2 * I/O functions for libusb
3 * Copyright (C) 2007-2008 Daniel Drake <dsd@gentoo.org>
4 * Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
6 * This library is free software; you can redistribute it and/or
7 * modify it under the terms of the GNU Lesser General Public
8 * License as published by the Free Software Foundation; either
9 * version 2.1 of the License, or (at your option) any later version.
11 * This library is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
14 * Lesser General Public License for more details.
16 * You should have received a copy of the GNU Lesser General Public
17 * License along with this library; if not, write to the Free Software
18 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
35 /* this is a list of in-flight transfer handles, sorted by timeout expiration.
36 * URBs to timeout the soonest are placed at the beginning of the list, URBs
37 * that will time out later are placed after, and urbs with infinite timeout
38 * are always placed at the very end. */
39 static struct list_head flying_transfers;
40 static pthread_mutex_t flying_transfers_lock = PTHREAD_MUTEX_INITIALIZER;
42 /* list of poll fd's */
43 static struct list_head pollfds;
44 static pthread_mutex_t pollfds_lock = PTHREAD_MUTEX_INITIALIZER;
46 /* user callbacks for pollfd changes */
47 static libusb_pollfd_added_cb fd_added_cb = NULL;
48 static libusb_pollfd_removed_cb fd_removed_cb = NULL;
51 * \page io Synchronous and asynchronous device I/O
53 * \section intro Introduction
55 * If you're using libusb in your application, you're probably wanting to
56 * perform I/O with devices - you want to perform USB data transfers.
58 * libusb offers two separate interfaces for device I/O. This page aims to
59 * introduce the two in order to help you decide which one is more suitable
60 * for your application. You can also choose to use both interfaces in your
61 * application by considering each transfer on a case-by-case basis.
63 * Once you have read through the following discussion, you should consult the
64 * detailed API documentation pages for the details:
68 * \section theory Transfers at a logical level
70 * At a logical level, USB transfers typically happen in two parts. For
71 * example, when reading data from a endpoint:
72 * -# A request for data is sent to the device
73 * -# Some time later, the incoming data is received by the host
75 * or when writing data to an endpoint:
77 * -# The data is sent to the device
78 * -# Some time later, the host receives acknowledgement from the device that
79 * the data has been transferred.
81 * There may be an indefinite delay between the two steps. Consider a
82 * fictional USB input device with a button that the user can press. In order
83 * to determine when the button is pressed, you would likely submit a request
84 * to read data on a bulk or interrupt endpoint and wait for data to arrive.
85 * Data will arrive when the button is pressed by the user, which is
86 * potentially hours later.
88 * libusb offers both a synchronous and an asynchronous interface to performing
89 * USB transfers. The main difference is that the synchronous interface
90 * combines both steps indicated above into a single function call, whereas
91 * the asynchronous interface separates them.
93 * \section sync The synchronous interface
95 * The synchronous I/O interface allows you to perform a USB transfer with
96 * a single function call. When the function call returns, the transfer has
97 * completed and you can parse the results.
99 * If you have used the libusb-0.1 before, this I/O style will seem familar to
100 * you. libusb-0.1 only offered a synchronous interface.
102 * In our input device example, to read button presses you might write code
103 * in the following style:
105 unsigned char data[4];
107 int r = libusb_bulk_transfer(handle, EP_IN, data, sizeof(data), &actual_length, 0);
108 if (r == 0 && actual_length == sizeof(data)) {
109 // results of the transaction can now be found in the data buffer
110 // parse them here and report button press
116 * The main advantage of this model is simplicity: you did everything with
117 * a single simple function call.
119 * However, this interface has its limitations. Your application will sleep
120 * inside libusb_bulk_transfer() until the transaction has completed. If it
121 * takes the user 3 hours to press the button, your application will be
122 * sleeping for that long. Execution will be tied up inside the library -
123 * the entire thread will be useless for that duration.
125 * Another issue is that by tieing up the thread with that single transaction
126 * there is no possibility of performing I/O with multiple endpoints and/or
127 * multiple devices simultaneously, unless you resort to creating one thread
130 * Additionally, there is no opportunity to cancel the transfer after the
131 * request has been submitted.
133 * For details on how to use the synchronous API, see the
134 * \ref syncio "synchronous I/O API documentation" pages.
136 * \section async The asynchronous interface
138 * Asynchronous I/O is the most significant new feature in libusb-1.0.
139 * Although it is a more complex interface, it solves all the issues detailed
142 * Instead of providing which functions that block until the I/O has complete,
143 * libusb's asynchronous interface presents non-blocking functions which
144 * begin a transfer and then return immediately. Your application passes a
145 * callback function pointer to this non-blocking function, which libusb will
146 * call with the results of the transaction when it has completed.
148 * Transfers which have been submitted through the non-blocking functions
149 * can be cancelled with a separate function call.
151 * The non-blocking nature of this interface allows you to be simultaneously
152 * performing I/O to multiple endpoints on multiple devices, without having
155 * This added flexibility does come with some complications though:
156 * - In the interest of being a lightweight library, libusb does not create
157 * threads and can only operate when your application is calling into it. Your
158 * application must call into libusb from it's main loop when events are ready
159 * to be handled, or you must use some other scheme to allow libusb to
160 * undertake whatever work needs to be done.
161 * - libusb also needs to be called into at certain fixed points in time in
162 * order to accurately handle transfer timeouts.
163 * - Memory handling becomes more complex. You cannot use stack memory unless
164 * the function with that stack is guaranteed not to return until the transfer
165 * callback has finished executing.
166 * - You generally lose some linearity from your code flow because submitting
167 * the transfer request is done in a separate function from where the transfer
168 * results are handled. This becomes particularly obvious when you want to
169 * submit a second transfer based on the results of an earlier transfer.
171 * Internally, libusb's synchronous interface is expressed in terms of function
172 * calls to the asynchronous interface.
174 * For details on how to use the asynchronous API, see the
175 * \ref asyncio "asynchronous I/O API" documentation pages.
179 * @defgroup asyncio Asynchronous device I/O
181 * This page details libusb's asynchronous (non-blocking) API for USB device
182 * I/O. This interface is very powerful but is also quite complex - you will
183 * need to read this page carefully to understand the necessary considerations
184 * and issues surrounding use of this interface. Simplistic applications
185 * may wish to consider the \ref syncio "synchronous I/O API" instead.
187 * The asynchronous interface is built around the idea of separating transfer
188 * submission and handling of transfer completion (the synchronous model
189 * combines both of these into one). There may be a long delay between
190 * submission and completion, however the asynchronous submission function
191 * is non-blocking so will return control to your application during that
192 * potentially long delay.
194 * \section asyncabstraction Transfer abstraction
196 * For the asynchronous I/O, libusb implements the concept of a generic
197 * transfer entity for all types of I/O (control, bulk, interrupt,
198 * isochronous). The generic transfer object must be treated slightly
199 * differently depending on which type of I/O you are performing with it.
201 * This is represented by the public libusb_transfer structure type.
203 * \section asynctrf Asynchronous transfers
205 * We can view asynchronous I/O as a 5 step process:
209 * -# Completion handling
212 * \subsection asyncalloc Allocation
214 * This step involves allocating memory for a USB transfer. This is the
215 * generic transfer object mentioned above. At this stage, the transfer
216 * is "blank" with no details about what type of I/O it will be used for.
218 * Allocation is done with the libusb_alloc_transfer() function. You must use
219 * this function rather than allocating your own transfers.
221 * \subsection asyncfill Filling
223 * This step is where you take a previously allocated transfer and fill it
224 * with information to determine the message type and direction, data buffer,
225 * callback function, etc.
227 * You can either fill the required fields yourself or you can use the
228 * helper functions: libusb_fill_control_transfer(), libusb_fill_bulk_transfer()
229 * and libusb_fill_interrupt_transfer().
231 * \subsection asyncsubmit Submission
233 * When you have allocated a transfer and filled it, you can submit it using
234 * libusb_submit_transfer(). This function returns immediately but can be
235 * regarded as firing off the I/O request in the background.
237 * \subsection asynccomplete Completion handling
239 * After a transfer has been submitted, one of four things can happen to it:
241 * - The transfer completes (i.e. some data was transferred)
242 * - The transfer has a timeout and the timeout expires before all data is
244 * - The transfer fails due to an error
245 * - The transfer is cancelled
247 * Each of these will cause the user-specified transfer callback function to
248 * be invoked. It is up to the callback function to determine which of the
249 * above actually happened and to act accordingly.
251 * \subsection Deallocation
253 * When a transfer has completed (i.e. the callback function has been invoked),
254 * you are advised to free the transfer (unless you wish to resubmit it, see
255 * below). Transfers are deallocated with libusb_free_transfer().
257 * It is undefined behaviour to free a transfer which has not completed.
259 * \section asyncresubmit Resubmission
261 * You may be wondering why allocation, filling, and submission are all
262 * separated above where they could reasonably be combined into a single
265 * The reason for separation is to allow you to resubmit transfers without
266 * having to allocate new ones every time. This is especially useful for
267 * common situations dealing with interrupt endpoints - you allocate one
268 * transfer, fill and submit it, and when it returns with results you just
269 * resubmit it for the next interrupt.
271 * \section asynccancel Cancellation
273 * Another advantage of using the asynchronous interface is that you have
274 * the ability to cancel transfers which have not yet completed. This is
275 * done by calling the libusb_cancel_transfer() function.
277 * libusb_cancel_transfer() is asynchronous/non-blocking in itself. When the
278 * cancellation actually completes, the transfer's callback function will
279 * be invoked, and the callback function should check the transfer status to
280 * determine that it was cancelled.
282 * Freeing the transfer after it has been cancelled but before cancellation
283 * has completed will result in undefined behaviour.
285 * \section asyncctrl Considerations for control transfers
287 * The <tt>libusb_transfer</tt> structure is generic and hence does not
288 * include specific fields for the control-specific setup packet structure.
290 * In order to perform a control transfer, you must place the 8-byte setup
291 * packet at the start of the data buffer. To simplify this, you could
292 * cast the buffer pointer to type struct libusb_control_setup, or you can
293 * use the helper function libusb_fill_control_setup().
295 * The wLength field placed in the setup packet must be the length you would
296 * expect to be sent in the setup packet: the length of the payload that
297 * follows (or the expected maximum number of bytes to receive). However,
298 * the length field of the libusb_transfer object must be the length of
299 * the data buffer - i.e. it should be wLength <em>plus</em> the size of
300 * the setup packet (LIBUSB_CONTROL_SETUP_SIZE).
302 * If you use the helper functions, this is simplified for you:
303 * -# Allocate a buffer of size LIBUSB_CONTROL_SETUP_SIZE plus the size of the
304 * data you are sending/requesting.
305 * -# Call libusb_fill_control_setup() on the data buffer, using the transfer
306 * request size as the wLength value (i.e. do not include the extra space you
307 * allocated for the control setup).
308 * -# If this is a host-to-device transfer, place the data to be transferred
309 * in the data buffer, starting at offset LIBUSB_CONTROL_SETUP_SIZE.
310 * -# Call libusb_fill_control_transfer() to associate the data buffer with
311 * the transfer (and to set the remaining details such as callback and timeout).
312 * - Note that there is no parameter to set the length field of the transfer.
313 * The length is automatically inferred from the wLength field of the setup
315 * -# Submit the transfer.
317 * The multi-byte control setup fields (wValue, wIndex and wLength) must
318 * be given in little-endian byte order (the endianness of the USB bus).
319 * Endianness conversion is transparently handled by
320 * libusb_fill_control_setup() which is documented to accept host-endian
323 * Further considerations are needed when handling transfer completion in
324 * your callback function:
325 * - As you might expect, the setup packet will still be sitting at the start
326 * of the data buffer.
327 * - If this was a device-to-host transfer, the received data will be sitting
328 * at offset LIBUSB_CONTROL_SETUP_SIZE into the buffer.
329 * - The actual_length field of the transfer structure is relative to the
330 * wLength of the setup packet, rather than the size of the data buffer. So,
331 * if your wLength was 4, your transfer's <tt>length</tt> was 12, then you
332 * should expect an <tt>actual_length</tt> of 4 to indicate that the data was
333 * transferred in entirity.
335 * To simplify parsing of setup packets and obtaining the data from the
336 * correct offset, you may wish to use the libusb_control_transfer_get_data()
337 * and libusb_control_transfer_get_setup() functions within your transfer
340 * Even though control endpoints do not halt, a completed control transfer
341 * may have a LIBUSB_TRANSFER_STALL status code. This indicates the control
342 * request was not supported.
344 * \section asyncintr Considerations for interrupt transfers
346 * All interrupt transfers are performed using the polling interval presented
347 * by the bInterval value of the endpoint descriptor.
349 * \section asynciso Considerations for isochronous transfers
351 * Isochronous transfers are more complicated than transfers to
352 * non-isochronous endpoints.
354 * To perform I/O to an isochronous endpoint, allocate the transfer by calling
355 * libusb_alloc_transfer() with an appropriate number of isochronous packets.
357 * During filling, set \ref libusb_transfer::type "type" to
358 * \ref libusb_transfer_type::LIBUSB_TRANSFER_TYPE_ISOCHRONOUS
359 * "LIBUSB_TRANSFER_TYPE_ISOCHRONOUS", and set
360 * \ref libusb_transfer::num_iso_packets "num_iso_packets" to a value less than
361 * or equal to the number of packets you requested during allocation.
362 * libusb_alloc_transfer() does not set either of these fields for you, given
363 * that you might not even use the transfer on an isochronous endpoint.
365 * Next, populate the length field for the first num_iso_packets entries in
366 * the \ref libusb_transfer::iso_packet_desc "iso_packet_desc" array. Section
367 * 5.6.3 of the USB2 specifications describe how the maximum isochronous
368 * packet length is determined by wMaxPacketSize field in the endpoint
369 * descriptor. Two functions can help you here:
371 * - libusb_get_max_packet_size() is an easy way to determine the max
372 * packet size for an endpoint.
373 * - libusb_set_iso_packet_lengths() assigns the same length to all packets
374 * within a transfer, which is usually what you want.
376 * For outgoing transfers, you'll obviously fill the buffer and populate the
377 * packet descriptors in hope that all the data gets transferred. For incoming
378 * transfers, you must ensure the buffer has sufficient capacity for
379 * the situation where all packets transfer the full amount of requested data.
381 * Completion handling requires some extra consideration. The
382 * \ref libusb_transfer::actual_length "actual_length" field of the transfer
383 * is meaningless and should not be examined; instead you must refer to the
384 * \ref libusb_iso_packet_descriptor::actual_length "actual_length" field of
385 * each individual packet.
387 * The \ref libusb_transfer::status "status" field of the transfer is also a
389 * - If the packets were submitted and the isochronous data microframes
390 * completed normally, status will have value
391 * \ref libusb_transfer_status::LIBUSB_TRANSFER_COMPLETED
392 * "LIBUSB_TRANSFER_COMPLETED". Note that bus errors and software-incurred
393 * delays are not counted as transfer errors; the transfer.status field may
394 * indicate COMPLETED even if some or all of the packets failed. Refer to
395 * the \ref libusb_iso_packet_descriptor::status "status" field of each
396 * individual packet to determine packet failures.
397 * - The status field will have value
398 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR
399 * "LIBUSB_TRANSFER_ERROR" only when serious errors were encountered.
400 * - Other transfer status codes occur with normal behaviour.
402 * The data for each packet will be found at an offset into the buffer that
403 * can be calculated as if each prior packet completed in full. The
404 * libusb_get_iso_packet_buffer() and libusb_get_iso_packet_buffer_simple()
405 * functions may help you here.
407 * \section asyncmem Memory caveats
409 * In most circumstances, it is not safe to use stack memory for transfer
410 * buffers. This is because the function that fired off the asynchronous
411 * transfer may return before libusb has finished using the buffer, and when
412 * the function returns it's stack gets destroyed. This is true for both
413 * host-to-device and device-to-host transfers.
415 * The only case in which it is safe to use stack memory is where you can
416 * guarantee that the function owning the stack space for the buffer does not
417 * return until after the transfer's callback function has completed. In every
418 * other case, you need to use heap memory instead.
420 * \section asyncflags Fine control
422 * Through using this asynchronous interface, you may find yourself repeating
423 * a few simple operations many times. You can apply a bitwise OR of certain
424 * flags to a transfer to simplify certain things:
425 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_SHORT_NOT_OK
426 * "LIBUSB_TRANSFER_SHORT_NOT_OK" results in transfers which transferred
427 * less than the requested amount of data being marked with status
428 * \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR "LIBUSB_TRANSFER_ERROR"
429 * (they would normally be regarded as COMPLETED)
430 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
431 * "LIBUSB_TRANSFER_FREE_BUFFER" allows you to ask libusb to free the transfer
432 * buffer when freeing the transfer.
433 * - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_TRANSFER
434 * "LIBUSB_TRANSFER_FREE_TRANSFER" causes libusb to automatically free the
435 * transfer after the transfer callback returns.
437 * \section asyncevent Event handling
439 * In accordance of the aim of being a lightweight library, libusb does not
440 * create threads internally. This means that libusb code does not execute
441 * at any time other than when your application is calling a libusb function.
442 * However, an asynchronous model requires that libusb perform work at various
443 * points in time - namely processing the results of previously-submitted
444 * transfers and invoking the user-supplied callback function.
446 * This gives rise to the libusb_handle_events() function which your
447 * application must call into when libusb has work do to. This gives libusb
448 * the opportunity to reap pending transfers, invoke callbacks, etc.
450 * The first issue to discuss here is how your application can figure out
451 * when libusb has work to do. In fact, there are two naive options which
452 * do not actually require your application to know this:
453 * -# Periodically call libusb_handle_events() in non-blocking mode at fixed
454 * short intervals from your main loop
455 * -# Repeatedly call libusb_handle_events() in blocking mode from a dedicated
458 * The first option is plainly not very nice, and will cause unnecessary
459 * CPU wakeups leading to increased power usage and decreased battery life.
460 * The second option is not very nice either, but may be the nicest option
461 * available to you if the "proper" approach can not be applied to your
462 * application (read on...).
464 * The recommended option is to integrate libusb with your application main
465 * event loop. libusb exposes a set of file descriptors which allow you to do
466 * this. Your main loop is probably already calling poll() or select() or a
467 * variant on a set of file descriptors for other event sources (e.g. keyboard
468 * button presses, mouse movements, network sockets, etc). You then add
469 * libusb's file descriptors to your poll()/select() calls, and when activity
470 * is detected on such descriptors you know it is time to call
471 * libusb_handle_events().
473 * There is one final event handling complication. libusb supports
474 * asynchronous transfers which time out after a specified time period, and
475 * this requires that libusb is called into at or after the timeout so that
476 * the timeout can be handled. So, in addition to considering libusb's file
477 * descriptors in your main event loop, you must also consider that libusb
478 * sometimes needs to be called into at fixed points in time even when there
479 * is no file descriptor activity.
481 * For the details on retrieving the set of file descriptors and determining
482 * the next timeout, see the \ref poll "polling and timing" API documentation.
486 * @defgroup poll Polling and timing
488 * This page documents libusb's functions for polling events and timing.
489 * These functions are only necessary for users of the
490 * \ref asyncio "asynchronous API". If you are only using the simpler
491 * \ref syncio "synchronous API" then you do not need to ever call these
494 * The justification for the functionality described here has already been
495 * discussed in the \ref asyncevent "event handling" section of the
496 * asynchronous API documentation. In summary, libusb does not create internal
497 * threads for event processing and hence relies on your application calling
498 * into libusb at certain points in time so that pending events can be handled.
499 * In order to know precisely when libusb needs to be called into, libusb
500 * offers you a set of pollable file descriptors and information about when
501 * the next timeout expires.
503 * If you are using the asynchronous I/O API, you must take one of the two
504 * following options, otherwise your I/O will not complete.
506 * \section pollsimple The simple option
508 * If your application revolves solely around libusb and does not need to
509 * handle other event sources, you can have a program structure as follows:
512 // find and open device
513 // maybe fire off some initial async I/O
515 while (user_has_not_requested_exit)
516 libusb_handle_events();
521 * With such a simple main loop, you do not have to worry about managing
522 * sets of file descriptors or handling timeouts. libusb_handle_events() will
523 * handle those details internally.
525 * \section pollmain The more advanced option
527 * In more advanced applications, you will already have a main loop which
528 * is monitoring other event sources: network sockets, X11 events, mouse
529 * movements, etc. Through exposing a set of file descriptors, libusb is
530 * designed to cleanly integrate into such main loops.
532 * In addition to polling file descriptors for the other event sources, you
533 * take a set of file descriptors from libusb and monitor those too. When you
534 * detect activity on libusb's file descriptors, you call
535 * libusb_handle_events_timeout() in non-blocking mode.
537 * You must also consider the fact that libusb sometimes has to handle events
538 * at certain known times which do not generate activity on file descriptors.
539 * Your main loop must also consider these times, modify it's poll()/select()
540 * timeout accordingly, and track time so that libusb_handle_events_timeout()
541 * is called in non-blocking mode when timeouts expire.
543 * In pseudo-code, you want something that looks like:
548 while (user has not requested application exit) {
549 libusb_get_next_timeout();
550 select(on libusb file descriptors plus any other event sources of interest,
551 using a timeout no larger than the value libusb just suggested)
552 if (select() indicated activity on libusb file descriptors)
553 libusb_handle_events_timeout(0);
554 if (time has elapsed to or beyond the libusb timeout)
555 libusb_handle_events_timeout(0);
561 * The set of file descriptors that libusb uses as event sources may change
562 * during the life of your application. Rather than having to repeatedly
563 * call libusb_get_pollfds(), you can set up notification functions for when
564 * the file descriptor set changes using libusb_set_pollfd_notifiers().
570 list_init(&flying_transfers);
573 fd_removed_cb = NULL;
576 static int calculate_timeout(struct usbi_transfer *transfer)
579 struct timespec current_time;
580 unsigned int timeout =
581 __USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout;
586 r = clock_gettime(CLOCK_MONOTONIC, ¤t_time);
588 usbi_err("failed to read monotonic clock, errno=%d", errno);
592 current_time.tv_sec += timeout / 1000;
593 current_time.tv_nsec += (timeout % 1000) * 1000000;
595 if (current_time.tv_nsec > 1000000000) {
596 current_time.tv_nsec -= 1000000000;
597 current_time.tv_sec++;
600 TIMESPEC_TO_TIMEVAL(&transfer->timeout, ¤t_time);
604 static void add_to_flying_list(struct usbi_transfer *transfer)
606 struct usbi_transfer *cur;
607 struct timeval *timeout = &transfer->timeout;
609 pthread_mutex_lock(&flying_transfers_lock);
611 /* if we have no other flying transfers, start the list with this one */
612 if (list_empty(&flying_transfers)) {
613 list_add(&transfer->list, &flying_transfers);
617 /* if we have infinite timeout, append to end of list */
618 if (!timerisset(timeout)) {
619 list_add_tail(&transfer->list, &flying_transfers);
623 /* otherwise, find appropriate place in list */
624 list_for_each_entry(cur, &flying_transfers, list) {
625 /* find first timeout that occurs after the transfer in question */
626 struct timeval *cur_tv = &cur->timeout;
628 if (!timerisset(cur_tv) || (cur_tv->tv_sec > timeout->tv_sec) ||
629 (cur_tv->tv_sec == timeout->tv_sec &&
630 cur_tv->tv_usec > timeout->tv_usec)) {
631 list_add_tail(&transfer->list, &cur->list);
636 /* otherwise we need to be inserted at the end */
637 list_add_tail(&transfer->list, &flying_transfers);
639 pthread_mutex_unlock(&flying_transfers_lock);
643 * Allocate a libusb transfer with a specified number of isochronous packet
644 * descriptors. The returned transfer is pre-initialized for you. When the new
645 * transfer is no longer needed, it should be freed with
646 * libusb_free_transfer().
648 * Transfers intended for non-isochronous endpoints (e.g. control, bulk,
649 * interrupt) should specify an iso_packets count of zero.
651 * For transfers intended for isochronous endpoints, specify an appropriate
652 * number of packet descriptors to be allocated as part of the transfer.
653 * The returned transfer is not specially initialized for isochronous I/O;
654 * you are still required to set the
655 * \ref libusb_transfer::num_iso_packets "num_iso_packets" and
656 * \ref libusb_transfer::type "type" fields accordingly.
658 * It is safe to allocate a transfer with some isochronous packets and then
659 * use it on a non-isochronous endpoint. If you do this, ensure that at time
660 * of submission, num_iso_packets is 0 and that type is set appropriately.
662 * \param iso_packets number of isochronous packet descriptors to allocate
663 * \returns a newly allocated transfer, or NULL on error
665 API_EXPORTED struct libusb_transfer *libusb_alloc_transfer(int iso_packets)
667 size_t os_alloc_size = usbi_backend->transfer_priv_size
668 + (usbi_backend->add_iso_packet_size * iso_packets);
669 int alloc_size = sizeof(struct usbi_transfer)
670 + sizeof(struct libusb_transfer)
671 + (sizeof(struct libusb_iso_packet_descriptor) * iso_packets)
673 struct usbi_transfer *itransfer = malloc(alloc_size);
677 memset(itransfer, 0, alloc_size);
678 itransfer->num_iso_packets = iso_packets;
679 return __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
683 * Free a transfer structure. This should be called for all transfers
684 * allocated with libusb_alloc_transfer().
686 * If the \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
687 * "LIBUSB_TRANSFER_FREE_BUFFER" flag is set and the transfer buffer is
688 * non-NULL, this function will also free the transfer buffer using the
689 * standard system memory allocator (e.g. free()).
691 * It is legal to call this function with a NULL transfer. In this case,
692 * the function will simply return safely.
694 * \param transfer the transfer to free
696 API_EXPORTED void libusb_free_transfer(struct libusb_transfer *transfer)
698 struct usbi_transfer *itransfer;
702 if (transfer->flags & LIBUSB_TRANSFER_FREE_BUFFER && transfer->buffer)
703 free(transfer->buffer);
705 itransfer = __LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
710 * Submit a transfer. This function will fire off the USB transfer and then
711 * return immediately.
713 * It is undefined behaviour to submit a transfer that has already been
714 * submitted but has not yet completed.
716 * \param transfer the transfer to submit
717 * \returns 0 on success
718 * \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
719 * \returns another LIBUSB_ERROR code on other failure
721 API_EXPORTED int libusb_submit_transfer(struct libusb_transfer *transfer)
723 struct usbi_transfer *itransfer =
724 __LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
727 itransfer->transferred = 0;
728 r = calculate_timeout(itransfer);
730 return LIBUSB_ERROR_OTHER;
732 add_to_flying_list(itransfer);
733 r = usbi_backend->submit_transfer(itransfer);
735 pthread_mutex_lock(&flying_transfers_lock);
736 list_del(&itransfer->list);
737 pthread_mutex_unlock(&flying_transfers_lock);
744 * Asynchronously cancel a previously submitted transfer.
745 * It is undefined behaviour to call this function on a transfer that is
746 * already being cancelled or has already completed.
747 * This function returns immediately, but this does not indicate cancellation
748 * is complete. Your callback function will be invoked at some later time
749 * with a transfer status of
750 * \ref libusb_transfer_status::LIBUSB_TRANSFER_CANCELLED
751 * "LIBUSB_TRANSFER_CANCELLED."
753 * \param transfer the transfer to cancel
754 * \returns 0 on success
755 * \returns a LIBUSB_ERROR code on failure
757 API_EXPORTED int libusb_cancel_transfer(struct libusb_transfer *transfer)
759 struct usbi_transfer *itransfer =
760 __LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
764 r = usbi_backend->cancel_transfer(itransfer);
766 usbi_err("cancel transfer failed error %d", r);
770 void usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
771 enum libusb_transfer_status status)
773 struct libusb_transfer *transfer =
774 __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
777 pthread_mutex_lock(&flying_transfers_lock);
778 list_del(&itransfer->list);
779 pthread_mutex_unlock(&flying_transfers_lock);
781 if (status == LIBUSB_TRANSFER_COMPLETED
782 && transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) {
783 int rqlen = transfer->length;
784 if (transfer->type == LIBUSB_TRANSFER_TYPE_CONTROL)
785 rqlen -= LIBUSB_CONTROL_SETUP_SIZE;
786 if (rqlen != itransfer->transferred) {
787 usbi_dbg("interpreting short transfer as error");
788 status = LIBUSB_TRANSFER_ERROR;
792 flags = transfer->flags;
793 transfer->status = status;
794 transfer->actual_length = itransfer->transferred;
795 if (transfer->callback)
796 transfer->callback(transfer);
797 /* transfer might have been freed by the above call, do not use from
799 if (flags & LIBUSB_TRANSFER_FREE_TRANSFER)
800 libusb_free_transfer(transfer);
803 void usbi_handle_transfer_cancellation(struct usbi_transfer *transfer)
805 /* if the URB was cancelled due to timeout, report timeout to the user */
806 if (transfer->flags & USBI_TRANSFER_TIMED_OUT) {
807 usbi_dbg("detected timeout cancellation");
808 usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_TIMED_OUT);
812 /* otherwise its a normal async cancel */
813 usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_CANCELLED);
816 static void handle_timeout(struct usbi_transfer *itransfer)
818 struct libusb_transfer *transfer =
819 __USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
822 itransfer->flags |= USBI_TRANSFER_TIMED_OUT;
823 r = libusb_cancel_transfer(transfer);
825 usbi_warn("async cancel failed %d errno=%d", r, errno);
828 static int handle_timeouts(void)
830 struct timespec systime_ts;
831 struct timeval systime;
832 struct usbi_transfer *transfer;
835 pthread_mutex_lock(&flying_transfers_lock);
836 if (list_empty(&flying_transfers))
839 /* get current time */
840 r = clock_gettime(CLOCK_MONOTONIC, &systime_ts);
844 TIMESPEC_TO_TIMEVAL(&systime, &systime_ts);
846 /* iterate through flying transfers list, finding all transfers that
847 * have expired timeouts */
848 list_for_each_entry(transfer, &flying_transfers, list) {
849 struct timeval *cur_tv = &transfer->timeout;
851 /* if we've reached transfers of infinite timeout, we're all done */
852 if (!timerisset(cur_tv))
855 /* ignore timeouts we've already handled */
856 if (transfer->flags & USBI_TRANSFER_TIMED_OUT)
859 /* if transfer has non-expired timeout, nothing more to do */
860 if ((cur_tv->tv_sec > systime.tv_sec) ||
861 (cur_tv->tv_sec == systime.tv_sec &&
862 cur_tv->tv_usec > systime.tv_usec))
865 /* otherwise, we've got an expired timeout to handle */
866 handle_timeout(transfer);
870 pthread_mutex_unlock(&flying_transfers_lock);
874 static int handle_events(struct timeval *tv)
877 struct usbi_pollfd *ipollfd;
878 struct timeval timeout;
879 struct timeval poll_timeout;
885 r = libusb_get_next_timeout(&timeout);
887 /* timeout already expired? */
888 if (!timerisset(&timeout))
889 return handle_timeouts();
891 /* choose the smallest of next URB timeout or user specified timeout */
892 if (timercmp(&timeout, tv, <))
893 poll_timeout = timeout;
900 pthread_mutex_lock(&pollfds_lock);
901 list_for_each_entry(ipollfd, &pollfds, list)
904 /* TODO: malloc when number of fd's changes, not on every poll */
905 fds = malloc(sizeof(*fds) * nfds);
907 return LIBUSB_ERROR_NO_MEM;
909 list_for_each_entry(ipollfd, &pollfds, list) {
910 struct libusb_pollfd *pollfd = &ipollfd->pollfd;
914 fds[i].events = pollfd->events;
917 pthread_mutex_unlock(&pollfds_lock);
919 timeout_ms = (poll_timeout.tv_sec * 1000) + (poll_timeout.tv_usec / 1000);
920 usbi_dbg("poll() %d fds with timeout in %dms", nfds, timeout_ms);
921 r = poll(fds, nfds, timeout_ms);
922 usbi_dbg("poll() returned %d", r);
924 return handle_timeouts();
925 } else if (r == -1 && errno == EINTR) {
926 return LIBUSB_ERROR_INTERRUPTED;
928 usbi_err("poll failed %d err=%d\n", r, errno);
929 return LIBUSB_ERROR_IO;
932 r = usbi_backend->handle_events(fds, nfds, r);
934 usbi_err("backend handle_events failed with error %d", r);
940 * Handle any pending events.
942 * libusb determines "pending events" by checking if any timeouts have expired
943 * and by checking the set of file descriptors for activity.
945 * If a zero timeval is passed, this function will handle any already-pending
946 * events and then immediately return in non-blocking style.
948 * If a non-zero timeval is passed and no events are currently pending, this
949 * function will block waiting for events to handle up until the specified
950 * timeout. If an event arrives or a signal is raised, this function will
953 * \param tv the maximum time to block waiting for events, or zero for
955 * \returns 0 on success, or a LIBUSB_ERROR code on failure
957 API_EXPORTED int libusb_handle_events_timeout(struct timeval *tv)
959 return handle_events(tv);
963 * Handle any pending events in blocking mode with a sensible timeout. This
964 * timeout is currently hardcoded at 2 seconds but we may change this if we
965 * decide other values are more sensible. For finer control over whether this
966 * function is blocking or non-blocking, or the maximum timeout, use
967 * libusb_handle_events_timeout() instead.
969 * \returns 0 on success, or a LIBUSB_ERROR code on failure
971 API_EXPORTED int libusb_handle_events(void)
976 return handle_events(&tv);
980 * Determine the next internal timeout that libusb needs to handle. You only
981 * need to use this function if you are calling poll() or select() or similar
982 * on libusb's file descriptors yourself - you do not need to use it if you
983 * are calling libusb_handle_events() or a variant directly.
985 * You should call this function in your main loop in order to determine how
986 * long to wait for select() or poll() to return results. libusb needs to be
987 * called into at this timeout, so you should use it as an upper bound on
988 * your select() or poll() call.
990 * When the timeout has expired, call into libusb_handle_events_timeout()
991 * (perhaps in non-blocking mode) so that libusb can handle the timeout.
993 * This function may return 1 (success) and an all-zero timeval. If this is
994 * the case, it indicates that libusb has a timeout that has already expired
995 * so you should call libusb_handle_events_timeout() or similar immediately.
996 * A return code of 0 indicates that there are no pending timeouts.
998 * \param tv output location for a relative time against the current
999 * clock in which libusb must be called into in order to process timeout events
1000 * \returns 0 if there are no pending timeouts, 1 if a timeout was returned,
1001 * or LIBUSB_ERROR_OTHER on failure
1003 API_EXPORTED int libusb_get_next_timeout(struct timeval *tv)
1005 struct usbi_transfer *transfer;
1006 struct timespec cur_ts;
1007 struct timeval cur_tv;
1008 struct timeval *next_timeout;
1012 pthread_mutex_lock(&flying_transfers_lock);
1013 if (list_empty(&flying_transfers)) {
1014 pthread_mutex_unlock(&flying_transfers_lock);
1015 usbi_dbg("no URBs, no timeout!");
1019 /* find next transfer which hasn't already been processed as timed out */
1020 list_for_each_entry(transfer, &flying_transfers, list) {
1021 if (!(transfer->flags & USBI_TRANSFER_TIMED_OUT)) {
1026 pthread_mutex_unlock(&flying_transfers_lock);
1029 usbi_dbg("all URBs have already been processed for timeouts");
1033 next_timeout = &transfer->timeout;
1035 /* no timeout for next transfer */
1036 if (!timerisset(next_timeout)) {
1037 usbi_dbg("no URBs with timeouts, no timeout!");
1041 r = clock_gettime(CLOCK_MONOTONIC, &cur_ts);
1043 usbi_err("failed to read monotonic clock, errno=%d", errno);
1044 return LIBUSB_ERROR_OTHER;
1046 TIMESPEC_TO_TIMEVAL(&cur_tv, &cur_ts);
1048 if (timercmp(&cur_tv, next_timeout, >=)) {
1049 usbi_dbg("first timeout already expired");
1052 timersub(next_timeout, &cur_tv, tv);
1053 usbi_dbg("next timeout in %d.%06ds", tv->tv_sec, tv->tv_usec);
1060 * Register notification functions for file descriptor additions/removals.
1061 * These functions will be invoked for every new or removed file descriptor
1062 * that libusb uses as an event source.
1064 * To remove notifiers, pass NULL values for the function pointers.
1066 * \param added_cb pointer to function for addition notifications
1067 * \param removed_cb pointer to function for removal notifications
1069 API_EXPORTED void libusb_set_pollfd_notifiers(libusb_pollfd_added_cb added_cb,
1070 libusb_pollfd_removed_cb removed_cb)
1072 fd_added_cb = added_cb;
1073 fd_removed_cb = removed_cb;
1076 int usbi_add_pollfd(int fd, short events)
1078 struct usbi_pollfd *ipollfd = malloc(sizeof(*ipollfd));
1080 return LIBUSB_ERROR_NO_MEM;
1082 usbi_dbg("add fd %d events %d", fd, events);
1083 ipollfd->pollfd.fd = fd;
1084 ipollfd->pollfd.events = events;
1085 pthread_mutex_lock(&pollfds_lock);
1086 list_add(&ipollfd->list, &pollfds);
1087 pthread_mutex_unlock(&pollfds_lock);
1090 fd_added_cb(fd, events);
1094 void usbi_remove_pollfd(int fd)
1096 struct usbi_pollfd *ipollfd;
1099 usbi_dbg("remove fd %d", fd);
1100 pthread_mutex_lock(&pollfds_lock);
1101 list_for_each_entry(ipollfd, &pollfds, list)
1102 if (ipollfd->pollfd.fd == fd) {
1108 usbi_dbg("couldn't find fd %d to remove", fd);
1109 pthread_mutex_unlock(&pollfds_lock);
1113 list_del(&ipollfd->list);
1114 pthread_mutex_unlock(&pollfds_lock);
1121 * Retrieve a list of file descriptors that should be polled by your main loop
1122 * as libusb event sources.
1124 * The returned list is NULL-terminated and should be freed with free() when
1125 * done. The actual list contents must not be touched.
1127 * \returns a NULL-terminated list of libusb_pollfd structures, or NULL on
1130 API_EXPORTED const struct libusb_pollfd **libusb_get_pollfds(void)
1132 struct libusb_pollfd **ret = NULL;
1133 struct usbi_pollfd *ipollfd;
1137 pthread_mutex_lock(&pollfds_lock);
1138 list_for_each_entry(ipollfd, &pollfds, list)
1141 ret = calloc(cnt + 1, sizeof(struct libusb_pollfd *));
1145 list_for_each_entry(ipollfd, &pollfds, list)
1146 ret[i++] = (struct libusb_pollfd *) ipollfd;
1150 pthread_mutex_unlock(&pollfds_lock);
1151 return (const struct libusb_pollfd **) ret;
1154 void usbi_handle_disconnect(struct libusb_device_handle *handle)
1156 struct usbi_transfer *cur;
1157 struct usbi_transfer *to_cancel;
1159 usbi_dbg("device %d.%d",
1160 handle->dev->bus_number, handle->dev->device_address);
1162 /* terminate all pending transfers with the LIBUSB_TRANSFER_NO_DEVICE
1165 * this is a bit tricky because:
1166 * 1. we can't do transfer completion while holding flying_transfers_lock
1167 * 2. the transfers list can change underneath us - if we were to build a
1168 * list of transfers to complete (while holding look), the situation
1169 * might be different by the time we come to free them
1171 * so we resort to a loop-based approach as below
1172 * FIXME: is this still potentially racy?
1176 pthread_mutex_lock(&flying_transfers_lock);
1178 list_for_each_entry(cur, &flying_transfers, list)
1179 if (__USBI_TRANSFER_TO_LIBUSB_TRANSFER(cur)->dev_handle == handle) {
1183 pthread_mutex_unlock(&flying_transfers_lock);
1188 usbi_backend->clear_transfer_priv(to_cancel);
1189 usbi_handle_transfer_completion(to_cancel, LIBUSB_TRANSFER_NO_DEVICE);