2 * Internal header 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
33 #define DEVICE_DESC_LENGTH 18
35 #define USB_MAXENDPOINTS 32
36 #define USB_MAXINTERFACES 32
37 #define USB_MAXCONFIG 8
40 struct list_head *prev, *next;
43 /* Get an entry from the list
44 * ptr - the address of this list_head element in "type"
45 * type - the data type that contains "member"
46 * member - the list_head element in "type"
48 #define list_entry(ptr, type, member) \
49 ((type *)((char *)(ptr) - (unsigned long)(&((type *)0L)->member)))
51 /* Get each entry from a list
52 * pos - A structure pointer has a "member" element
54 * member - the list_head element in "pos"
56 #define list_for_each_entry(pos, head, member) \
57 for (pos = list_entry((head)->next, typeof(*pos), member); \
58 &pos->member != (head); \
59 pos = list_entry(pos->member.next, typeof(*pos), member))
61 #define list_for_each_entry_safe(pos, n, head, member) \
62 for (pos = list_entry((head)->next, typeof(*pos), member), \
63 n = list_entry(pos->member.next, typeof(*pos), member); \
64 &pos->member != (head); \
65 pos = n, n = list_entry(n->member.next, typeof(*n), member))
67 #define list_empty(entry) ((entry)->next == (entry))
69 static inline void list_init(struct list_head *entry)
71 entry->prev = entry->next = entry;
74 static inline void list_add(struct list_head *entry, struct list_head *head)
76 entry->next = head->next;
79 head->next->prev = entry;
83 static inline void list_add_tail(struct list_head *entry,
84 struct list_head *head)
87 entry->prev = head->prev;
89 head->prev->next = entry;
93 static inline void list_del(struct list_head *entry)
95 entry->next->prev = entry->prev;
96 entry->prev->next = entry->next;
99 #define container_of(ptr, type, member) ({ \
100 const typeof( ((type *)0)->member ) *__mptr = (ptr); \
101 (type *)( (char *)__mptr - offsetof(type,member) );})
103 #define MIN(a, b) ((a) < (b) ? (a) : (b))
104 #define MAX(a, b) ((a) > (b) ? (a) : (b))
106 #define TIMESPEC_IS_SET(ts) ((ts)->tv_sec != 0 || (ts)->tv_nsec != 0)
108 enum usbi_log_level {
115 void usbi_log(struct libusb_context *ctx, enum usbi_log_level,
116 const char *function, const char *format, ...);
118 #ifdef ENABLE_LOGGING
119 #define _usbi_log(ctx, level, fmt...) usbi_log(ctx, level, __FUNCTION__, fmt)
121 #define _usbi_log(ctx, level, fmt...)
124 #ifdef ENABLE_DEBUG_LOGGING
125 #define usbi_dbg(fmt...) _usbi_log(NULL, LOG_LEVEL_DEBUG, fmt)
127 #define usbi_dbg(fmt...)
130 #define usbi_info(ctx, fmt...) _usbi_log(ctx, LOG_LEVEL_INFO, fmt)
131 #define usbi_warn(ctx, fmt...) _usbi_log(ctx, LOG_LEVEL_WARNING, fmt)
132 #define usbi_err(ctx, fmt...) _usbi_log(ctx, LOG_LEVEL_ERROR, fmt)
134 #define USBI_GET_CONTEXT(ctx) if (!(ctx)) (ctx) = usbi_default_context
135 #define DEVICE_CTX(dev) ((dev)->ctx)
136 #define HANDLE_CTX(handle) (DEVICE_CTX((handle)->dev))
137 #define TRANSFER_CTX(transfer) (HANDLE_CTX((transfer)->dev_handle))
138 #define ITRANSFER_CTX(transfer) \
139 (TRANSFER_CTX(__USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)))
141 extern struct libusb_context *usbi_default_context;
143 struct libusb_context {
147 /* internal control pipe, used for interrupting event handling when
148 * something needs to modify poll fds. */
151 struct list_head usb_devs;
152 pthread_mutex_t usb_devs_lock;
154 /* A list of open handles. Backends are free to traverse this if required.
156 struct list_head open_devs;
157 pthread_mutex_t open_devs_lock;
159 /* this is a list of in-flight transfer handles, sorted by timeout
160 * expiration. URBs to timeout the soonest are placed at the beginning of
161 * the list, URBs that will time out later are placed after, and urbs with
162 * infinite timeout are always placed at the very end. */
163 struct list_head flying_transfers;
164 pthread_mutex_t flying_transfers_lock;
166 /* list of poll fds */
167 struct list_head pollfds;
168 pthread_mutex_t pollfds_lock;
170 /* a counter that is set when we want to interrupt event handling, in order
171 * to modify the poll fd set. and a lock to protect it. */
172 unsigned int pollfd_modify;
173 pthread_mutex_t pollfd_modify_lock;
175 /* user callbacks for pollfd changes */
176 libusb_pollfd_added_cb fd_added_cb;
177 libusb_pollfd_removed_cb fd_removed_cb;
178 void *fd_cb_user_data;
180 /* ensures that only one thread is handling events at any one time */
181 pthread_mutex_t events_lock;
183 /* used to see if there is an active thread doing event handling */
184 int event_handler_active;
186 /* used to wait for event completion in threads other than the one that is
188 pthread_mutex_t event_waiters_lock;
189 pthread_cond_t event_waiters_cond;
192 struct libusb_device {
193 /* lock protects refcnt, everything else is finalized at initialization
195 pthread_mutex_t lock;
198 struct libusb_context *ctx;
201 uint8_t device_address;
202 uint8_t num_configurations;
204 struct list_head list;
205 unsigned long session_data;
206 unsigned char os_priv[0];
209 struct libusb_device_handle {
210 /* lock protects claimed_interfaces */
211 pthread_mutex_t lock;
212 unsigned long claimed_interfaces;
214 struct list_head list;
215 struct libusb_device *dev;
216 unsigned char os_priv[0];
219 #define USBI_TRANSFER_TIMED_OUT (1<<0)
222 USBI_CLOCK_MONOTONIC,
226 /* in-memory transfer layout:
228 * 1. struct usbi_transfer
229 * 2. struct libusb_transfer (which includes iso packets) [variable size]
230 * 3. os private data [variable size]
232 * from a libusb_transfer, you can get the usbi_transfer by rewinding the
233 * appropriate number of bytes.
234 * the usbi_transfer includes the number of allocated packets, so you can
235 * determine the size of the transfer and hence the start and length of the
239 struct usbi_transfer {
241 struct list_head list;
242 struct timeval timeout;
247 #define __USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer) \
248 ((struct libusb_transfer *)(((void *)(transfer)) \
249 + sizeof(struct usbi_transfer)))
250 #define __LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer) \
251 ((struct usbi_transfer *)(((void *)(transfer)) \
252 - sizeof(struct usbi_transfer)))
254 static inline void *usbi_transfer_get_os_priv(struct usbi_transfer *transfer)
256 return ((void *)transfer) + sizeof(struct usbi_transfer)
257 + sizeof(struct libusb_transfer)
258 + (transfer->num_iso_packets
259 * sizeof(struct libusb_iso_packet_descriptor));
264 /* All standard descriptors have these 2 fields in common */
265 struct usb_descriptor_header {
267 uint8_t bDescriptorType;
270 /* shared data and functions */
272 int usbi_io_init(struct libusb_context *ctx);
273 void usbi_io_exit(struct libusb_context *ctx);
275 struct libusb_device *usbi_alloc_device(struct libusb_context *ctx,
276 unsigned long session_id);
277 struct libusb_device *usbi_get_device_by_session_id(struct libusb_context *ctx,
278 unsigned long session_id);
279 int usbi_sanitize_device(struct libusb_device *dev);
280 void usbi_handle_disconnect(struct libusb_device_handle *handle);
282 void usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
283 enum libusb_transfer_status status);
284 void usbi_handle_transfer_cancellation(struct usbi_transfer *transfer);
286 int usbi_parse_descriptor(unsigned char *source, char *descriptor, void *dest,
288 int usbi_get_config_index_by_value(struct libusb_device *dev,
289 uint8_t bConfigurationValue, int *idx);
294 /* must come first */
295 struct libusb_pollfd pollfd;
297 struct list_head list;
300 int usbi_add_pollfd(struct libusb_context *ctx, int fd, short events);
301 void usbi_remove_pollfd(struct libusb_context *ctx, int fd);
303 /* device discovery */
305 /* we traverse usbfs without knowing how many devices we are going to find.
306 * so we create this discovered_devs model which is similar to a linked-list
307 * which grows when required. it can be freed once discovery has completed,
308 * eliminating the need for a list node in the libusb_device structure
310 struct discovered_devs {
313 struct libusb_device *devices[0];
316 struct discovered_devs *discovered_devs_append(
317 struct discovered_devs *discdevs, struct libusb_device *dev);
321 /* This is the interface that OS backends need to implement.
322 * All fields are mandatory, except ones explicitly noted as optional. */
323 struct usbi_os_backend {
324 /* A human-readable name for your backend, e.g. "Linux usbfs" */
327 /* Perform initialization of your backend. You might use this function
328 * to determine specific capabilities of the system, allocate required
329 * data structures for later, etc.
331 * This function is called when a libusb user initializes the library
334 * Return 0 on success, or a LIBUSB_ERROR code on failure.
336 int (*init)(struct libusb_context *ctx);
338 /* Deinitialization. Optional. This function should destroy anything
339 * that was set up by init.
341 * This function is called when the user deinitializes the library.
345 /* Enumerate all the USB devices on the system, returning them in a list
346 * of discovered devices.
348 * Your implementation should enumerate all devices on the system,
349 * regardless of whether they have been seen before or not.
351 * When you have found a device, compute a session ID for it. The session
352 * ID should uniquely represent that particular device for that particular
353 * connection session since boot (i.e. if you disconnect and reconnect a
354 * device immediately after, it should be assigned a different session ID).
355 * If your OS cannot provide a unique session ID as described above,
356 * presenting a session ID of (bus_number << 8 | device_address) should
357 * be sufficient. Bus numbers and device addresses wrap and get reused,
358 * but that is an unlikely case.
360 * After computing a session ID for a device, call
361 * usbi_get_device_by_session_id(). This function checks if libusb already
362 * knows about the device, and if so, it provides you with a libusb_device
365 * If usbi_get_device_by_session_id() returns NULL, it is time to allocate
366 * a new device structure for the device. Call usbi_alloc_device() to
367 * obtain a new libusb_device structure with reference count 1. Populate
368 * the bus_number and device_address attributes of the new device, and
369 * perform any other internal backend initialization you need to do. At
370 * this point, you should be ready to provide device descriptors and so
371 * on through the get_*_descriptor functions. Finally, call
372 * usbi_sanitize_device() to perform some final sanity checks on the
373 * device. Assuming all of the above succeeded, we can now continue.
374 * If any of the above failed, remember to unreference the device that
375 * was returned by usbi_alloc_device().
377 * At this stage we have a populated libusb_device structure (either one
378 * that was found earlier, or one that we have just allocated and
379 * populated). This can now be added to the discovered devices list
380 * using discovered_devs_append(). Note that discovered_devs_append()
381 * may reallocate the list, returning a new location for it, and also
382 * note that reallocation can fail. Your backend should handle these
383 * error conditions appropriately.
385 * This function should not generate any bus I/O and should not block.
386 * If I/O is required (e.g. reading the active configuration value), it is
387 * OK to ignore these suggestions :)
389 * This function is executed when the user wishes to retrieve a list
390 * of USB devices connected to the system.
392 * Return 0 on success, or a LIBUSB_ERROR code on failure.
394 int (*get_device_list)(struct libusb_context *ctx,
395 struct discovered_devs **discdevs);
397 /* Open a device for I/O and other USB operations. The device handle
398 * is preallocated for you, you can retrieve the device in question
399 * through handle->dev.
401 * Your backend should allocate any internal resources required for I/O
402 * and other operations so that those operations can happen (hopefully)
403 * without hiccup. This is also a good place to inform libusb that it
404 * should monitor certain file descriptors related to this device -
405 * see the usbi_add_pollfd() function.
407 * This function should not generate any bus I/O and should not block.
409 * This function is called when the user attempts to obtain a device
410 * handle for a device.
414 * - LIBUSB_ERROR_ACCESS if the user has insufficient permissions
415 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since
417 * - another LIBUSB_ERROR code on other failure
419 * Do not worry about freeing the handle on failed open, the upper layers
422 int (*open)(struct libusb_device_handle *handle);
424 /* Close a device such that the handle cannot be used again. Your backend
425 * should destroy any resources that were allocated in the open path.
426 * This may also be a good place to call usbi_remove_pollfd() to inform
427 * libusb of any file descriptors associated with this device that should
428 * no longer be monitored.
430 * This function is called when the user closes a device handle.
432 void (*close)(struct libusb_device_handle *handle);
434 /* Retrieve the device descriptor from a device.
436 * The descriptor should be retrieved from memory, NOT via bus I/O to the
437 * device. This means that you may have to cache it in a private structure
438 * during get_device_list enumeration. Alternatively, you may be able
439 * to retrieve it from a kernel interface (some Linux setups can do this)
440 * still without generating bus I/O.
442 * This function is expected to write DEVICE_DESC_LENGTH (18) bytes into
443 * buffer, which is guaranteed to be big enough.
445 * This function is called when sanity-checking a device before adding
446 * it to the list of discovered devices, and also when the user requests
447 * to read the device descriptor.
449 * This function is expected to return the descriptor in bus-endian format
450 * (LE). If it returns the multi-byte values in host-endian format,
451 * set the host_endian output parameter to "1".
453 * Return 0 on success or a LIBUSB_ERROR code on failure.
455 int (*get_device_descriptor)(struct libusb_device *device,
456 unsigned char *buffer, int *host_endian);
458 /* Get the ACTIVE configuration descriptor for a device.
460 * The descriptor should be retrieved from memory, NOT via bus I/O to the
461 * device. This means that you may have to cache it in a private structure
462 * during get_device_list enumeration. You may also have to keep track
463 * of which configuration is active when the user changes it.
465 * This function is expected to write len bytes of data into buffer, which
466 * is guaranteed to be big enough. If you can only do a partial write,
467 * return an error code.
469 * This function is expected to return the descriptor in bus-endian format
470 * (LE). If it returns the multi-byte values in host-endian format,
471 * set the host_endian output parameter to "1".
475 * - LIBUSB_ERROR_NOT_FOUND if the device is in unconfigured state
476 * - another LIBUSB_ERROR code on other failure
478 int (*get_active_config_descriptor)(struct libusb_device *device,
479 unsigned char *buffer, size_t len, int *host_endian);
481 /* Get a specific configuration descriptor for a device.
483 * The descriptor should be retrieved from memory, NOT via bus I/O to the
484 * device. This means that you may have to cache it in a private structure
485 * during get_device_list enumeration.
487 * The requested descriptor is expressed as a zero-based index (i.e. 0
488 * indicates that we are requesting the first descriptor). The index does
489 * not (necessarily) equal the bConfigurationValue of the configuration
492 * This function is expected to write len bytes of data into buffer, which
493 * is guaranteed to be big enough. If you can only do a partial write,
494 * return an error code.
496 * This function is expected to return the descriptor in bus-endian format
497 * (LE). If it returns the multi-byte values in host-endian format,
498 * set the host_endian output parameter to "1".
500 * Return 0 on success or a LIBUSB_ERROR code on failure.
502 int (*get_config_descriptor)(struct libusb_device *device,
503 uint8_t config_index, unsigned char *buffer, size_t len,
506 /* Get the bConfigurationValue for the active configuration for a device.
507 * Optional. This should only be implemented if you can retrieve it from
508 * cache (don't generate I/O).
510 * If you cannot retrieve this from cache, either do not implement this
511 * function, or return LIBUSB_ERROR_NOT_SUPPORTED. This will cause
512 * libusb to retrieve the information through a standard control transfer.
514 * This function must be non-blocking.
517 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
519 * - LIBUSB_ERROR_NOT_SUPPORTED if the value cannot be retrieved without
521 * - another LIBUSB_ERROR code on other failure.
523 int (*get_configuration)(struct libusb_device_handle *handle, int *config);
525 /* Set the active configuration for a device.
527 * A configuration value of -1 should put the device in unconfigured state.
529 * This function can block.
533 * - LIBUSB_ERROR_NOT_FOUND if the configuration does not exist
534 * - LIBUSB_ERROR_BUSY if interfaces are currently claimed (and hence
535 * configuration cannot be changed)
536 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
538 * - another LIBUSB_ERROR code on other failure.
540 int (*set_configuration)(struct libusb_device_handle *handle, int config);
542 /* Claim an interface. When claimed, the application can then perform
543 * I/O to an interface's endpoints.
545 * This function should not generate any bus I/O and should not block.
546 * Interface claiming is a logical operation that simply ensures that
547 * no other drivers/applications are using the interface, and after
548 * claiming, no other drivers/applicatiosn can use the interface because
553 * - LIBUSB_ERROR_NOT_FOUND if the interface does not exist
554 * - LIBUSB_ERROR_BUSY if the interface is in use by another driver/app
555 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
557 * - another LIBUSB_ERROR code on other failure
559 int (*claim_interface)(struct libusb_device_handle *handle, int iface);
561 /* Release a previously claimed interface.
563 * This function should also generate a SET_INTERFACE control request,
564 * resetting the alternate setting of that interface to 0. It's OK for
565 * this function to block as a result.
567 * You will only ever be asked to release an interface which was
568 * successfully claimed earlier.
572 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
574 * - another LIBUSB_ERROR code on other failure
576 int (*release_interface)(struct libusb_device_handle *handle, int iface);
578 /* Set the alternate setting for an interface.
580 * You will only ever be asked to set the alternate setting for an
581 * interface which was successfully claimed earlier.
583 * It's OK for this function to block.
587 * - LIBUSB_ERROR_NOT_FOUND if the alternate setting does not exist
588 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
590 * - another LIBUSB_ERROR code on other failure
592 int (*set_interface_altsetting)(struct libusb_device_handle *handle,
593 int iface, int altsetting);
595 /* Clear a halt/stall condition on an endpoint.
597 * It's OK for this function to block.
601 * - LIBUSB_ERROR_NOT_FOUND if the endpoint does not exist
602 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
604 * - another LIBUSB_ERROR code on other failure
606 int (*clear_halt)(struct libusb_device_handle *handle,
607 unsigned char endpoint);
609 /* Perform a USB port reset to reinitialize a device.
611 * If possible, the handle should still be usable after the reset
612 * completes, assuming that the device descriptors did not change during
613 * reset and all previous interface state can be restored.
615 * If something changes, or you cannot easily locate/verify the resetted
616 * device, return LIBUSB_ERROR_NOT_FOUND. This prompts the application
617 * to close the old handle and re-enumerate the device.
621 * - LIBUSB_ERROR_NOT_FOUND if re-enumeration is required, or if the device
622 * has been disconnected since it was opened
623 * - another LIBUSB_ERROR code on other failure
625 int (*reset_device)(struct libusb_device_handle *handle);
627 /* Determine if a kernel driver is active on an interface. Optional.
629 * The presence of a kernel driver on an interface indicates that any
630 * calls to claim_interface would fail with the LIBUSB_ERROR_BUSY code.
633 * - 0 if no driver is active
634 * - 1 if a driver is active
635 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
637 * - another LIBUSB_ERROR code on other failure
639 int (*kernel_driver_active)(struct libusb_device_handle *handle,
642 /* Detach a kernel driver from an interface. Optional.
644 * After detaching a kernel driver, the interface should be available
649 * - LIBUSB_ERROR_NOT_FOUND if no kernel driver was active
650 * - LIBUSB_ERROR_INVALID_PARAM if the interface does not exist
651 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
653 * - another LIBUSB_ERROR code on other failure
655 int (*detach_kernel_driver)(struct libusb_device_handle *handle,
658 /* Attach a kernel driver to an interface. Optional.
660 * Reattach a kernel driver to the device.
664 * - LIBUSB_ERROR_NOT_FOUND if no kernel driver was active
665 * - LIBUSB_ERROR_INVALID_PARAM if the interface does not exist
666 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected since it
668 * - LIBUSB_ERROR_BUSY if a program or driver has claimed the interface,
669 * preventing reattachment
670 * - another LIBUSB_ERROR code on other failure
672 int (*attach_kernel_driver)(struct libusb_device_handle *handle,
675 /* Destroy a device. Optional.
677 * This function is called when the last reference to a device is
678 * destroyed. It should free any resources allocated in the get_device_list
681 void (*destroy_device)(struct libusb_device *dev);
683 /* Submit a transfer. Your implementation should take the transfer,
684 * morph it into whatever form your platform requires, and submit it
687 * This function must not block.
691 * - LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
692 * - another LIBUSB_ERROR code on other failure
694 int (*submit_transfer)(struct usbi_transfer *itransfer);
696 /* Cancel a previously submitted transfer.
698 * This function must not block. The transfer cancellation must complete
699 * later, resulting in a call to usbi_handle_transfer_cancellation()
700 * from the context of handle_events.
702 int (*cancel_transfer)(struct usbi_transfer *itransfer);
704 /* Clear a transfer as if it has completed or cancelled, but do not
705 * report any completion/cancellation to the library. You should free
706 * all private data from the transfer as if you were just about to report
707 * completion or cancellation.
709 * This function might seem a bit out of place. It is used when libusb
710 * detects a disconnected device - it calls this function for all pending
711 * transfers before reporting completion (with the disconnect code) to
712 * the user. Maybe we can improve upon this internal interface in future.
714 void (*clear_transfer_priv)(struct usbi_transfer *itransfer);
716 /* Handle any pending events. This involves monitoring any active
717 * transfers and processing their completion or cancellation.
719 * The function is passed an array of pollfd structures (size nfds)
720 * as a result of the poll() system call. The num_ready parameter
721 * indicates the number of file descriptors that have reported events
722 * (i.e. the poll() return value). This should be enough information
723 * for you to determine which actions need to be taken on the currently
726 * For any cancelled transfers, call usbi_handle_transfer_cancellation().
727 * For completed transfers, call usbi_handle_transfer_completion().
728 * For control/bulk/interrupt transfers, populate the "transferred"
729 * element of the appropriate usbi_transfer structure before calling the
730 * above functions. For isochronous transfers, populate the status and
731 * transferred fields of the iso packet descriptors of the transfer.
733 * This function should also be able to detect disconnection of the
734 * device, reporting that situation with usbi_handle_disconnect().
736 * Return 0 on success, or a LIBUSB_ERROR code on failure.
738 int (*handle_events)(struct libusb_context *ctx,
739 struct pollfd *fds, nfds_t nfds, int num_ready);
741 /* Get time from specified clock. At least two clocks must be implemented
742 by the backend: USBI_CLOCK_REALTIME, and USBI_CLOCK_MONOTONIC.
744 Description of clocks:
745 USBI_CLOCK_REALTIME : clock returns time since system epoch.
746 USBI_CLOCK_MONOTONIC: clock returns time since unspecified start
749 int (*clock_gettime)(int clkid, struct timespec *tp);
751 /* Number of bytes to reserve for per-device private backend data.
752 * This private data area is accessible through the "os_priv" field of
753 * struct libusb_device. */
754 size_t device_priv_size;
756 /* Number of bytes to reserve for per-handle private backend data.
757 * This private data area is accessible through the "os_priv" field of
758 * struct libusb_device. */
759 size_t device_handle_priv_size;
761 /* Number of bytes to reserve for per-transfer private backend data.
762 * This private data area is accessible by calling
763 * usbi_transfer_get_os_priv() on the appropriate usbi_transfer instance.
765 size_t transfer_priv_size;
767 /* Mumber of additional bytes for os_priv for each iso packet.
768 * Can your backend use this? */
769 /* FIXME: linux can't use this any more. if other OS's cannot either,
770 * then remove this */
771 size_t add_iso_packet_size;
774 extern const struct usbi_os_backend * const usbi_backend;
776 extern const struct usbi_os_backend linux_usbfs_backend;
777 extern const struct usbi_os_backend darwin_backend;