At this stage, the transfer
253 * is "blank" with no details about what type of I/O it will be used for.
255 * Allocation is done with the libusb_alloc_transfer() function. You must use
256 * this function rather than allocating your own transfers.
258 * \subsection asyncfill Filling
260 * This step is where you take a previously allocated transfer and fill it
261 * with information to determine the message type and direction, data buffer,
262 * callback function, etc.
264 * You can either fill the required fields yourself or you can use the
265 * helper functions: libusb_fill_control_transfer(), libusb_fill_bulk_transfer()
266 * and libusb_fill_interrupt_transfer().
268 * \subsection asyncsubmit Submission
270 * When you have allocated a transfer and filled it, you can submit it using
271 * libusb_submit_transfer(). This function returns immediately but can be
272 * regarded as firing off the I/O request in the background.
274 * \subsection asynccomplete Completion handling
276 * After a transfer has been submitted, one of four things can happen to it:
278 * - The transfer completes (i.e. some data was transferred)
279 * - The transfer has a timeout and the timeout expires before all data is
281 * - The transfer fails due to an error
282 * - The transfer is cancelled
284 * Each of these will cause the user-specified transfer callback function to
285 * be invoked. It is up to the callback function to determine which of the
286 * above actually happened and to act accordingly.
288 * The user-specified callback is passed a pointer to the libusb_transfer
289 * structure which was used to setup and submit the transfer. At completion
290 * time, libusbx has populated this structure with results of the transfer:
291 * success or failure reason, number of bytes of data transferred, etc. See
292 * the libusb_transfer structure documentation for more information.
294 * \subsection Deallocation
296 * When a transfer has completed (i.e. the callback function has been invoked),
297 * you are advised to free the transfer (unless you wish to resubmit it, see
298 * below). Transfers are deallocated with libusb_free_transfer().
300 * It is undefined behaviour to free a transfer which has not completed.
302 * \section asyncresubmit Resubmission
304 * You may be wondering why allocation, filling, and submission are all
305 * separated above where they could reasonably be combined into a single
308 * The reason for separation is to allow you to resubmit transfers without
309 * having to allocate new ones every time. This is especially useful for
310 * common situations dealing with interrupt endpoints - you allocate one
311 * transfer, fill and submit it, and when it returns with results you just
312 * resubmit it for the next interrupt.
314 * \section asynccancel Cancellation
316 * Another advantage of using the asynchronous interface is that you have
317 * the ability to cancel transfers which have not yet completed. This is
318 * done by calling the libusb_cancel_transfer() function.
320 * libusb_cancel_transfer() is asynchronous/non-blocking in itself. When the
321 * cancellation actually completes, the transfer's callback function will
322 * be invoked, and the callback function should check the transfer status to
323 * determine that it was cancelled.
325 * Freeing the transfer after it has been cancelled but before cancellation
326 * has completed will result in undefined behaviour.
328 * When a transfer is cancelled, some of the data may have been transferred.
329 * libusbx will communicate this to you in the transfer callback. Do not assume
330 * that no data was transferred.
332 * \section bulk_overflows Overflows on device-to-host bulk/interrupt endpoints
334 * If your device does not have predictable transfer sizes (or it misbehaves),
335 * your application may submit a request for data on an IN endpoint which is
336 * smaller than the data that the device wishes to send. In some circumstances
337 * this will cause an overflow, which is a nasty condition to deal with. See
338 * the \ref packetoverflow page for discussion.
340 * \section asyncctrl Considerations for control transfers
342 * The <tt>libusb_transfer</tt> structure is generic and hence does not
343 * include specific fields for the control-specific setup packet structure.
345 * In order to perform a control transfer, you must place the 8-byte setup
346 * packet at the start of the data buffer. To simplify this, you could
347 * cast the buffer pointer to type struct libusb_control_setup, or you can
348 * use the helper function libusb_fill_control_setup().
350 * The wLength field placed in the setup packet must be the length you would
351 * expect to be sent in the setup packet: the length of the payload that
352 * follows (or the expected maximum number of bytes to receive). However,
353 * the length field of the libusb_transfer object must be the length of
354 * the data buffer - i.e. it should be wLength <em>plus</em> the size of
355 * the setup packet (LIBUSB_CONTROL_SETUP_SIZE).
357 * If you use the helper functions, this is simplified for you:
358 * -# Allocate a buffer of size LIBUSB_CONTROL_SETUP_SIZE plus the size of the
359 * data you are sending/requesting.
360 * -# Call libusb_fill_control_setup() on the data buffer, using the transfer
361 * request size as the wLength value (i.e. do not include the extra space you
362 * allocated for the control setup).
363 * -# If this is a host-to-device transfer, place the data to be transferred
364 * in the data buffer, starting at offset LIBUSB_CONTROL_SETUP_SIZE.
365 * -# Call libusb_fill_control_transfer() to associate the data buffer with
366 * the transfer (and to set the remaining details such as callback and timeout).
367 * - Note that there is no parameter to set the length field of the transfer.
368 * The length is automatically inferred from the wLength field of the setup
370 * -# Submit the transfer.
372 * The multi-byte control setup fields (wValue, wIndex and wLength) must
373 * be given in little-endian byte order (the endianness of the USB bus).
374 * Endianness conversion is transparently handled by
375 * libusb_fill_control_setup() which is documented to accept host-endian
378 * Further considerations are needed when handling transfer completion in
379 * your callback function:
380 * - As you might expect, the setup packet will still be sitting at the start
381 * of the data buffer.
382 * - If this was a device-to-host transfer, the received data will be sitting
383 * at offset LIBUSB_CONTROL_SETUP_SIZE into the buffer.
384 * - The actual_length field of the transfer structure is relative to the
385 * wLength of the setup packet, rather than the size of the data buffer. So,
386 * if your wLength was 4, your transfer's <tt>length</tt> was 12, then you
387 * should expect an <tt>actual_length</tt> of 4 to indicate that the data was
388 * transferred in entirity.
390 * To simplify parsing of setup packets and obtaining the data from the
391 * correct offset, you may wish to use the libusb_control_transfer_get_data()
392 * and libusb_control_transfer_get_setup() functions within your transfer
395 * Even though control endpoints do not halt, a completed control transfer
396 * may have a LIBUSB_TRANSFER_STALL status code. This indicates the control
397 * request was not supported.
399 * \section asyncintr Considerations for interrupt transfers
401 * All interrupt transfers are performed using the polling interval presented
402 * by the bInterval value of the endpoint descriptor.
404 * \section asynciso Considerations for isochronous transfers
406 * Isochronous transfers are more complicated than transfers to
407 * non-isochronous endpoints.
409 * To perform I/O to an isochronous endpoint, allocate the transfer by calling
410 * libusb_alloc_transfer() with an appropriate number of isochronous packets.
412 * During filling, set \ref libusb_transfer::type "type" to
413 * \ref libusb_transfer_type::LIBUSB_TRANSFER_TYPE_ISOCHRONOUS
414 * "LIBUSB_TRANSFER_TYPE_ISOCHRONOUS", and set
415 * \ref libusb_transfer::num_iso_packets "num_iso_packets" to a value less than
416 * or equal to the number of packets you requested during allocation.
417 * libusb_alloc_transfer() does not set either of these fields for you, given
418 * that you might not even use the transfer on an isochronous endpoint.
420 * Next, populate the length field for the first num_iso_packets entries in
421 * the \ref libusb_transfer::iso_packet_desc "iso_packet_desc" array. Section
422 * 5.6.3 of the USB2 specifications describe how the maximum isochronous
423 * packet length is determined by the wMaxPacketSize field in the endpoint
425 * Two functions can help you here:
427 * - libusb_get_max_iso_packet_size() is an easy way to determine the max
428 * packet size for an isochronous endpoint. Note that the maximum packet
429 * size is actually the maximum number of bytes that can be transmitted in
430 * a single microframe, therefore this function multiplies the maximum number
431 * of bytes per transaction by the number of transaction opportunities per
433 * - libusb_set_iso_packet_lengths() assigns the same length to all packets
434 * within a transfer, which is usually what you want.
436 * For outgoing transfers, you'll obviously fill the buffer and populate the
437 * packet descriptors in hope that all the data gets transferred. For incoming
438 * transfers, you must ensure the buffer has sufficient capacity for
439 * the situation where all packets transfer the full amount of requested data.
441 * Completion handling requires some extra consideration. The
442 * \ref libusb_transfer::actual_length "actual_length" field of the transfer
443 * is meaningless and should not be examined; instead you must refer to the
444 * \ref libusb_iso_packet_descriptor::actual_length "actual_length" field of
445 * each individual packet.
447 * The \ref libusb_transfer::status "status" field of the transfer is also a
449 * - If the packets were submitted and the isochronous data microframes
450 * completed normally, status will have value
451 * \ref libusb_transfer_status::LIBUSB_TRANSFER_COMPLETED
452 * "LIBUSB_TRANSFER_COMPLETED". Note that bus errors and software-incurred
453 * delays are not counted as transfer errors; the transfer.status field may
454 * indicate COMPLETED even if some or all of the packets failed. Refer to
455 * the \ref libusb_iso_packet_descriptor::status "status" field of each
456 * individual packet to determine packet failures.
457 * - The status field will have value
458 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR
459 * "LIBUSB_TRANSFER_ERROR" only when serious errors were encountered.
460 * - Other transfer status codes occur with normal behaviour.
462 * The data for each packet will be found at an offset into the buffer that
463 * can be calculated as if each prior packet completed in full. The
464 * libusb_get_iso_packet_buffer() and libusb_get_iso_packet_buffer_simple()
465 * functions may help you here.
467 * \section asyncmem Memory caveats
469 * In most circumstances, it is not safe to use stack memory for transfer
470 * buffers. This is because the function that fired off the asynchronous
471 * transfer may return before libusbx has finished using the buffer, and when
472 * the function returns it's stack gets destroyed. This is true for both
473 * host-to-device and device-to-host transfers.
475 * The only case in which it is safe to use stack memory is where you can
476 * guarantee that the function owning the stack space for the buffer does not
477 * return until after the transfer's callback function has completed. In every
478 * other case, you need to use heap memory instead.
480 * \section asyncflags Fine control
482 * Through using this asynchronous interface, you may find yourself repeating
483 * a few simple operations many times. You can apply a bitwise OR of certain
484 * flags to a transfer to simplify certain things:
485 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_SHORT_NOT_OK
486 * "LIBUSB_TRANSFER_SHORT_NOT_OK" results in transfers which transferred
487 * less than the requested amount of data being marked with status
488 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR "LIBUSB_TRANSFER_ERROR"
489 * (they would normally be regarded as COMPLETED)
490 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
491 * "LIBUSB_TRANSFER_FREE_BUFFER" allows you to ask libusbx to free the transfer
492 * buffer when freeing the transfer.
493 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_TRANSFER
494 * "LIBUSB_TRANSFER_FREE_TRANSFER" causes libusbx to automatically free the
495 * transfer after the transfer callback returns.
497 * \section asyncevent Event handling
499 * An asynchronous model requires that libusbx perform work at various
500 * points in time - namely processing the results of previously-submitted
501 * transfers and invoking the user-supplied callback function.
503 * This gives rise to the libusb_handle_events() function which your
504 * application must call into when libusbx has work do to. This gives libusbx
505 * the opportunity to reap pending transfers, invoke callbacks, etc.
507 * There are 2 different approaches to dealing with libusb_handle_events:
509 * -# Repeatedly call libusb_handle_events() in blocking mode from a dedicated
511 * -# Integrate libusbx with your application's main event loop. libusbx
512 * exposes a set of file descriptors which allow you to do this.
514 * The first approach has the big advantage that it will also work on Windows
515 * were libusbx' poll API for select / poll integration is not available. So
516 * if you want to support Windows and use the async API, you must use this
519 * If you prefer a single threaded approach with a single central event loop,
520 * see the \ref poll "polling and timing" section for how to integrate libusbx
521 * into your application's main event loop.
525 * @defgroup poll Polling and timing
527 * This page documents libusbx's functions for polling events and timing.
528 * These functions are only necessary for users of the
529 * \ref asyncio "asynchronous API". If you are only using the simpler
530 * \ref syncio "synchronous API" then you do not need to ever call these
533 * The justification for the functionality described here has already been
534 * discussed in the \ref asyncevent "event handling" section of the
535 * asynchronous API documentation. In summary, libusbx does not create internal
536 * threads for event processing and hence relies on your application calling
537 * into libusbx at certain points in time so that pending events can be handled.
539 * Your main loop is probably already calling poll() or select() or a
540 * variant on a set of file descriptors for other event sources (e.g. keyboard
541 * button presses, mouse movements, network sockets, etc). You then add
542 * libusbx's file descriptors to your poll()/select() calls, and when activity
543 * is detected on such descriptors you know it is time to call
544 * libusb_handle_events().
546 * There is one final event handling complication. libusbx supports
547 * asynchronous transfers which time out after a specified time period.
549 * On some platforms a timerfd is used, so the timeout handling is just another
550 * fd, on other platforms this requires that libusbx is called into at or after
551 * the timeout to handle it. So, in addition to considering libusbx's file
552 * descriptors in your main event loop, you must also consider that libusbx
553 * sometimes needs to be called into at fixed points in time even when there
554 * is no file descriptor activity, see \ref polltime details.
556 * In order to know precisely when libusbx needs to be called into, libusbx
557 * offers you a set of pollable file descriptors and information about when
558 * the next timeout expires.
560 * If you are using the asynchronous I/O API, you must take one of the two
561 * following options, otherwise your I/O will not complete.
563 * \section pollsimple The simple option
565 * If your application revolves solely around libusbx and does not need to
566 * handle other event sources, you can have a program structure as follows:
568 // initialize libusbx
569 // find and open device
570 // maybe fire off some initial async I/O
572 while (user_has_not_requested_exit)
573 libusb_handle_events(ctx);
578 * With such a simple main loop, you do not have to worry about managing
579 * sets of file descriptors or handling timeouts. libusb_handle_events() will
580 * handle those details internally.
582 * \section pollmain The more advanced option
584 * \note This functionality is currently only available on Unix-like platforms.
585 * On Windows, libusb_get_pollfds() simply returns NULL. Exposing event sources
586 * on Windows will require some further thought and design.
588 * In more advanced applications, you will already have a main loop which
589 * is monitoring other event sources: network sockets, X11 events, mouse
590 * movements, etc. Through exposing a set of file descriptors, libusbx is
591 * designed to cleanly integrate into such main loops.
593 * In addition to polling file descriptors for the other event sources, you
594 * take a set of file descriptors from libusbx and monitor those too. When you
595 * detect activity on libusbx's file descriptors, you call
596 * libusb_handle_events_timeout() in non-blocking mode.
598 * What's more, libusbx may also need to handle events at specific moments in
599 * time. No file descriptor activity is generated at these times, so your
600 * own application needs to be continually aware of when the next one of these
601 * moments occurs (through calling libusb_get_next_timeout()), and then it
602 * needs to call libusb_handle_events_timeout() in non-blocking mode when
603 * these moments occur. This means that you need to adjust your
604 * poll()/select() timeout accordingly.
606 * libusbx provides you with a set of file descriptors to poll and expects you
607 * to poll all of them, treating them as a single entity. The meaning of each
608 * file descriptor in the set is an internal implementation detail,
609 * platform-dependent and may vary from release to release. Don't try and
610 * interpret the meaning of the file descriptors, just do as libusbx indicates,
611 * polling all of them at once.
613 * In pseudo-code, you want something that looks like:
615 // initialise libusbx
617 libusb_get_pollfds(ctx)
618 while (user has not requested application exit) {
619 libusb_get_next_timeout(ctx);
620 poll(on libusbx file descriptors plus any other event sources of interest,
621 using a timeout no larger than the value libusbx just suggested)
622 if (poll() indicated activity on libusbx file descriptors)
623 libusb_handle_events_timeout(ctx, &zero_tv);
624 if (time has elapsed to or beyond the libusbx timeout)
625 libusb_handle_events_timeout(ctx, &zero_tv);
626 // handle events from other sources here
632 * \subsection polltime Notes on time-based events
634 * The above complication with having to track time and call into libusbx at
635 * specific moments is a bit of a headache. For maximum compatibility, you do
636 * need to write your main loop as above, but you may decide that you can
637 * restrict the supported platforms of your application and get away with
638 * a more simplistic scheme.
640 * These time-based event complications are \b not required on the following
643 * - Linux, provided that the following version requirements are satisfied:
644 * - Linux v2.6.27 or newer, compiled with timerfd support
645 * - glibc v2.9 or newer
646 * - libusbx v1.0.5 or newer
648 * Under these configurations, libusb_get_next_timeout() will \em always return
649 * 0, so your main loop can be simplified to:
651 // initialise libusbx
653 libusb_get_pollfds(ctx)
654 while (user has not requested application exit) {
655 poll(on libusbx file descriptors plus any other event sources of interest,
656 using any timeout that you like)
657 if (poll() indicated activity on libusbx file descriptors)
658 libusb_handle_events_timeout(ctx, &zero_tv);
659 // handle events from other sources here
665 * Do remember that if you simplify your main loop to the above, you will
666 * lose compatibility with some platforms (including legacy Linux platforms,
667 * and <em>any future platforms supported by libusbx which may have time-based
668 * event requirements</em>). The resultant problems will likely appear as
669 * strange bugs in your application.
671 * You can use the libusb_pollfds_handle_timeouts() function to do a runtime
672 * check to see if it is safe to ignore the time-based event complications.
673 * If your application has taken the shortcut of ignoring libusbx's next timeout
674 * in your main loop, then you are advised to check the return value of
675 * libusb_pollfds_handle_timeouts() during application startup, and to abort
676 * if the platform does suffer from these timing complications.
678 * \subsection fdsetchange Changes in the file descriptor set
680 * The set of file descriptors that libusbx uses as event sources may change
681 * during the life of your application. Rather than having to repeatedly
682 * call libusb_get_pollfds(), you can set up notification functions for when
683 * the file descriptor set changes using libusb_set_pollfd_notifiers().
685 * \subsection mtissues Multi-threaded considerations
687 * Unfortunately, the situation is complicated further when multiple threads
688 * come into play. If two threads are monitoring the same file descriptors,
689 * the fact that only one thread will be woken up when an event occurs causes
692 * The events lock, event waiters lock, and libusb_handle_events_locked()
693 * entities are added to solve these problems. You do not need to be concerned
694 * with these entities otherwise.
696 * See the extra documentation: \ref mtasync
699 /** \page mtasync Multi-threaded applications and asynchronous I/O
701 * libusbx is a thread-safe library, but extra considerations must be applied
702 * to applications which interact with libusbx from multiple threads.
704 * The underlying issue that must be addressed is that all libusbx I/O
705 * revolves around monitoring file descriptors through the poll()/select()
706 * system calls. This is directly exposed at the
707 * \ref asyncio "asynchronous interface" but it is important to note that the
708 * \ref syncio "synchronous interface" is implemented on top of the
709 * asynchonrous interface, therefore the same considerations apply.
711 * The issue is that if two or more threads are concurrently calling poll()
712 * or select() on libusbx's file descriptors then only one of those threads
713 * will be woken up when an event arrives. The others will be completely
714 * oblivious that anything has happened.
716 * Consider the following pseudo-code, which submits an asynchronous transfer
717 * then waits for its completion. This style is one way you could implement a
718 * synchronous interface on top of the asynchronous interface (and libusbx
719 * does something similar, albeit more advanced due to the complications
720 * explained on this page).
723 void cb(struct libusb_transfer *transfer)
725 int *completed = transfer->user_data;
730 struct libusb_transfer *transfer;
731 unsigned char buffer[LIBUSB_CONTROL_SETUP_SIZE];
734 transfer = libusb_alloc_transfer(0);
735 libusb_fill_control_setup(buffer,
736 LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_OUT, 0x04, 0x01, 0, 0);
737 libusb_fill_control_transfer(transfer, dev, buffer, cb, &completed, 1000);
738 libusb_submit_transfer(transfer);
741 poll(libusbx file descriptors, 120*1000);
742 if (poll indicates activity)
743 libusb_handle_events_timeout(ctx, &zero_tv);
745 printf("completed!");
750 * Here we are <em>serializing</em> completion of an asynchronous event
751 * against a condition - the condition being completion of a specific transfer.
752 * The poll() loop has a long timeout to minimize CPU usage during situations
753 * when nothing is happening (it could reasonably be unlimited).
755 * If this is the only thread that is polling libusbx's file descriptors, there
756 * is no problem: there is no danger that another thread will swallow up the
757 * event that we are interested in. On the other hand, if there is another
758 * thread polling the same descriptors, there is a chance that it will receive
759 * the event that we were interested in. In this situation, <tt>myfunc()</tt>
760 * will only realise that the transfer has completed on the next iteration of
761 * the loop, <em>up to 120 seconds later.</em> Clearly a two-minute delay is
762 * undesirable, and don't even think about using short timeouts to circumvent
765 * The solution here is to ensure that no two threads are ever polling the
766 * file descriptors at the same time. A naive implementation of this would
767 * impact the capabilities of the library, so libusbx offers the scheme
768 * documented below to ensure no loss of functionality.
770 * Before we go any further, it is worth mentioning that all libusb-wrapped
771 * event handling procedures fully adhere to the scheme documented below.
772 * This includes libusb_handle_events() and its variants, and all the
773 * synchronous I/O functions - libusbx hides this headache from you.
775 * \section Using libusb_handle_events() from multiple threads
777 * Even when only using libusb_handle_events() and synchronous I/O functions,
778 * you can still have a race condition. You might be tempted to solve the
779 * above with libusb_handle_events() like so:
782 libusb_submit_transfer(transfer);
785 libusb_handle_events(ctx);
787 printf("completed!");
790 * This however has a race between the checking of completed and
791 * libusb_handle_events() acquiring the events lock, so another thread
792 * could have completed the transfer, resulting in this thread hanging
793 * until either a timeout or another event occurs. See also commit
794 * 6696512aade99bb15d6792af90ae329af270eba6 which fixes this in the
795 * synchronous API implementation of libusb.
797 * Fixing this race requires checking the variable completed only after
798 * taking the event lock, which defeats the concept of just calling
799 * libusb_handle_events() without worrying about locking. This is why
800 * libusb-1.0.9 introduces the new libusb_handle_events_timeout_completed()
801 * and libusb_handle_events_completed() functions, which handles doing the
802 * completion check for you after they have acquired the lock:
805 libusb_submit_transfer(transfer);
808 libusb_handle_events_completed(ctx, &completed);
810 printf("completed!");
813 * This nicely fixes the race in our example. Note that if all you want to
814 * do is submit a single transfer and wait for its completion, then using
815 * one of the synchronous I/O functions is much easier.
817 * \section eventlock The events lock
819 * The problem is when we consider the fact that libusbx exposes file
820 * descriptors to allow for you to integrate asynchronous USB I/O into
821 * existing main loops, effectively allowing you to do some work behind
822 * libusbx's back. If you do take libusbx's file descriptors and pass them to
823 * poll()/select() yourself, you need to be aware of the associated issues.
825 * The first concept to be introduced is the events lock. The events lock
826 * is used to serialize threads that want to handle events, such that only
827 * one thread is handling events at any one time.
829 * You must take the events lock before polling libusbx file descriptors,
830 * using libusb_lock_events(). You must release the lock as soon as you have
831 * aborted your poll()/select() loop, using libusb_unlock_events().
833 * \section threadwait Letting other threads do the work for you
835 * Although the events lock is a critical part of the solution, it is not
836 * enough on it's own. You might wonder if the following is sufficient...
838 libusb_lock_events(ctx);
840 poll(libusbx file descriptors, 120*1000);
841 if (poll indicates activity)
842 libusb_handle_events_timeout(ctx, &zero_tv);
844 libusb_unlock_events(ctx);
846 * ...and the answer is that it is not. This is because the transfer in the
847 * code shown above may take a long time (say 30 seconds) to complete, and
848 * the lock is not released until the transfer is completed.
850 * Another thread with similar code that wants to do event handling may be
851 * working with a transfer that completes after a few milliseconds. Despite
852 * having such a quick completion time, the other thread cannot check that
853 * status of its transfer until the code above has finished (30 seconds later)
854 * due to contention on the lock.
856 * To solve this, libusbx offers you a mechanism to determine when another
857 * thread is handling events. It also offers a mechanism to block your thread
858 * until the event handling thread has completed an event (and this mechanism
859 * does not involve polling of file descriptors).
861 * After determining that another thread is currently handling events, you
862 * obtain the <em>event waiters</em> lock using libusb_lock_event_waiters().
863 * You then re-check that some other thread is still handling events, and if
864 * so, you call libusb_wait_for_event().
866 * libusb_wait_for_event() puts your application to sleep until an event
867 * occurs, or until a thread releases the events lock. When either of these
868 * things happen, your thread is woken up, and should re-check the condition
869 * it was waiting on. It should also re-check that another thread is handling
870 * events, and if not, it should start handling events itself.
872 * This looks like the following, as pseudo-code:
875 if (libusb_try_lock_events(ctx) == 0) {
876 // we obtained the event lock: do our own event handling
878 if (!libusb_event_handling_ok(ctx)) {
879 libusb_unlock_events(ctx);
882 poll(libusbx file descriptors, 120*1000);
883 if (poll indicates activity)
884 libusb_handle_events_locked(ctx, 0);
886 libusb_unlock_events(ctx);
888 // another thread is doing event handling. wait for it to signal us that
889 // an event has completed
890 libusb_lock_event_waiters(ctx);
893 // now that we have the event waiters lock, double check that another
894 // thread is still handling events for us. (it may have ceased handling
895 // events in the time it took us to reach this point)
896 if (!libusb_event_handler_active(ctx)) {
897 // whoever was handling events is no longer doing so, try again
898 libusb_unlock_event_waiters(ctx);
902 libusb_wait_for_event(ctx, NULL);
904 libusb_unlock_event_waiters(ctx);
906 printf("completed!\n");
909 * A naive look at the above code may suggest that this can only support
910 * one event waiter (hence a total of 2 competing threads, the other doing
911 * event handling), because the event waiter seems to have taken the event
912 * waiters lock while waiting for an event. However, the system does support
913 * multiple event waiters, because libusb_wait_for_event() actually drops
914 * the lock while waiting, and reaquires it before continuing.
916 * We have now implemented code which can dynamically handle situations where
917 * nobody is handling events (so we should do it ourselves), and it can also
918 * handle situations where another thread is doing event handling (so we can
919 * piggyback onto them). It is also equipped to handle a combination of
920 * the two, for example, another thread is doing event handling, but for
921 * whatever reason it stops doing so before our condition is met, so we take
922 * over the event handling.
924 * Four functions were introduced in the above pseudo-code. Their importance
925 * should be apparent from the code shown above.
926 * -# libusb_try_lock_events() is a non-blocking function which attempts
927 * to acquire the events lock but returns a failure code if it is contended.
928 * -# libusb_event_handling_ok() checks that libusbx is still happy for your
929 * thread to be performing event handling. Sometimes, libusbx needs to
930 * interrupt the event handler, and this is how you can check if you have
931 * been interrupted. If this function returns 0, the correct behaviour is
932 * for you to give up the event handling lock, and then to repeat the cycle.
933 * The following libusb_try_lock_events() will fail, so you will become an
934 * events waiter. For more information on this, read \ref fullstory below.
935 * -# libusb_handle_events_locked() is a variant of
936 * libusb_handle_events_timeout() that you can call while holding the
937 * events lock. libusb_handle_events_timeout() itself implements similar
938 * logic to the above, so be sure not to call it when you are
939 * "working behind libusbx's back", as is the case here.
940 * -# libusb_event_handler_active() determines if someone is currently
941 * holding the events lock
943 * You might be wondering why there is no function to wake up all threads
944 * blocked on libusb_wait_for_event(). This is because libusbx can do this
945 * internally: it will wake up all such threads when someone calls
946 * libusb_unlock_events() or when a transfer completes (at the point after its
947 * callback has returned).
949 * \subsection fullstory The full story
951 * The above explanation should be enough to get you going, but if you're
952 * really thinking through the issues then you may be left with some more
953 * questions regarding libusbx's internals. If you're curious, read on, and if
954 * not, skip to the next section to avoid confusing yourself!
956 * The immediate question that may spring to mind is: what if one thread
957 * modifies the set of file descriptors that need to be polled while another
958 * thread is doing event handling?
960 * There are 2 situations in which this may happen.
961 * -# libusb_open() will add another file descriptor to the poll set,
962 * therefore it is desirable to interrupt the event handler so that it
963 * restarts, picking up the new descriptor.
964 * -# libusb_close() will remove a file descriptor from the poll set. There
965 * are all kinds of race conditions that could arise here, so it is
966 * important that nobody is doing event handling at this time.
968 * libusbx handles these issues internally, so application developers do not
969 * have to stop their event handlers while opening/closing devices. Here's how
970 * it works, focusing on the libusb_close() situation first:
972 * -# During initialization, libusbx opens an internal pipe, and it adds the read
973 * end of this pipe to the set of file descriptors to be polled.
974 * -# During libusb_close(), libusbx writes some dummy data on this control pipe.
975 * This immediately interrupts the event handler. libusbx also records
976 * internally that it is trying to interrupt event handlers for this
977 * high-priority event.
978 * -# At this point, some of the functions described above start behaving
980 * - libusb_event_handling_ok() starts returning 1, indicating that it is NOT
981 * OK for event handling to continue.
982 * - libusb_try_lock_events() starts returning 1, indicating that another
983 * thread holds the event handling lock, even if the lock is uncontended.
984 * - libusb_event_handler_active() starts returning 1, indicating that
985 * another thread is doing event handling, even if that is not true.
986 * -# The above changes in behaviour result in the event handler stopping and
987 * giving up the events lock very quickly, giving the high-priority
988 * libusb_close() operation a "free ride" to acquire the events lock. All
989 * threads that are competing to do event handling become event waiters.
990 * -# With the events lock held inside libusb_close(), libusbx can safely remove
991 * a file descriptor from the poll set, in the safety of knowledge that
992 * nobody is polling those descriptors or trying to access the poll set.
993 * -# After obtaining the events lock, the close operation completes very
994 * quickly (usually a matter of milliseconds) and then immediately releases
996 * -# At the same time, the behaviour of libusb_event_handling_ok() and friends
997 * reverts to the original, documented behaviour.
998 * -# The release of the events lock causes the threads that are waiting for
999 * events to be woken up and to start competing to become event handlers
1000 * again. One of them will succeed; it will then re-obtain the list of poll
1001 * descriptors, and USB I/O will then continue as normal.
1003 * libusb_open() is similar, and is actually a more simplistic case. Upon a
1004 * call to libusb_open():
1006 * -# The device is opened and a file descriptor is added to the poll set.
1007 * -# libusbx sends some dummy data on the control pipe, and records that it
1008 * is trying to modify the poll descriptor set.
1009 * -# The event handler is interrupted, and the same behaviour change as for
1010 * libusb_close() takes effect, causing all event handling threads to become
1012 * -# The libusb_open() implementation takes its free ride to the events lock.
1013 * -# Happy that it has successfully paused the events handler, libusb_open()
1014 * releases the events lock.
1015 * -# The event waiter threads are all woken up and compete to become event
1016 * handlers again. The one that succeeds will obtain the list of poll
1017 * descriptors again, which will include the addition of the new device.
1019 * \subsection concl Closing remarks
1021 * The above may seem a little complicated, but hopefully I have made it clear
1022 * why such complications are necessary. Also, do not forget that this only
1023 * applies to applications that take libusbx's file descriptors and integrate
1024 * them into their own polling loops.
1026 * You may decide that it is OK for your multi-threaded application to ignore
1027 * some of the rules and locks detailed above, because you don't think that
1028 * two threads can ever be polling the descriptors at the same time. If that
1029 * is the case, then that's good news for you because you don't have to worry.
1030 * But be careful here; remember that the synchronous I/O functions do event
1031 * handling internally. If you have one thread doing event handling in a loop
1032 * (without implementing the rules and locking semantics documented above)
1033 * and another trying to send a synchronous USB transfer, you will end up with
1034 * two threads monitoring the same descriptors, and the above-described
1035 * undesirable behaviour occuring. The solution is for your polling thread to
1036 * play by the rules; the synchronous I/O functions do so, and this will result
1037 * in them getting along in perfect harmony.
1039 * If you do have a dedicated thread doing event handling, it is perfectly
1040 * legal for it to take the event handling lock for long periods of time. Any
1041 * synchronous I/O functions you call from other threads will transparently
1042 * fall back to the "event waiters" mechanism detailed above. The only
1043 * consideration that your event handling thread must apply is the one related
1044 * to libusb_event_handling_ok(): you must call this before every poll(), and
1045 * give up the events lock if instructed.
1048 int usbi_io_init(struct libusb_context *ctx)
1052 usbi_mutex_init(&ctx->flying_transfers_lock, NULL);
1053 usbi_mutex_init(&ctx->pollfds_lock, NULL);
1054 usbi_mutex_init(&ctx->pollfd_modify_lock, NULL);
1055 usbi_mutex_init_recursive(&ctx->events_lock, NULL);
1056 usbi_mutex_init(&ctx->event_waiters_lock, NULL);
1057 usbi_cond_init(&ctx->event_waiters_cond, NULL);
1058 list_init(&ctx->flying_transfers);
1059 list_init(&ctx->pollfds);
1061 /* FIXME should use an eventfd on kernels that support it */
1062 r = usbi_pipe(ctx->ctrl_pipe);
1064 r = LIBUSB_ERROR_OTHER;
1068 r = usbi_add_pollfd(ctx, ctx->ctrl_pipe[0], POLLIN);
1070 goto err_close_pipe;
1072 /* create hotplug pipe */
1073 r = usbi_pipe(ctx->hotplug_pipe);
1075 r = LIBUSB_ERROR_OTHER;
1079 r = usbi_add_pollfd(ctx, ctx->hotplug_pipe[0], POLLIN);
1081 goto err_close_hp_pipe;
1083 #ifdef USBI_TIMERFD_AVAILABLE
1084 ctx->timerfd = timerfd_create(usbi_backend->get_timerfd_clockid(),
1086 if (ctx->timerfd >= 0) {
1087 usbi_dbg("using timerfd for timeouts");
1088 r = usbi_add_pollfd(ctx, ctx->timerfd, POLLIN);
1090 usbi_remove_pollfd(ctx, ctx->ctrl_pipe[0]);
1091 close(ctx->timerfd);
1092 goto err_close_hp_pipe;
1095 usbi_dbg("timerfd not available (code %d error %d)", ctx->timerfd, errno);
1103 usbi_close(ctx->hotplug_pipe[0]);
1104 usbi_close(ctx->hotplug_pipe[1]);
1106 usbi_close(ctx->ctrl_pipe[0]);
1107 usbi_close(ctx->ctrl_pipe[1]);
1109 usbi_mutex_destroy(&ctx->flying_transfers_lock);
1110 usbi_mutex_destroy(&ctx->pollfds_lock);
1111 usbi_mutex_destroy(&ctx->pollfd_modify_lock);
1112 usbi_mutex_destroy(&ctx->events_lock);
1113 usbi_mutex_destroy(&ctx->event_waiters_lock);
1114 usbi_cond_destroy(&ctx->event_waiters_cond);
1118 void usbi_io_exit(struct libusb_context *ctx)
1120 usbi_remove_pollfd(ctx, ctx->ctrl_pipe[0]);
1121 usbi_close(ctx->ctrl_pipe[0]);
1122 usbi_close(ctx->ctrl_pipe[1]);
1123 usbi_remove_pollfd(ctx, ctx->hotplug_pipe[0]);
1124 usbi_close(ctx->hotplug_pipe[0]);
1125 usbi_close(ctx->hotplug_pipe[1]);
1126 #ifdef USBI_TIMERFD_AVAILABLE
1127 if (usbi_using_timerfd(ctx)) {
1128 usbi_remove_pollfd(ctx, ctx->timerfd);
1129 close(ctx->timerfd);
1132 usbi_mutex_destroy(&ctx->flying_transfers_lock);
1133 usbi_mutex_destroy(&ctx->pollfds_lock);
1134 usbi_mutex_destroy(&ctx->pollfd_modify_lock);
1135 usbi_mutex_destroy(&ctx->events_lock);
1136 usbi_mutex_destroy(&ctx->event_waiters_lock);
1137 usbi_cond_destroy(&ctx->event_waiters_cond);
1140 static int calculate_timeout(struct usbi_transfer *transfer)
1143 struct timespec current_time;
1144 unsigned int timeout =
1145 USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout;
1150 r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, ¤t_time);
1152 usbi_err(ITRANSFER_CTX(transfer),
1153 "failed to read monotonic clock, errno=%d", errno);
1157 current_time.tv_sec += timeout / 1000;
1158 current_time.tv_nsec += (timeout % 1000) * 1000000;
1160 while (current_time.tv_nsec >= 1000000000) {
1161 current_time.tv_nsec -= 1000000000;
1162 current_time.tv_sec++;
1165 TIMESPEC_TO_TIMEVAL(&transfer->timeout, ¤t_time);
1169 /* add a transfer to the (timeout-sorted) active transfers list.
1170 * Callers of this function must hold the flying_transfers_lock.
1171 * This function *always* adds the transfer to the flying_transfers list,
1172 * it will return non 0 if it fails to update the timer, but even then the
1173 * transfer is added to the flying_transfers list. */
1174 static int add_to_flying_list(struct usbi_transfer *transfer)
1176 struct usbi_transfer *cur;
1177 struct timeval *timeout = &transfer->timeout;
1178 struct libusb_context *ctx = ITRANSFER_CTX(transfer);
1182 /* if we have no other flying transfers, start the list with this one */
1183 if (list_empty(&ctx->flying_transfers)) {
1184 list_add(&transfer->list, &ctx->flying_transfers);
1188 /* if we have infinite timeout, append to end of list */
1189 if (!timerisset(timeout)) {
1190 list_add_tail(&transfer->list, &ctx->flying_transfers);
1191 /* first is irrelevant in this case */
1195 /* otherwise, find appropriate place in list */
1196 list_for_each_entry(cur, &ctx->flying_transfers, list, struct usbi_transfer) {
1197 /* find first timeout that occurs after the transfer in question */
1198 struct timeval *cur_tv = &cur->timeout;
1200 if (!timerisset(cur_tv) || (cur_tv->tv_sec > timeout->tv_sec) ||
1201 (cur_tv->tv_sec == timeout->tv_sec &&
1202 cur_tv->tv_usec > timeout->tv_usec)) {
1203 list_add_tail(&transfer->list, &cur->list);
1208 /* first is 0 at this stage (list not empty) */
1210 /* otherwise we need to be inserted at the end */
1211 list_add_tail(&transfer->list, &ctx->flying_transfers);
1213 #ifdef USBI_TIMERFD_AVAILABLE
1214 if (first && usbi_using_timerfd(ctx) && timerisset(timeout)) {
1215 /* if this transfer has the lowest timeout of all active transfers,
1216 * rearm the timerfd with this transfer's timeout */
1217 const struct itimerspec it = { {0, 0},
1218 { timeout->tv_sec, timeout->tv_usec * 1000 } };
1219 usbi_dbg("arm timerfd for timeout in %dms (first in line)",
1220 USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout);
1221 r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
1223 usbi_warn(ctx, "failed to arm first timerfd (errno %d)", errno);
1224 r = LIBUSB_ERROR_OTHER;
1234 /** \ingroup asyncio
1235 * Allocate a libusbx transfer with a specified number of isochronous packet
1236 * descriptors. The returned transfer is pre-initialized for you. When the new
1237 * transfer is no longer needed, it should be freed with
1238 * libusb_free_transfer().
1240 * Transfers intended for non-isochronous endpoints (e.g. control, bulk,
1241 * interrupt) should specify an iso_packets count of zero.
1243 * For transfers intended for isochronous endpoints, specify an appropriate
1244 * number of packet descriptors to be allocated as part of the transfer.
1245 * The returned transfer is not specially initialized for isochronous I/O;
1246 * you are still required to set the
1247 * \ref libusb_transfer::num_iso_packets "num_iso_packets" and
1248 * \ref libusb_transfer::type "type" fields accordingly.
1250 * It is safe to allocate a transfer with some isochronous packets and then
1251 * use it on a non-isochronous endpoint. If you do this, ensure that at time
1252 * of submission, num_iso_packets is 0 and that type is set appropriately.
1254 * \param iso_packets number of isochronous packet descriptors to allocate
1255 * \returns a newly allocated transfer, or NULL on error
1258 struct libusb_transfer * LIBUSB_CALL libusb_alloc_transfer(
1261 size_t os_alloc_size = usbi_backend->transfer_priv_size
1262 + (usbi_backend->add_iso_packet_size * iso_packets);
1263 size_t alloc_size = sizeof(struct usbi_transfer)
1264 + sizeof(struct libusb_transfer)
1265 + (sizeof(struct libusb_iso_packet_descriptor) * iso_packets)
1267 struct usbi_transfer *itransfer = calloc(1, alloc_size);
1271 itransfer->num_iso_packets = iso_packets;
1272 usbi_mutex_init(&itransfer->lock, NULL);
1273 return USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1276 /** \ingroup asyncio
1277 * Free a transfer structure. This should be called for all transfers
1278 * allocated with libusb_alloc_transfer().
1280 * If the \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
1281 * "LIBUSB_TRANSFER_FREE_BUFFER" flag is set and the transfer buffer is
1282 * non-NULL, this function will also free the transfer buffer using the
1283 * standard system memory allocator (e.g. free()).
1285 * It is legal to call this function with a NULL transfer. In this case,
1286 * the function will simply return safely.
1288 * It is not legal to free an active transfer (one which has been submitted
1289 * and has not yet completed).
1291 * \param transfer the transfer to free
1293 void API_EXPORTED libusb_free_transfer(struct libusb_transfer *transfer)
1295 struct usbi_transfer *itransfer;
1299 if (transfer->flags & LIBUSB_TRANSFER_FREE_BUFFER && transfer->buffer)
1300 free(transfer->buffer);
1302 itransfer = LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1303 usbi_mutex_destroy(&itransfer->lock);
1307 #ifdef USBI_TIMERFD_AVAILABLE
1308 static int disarm_timerfd(struct libusb_context *ctx)
1310 const struct itimerspec disarm_timer = { { 0, 0 }, { 0, 0 } };
1314 r = timerfd_settime(ctx->timerfd, 0, &disarm_timer, NULL);
1316 return LIBUSB_ERROR_OTHER;
1321 /* iterates through the flying transfers, and rearms the timerfd based on the
1322 * next upcoming timeout.
1323 * must be called with flying_list locked.
1324 * returns 0 if there was no timeout to arm, 1 if the next timeout was armed,
1325 * or a LIBUSB_ERROR code on failure.
1327 static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
1329 struct usbi_transfer *transfer;
1331 list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
1332 struct timeval *cur_tv = &transfer->timeout;
1334 /* if we've reached transfers of infinite timeout, then we have no
1336 if (!timerisset(cur_tv))
1339 /* act on first transfer that is not already cancelled */
1340 if (!(transfer->flags & USBI_TRANSFER_TIMED_OUT)) {
1342 const struct itimerspec it = { {0, 0},
1343 { cur_tv->tv_sec, cur_tv->tv_usec * 1000 } };
1344 usbi_dbg("next timeout originally %dms", USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout);
1345 r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
1347 return LIBUSB_ERROR_OTHER;
1353 return disarm_timerfd(ctx);
1356 static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
1363 /** \ingroup asyncio
1364 * Submit a transfer. This function will fire off the USB transfer and then
1365 * return immediately.
1367 * \param transfer the transfer to submit
1368 * \returns 0 on success
1369 * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
1370 * \returns LIBUSB_ERROR_BUSY if the transfer has already been submitted.
1371 * \returns LIBUSB_ERROR_NOT_SUPPORTED if the transfer flags are not supported
1372 * by the operating system.
1373 * \returns another LIBUSB_ERROR code on other failure
1375 int API_EXPORTED libusb_submit_transfer(struct libusb_transfer *transfer)
1377 struct libusb_context *ctx = TRANSFER_CTX(transfer);
1378 struct usbi_transfer *itransfer =
1379 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1383 usbi_mutex_lock(&itransfer->lock);
1384 itransfer->transferred = 0;
1385 itransfer->flags = 0;
1386 r = calculate_timeout(itransfer);
1388 r = LIBUSB_ERROR_OTHER;
1392 usbi_mutex_lock(&ctx->flying_transfers_lock);
1393 r = add_to_flying_list(itransfer);
1394 if (r == LIBUSB_SUCCESS) {
1395 r = usbi_backend->submit_transfer(itransfer);
1397 if (r != LIBUSB_SUCCESS) {
1398 list_del(&itransfer->list);
1399 arm_timerfd_for_next_timeout(ctx);
1401 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1404 updated_fds = (itransfer->flags & USBI_TRANSFER_UPDATED_FDS);
1405 usbi_mutex_unlock(&itransfer->lock);
1407 usbi_fd_notification(ctx);
1411 /** \ingroup asyncio
1412 * Asynchronously cancel a previously submitted transfer.
1413 * This function returns immediately, but this does not indicate cancellation
1414 * is complete. Your callback function will be invoked at some later time
1415 * with a transfer status of
1416 * \ref libusb_transfer_status::LIBUSB_TRANSFER_CANCELLED
1417 * "LIBUSB_TRANSFER_CANCELLED."
1419 * \param transfer the transfer to cancel
1420 * \returns 0 on success
1421 * \returns LIBUSB_ERROR_NOT_FOUND if the transfer is already complete or
1423 * \returns a LIBUSB_ERROR code on failure
1425 int API_EXPORTED libusb_cancel_transfer(struct libusb_transfer *transfer)
1427 struct usbi_transfer *itransfer =
1428 LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
1432 usbi_mutex_lock(&itransfer->lock);
1433 r = usbi_backend->cancel_transfer(itransfer);
1435 if (r != LIBUSB_ERROR_NOT_FOUND &&
1436 r != LIBUSB_ERROR_NO_DEVICE)
1437 usbi_err(TRANSFER_CTX(transfer),
1438 "cancel transfer failed error %d", r);
1440 usbi_dbg("cancel transfer failed error %d", r);
1442 if (r == LIBUSB_ERROR_NO_DEVICE)
1443 itransfer->flags |= USBI_TRANSFER_DEVICE_DISAPPEARED;
1446 itransfer->flags |= USBI_TRANSFER_CANCELLING;
1448 usbi_mutex_unlock(&itransfer->lock);
1452 /* Handle completion of a transfer (completion might be an error condition).
1453 * This will invoke the user-supplied callback function, which may end up
1454 * freeing the transfer. Therefore you cannot use the transfer structure
1455 * after calling this function, and you should free all backend-specific
1456 * data before calling it.
1457 * Do not call this function with the usbi_transfer lock held. User-specified
1458 * callback functions may attempt to directly resubmit the transfer, which
1459 * will attempt to take the lock. */
1460 int usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
1461 enum libusb_transfer_status status)
1463 struct libusb_transfer *transfer =
1464 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1465 struct libusb_context *ctx = TRANSFER_CTX(transfer);
1469 /* FIXME: could be more intelligent with the timerfd here. we don't need
1470 * to disarm the timerfd if there was no timer running, and we only need
1471 * to rearm the timerfd if the transfer that expired was the one with
1472 * the shortest timeout. */
1474 usbi_mutex_lock(&ctx->flying_transfers_lock);
1475 list_del(&itransfer->list);
1476 if (usbi_using_timerfd(ctx))
1477 r = arm_timerfd_for_next_timeout(ctx);
1478 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1479 if (usbi_using_timerfd(ctx) && (r < 0))
1482 if (status == LIBUSB_TRANSFER_COMPLETED
1483 && transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) {
1484 int rqlen = transfer->length;
1485 if (transfer->type == LIBUSB_TRANSFER_TYPE_CONTROL)
1486 rqlen -= LIBUSB_CONTROL_SETUP_SIZE;
1487 if (rqlen != itransfer->transferred) {
1488 usbi_dbg("interpreting short transfer as error");
1489 status = LIBUSB_TRANSFER_ERROR;
1493 flags = transfer->flags;
1494 transfer->status = status;
1495 transfer->actual_length = itransfer->transferred;
1496 usbi_dbg("transfer %p has callback %p", transfer, transfer->callback);
1497 if (transfer->callback)
1498 transfer->callback(transfer);
1499 /* transfer might have been freed by the above call, do not use from
1501 if (flags & LIBUSB_TRANSFER_FREE_TRANSFER)
1502 libusb_free_transfer(transfer);
1503 usbi_mutex_lock(&ctx->event_waiters_lock);
1504 usbi_cond_broadcast(&ctx->event_waiters_cond);
1505 usbi_mutex_unlock(&ctx->event_waiters_lock);
1509 /* Similar to usbi_handle_transfer_completion() but exclusively for transfers
1510 * that were asynchronously cancelled. The same concerns w.r.t. freeing of
1511 * transfers exist here.
1512 * Do not call this function with the usbi_transfer lock held. User-specified
1513 * callback functions may attempt to directly resubmit the transfer, which
1514 * will attempt to take the lock. */
1515 int usbi_handle_transfer_cancellation(struct usbi_transfer *transfer)
1517 /* if the URB was cancelled due to timeout, report timeout to the user */
1518 if (transfer->flags & USBI_TRANSFER_TIMED_OUT) {
1519 usbi_dbg("detected timeout cancellation");
1520 return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_TIMED_OUT);
1523 /* otherwise its a normal async cancel */
1524 return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_CANCELLED);
1528 * Attempt to acquire the event handling lock. This lock is used to ensure that
1529 * only one thread is monitoring libusbx event sources at any one time.
1531 * You only need to use this lock if you are developing an application
1532 * which calls poll() or select() on libusbx's file descriptors directly.
1533 * If you stick to libusbx's event handling loop functions (e.g.
1534 * libusb_handle_events()) then you do not need to be concerned with this
1537 * While holding this lock, you are trusted to actually be handling events.
1538 * If you are no longer handling events, you must call libusb_unlock_events()
1539 * as soon as possible.
1541 * \param ctx the context to operate on, or NULL for the default context
1542 * \returns 0 if the lock was obtained successfully
1543 * \returns 1 if the lock was not obtained (i.e. another thread holds the lock)
1546 int API_EXPORTED libusb_try_lock_events(libusb_context *ctx)
1550 USBI_GET_CONTEXT(ctx);
1552 /* is someone else waiting to modify poll fds? if so, don't let this thread
1553 * start event handling */
1554 usbi_mutex_lock(&ctx->pollfd_modify_lock);
1555 ru = ctx->pollfd_modify;
1556 usbi_mutex_unlock(&ctx->pollfd_modify_lock);
1558 usbi_dbg("someone else is modifying poll fds");
1562 r = usbi_mutex_trylock(&ctx->events_lock);
1566 ctx->event_handler_active = 1;
1571 * Acquire the event handling lock, blocking until successful acquisition if
1572 * it is contended. This lock is used to ensure that only one thread is
1573 * monitoring libusbx event sources at any one time.
1575 * You only need to use this lock if you are developing an application
1576 * which calls poll() or select() on libusbx's file descriptors directly.
1577 * If you stick to libusbx's event handling loop functions (e.g.
1578 * libusb_handle_events()) then you do not need to be concerned with this
1581 * While holding this lock, you are trusted to actually be handling events.
1582 * If you are no longer handling events, you must call libusb_unlock_events()
1583 * as soon as possible.
1585 * \param ctx the context to operate on, or NULL for the default context
1588 void API_EXPORTED libusb_lock_events(libusb_context *ctx)
1590 USBI_GET_CONTEXT(ctx);
1591 usbi_mutex_lock(&ctx->events_lock);
1592 ctx->event_handler_active = 1;
1596 * Release the lock previously acquired with libusb_try_lock_events() or
1597 * libusb_lock_events(). Releasing this lock will wake up any threads blocked
1598 * on libusb_wait_for_event().
1600 * \param ctx the context to operate on, or NULL for the default context
1603 void API_EXPORTED libusb_unlock_events(libusb_context *ctx)
1605 USBI_GET_CONTEXT(ctx);
1606 ctx->event_handler_active = 0;
1607 usbi_mutex_unlock(&ctx->events_lock);
1609 /* FIXME: perhaps we should be a bit more efficient by not broadcasting
1610 * the availability of the events lock when we are modifying pollfds
1611 * (check ctx->pollfd_modify)? */
1612 usbi_mutex_lock(&ctx->event_waiters_lock);
1613 usbi_cond_broadcast(&ctx->event_waiters_cond);
1614 usbi_mutex_unlock(&ctx->event_waiters_lock);
1618 * Determine if it is still OK for this thread to be doing event handling.
1620 * Sometimes, libusbx needs to temporarily pause all event handlers, and this
1621 * is the function you should use before polling file descriptors to see if
1624 * If this function instructs your thread to give up the events lock, you
1625 * should just continue the usual logic that is documented in \ref mtasync.
1626 * On the next iteration, your thread will fail to obtain the events lock,
1627 * and will hence become an event waiter.
1629 * This function should be called while the events lock is held: you don't
1630 * need to worry about the results of this function if your thread is not
1631 * the current event handler.
1633 * \param ctx the context to operate on, or NULL for the default context
1634 * \returns 1 if event handling can start or continue
1635 * \returns 0 if this thread must give up the events lock
1636 * \see \ref fullstory "Multi-threaded I/O: the full story"
1638 int API_EXPORTED libusb_event_handling_ok(libusb_context *ctx)
1641 USBI_GET_CONTEXT(ctx);
1643 /* is someone else waiting to modify poll fds? if so, don't let this thread
1644 * continue event handling */
1645 usbi_mutex_lock(&ctx->pollfd_modify_lock);
1646 r = ctx->pollfd_modify;
1647 usbi_mutex_unlock(&ctx->pollfd_modify_lock);
1649 usbi_dbg("someone else is modifying poll fds");
1658 * Determine if an active thread is handling events (i.e. if anyone is holding
1659 * the event handling lock).
1661 * \param ctx the context to operate on, or NULL for the default context
1662 * \returns 1 if a thread is handling events
1663 * \returns 0 if there are no threads currently handling events
1666 int API_EXPORTED libusb_event_handler_active(libusb_context *ctx)
1669 USBI_GET_CONTEXT(ctx);
1671 /* is someone else waiting to modify poll fds? if so, don't let this thread
1672 * start event handling -- indicate that event handling is happening */
1673 usbi_mutex_lock(&ctx->pollfd_modify_lock);
1674 r = ctx->pollfd_modify;
1675 usbi_mutex_unlock(&ctx->pollfd_modify_lock);
1677 usbi_dbg("someone else is modifying poll fds");
1681 return ctx->event_handler_active;
1685 * Acquire the event waiters lock. This lock is designed to be obtained under
1686 * the situation where you want to be aware when events are completed, but
1687 * some other thread is event handling so calling libusb_handle_events() is not
1690 * You then obtain this lock, re-check that another thread is still handling
1691 * events, then call libusb_wait_for_event().
1693 * You only need to use this lock if you are developing an application
1694 * which calls poll() or select() on libusbx's file descriptors directly,
1695 * <b>and</b> may potentially be handling events from 2 threads simultaenously.
1696 * If you stick to libusbx's event handling loop functions (e.g.
1697 * libusb_handle_events()) then you do not need to be concerned with this
1700 * \param ctx the context to operate on, or NULL for the default context
1703 void API_EXPORTED libusb_lock_event_waiters(libusb_context *ctx)
1705 USBI_GET_CONTEXT(ctx);
1706 usbi_mutex_lock(&ctx->event_waiters_lock);
1710 * Release the event waiters lock.
1711 * \param ctx the context to operate on, or NULL for the default context
1714 void API_EXPORTED libusb_unlock_event_waiters(libusb_context *ctx)
1716 USBI_GET_CONTEXT(ctx);
1717 usbi_mutex_unlock(&ctx->event_waiters_lock);
1721 * Wait for another thread to signal completion of an event. Must be called
1722 * with the event waiters lock held, see libusb_lock_event_waiters().
1724 * This function will block until any of the following conditions are met:
1725 * -# The timeout expires
1726 * -# A transfer completes
1727 * -# A thread releases the event handling lock through libusb_unlock_events()
1729 * Condition 1 is obvious. Condition 2 unblocks your thread <em>after</em>
1730 * the callback for the transfer has completed. Condition 3 is important
1731 * because it means that the thread that was previously handling events is no
1732 * longer doing so, so if any events are to complete, another thread needs to
1733 * step up and start event handling.
1735 * This function releases the event waiters lock before putting your thread
1736 * to sleep, and reacquires the lock as it is being woken up.
1738 * \param ctx the context to operate on, or NULL for the default context
1739 * \param tv maximum timeout for this blocking function. A NULL value
1740 * indicates unlimited timeout.
1741 * \returns 0 after a transfer completes or another thread stops event handling
1742 * \returns 1 if the timeout expired
1745 int API_EXPORTED libusb_wait_for_event(libusb_context *ctx, struct timeval *tv)
1747 struct timespec timeout;
1750 USBI_GET_CONTEXT(ctx);
1752 usbi_cond_wait(&ctx->event_waiters_cond, &ctx->event_waiters_lock);
1756 r = usbi_backend->clock_gettime(USBI_CLOCK_REALTIME, &timeout);
1758 usbi_err(ctx, "failed to read realtime clock, error %d", errno);
1759 return LIBUSB_ERROR_OTHER;
1762 timeout.tv_sec += tv->tv_sec;
1763 timeout.tv_nsec += tv->tv_usec * 1000;
1764 while (timeout.tv_nsec >= 1000000000) {
1765 timeout.tv_nsec -= 1000000000;
1769 r = usbi_cond_timedwait(&ctx->event_waiters_cond,
1770 &ctx->event_waiters_lock, &timeout);
1771 return (r == ETIMEDOUT);
1774 static void handle_timeout(struct usbi_transfer *itransfer)
1776 struct libusb_transfer *transfer =
1777 USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
1780 itransfer->flags |= USBI_TRANSFER_TIMED_OUT;
1781 r = libusb_cancel_transfer(transfer);
1783 usbi_warn(TRANSFER_CTX(transfer),
1784 "async cancel failed %d errno=%d", r, errno);
1787 static int handle_timeouts_locked(struct libusb_context *ctx)
1790 struct timespec systime_ts;
1791 struct timeval systime;
1792 struct usbi_transfer *transfer;
1794 if (list_empty(&ctx->flying_transfers))
1797 /* get current time */
1798 r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, &systime_ts);
1802 TIMESPEC_TO_TIMEVAL(&systime, &systime_ts);
1804 /* iterate through flying transfers list, finding all transfers that
1805 * have expired timeouts */
1806 list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
1807 struct timeval *cur_tv = &transfer->timeout;
1809 /* if we've reached transfers of infinite timeout, we're all done */
1810 if (!timerisset(cur_tv))
1813 /* ignore timeouts we've already handled */
1814 if (transfer->flags & (USBI_TRANSFER_TIMED_OUT | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
1817 /* if transfer has non-expired timeout, nothing more to do */
1818 if ((cur_tv->tv_sec > systime.tv_sec) ||
1819 (cur_tv->tv_sec == systime.tv_sec &&
1820 cur_tv->tv_usec > systime.tv_usec))
1823 /* otherwise, we've got an expired timeout to handle */
1824 handle_timeout(transfer);
1829 static int handle_timeouts(struct libusb_context *ctx)
1832 USBI_GET_CONTEXT(ctx);
1833 usbi_mutex_lock(&ctx->flying_transfers_lock);
1834 r = handle_timeouts_locked(ctx);
1835 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1839 #ifdef USBI_TIMERFD_AVAILABLE
1840 static int handle_timerfd_trigger(struct libusb_context *ctx)
1844 usbi_mutex_lock(&ctx->flying_transfers_lock);
1846 /* process the timeout that just happened */
1847 r = handle_timeouts_locked(ctx);
1851 /* arm for next timeout*/
1852 r = arm_timerfd_for_next_timeout(ctx);
1855 usbi_mutex_unlock(&ctx->flying_transfers_lock);
1860 /* do the actual event handling. assumes that no other thread is concurrently
1861 * doing the same thing. */
1862 static int handle_events(struct libusb_context *ctx, struct timeval *tv)
1865 struct usbi_pollfd *ipollfd;
1866 POLL_NFDS_TYPE nfds = 0;
1867 struct pollfd *fds = NULL;
1871 usbi_mutex_lock(&ctx->pollfds_lock);
1872 list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
1875 /* TODO: malloc when number of fd's changes, not on every poll */
1877 fds = malloc(sizeof(*fds) * nfds);
1879 usbi_mutex_unlock(&ctx->pollfds_lock);
1880 return LIBUSB_ERROR_NO_MEM;
1883 list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd) {
1884 struct libusb_pollfd *pollfd = &ipollfd->pollfd;
1885 int fd = pollfd->fd;
1888 fds[i].events = pollfd->events;
1891 usbi_mutex_unlock(&ctx->pollfds_lock);
1893 timeout_ms = (int)(tv->tv_sec * 1000) + (tv->tv_usec / 1000);
1895 /* round up to next millisecond */
1896 if (tv->tv_usec % 1000)
1899 usbi_dbg("poll() %d fds with timeout in %dms", nfds, timeout_ms);
1900 r = usbi_poll(fds, nfds, timeout_ms);
1901 usbi_dbg("poll() returned %d", r);
1904 return handle_timeouts(ctx);
1905 } else if (r == -1 && errno == EINTR) {
1907 return LIBUSB_ERROR_INTERRUPTED;
1910 usbi_err(ctx, "poll failed %d err=%d\n", r, errno);
1911 return LIBUSB_ERROR_IO;
1914 /* fd[0] is always the ctrl pipe */
1915 if (fds[0].revents) {
1916 /* another thread wanted to interrupt event handling, and it succeeded!
1917 * handle any other events that cropped up at the same time, and
1919 usbi_dbg("caught a fish on the control pipe");
1925 /* prevent OS backend from trying to handle events on ctrl pipe */
1931 /* fd[1] is always the hotplug pipe */
1932 if (libusb_has_capability(LIBUSB_CAP_HAS_HOTPLUG) && fds[1].revents) {
1933 libusb_hotplug_message message;
1936 usbi_dbg("caught a fish on the hotplug pipe");
1938 /* read the message from the hotplug thread */
1939 ret = usbi_read(ctx->hotplug_pipe[0], &message, sizeof (message));
1940 if (ret < sizeof(message)) {
1941 usbi_err(ctx, "hotplug pipe read error %d < %d",
1942 ret, sizeof(message));
1943 r = LIBUSB_ERROR_OTHER;
1947 usbi_hotplug_match(ctx, message.device, message.event);
1949 /* the device left. dereference the device */
1950 if (LIBUSB_HOTPLUG_EVENT_DEVICE_LEFT == message.event)
1951 libusb_unref_device(message.device);
1956 } /* else there shouldn't be anything on this pipe */
1958 #ifdef USBI_TIMERFD_AVAILABLE
1959 /* on timerfd configurations, fds[2] is the timerfd */
1960 if (usbi_using_timerfd(ctx) && fds[2].revents) {
1961 /* timerfd indicates that a timeout has expired */
1963 usbi_dbg("timerfd triggered");
1965 ret = handle_timerfd_trigger(ctx);
1967 /* return error code */
1970 } else if (r == 1) {
1971 /* no more active file descriptors, nothing more to do */
1975 /* more events pending...
1976 * prevent OS backend from trying to handle events on timerfd */
1983 r = usbi_backend->handle_events(ctx, fds, nfds, r);
1985 usbi_err(ctx, "backend handle_events failed with error %d", r);
1992 /* returns the smallest of:
1993 * 1. timeout of next URB
1994 * 2. user-supplied timeout
1995 * returns 1 if there is an already-expired timeout, otherwise returns 0
1998 static int get_next_timeout(libusb_context *ctx, struct timeval *tv,
1999 struct timeval *out)
2001 struct timeval timeout;
2002 int r = libusb_get_next_timeout(ctx, &timeout);
2004 /* timeout already expired? */
2005 if (!timerisset(&timeout))
2008 /* choose the smallest of next URB timeout or user specified timeout */
2009 if (timercmp(&timeout, tv, <))
2020 * Handle any pending events.
2022 * libusbx determines "pending events" by checking if any timeouts have expired
2023 * and by checking the set of file descriptors for activity.
2025 * If a zero timeval is passed, this function will handle any already-pending
2026 * events and then immediately return in non-blocking style.
2028 * If a non-zero timeval is passed and no events are currently pending, this
2029 * function will block waiting for events to handle up until the specified
2030 * timeout. If an event arrives or a signal is raised, this function will
2033 * If the parameter completed is not NULL then <em>after obtaining the event
2034 * handling lock</em> this function will return immediately if the integer
2035 * pointed to is not 0. This allows for race free waiting for the completion
2036 * of a specific transfer.
2038 * \param ctx the context to operate on, or NULL for the default context
2039 * \param tv the maximum time to block waiting for events, or an all zero
2040 * timeval struct for non-blocking mode
2041 * \param completed pointer to completion integer to check, or NULL
2042 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2045 int API_EXPORTED libusb_handle_events_timeout_completed(libusb_context *ctx,
2046 struct timeval *tv, int *completed)
2049 struct timeval poll_timeout;
2051 USBI_GET_CONTEXT(ctx);
2052 r = get_next_timeout(ctx, tv, &poll_timeout);
2054 /* timeout already expired */
2055 return handle_timeouts(ctx);
2059 if (libusb_try_lock_events(ctx) == 0) {
2060 if (completed == NULL || !*completed) {
2061 /* we obtained the event lock: do our own event handling */
2062 usbi_dbg("doing our own event handling");
2063 r = handle_events(ctx, &poll_timeout);
2065 libusb_unlock_events(ctx);
2069 /* another thread is doing event handling. wait for thread events that
2070 * notify event completion. */
2071 libusb_lock_event_waiters(ctx);
2073 if (completed && *completed)
2076 if (!libusb_event_handler_active(ctx)) {
2077 /* we hit a race: whoever was event handling earlier finished in the
2078 * time it took us to reach this point. try the cycle again. */
2079 libusb_unlock_event_waiters(ctx);
2080 usbi_dbg("event handler was active but went away, retrying");
2084 usbi_dbg("another thread is doing event handling");
2085 r = libusb_wait_for_event(ctx, &poll_timeout);
2088 libusb_unlock_event_waiters(ctx);
2093 return handle_timeouts(ctx);
2099 * Handle any pending events
2101 * Like libusb_handle_events_timeout_completed(), but without the completed
2102 * parameter, calling this function is equivalent to calling
2103 * libusb_handle_events_timeout_completed() with a NULL completed parameter.
2105 * This function is kept primarily for backwards compatibility.
2106 * All new code should call libusb_handle_events_completed() or
2107 * libusb_handle_events_timeout_completed() to avoid race conditions.
2109 * \param ctx the context to operate on, or NULL for the default context
2110 * \param tv the maximum time to block waiting for events, or an all zero
2111 * timeval struct for non-blocking mode
2112 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2114 int API_EXPORTED libusb_handle_events_timeout(libusb_context *ctx,
2117 return libusb_handle_events_timeout_completed(ctx, tv, NULL);
2121 * Handle any pending events in blocking mode. There is currently a timeout
2122 * hardcoded at 60 seconds but we plan to make it unlimited in future. For
2123 * finer control over whether this function is blocking or non-blocking, or
2124 * for control over the timeout, use libusb_handle_events_timeout_completed()
2127 * This function is kept primarily for backwards compatibility.
2128 * All new code should call libusb_handle_events_completed() or
2129 * libusb_handle_events_timeout_completed() to avoid race conditions.
2131 * \param ctx the context to operate on, or NULL for the default context
2132 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2134 int API_EXPORTED libusb_handle_events(libusb_context *ctx)
2139 return libusb_handle_events_timeout_completed(ctx, &tv, NULL);
2143 * Handle any pending events in blocking mode.
2145 * Like libusb_handle_events(), with the addition of a completed parameter
2146 * to allow for race free waiting for the completion of a specific transfer.
2148 * See libusb_handle_events_timeout_completed() for details on the completed
2151 * \param ctx the context to operate on, or NULL for the default context
2152 * \param completed pointer to completion integer to check, or NULL
2153 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2156 int API_EXPORTED libusb_handle_events_completed(libusb_context *ctx,
2162 return libusb_handle_events_timeout_completed(ctx, &tv, completed);
2166 * Handle any pending events by polling file descriptors, without checking if
2167 * any other threads are already doing so. Must be called with the event lock
2168 * held, see libusb_lock_events().
2170 * This function is designed to be called under the situation where you have
2171 * taken the event lock and are calling poll()/select() directly on libusbx's
2172 * file descriptors (as opposed to using libusb_handle_events() or similar).
2173 * You detect events on libusbx's descriptors, so you then call this function
2174 * with a zero timeout value (while still holding the event lock).
2176 * \param ctx the context to operate on, or NULL for the default context
2177 * \param tv the maximum time to block waiting for events, or zero for
2179 * \returns 0 on success, or a LIBUSB_ERROR code on failure
2182 int API_EXPORTED libusb_handle_events_locked(libusb_context *ctx,
2186 struct timeval poll_timeout;
2188 USBI_GET_CONTEXT(ctx);
2189 r = get_next_timeout(ctx, tv, &poll_timeout);
2191 /* timeout already expired */
2192 return handle_timeouts(ctx);
2195 return handle_events(ctx, &poll_timeout);
2199 * Determines whether your application must apply special timing considerations
2200 * when monitoring libusbx's file descriptors.
2202 * This function is only useful for applications which retrieve and poll
2203 * libusbx's file descriptors in their own main loop (\ref pollmain).
2205 * Ordinarily, libusbx's event handler needs to be called into at specific
2206 * moments in time (in addition to times when there is activity on the file
2207 * descriptor set). The usual approach is to use libusb_get_next_timeout()
2208 * to learn about when the next timeout occurs, and to adjust your
2209 * poll()/select() timeout accordingly so that you can make a call into the
2210 * library at that time.
2212 * Some platforms supported by libusbx do not come with this baggage - any
2213 * events relevant to timing will be represented by activity on the file
2214 * descriptor set, and libusb_get_next_timeout() will always return 0.
2215 * This function allows you to detect whether you are running on such a
2220 * \param ctx the context to operate on, or NULL for the default context
2221 * \returns 0 if you must call into libusbx at times determined by
2222 * libusb_get_next_timeout(), or 1 if all timeout events are handled internally
2223 * or through regular activity on the file descriptors.
2224 * \see \ref pollmain "Polling libusbx file descriptors for event handling"
2226 int API_EXPORTED libusb_pollfds_handle_timeouts(libusb_context *ctx)
2228 #if defined(USBI_TIMERFD_AVAILABLE)
2229 USBI_GET_CONTEXT(ctx);
2230 return usbi_using_timerfd(ctx);
2238 * Determine the next internal timeout that libusbx needs to handle. You only
2239 * need to use this function if you are calling poll() or select() or similar
2240 * on libusbx's file descriptors yourself - you do not need to use it if you
2241 * are calling libusb_handle_events() or a variant directly.
2243 * You should call this function in your main loop in order to determine how
2244 * long to wait for select() or poll() to return results. libusbx needs to be
2245 * called into at this timeout, so you should use it as an upper bound on
2246 * your select() or poll() call.
2248 * When the timeout has expired, call into libusb_handle_events_timeout()
2249 * (perhaps in non-blocking mode) so that libusbx can handle the timeout.
2251 * This function may return 1 (success) and an all-zero timeval. If this is
2252 * the case, it indicates that libusbx has a timeout that has already expired
2253 * so you should call libusb_handle_events_timeout() or similar immediately.
2254 * A return code of 0 indicates that there are no pending timeouts.
2256 * On some platforms, this function will always returns 0 (no pending
2257 * timeouts). See \ref polltime.
2259 * \param ctx the context to operate on, or NULL for the default context
2260 * \param tv output location for a relative time against the current
2261 * clock in which libusbx must be called into in order to process timeout events
2262 * \returns 0 if there are no pending timeouts, 1 if a timeout was returned,
2263 * or LIBUSB_ERROR_OTHER on failure
2265 int API_EXPORTED libusb_get_next_timeout(libusb_context *ctx,
2268 struct usbi_transfer *transfer;
2269 struct timespec cur_ts;
2270 struct timeval cur_tv;
2271 struct timeval *next_timeout;
2275 USBI_GET_CONTEXT(ctx);
2276 if (usbi_using_timerfd(ctx))
2279 usbi_mutex_lock(&ctx->flying_transfers_lock);
2280 if (list_empty(&ctx->flying_transfers)) {
2281 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2282 usbi_dbg("no URBs, no timeout!");
2286 /* find next transfer which hasn't already been processed as timed out */
2287 list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
2288 if (transfer->flags & (USBI_TRANSFER_TIMED_OUT | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
2291 /* no timeout for this transfer? */
2292 if (!timerisset(&transfer->timeout))
2298 usbi_mutex_unlock(&ctx->flying_transfers_lock);
2301 usbi_dbg("no URB with timeout or all handled by OS; no timeout!");
2305 next_timeout = &transfer->timeout;
2307 r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, &cur_ts);
2309 usbi_err(ctx, "failed to read monotonic clock, errno=%d", errno);
2312 TIMESPEC_TO_TIMEVAL(&cur_tv, &cur_ts);
2314 if (!timercmp(&cur_tv, next_timeout, <)) {
2315 usbi_dbg("first timeout already expired");
2318 timersub(next_timeout, &cur_tv, tv);
2319 usbi_dbg("next timeout in %d.%06ds", tv->tv_sec, tv->tv_usec);
2326 * Register notification functions for file descriptor additions/removals.
2327 * These functions will be invoked for every new or removed file descriptor
2328 * that libusbx uses as an event source.
2330 * To remove notifiers, pass NULL values for the function pointers.
2332 * Note that file descriptors may have been added even before you register
2333 * these notifiers (e.g. at libusb_init() time).
2335 * Additionally, note that the removal notifier may be called during
2336 * libusb_exit() (e.g. when it is closing file descriptors that were opened
2337 * and added to the poll set at libusb_init() time). If you don't want this,
2338 * remove the notifiers immediately before calling libusb_exit().
2340 * \param ctx the context to operate on, or NULL for the default context
2341 * \param added_cb pointer to function for addition notifications
2342 * \param removed_cb pointer to function for removal notifications
2343 * \param user_data User data to be passed back to callbacks (useful for
2344 * passing context information)
2346 void API_EXPORTED libusb_set_pollfd_notifiers(libusb_context *ctx,
2347 libusb_pollfd_added_cb added_cb, libusb_pollfd_removed_cb removed_cb,
2350 USBI_GET_CONTEXT(ctx);
2351 ctx->fd_added_cb = added_cb;
2352 ctx->fd_removed_cb = removed_cb;
2353 ctx->fd_cb_user_data = user_data;
2356 /* Add a file descriptor to the list of file descriptors to be monitored.
2357 * events should be specified as a bitmask of events passed to poll(), e.g.
2358 * POLLIN and/or POLLOUT. */
2359 int usbi_add_pollfd(struct libusb_context *ctx, int fd, short events)
2361 struct usbi_pollfd *ipollfd = malloc(sizeof(*ipollfd));
2363 return LIBUSB_ERROR_NO_MEM;
2365 usbi_dbg("add fd %d events %d", fd, events);
2366 ipollfd->pollfd.fd = fd;
2367 ipollfd->pollfd.events = events;
2368 usbi_mutex_lock(&ctx->pollfds_lock);
2369 list_add_tail(&ipollfd->list, &ctx->pollfds);
2370 usbi_mutex_unlock(&ctx->pollfds_lock);
2372 if (ctx->fd_added_cb)
2373 ctx->fd_added_cb(fd, events, ctx->fd_cb_user_data);
2377 /* Remove a file descriptor from the list of file descriptors to be polled. */
2378 void usbi_remove_pollfd(struct libusb_context *ctx, int fd)
2380 struct usbi_pollfd *ipollfd;
2383 usbi_dbg("remove fd %d", fd);
2384 usbi_mutex_lock(&ctx->pollfds_lock);
2385 list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
2386 if (ipollfd->pollfd.fd == fd) {
2392 usbi_dbg("couldn't find fd %d to remove", fd);
2393 usbi_mutex_unlock(&ctx->pollfds_lock);
2397 list_del(&ipollfd->list);
2398 usbi_mutex_unlock(&ctx->pollfds_lock);
2400 if (ctx->fd_removed_cb)
2401 ctx->fd_removed_cb(fd, ctx->fd_cb_user_data);
2405 * Retrieve a list of file descriptors that should be polled by your main loop
2406 * as libusbx event sources.
2408 * The returned list is NULL-terminated and should be freed with free() when
2409 * done. The actual list contents must not be touched.
2411 * As file descriptors are a Unix-specific concept, this function is not
2412 * available on Windows and will always return NULL.
2414 * \param ctx the context to operate on, or NULL for the default context
2415 * \returns a NULL-terminated list of libusb_pollfd structures
2416 * \returns NULL on error
2417 * \returns NULL on platforms where the functionality is not available
2420 const struct libusb_pollfd ** LIBUSB_CALL libusb_get_pollfds(
2421 libusb_context *ctx)
2424 struct libusb_pollfd **ret = NULL;
2425 struct usbi_pollfd *ipollfd;
2428 USBI_GET_CONTEXT(ctx);
2430 usbi_mutex_lock(&ctx->pollfds_lock);
2431 list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
2434 ret = calloc(cnt + 1, sizeof(struct libusb_pollfd *));
2438 list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
2439 ret[i++] = (struct libusb_pollfd *) ipollfd;
2443 usbi_mutex_unlock(&ctx->pollfds_lock);
2444 return (const struct libusb_pollfd **) ret;
2446 usbi_err(ctx, "external polling of libusbx's internal descriptors "\
2447 "is not yet supported on Windows platforms");
2452 /* Backends may call this from handle_events to report disconnection of a
2453 * device. This function ensures transfers get cancelled appropriately.
2454 * Callers of this function must hold the events_lock.
2456 void usbi_handle_disconnect(struct libusb_device_handle *handle)
2458 struct usbi_transfer *cur;
2459 struct usbi_transfer *to_cancel;
2461 usbi_dbg("device %d.%d",
2462 handle->dev->bus_number, handle->dev->device_address);
2464 /* terminate all pending transfers with the LIBUSB_TRANSFER_NO_DEVICE
2467 * this is a bit tricky because:
2468 * 1. we can't do transfer completion while holding flying_transfers_lock
2469 * because the completion handler may try to re-submit the transfer
2470 * 2. the transfers list can change underneath us - if we were to build a
2471 * list of transfers to complete (while holding lock), the situation
2472 * might be different by the time we come to free them
2474 * so we resort to a loop-based approach as below
2476 * This is safe because transfers are only removed from the
2477 * flying_transfer list by usbi_handle_transfer_completion and
2478 * libusb_close, both of which hold the events_lock while doing so,
2479 * so usbi_handle_disconnect cannot be running at the same time.
2481 * Note that libusb_submit_transfer also removes the transfer from
2482 * the flying_transfer list on submission failure, but it keeps the
2483 * flying_transfer list locked between addition and removal, so
2484 * usbi_handle_disconnect never sees such transfers.
2488 usbi_mutex_lock(&HANDLE_CTX(handle)->flying_transfers_lock);
2490 list_for_each_entry(cur, &HANDLE_CTX(handle)->flying_transfers, list, struct usbi_transfer)
2491 if (USBI_TRANSFER_TO_LIBUSB_TRANSFER(cur)->dev_handle == handle) {
2495 usbi_mutex_unlock(&HANDLE_CTX(handle)->flying_transfers_lock);
2500 usbi_dbg("cancelling transfer %p from disconnect",
2501 USBI_TRANSFER_TO_LIBUSB_TRANSFER(to_cancel));
2503 usbi_backend->clear_transfer_priv(to_cancel);
2504 usbi_handle_transfer_completion(to_cancel, LIBUSB_TRANSFER_NO_DEVICE);