www.pudn.com > libusb-jni.zip > io.c, change:2013-12-30,size:95245b

/*
* I/O functions for libusb
* Copyright (C) 2007-2009 Daniel Drake <dsd@gentoo.org>
* Copyright (c) 2001 Johannes Erdfelt <johannes@erdfelt.com>
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* version 2.1 of the License, or (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public
* License along with this library; if not, write to the Free Software
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/

#include <config.h>
#include <errno.h>
#include <signal.h>
#include <stdint.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>

#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

#ifdef USBI_TIMERFD_AVAILABLE
#include <sys/timerfd.h>
#endif

#include "libusbi.h"

#ifndef TIMESPEC_TO_TIMEVAL
#define TIMESPEC_TO_TIMEVAL(tv, ts)                 \
do {                                          \
(tv)->tv_sec = (ts)->tv_sec;          \
(tv)->tv_usec = (ts)->tv_nsec / 1000; \
} while (0)
#endif

/**
* \page io Synchronous and asynchronous device I/O
*
* \section intro Introduction
*
* If you're using libusb in your application, you're probably wanting to
* perform I/O with devices - you want to perform USB data transfers.
*
* libusb offers two separate interfaces for device I/O. This page aims to
* introduce the two in order to help you decide which one is more suitable
* for your application. You can also choose to use both interfaces in your
* application by considering each transfer on a case-by-case basis.
*
* Once you have read through the following discussion, you should consult the
* detailed API documentation pages for the details:
* - \ref syncio
* - \ref asyncio
*
* \section theory Transfers at a logical level
*
* At a logical level, USB transfers typically happen in two parts. For
* example, when reading data from a endpoint:
* -# A request for data is sent to the device
* -# Some time later, the incoming data is received by the host
*
* or when writing data to an endpoint:
*
* -# The data is sent to the device
* -# Some time later, the host receives acknowledgement from the device that
*    the data has been transferred.
*
* There may be an indefinite delay between the two steps. Consider a
* fictional USB input device with a button that the user can press. In order
* to determine when the button is pressed, you would likely submit a request
* to read data on a bulk or interrupt endpoint and wait for data to arrive.
* Data will arrive when the button is pressed by the user, which is
* potentially hours later.
*
* libusb offers both a synchronous and an asynchronous interface to performing
* USB transfers. The main difference is that the synchronous interface
* combines both steps indicated above into a single function call, whereas
* the asynchronous interface separates them.
*
* \section sync The synchronous interface
*
* The synchronous I/O interface allows you to perform a USB transfer with
* a single function call. When the function call returns, the transfer has
* completed and you can parse the results.
*
* If you have used the libusb-0.1 before, this I/O style will seem familar to
* you. libusb-0.1 only offered a synchronous interface.
*
* In our input device example, to read button presses you might write code
* in the following style:
\code
unsigned char data[4];
int actual_length;
int r = libusb_bulk_transfer(handle, LIBUSB_ENDPOINT_IN, data, sizeof(data), &actual_length, 0);
if (r == 0 && actual_length == sizeof(data)) {
// results of the transaction can now be found in the data buffer
// parse them here and report button press
} else {
error();
}
\endcode
*
* The main advantage of this model is simplicity: you did everything with
* a single simple function call.
*
* However, this interface has its limitations. Your application will sleep
* inside libusb_bulk_transfer() until the transaction has completed. If it
* takes the user 3 hours to press the button, your application will be
* sleeping for that long. Execution will be tied up inside the library -
* the entire thread will be useless for that duration.
*
* Another issue is that by tieing up the thread with that single transaction
* there is no possibility of performing I/O with multiple endpoints and/or
* multiple devices simultaneously, unless you resort to creating one thread
* per transaction.
*
* Additionally, there is no opportunity to cancel the transfer after the
* request has been submitted.
*
* For details on how to use the synchronous API, see the
* \ref syncio "synchronous I/O API documentation" pages.
*
* \section async The asynchronous interface
*
* Asynchronous I/O is the most significant new feature in libusb-1.0.
* Although it is a more complex interface, it solves all the issues detailed
* above.
*
* Instead of providing which functions that block until the I/O has complete,
* libusb's asynchronous interface presents non-blocking functions which
* begin a transfer and then return immediately. Your application passes a
* callback function pointer to this non-blocking function, which libusb will
* call with the results of the transaction when it has completed.
*
* Transfers which have been submitted through the non-blocking functions
* can be cancelled with a separate function call.
*
* The non-blocking nature of this interface allows you to be simultaneously
* performing I/O to multiple endpoints on multiple devices, without having
*
* This added flexibility does come with some complications though:
* - In the interest of being a lightweight library, libusb does not create
* threads and can only operate when your application is calling into it. Your
* application must call into libusb from it's main loop when events are ready
* to be handled, or you must use some other scheme to allow libusb to
* undertake whatever work needs to be done.
* - libusb also needs to be called into at certain fixed points in time in
* order to accurately handle transfer timeouts.
* - Memory handling becomes more complex. You cannot use stack memory unless
* the function with that stack is guaranteed not to return until the transfer
* callback has finished executing.
* - You generally lose some linearity from your code flow because submitting
* the transfer request is done in a separate function from where the transfer
* results are handled. This becomes particularly obvious when you want to
* submit a second transfer based on the results of an earlier transfer.
*
* Internally, libusb's synchronous interface is expressed in terms of function
* calls to the asynchronous interface.
*
* For details on how to use the asynchronous API, see the
* \ref asyncio "asynchronous I/O API" documentation pages.
*/

/**
* \page packetoverflow Packets and overflows
*
* \section packets Packet abstraction
*
* The USB specifications describe how data is transmitted in packets, with
* constraints on packet size defined by endpoint descriptors. The host must
* not send data payloads larger than the endpoint's maximum packet size.
*
* libusb and the underlying OS abstract out the packet concept, allowing you
* to request transfers of any size. Internally, the request will be divided
* up into correctly-sized packets. You do not have to be concerned with
* packet sizes, but there is one exception when considering overflows.
*
* \section overflow Bulk/interrupt transfer overflows
*
* When requesting data on a bulk endpoint, libusb requires you to supply a
* buffer and the maximum number of bytes of data that libusb can put in that
* buffer. However, the size of the buffer is not communicated to the device -
* the device is just asked to send any amount of data.
*
* There is no problem if the device sends an amount of data that is less than
* or equal to the buffer size. libusb reports this condition to you through
* the \ref libusb_transfer::actual_length "libusb_transfer.actual_length"
* field.
*
* Problems may occur if the device attempts to send more data than can fit in
* the buffer. libusb reports LIBUSB_TRANSFER_OVERFLOW for this condition but
* other behaviour is largely undefined: actual_length may or may not be
* accurate, the chunk of data that can fit in the buffer (before overflow)
* may or may not have been transferred.
*
* Overflows are nasty, but can be avoided. Even though you were told to
* ignore packets above, think about the lower level details: each transfer is
* split into packets (typically small, with a maximum size of 512 bytes).
* Overflows can only happen if the final packet in an incoming data transfer
* is smaller than the actual packet that the device wants to transfer.
* Therefore, you will never see an overflow if your transfer buffer size is a
* multiple of the endpoint's packet size: the final packet will either
* fill up completely or will be only partially filled.
*/

/**
* @defgroup asyncio Asynchronous device I/O
*
* I/O. This interface is very powerful but is also quite complex - you will
* and issues surrounding use of this interface. Simplistic applications
* may wish to consider the \ref syncio "synchronous I/O API" instead.
*
* The asynchronous interface is built around the idea of separating transfer
* submission and handling of transfer completion (the synchronous model
* combines both of these into one). There may be a long delay between
* submission and completion, however the asynchronous submission function
* is non-blocking so will return control to your application during that
* potentially long delay.
*
* \section asyncabstraction Transfer abstraction
*
* For the asynchronous I/O, libusb implements the concept of a generic
* transfer entity for all types of I/O (control, bulk, interrupt,
* isochronous). The generic transfer object must be treated slightly
* differently depending on which type of I/O you are performing with it.
*
* This is represented by the public libusb_transfer structure type.
*
* \section asynctrf Asynchronous transfers
*
* We can view asynchronous I/O as a 5 step process:
* -# <b>Allocation</b>: allocate a libusb_transfer
* -# <b>Filling</b>: populate the libusb_transfer instance with information
*    about the transfer you wish to perform
* -# <b>Submission</b>: ask libusb to submit the transfer
* -# <b>Completion handling</b>: examine transfer results in the
*    libusb_transfer structure
* -# <b>Deallocation</b>: clean up resources
*
*
* \subsection asyncalloc Allocation
*
* This step involves allocating memory for a USB transfer. This is the
* generic transfer object mentioned above. At this stage, the transfer
* is "blank" with no details about what type of I/O it will be used for.
*
* Allocation is done with the libusb_alloc_transfer() function. You must use
* this function rather than allocating your own transfers.
*
* \subsection asyncfill Filling
*
* This step is where you take a previously allocated transfer and fill it
* with information to determine the message type and direction, data buffer,
* callback function, etc.
*
* You can either fill the required fields yourself or you can use the
* helper functions: libusb_fill_control_transfer(), libusb_fill_bulk_transfer()
* and libusb_fill_interrupt_transfer().
*
* \subsection asyncsubmit Submission
*
* When you have allocated a transfer and filled it, you can submit it using
* libusb_submit_transfer(). This function returns immediately but can be
* regarded as firing off the I/O request in the background.
*
* \subsection asynccomplete Completion handling
*
* After a transfer has been submitted, one of four things can happen to it:
*
* - The transfer completes (i.e. some data was transferred)
* - The transfer has a timeout and the timeout expires before all data is
* transferred
* - The transfer fails due to an error
* - The transfer is cancelled
*
* Each of these will cause the user-specified transfer callback function to
* be invoked. It is up to the callback function to determine which of the
* above actually happened and to act accordingly.
*
* The user-specified callback is passed a pointer to the libusb_transfer
* structure which was used to setup and submit the transfer. At completion
* time, libusb has populated this structure with results of the transfer:
* success or failure reason, number of bytes of data transferred, etc. See
*
* \subsection Deallocation
*
* When a transfer has completed (i.e. the callback function has been invoked),
* you are advised to free the transfer (unless you wish to resubmit it, see
* below). Transfers are deallocated with libusb_free_transfer().
*
* It is undefined behaviour to free a transfer which has not completed.
*
* \section asyncresubmit Resubmission
*
* You may be wondering why allocation, filling, and submission are all
* separated above where they could reasonably be combined into a single
* operation.
*
* The reason for separation is to allow you to resubmit transfers without
* having to allocate new ones every time. This is especially useful for
* common situations dealing with interrupt endpoints - you allocate one
* transfer, fill and submit it, and when it returns with results you just
* resubmit it for the next interrupt.
*
* \section asynccancel Cancellation
*
* Another advantage of using the asynchronous interface is that you have
* the ability to cancel transfers which have not yet completed. This is
* done by calling the libusb_cancel_transfer() function.
*
* libusb_cancel_transfer() is asynchronous/non-blocking in itself. When the
* cancellation actually completes, the transfer's callback function will
* be invoked, and the callback function should check the transfer status to
* determine that it was cancelled.
*
* Freeing the transfer after it has been cancelled but before cancellation
* has completed will result in undefined behaviour.
*
* When a transfer is cancelled, some of the data may have been transferred.
* libusb will communicate this to you in the transfer callback. Do not assume
* that no data was transferred.
*
* \section bulk_overflows Overflows on device-to-host bulk/interrupt endpoints
*
* If your device does not have predictable transfer sizes (or it misbehaves),
* your application may submit a request for data on an IN endpoint which is
* smaller than the data that the device wishes to send. In some circumstances
* this will cause an overflow, which is a nasty condition to deal with. See
* the \ref packetoverflow page for discussion.
*
* \section asyncctrl Considerations for control transfers
*
* The <tt>libusb_transfer</tt> structure is generic and hence does not
* include specific fields for the control-specific setup packet structure.
*
* In order to perform a control transfer, you must place the 8-byte setup
* packet at the start of the data buffer. To simplify this, you could
* cast the buffer pointer to type struct libusb_control_setup, or you can
* use the helper function libusb_fill_control_setup().
*
* The wLength field placed in the setup packet must be the length you would
* expect to be sent in the setup packet: the length of the payload that
* follows (or the expected maximum number of bytes to receive). However,
* the length field of the libusb_transfer object must be the length of
* the data buffer - i.e. it should be wLength <em>plus</em> the size of
* the setup packet (LIBUSB_CONTROL_SETUP_SIZE).
*
* If you use the helper functions, this is simplified for you:
* -# Allocate a buffer of size LIBUSB_CONTROL_SETUP_SIZE plus the size of the
* data you are sending/requesting.
* -# Call libusb_fill_control_setup() on the data buffer, using the transfer
* request size as the wLength value (i.e. do not include the extra space you
* allocated for the control setup).
* -# If this is a host-to-device transfer, place the data to be transferred
* in the data buffer, starting at offset LIBUSB_CONTROL_SETUP_SIZE.
* -# Call libusb_fill_control_transfer() to associate the data buffer with
* the transfer (and to set the remaining details such as callback and timeout).
*   - Note that there is no parameter to set the length field of the transfer.
*     The length is automatically inferred from the wLength field of the setup
*     packet.
* -# Submit the transfer.
*
* The multi-byte control setup fields (wValue, wIndex and wLength) must
* be given in little-endian byte order (the endianness of the USB bus).
* Endianness conversion is transparently handled by
* libusb_fill_control_setup() which is documented to accept host-endian
* values.
*
* Further considerations are needed when handling transfer completion in
* - As you might expect, the setup packet will still be sitting at the start
* of the data buffer.
* - If this was a device-to-host transfer, the received data will be sitting
* at offset LIBUSB_CONTROL_SETUP_SIZE into the buffer.
* - The actual_length field of the transfer structure is relative to the
* wLength of the setup packet, rather than the size of the data buffer. So,
* if your wLength was 4, your transfer's <tt>length</tt> was 12, then you
* should expect an <tt>actual_length</tt> of 4 to indicate that the data was
* transferred in entirity.
*
* To simplify parsing of setup packets and obtaining the data from the
* correct offset, you may wish to use the libusb_control_transfer_get_data()
* and libusb_control_transfer_get_setup() functions within your transfer
* callback.
*
* Even though control endpoints do not halt, a completed control transfer
* may have a LIBUSB_TRANSFER_STALL status code. This indicates the control
* request was not supported.
*
* \section asyncintr Considerations for interrupt transfers
*
* All interrupt transfers are performed using the polling interval presented
* by the bInterval value of the endpoint descriptor.
*
* \section asynciso Considerations for isochronous transfers
*
* Isochronous transfers are more complicated than transfers to
* non-isochronous endpoints.
*
* To perform I/O to an isochronous endpoint, allocate the transfer by calling
* libusb_alloc_transfer() with an appropriate number of isochronous packets.
*
* During filling, set \ref libusb_transfer::type "type" to
* \ref libusb_transfer_type::LIBUSB_TRANSFER_TYPE_ISOCHRONOUS
* "LIBUSB_TRANSFER_TYPE_ISOCHRONOUS", and set
* \ref libusb_transfer::num_iso_packets "num_iso_packets" to a value less than
* or equal to the number of packets you requested during allocation.
* libusb_alloc_transfer() does not set either of these fields for you, given
* that you might not even use the transfer on an isochronous endpoint.
*
* Next, populate the length field for the first num_iso_packets entries in
* the \ref libusb_transfer::iso_packet_desc "iso_packet_desc" array. Section
* 5.6.3 of the USB2 specifications describe how the maximum isochronous
* packet length is determined by the wMaxPacketSize field in the endpoint
* descriptor.
*
* - libusb_get_max_iso_packet_size() is an easy way to determine the max
*   packet size for an isochronous endpoint. Note that the maximum packet
*   size is actually the maximum number of bytes that can be transmitted in
*   a single microframe, therefore this function multiplies the maximum number
*   of bytes per transaction by the number of transaction opportunities per
*   microframe.
* - libusb_set_iso_packet_lengths() assigns the same length to all packets
*   within a transfer, which is usually what you want.
*
* For outgoing transfers, you'll obviously fill the buffer and populate the
* packet descriptors in hope that all the data gets transferred. For incoming
* transfers, you must ensure the buffer has sufficient capacity for
* the situation where all packets transfer the full amount of requested data.
*
* Completion handling requires some extra consideration. The
* \ref libusb_transfer::actual_length "actual_length" field of the transfer
* is meaningless and should not be examined; instead you must refer to the
* \ref libusb_iso_packet_descriptor::actual_length "actual_length" field of
* each individual packet.
*
* The \ref libusb_transfer::status "status" field of the transfer is also a
*  - If the packets were submitted and the isochronous data microframes
*    completed normally, status will have value
*    \ref libusb_transfer_status::LIBUSB_TRANSFER_COMPLETED
*    "LIBUSB_TRANSFER_COMPLETED". Note that bus errors and software-incurred
*    delays are not counted as transfer errors; the transfer.status field may
*    indicate COMPLETED even if some or all of the packets failed. Refer to
*    the \ref libusb_iso_packet_descriptor::status "status" field of each
*    individual packet to determine packet failures.
*  - The status field will have value
*    \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR
*    "LIBUSB_TRANSFER_ERROR" only when serious errors were encountered.
*  - Other transfer status codes occur with normal behaviour.
*
* The data for each packet will be found at an offset into the buffer that
* can be calculated as if each prior packet completed in full. The
* libusb_get_iso_packet_buffer() and libusb_get_iso_packet_buffer_simple()
*
* \section asyncmem Memory caveats
*
* In most circumstances, it is not safe to use stack memory for transfer
* buffers. This is because the function that fired off the asynchronous
* transfer may return before libusb has finished using the buffer, and when
* the function returns it's stack gets destroyed. This is true for both
* host-to-device and device-to-host transfers.
*
* The only case in which it is safe to use stack memory is where you can
* guarantee that the function owning the stack space for the buffer does not
* return until after the transfer's callback function has completed. In every
* other case, you need to use heap memory instead.
*
* \section asyncflags Fine control
*
* Through using this asynchronous interface, you may find yourself repeating
* a few simple operations many times. You can apply a bitwise OR of certain
* flags to a transfer to simplify certain things:
* - \ref libusb_transfer_flags::LIBUSB_TRANSFER_SHORT_NOT_OK
*   "LIBUSB_TRANSFER_SHORT_NOT_OK" results in transfers which transferred
*   less than the requested amount of data being marked with status
*   \ref libusb_transfer_status::LIBUSB_TRANSFER_ERROR "LIBUSB_TRANSFER_ERROR"
*   (they would normally be regarded as COMPLETED)
* - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
*   "LIBUSB_TRANSFER_FREE_BUFFER" allows you to ask libusb to free the transfer
*   buffer when freeing the transfer.
* - \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_TRANSFER
*   "LIBUSB_TRANSFER_FREE_TRANSFER" causes libusb to automatically free the
*   transfer after the transfer callback returns.
*
* \section asyncevent Event handling
*
* In accordance of the aim of being a lightweight library, libusb does not
* create threads internally. This means that libusb code does not execute
* at any time other than when your application is calling a libusb function.
* However, an asynchronous model requires that libusb perform work at various
* points in time - namely processing the results of previously-submitted
* transfers and invoking the user-supplied callback function.
*
* This gives rise to the libusb_handle_events() function which your
* application must call into when libusb has work do to. This gives libusb
* the opportunity to reap pending transfers, invoke callbacks, etc.
*
* The first issue to discuss here is how your application can figure out
* when libusb has work to do. In fact, there are two naive options which
* do not actually require your application to know this:
* -# Periodically call libusb_handle_events() in non-blocking mode at fixed
*    short intervals from your main loop
* -# Repeatedly call libusb_handle_events() in blocking mode from a dedicated
*
* The first option is plainly not very nice, and will cause unnecessary
* CPU wakeups leading to increased power usage and decreased battery life.
* The second option is not very nice either, but may be the nicest option
* available to you if the "proper" approach can not be applied to your
*
* The recommended option is to integrate libusb with your application main
* event loop. libusb exposes a set of file descriptors which allow you to do
* this. Your main loop is probably already calling poll() or select() or a
* variant on a set of file descriptors for other event sources (e.g. keyboard
* button presses, mouse movements, network sockets, etc). You then add
* libusb's file descriptors to your poll()/select() calls, and when activity
* is detected on such descriptors you know it is time to call
* libusb_handle_events().
*
* There is one final event handling complication. libusb supports
* asynchronous transfers which time out after a specified time period, and
* this requires that libusb is called into at or after the timeout so that
* the timeout can be handled. So, in addition to considering libusb's file
* descriptors in your main event loop, you must also consider that libusb
* sometimes needs to be called into at fixed points in time even when there
* is no file descriptor activity.
*
* For the details on retrieving the set of file descriptors and determining
* the next timeout, see the \ref poll "polling and timing" API documentation.
*/

/**
* @defgroup poll Polling and timing
*
* These functions are only necessary for users of the
* \ref asyncio "asynchronous API". If you are only using the simpler
* \ref syncio "synchronous API" then you do not need to ever call these
* functions.
*
* The justification for the functionality described here has already been
* discussed in the \ref asyncevent "event handling" section of the
* asynchronous API documentation. In summary, libusb does not create internal
* threads for event processing and hence relies on your application calling
* into libusb at certain points in time so that pending events can be handled.
* In order to know precisely when libusb needs to be called into, libusb
* offers you a set of pollable file descriptors and information about when
* the next timeout expires.
*
* If you are using the asynchronous I/O API, you must take one of the two
* following options, otherwise your I/O will not complete.
*
* \section pollsimple The simple option
*
* If your application revolves solely around libusb and does not need to
* handle other event sources, you can have a program structure as follows:
\code
// initialize libusb
// find and open device
// maybe fire off some initial async I/O

while (user_has_not_requested_exit)
libusb_handle_events(ctx);

// clean up and exit
\endcode
*
* With such a simple main loop, you do not have to worry about managing
* sets of file descriptors or handling timeouts. libusb_handle_events() will
* handle those details internally.
*
* \section pollmain The more advanced option
*
* \note This functionality is currently only available on Unix-like platforms.
* On Windows, libusb_get_pollfds() simply returns NULL. Exposing event sources
* on Windows will require some further thought and design.
*
* In more advanced applications, you will already have a main loop which
* is monitoring other event sources: network sockets, X11 events, mouse
* movements, etc. Through exposing a set of file descriptors, libusb is
* designed to cleanly integrate into such main loops.
*
* In addition to polling file descriptors for the other event sources, you
* take a set of file descriptors from libusb and monitor those too. When you
* detect activity on libusb's file descriptors, you call
* libusb_handle_events_timeout() in non-blocking mode.
*
* What's more, libusb may also need to handle events at specific moments in
* time. No file descriptor activity is generated at these times, so your
* own application needs to be continually aware of when the next one of these
* moments occurs (through calling libusb_get_next_timeout()), and then it
* needs to call libusb_handle_events_timeout() in non-blocking mode when
* these moments occur. This means that you need to adjust your
* poll()/select() timeout accordingly.
*
* libusb provides you with a set of file descriptors to poll and expects you
* to poll all of them, treating them as a single entity. The meaning of each
* file descriptor in the set is an internal implementation detail,
* platform-dependent and may vary from release to release. Don't try and
* interpret the meaning of the file descriptors, just do as libusb indicates,
* polling all of them at once.
*
* In pseudo-code, you want something that looks like:
\code
// initialise libusb

libusb_get_pollfds(ctx)
while (user has not requested application exit) {
libusb_get_next_timeout(ctx);
poll(on libusb file descriptors plus any other event sources of interest,
using a timeout no larger than the value libusb just suggested)
if (poll() indicated activity on libusb file descriptors)
libusb_handle_events_timeout(ctx, &zero_tv);
if (time has elapsed to or beyond the libusb timeout)
libusb_handle_events_timeout(ctx, &zero_tv);
// handle events from other sources here
}

// clean up and exit
\endcode
*
* \subsection polltime Notes on time-based events
*
* The above complication with having to track time and call into libusb at
* specific moments is a bit of a headache. For maximum compatibility, you do
* need to write your main loop as above, but you may decide that you can
* restrict the supported platforms of your application and get away with
* a more simplistic scheme.
*
* These time-based event complications are \b not required on the following
* platforms:
*  - Darwin
*  - Linux, provided that the following version requirements are satisfied:
*   - Linux v2.6.27 or newer, compiled with timerfd support
*   - glibc v2.9 or newer
*   - libusb v1.0.5 or newer
*
* Under these configurations, libusb_get_next_timeout() will \em always return
* 0, so your main loop can be simplified to:
\code
// initialise libusb

libusb_get_pollfds(ctx)
while (user has not requested application exit) {
poll(on libusb file descriptors plus any other event sources of interest,
using any timeout that you like)
if (poll() indicated activity on libusb file descriptors)
libusb_handle_events_timeout(ctx, &zero_tv);
// handle events from other sources here
}

// clean up and exit
\endcode
*
* Do remember that if you simplify your main loop to the above, you will
* lose compatibility with some platforms (including legacy Linux platforms,
* and <em>any future platforms supported by libusb which may have time-based
* event requirements</em>). The resultant problems will likely appear as
* strange bugs in your application.
*
* You can use the libusb_pollfds_handle_timeouts() function to do a runtime
* check to see if it is safe to ignore the time-based event complications.
* If your application has taken the shortcut of ignoring libusb's next timeout
* in your main loop, then you are advised to check the return value of
* libusb_pollfds_handle_timeouts() during application startup, and to abort
* if the platform does suffer from these timing complications.
*
* \subsection fdsetchange Changes in the file descriptor set
*
* The set of file descriptors that libusb uses as event sources may change
* during the life of your application. Rather than having to repeatedly
* call libusb_get_pollfds(), you can set up notification functions for when
* the file descriptor set changes using libusb_set_pollfd_notifiers().
*
*
* Unfortunately, the situation is complicated further when multiple threads
* come into play. If two threads are monitoring the same file descriptors,
* the fact that only one thread will be woken up when an event occurs causes
*
* The events lock, event waiters lock, and libusb_handle_events_locked()
* entities are added to solve these problems. You do not need to be concerned
* with these entities otherwise.
*
* See the extra documentation: \ref mtasync
*/

/** \page mtasync Multi-threaded applications and asynchronous I/O
*
* libusb is a thread-safe library, but extra considerations must be applied
* to applications which interact with libusb from multiple threads.
*
* The underlying issue that must be addressed is that all libusb I/O
* revolves around monitoring file descriptors through the poll()/select()
* system calls. This is directly exposed at the
* \ref asyncio "asynchronous interface" but it is important to note that the
* \ref syncio "synchronous interface" is implemented on top of the
* asynchonrous interface, therefore the same considerations apply.
*
* The issue is that if two or more threads are concurrently calling poll()
* or select() on libusb's file descriptors then only one of those threads
* will be woken up when an event arrives. The others will be completely
* oblivious that anything has happened.
*
* Consider the following pseudo-code, which submits an asynchronous transfer
* then waits for its completion. This style is one way you could implement a
* synchronous interface on top of the asynchronous interface (and libusb
* does something similar, albeit more advanced due to the complications
*
\code
void cb(struct libusb_transfer *transfer)
{
int *completed = transfer->user_data;
*completed = 1;
}

void myfunc() {
struct libusb_transfer *transfer;
unsigned char buffer[LIBUSB_CONTROL_SETUP_SIZE];
int completed = 0;

transfer = libusb_alloc_transfer(0);
libusb_fill_control_setup(buffer,
LIBUSB_REQUEST_TYPE_VENDOR | LIBUSB_ENDPOINT_OUT, 0x04, 0x01, 0, 0);
libusb_fill_control_transfer(transfer, dev, buffer, cb, &completed, 1000);
libusb_submit_transfer(transfer);

while (!completed) {
poll(libusb file descriptors, 120*1000);
if (poll indicates activity)
libusb_handle_events_timeout(ctx, &zero_tv);
}
printf("completed!");
// other code here
}
\endcode
*
* Here we are <em>serializing</em> completion of an asynchronous event
* against a condition - the condition being completion of a specific transfer.
* The poll() loop has a long timeout to minimize CPU usage during situations
* when nothing is happening (it could reasonably be unlimited).
*
* If this is the only thread that is polling libusb's file descriptors, there
* is no problem: there is no danger that another thread will swallow up the
* event that we are interested in. On the other hand, if there is another
* thread polling the same descriptors, there is a chance that it will receive
* the event that we were interested in. In this situation, <tt>myfunc()</tt>
* will only realise that the transfer has completed on the next iteration of
* the loop, <em>up to 120 seconds later.</em> Clearly a two-minute delay is
* undesirable, and don't even think about using short timeouts to circumvent
* this issue!
*
* The solution here is to ensure that no two threads are ever polling the
* file descriptors at the same time. A naive implementation of this would
* impact the capabilities of the library, so libusb offers the scheme
* documented below to ensure no loss of functionality.
*
* Before we go any further, it is worth mentioning that all libusb-wrapped
* event handling procedures fully adhere to the scheme documented below.
* This includes libusb_handle_events() and its variants, and all the
* synchronous I/O functions - libusb hides this headache from you.
*
* \section Using libusb_handle_events() from multiple threads
*
* Even when only using libusb_handle_events() and synchronous I/O functions,
* you can still have a race condition. You might be tempted to solve the
* above with libusb_handle_events() like so:
*
\code
libusb_submit_transfer(transfer);

while (!completed) {
libusb_handle_events(ctx);
}
printf("completed!");
\endcode
*
* This however has a race between the checking of completed and
* libusb_handle_events() acquiring the events lock, so another thread
* could have completed the transfer, resulting in this thread hanging
* until either a timeout or another event occurs. See also commit
* 6696512aade99bb15d6792af90ae329af270eba6 which fixes this in the
* synchronous API implementation of libusb.
*
* Fixing this race requires checking the variable completed only after
* taking the event lock, which defeats the concept of just calling
* libusb_handle_events() without worrying about locking. This is why
* libusb-1.0.9 introduces the new libusb_handle_events_timeout_completed()
* and libusb_handle_events_completed() functions, which handles doing the
* completion check for you after they have acquired the lock:
*
\code
libusb_submit_transfer(transfer);

while (!completed) {
libusb_handle_events_completed(ctx, &completed);
}
printf("completed!");
\endcode
*
* This nicely fixes the race in our example. Note that if all you want to
* do is submit a single transfer and wait for its completion, then using
* one of the synchronous I/O functions is much easier.
*
* \section eventlock The events lock
*
* The problem is when we consider the fact that libusb exposes file
* descriptors to allow for you to integrate asynchronous USB I/O into
* existing main loops, effectively allowing you to do some work behind
* libusb's back. If you do take libusb's file descriptors and pass them to
* poll()/select() yourself, you need to be aware of the associated issues.
*
* The first concept to be introduced is the events lock. The events lock
* is used to serialize threads that want to handle events, such that only
* one thread is handling events at any one time.
*
* You must take the events lock before polling libusb file descriptors,
* using libusb_lock_events(). You must release the lock as soon as you have
* aborted your poll()/select() loop, using libusb_unlock_events().
*
*
* Although the events lock is a critical part of the solution, it is not
* enough on it's own. You might wonder if the following is sufficient...
\code
libusb_lock_events(ctx);
while (!completed) {
poll(libusb file descriptors, 120*1000);
if (poll indicates activity)
libusb_handle_events_timeout(ctx, &zero_tv);
}
libusb_unlock_events(ctx);
\endcode
* ...and the answer is that it is not. This is because the transfer in the
* code shown above may take a long time (say 30 seconds) to complete, and
* the lock is not released until the transfer is completed.
*
* Another thread with similar code that wants to do event handling may be
* working with a transfer that completes after a few milliseconds. Despite
* having such a quick completion time, the other thread cannot check that
* status of its transfer until the code above has finished (30 seconds later)
* due to contention on the lock.
*
* To solve this, libusb offers you a mechanism to determine when another
* until the event handling thread has completed an event (and this mechanism
* does not involve polling of file descriptors).
*
* After determining that another thread is currently handling events, you
* obtain the <em>event waiters</em> lock using libusb_lock_event_waiters().
* You then re-check that some other thread is still handling events, and if
* so, you call libusb_wait_for_event().
*
* libusb_wait_for_event() puts your application to sleep until an event
* occurs, or until a thread releases the events lock. When either of these
* things happen, your thread is woken up, and should re-check the condition
* it was waiting on. It should also re-check that another thread is handling
* events, and if not, it should start handling events itself.
*
* This looks like the following, as pseudo-code:
\code
retry:
if (libusb_try_lock_events(ctx) == 0) {
// we obtained the event lock: do our own event handling
while (!completed) {
if (!libusb_event_handling_ok(ctx)) {
libusb_unlock_events(ctx);
goto retry;
}
poll(libusb file descriptors, 120*1000);
if (poll indicates activity)
libusb_handle_events_locked(ctx, 0);
}
libusb_unlock_events(ctx);
} else {
// another thread is doing event handling. wait for it to signal us that
// an event has completed
libusb_lock_event_waiters(ctx);

while (!completed) {
// now that we have the event waiters lock, double check that another
// thread is still handling events for us. (it may have ceased handling
// events in the time it took us to reach this point)
if (!libusb_event_handler_active(ctx)) {
// whoever was handling events is no longer doing so, try again
libusb_unlock_event_waiters(ctx);
goto retry;
}

libusb_wait_for_event(ctx, NULL);
}
libusb_unlock_event_waiters(ctx);
}
printf("completed!\n");
\endcode
*
* A naive look at the above code may suggest that this can only support
* one event waiter (hence a total of 2 competing threads, the other doing
* event handling), because the event waiter seems to have taken the event
* waiters lock while waiting for an event. However, the system does support
* multiple event waiters, because libusb_wait_for_event() actually drops
* the lock while waiting, and reaquires it before continuing.
*
* We have now implemented code which can dynamically handle situations where
* nobody is handling events (so we should do it ourselves), and it can also
* handle situations where another thread is doing event handling (so we can
* piggyback onto them). It is also equipped to handle a combination of
* the two, for example, another thread is doing event handling, but for
* whatever reason it stops doing so before our condition is met, so we take
* over the event handling.
*
* Four functions were introduced in the above pseudo-code. Their importance
* should be apparent from the code shown above.
* -# libusb_try_lock_events() is a non-blocking function which attempts
*    to acquire the events lock but returns a failure code if it is contended.
* -# libusb_event_handling_ok() checks that libusb is still happy for your
*    thread to be performing event handling. Sometimes, libusb needs to
*    interrupt the event handler, and this is how you can check if you have
*    been interrupted. If this function returns 0, the correct behaviour is
*    for you to give up the event handling lock, and then to repeat the cycle.
*    The following libusb_try_lock_events() will fail, so you will become an
* -# libusb_handle_events_locked() is a variant of
*    libusb_handle_events_timeout() that you can call while holding the
*    events lock. libusb_handle_events_timeout() itself implements similar
*    logic to the above, so be sure not to call it when you are
*    "working behind libusb's back", as is the case here.
* -# libusb_event_handler_active() determines if someone is currently
*    holding the events lock
*
* You might be wondering why there is no function to wake up all threads
* blocked on libusb_wait_for_event(). This is because libusb can do this
* internally: it will wake up all such threads when someone calls
* libusb_unlock_events() or when a transfer completes (at the point after its
* callback has returned).
*
* \subsection fullstory The full story
*
* The above explanation should be enough to get you going, but if you're
* really thinking through the issues then you may be left with some more
* questions regarding libusb's internals. If you're curious, read on, and if
*
* The immediate question that may spring to mind is: what if one thread
* modifies the set of file descriptors that need to be polled while another
* thread is doing event handling?
*
* There are 2 situations in which this may happen.
* -# libusb_open() will add another file descriptor to the poll set,
*    therefore it is desirable to interrupt the event handler so that it
*    restarts, picking up the new descriptor.
* -# libusb_close() will remove a file descriptor from the poll set. There
*    are all kinds of race conditions that could arise here, so it is
*    important that nobody is doing event handling at this time.
*
* libusb handles these issues internally, so application developers do not
* have to stop their event handlers while opening/closing devices. Here's how
* it works, focusing on the libusb_close() situation first:
*
* -# During initialization, libusb opens an internal pipe, and it adds the read
*    end of this pipe to the set of file descriptors to be polled.
* -# During libusb_close(), libusb writes some dummy data on this control pipe.
*    This immediately interrupts the event handler. libusb also records
*    internally that it is trying to interrupt event handlers for this
*    high-priority event.
* -# At this point, some of the functions described above start behaving
*    differently:
*   - libusb_event_handling_ok() starts returning 1, indicating that it is NOT
*     OK for event handling to continue.
*   - libusb_try_lock_events() starts returning 1, indicating that another
*     thread holds the event handling lock, even if the lock is uncontended.
*   - libusb_event_handler_active() starts returning 1, indicating that
*     another thread is doing event handling, even if that is not true.
* -# The above changes in behaviour result in the event handler stopping and
*    giving up the events lock very quickly, giving the high-priority
*    libusb_close() operation a "free ride" to acquire the events lock. All
*    threads that are competing to do event handling become event waiters.
* -# With the events lock held inside libusb_close(), libusb can safely remove
*    a file descriptor from the poll set, in the safety of knowledge that
*    nobody is polling those descriptors or trying to access the poll set.
* -# After obtaining the events lock, the close operation completes very
*    quickly (usually a matter of milliseconds) and then immediately releases
*    the events lock.
* -# At the same time, the behaviour of libusb_event_handling_ok() and friends
*    reverts to the original, documented behaviour.
* -# The release of the events lock causes the threads that are waiting for
*    events to be woken up and to start competing to become event handlers
*    again. One of them will succeed; it will then re-obtain the list of poll
*    descriptors, and USB I/O will then continue as normal.
*
* libusb_open() is similar, and is actually a more simplistic case. Upon a
* call to libusb_open():
*
* -# The device is opened and a file descriptor is added to the poll set.
* -# libusb sends some dummy data on the control pipe, and records that it
*    is trying to modify the poll descriptor set.
* -# The event handler is interrupted, and the same behaviour change as for
*    libusb_close() takes effect, causing all event handling threads to become
*    event waiters.
* -# The libusb_open() implementation takes its free ride to the events lock.
* -# Happy that it has successfully paused the events handler, libusb_open()
*    releases the events lock.
* -# The event waiter threads are all woken up and compete to become event
*    handlers again. The one that succeeds will obtain the list of poll
*    descriptors again, which will include the addition of the new device.
*
* \subsection concl Closing remarks
*
* The above may seem a little complicated, but hopefully I have made it clear
* why such complications are necessary. Also, do not forget that this only
* applies to applications that take libusb's file descriptors and integrate
* them into their own polling loops.
*
* You may decide that it is OK for your multi-threaded application to ignore
* some of the rules and locks detailed above, because you don't think that
* two threads can ever be polling the descriptors at the same time. If that
* is the case, then that's good news for you because you don't have to worry.
* But be careful here; remember that the synchronous I/O functions do event
* handling internally. If you have one thread doing event handling in a loop
* (without implementing the rules and locking semantics documented above)
* and another trying to send a synchronous USB transfer, you will end up with
* two threads monitoring the same descriptors, and the above-described
* undesirable behaviour occuring. The solution is for your polling thread to
* play by the rules; the synchronous I/O functions do so, and this will result
* in them getting along in perfect harmony.
*
* If you do have a dedicated thread doing event handling, it is perfectly
* legal for it to take the event handling lock for long periods of time. Any
* synchronous I/O functions you call from other threads will transparently
* fall back to the "event waiters" mechanism detailed above. The only
* consideration that your event handling thread must apply is the one related
* to libusb_event_handling_ok(): you must call this before every poll(), and
* give up the events lock if instructed.
*/

int usbi_io_init(struct libusb_context *ctx)
{
int r;

usbi_mutex_init(&ctx->flying_transfers_lock, NULL);
usbi_mutex_init(&ctx->pollfds_lock, NULL);
usbi_mutex_init(&ctx->pollfd_modify_lock, NULL);
usbi_mutex_init_recursive(&ctx->events_lock, NULL);
usbi_mutex_init(&ctx->event_waiters_lock, NULL);
usbi_cond_init(&ctx->event_waiters_cond, NULL);
list_init(&ctx->flying_transfers);
list_init(&ctx->pollfds);

/* FIXME should use an eventfd on kernels that support it */
r = usbi_pipe(ctx->ctrl_pipe);
if (r < 0) {
r = LIBUSB_ERROR_OTHER;
goto err;
}

if (r < 0)
goto err_close_pipe;

#ifdef USBI_TIMERFD_AVAILABLE
ctx->timerfd = timerfd_create(usbi_backend->get_timerfd_clockid(),
TFD_NONBLOCK);
if (ctx->timerfd >= 0) {
usbi_dbg("using timerfd for timeouts");
if (r < 0) {
usbi_remove_pollfd(ctx, ctx->ctrl_pipe[0]);
close(ctx->timerfd);
goto err_close_pipe;
}
} else {
usbi_dbg("timerfd not available (code %d error %d)", ctx->timerfd, errno);
ctx->timerfd = -1;
}
#endif

return 0;

err_close_pipe:
usbi_close(ctx->ctrl_pipe[0]);
usbi_close(ctx->ctrl_pipe[1]);
err:
usbi_mutex_destroy(&ctx->flying_transfers_lock);
usbi_mutex_destroy(&ctx->pollfds_lock);
usbi_mutex_destroy(&ctx->pollfd_modify_lock);
usbi_mutex_destroy(&ctx->events_lock);
usbi_mutex_destroy(&ctx->event_waiters_lock);
usbi_cond_destroy(&ctx->event_waiters_cond);
return r;
}

void usbi_io_exit(struct libusb_context *ctx)
{
usbi_remove_pollfd(ctx, ctx->ctrl_pipe[0]);
usbi_close(ctx->ctrl_pipe[0]);
usbi_close(ctx->ctrl_pipe[1]);
#ifdef USBI_TIMERFD_AVAILABLE
if (usbi_using_timerfd(ctx)) {
usbi_remove_pollfd(ctx, ctx->timerfd);
close(ctx->timerfd);
}
#endif
usbi_mutex_destroy(&ctx->flying_transfers_lock);
usbi_mutex_destroy(&ctx->pollfds_lock);
usbi_mutex_destroy(&ctx->pollfd_modify_lock);
usbi_mutex_destroy(&ctx->events_lock);
usbi_mutex_destroy(&ctx->event_waiters_lock);
usbi_cond_destroy(&ctx->event_waiters_cond);
}

static int calculate_timeout(struct usbi_transfer *transfer)
{
int r;
struct timespec current_time;
unsigned int timeout =
USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout;

if (!timeout)
return 0;

r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, ¤t_time);
if (r < 0) {
usbi_err(ITRANSFER_CTX(transfer),
"failed to read monotonic clock, errno=%d", errno);
return r;
}

current_time.tv_sec += timeout / 1000;
current_time.tv_nsec += (timeout % 1000) * 1000000;

if (current_time.tv_nsec > 1000000000) {
current_time.tv_nsec -= 1000000000;
current_time.tv_sec++;
}

TIMESPEC_TO_TIMEVAL(&transfer->timeout, ¤t_time);
return 0;
}

/* add a transfer to the (timeout-sorted) active transfers list.
* returns 1 if the transfer has a timeout and it is the timeout next to
* expire */
{
struct usbi_transfer *cur;
struct timeval *timeout = &transfer->timeout;
struct libusb_context *ctx = ITRANSFER_CTX(transfer);
int r = 0;
int first = 1;

usbi_mutex_lock(&ctx->flying_transfers_lock);

/* if we have no other flying transfers, start the list with this one */
if (list_empty(&ctx->flying_transfers)) {
if (timerisset(timeout))
r = 1;
goto out;
}

/* if we have infinite timeout, append to end of list */
if (!timerisset(timeout)) {
goto out;
}

/* otherwise, find appropriate place in list */
list_for_each_entry(cur, &ctx->flying_transfers, list, struct usbi_transfer) {
/* find first timeout that occurs after the transfer in question */
struct timeval *cur_tv = &cur->timeout;

if (!timerisset(cur_tv) || (cur_tv->tv_sec > timeout->tv_sec) ||
(cur_tv->tv_sec == timeout->tv_sec &&
cur_tv->tv_usec > timeout->tv_usec)) {
r = first;
goto out;
}
first = 0;
}

/* otherwise we need to be inserted at the end */
out:
usbi_mutex_unlock(&ctx->flying_transfers_lock);
return r;
}

/** \ingroup asyncio
* Allocate a libusb transfer with a specified number of isochronous packet
* descriptors. The returned transfer is pre-initialized for you. When the new
* transfer is no longer needed, it should be freed with
* libusb_free_transfer().
*
* Transfers intended for non-isochronous endpoints (e.g. control, bulk,
* interrupt) should specify an iso_packets count of zero.
*
* For transfers intended for isochronous endpoints, specify an appropriate
* number of packet descriptors to be allocated as part of the transfer.
* The returned transfer is not specially initialized for isochronous I/O;
* you are still required to set the
* \ref libusb_transfer::num_iso_packets "num_iso_packets" and
* \ref libusb_transfer::type "type" fields accordingly.
*
* It is safe to allocate a transfer with some isochronous packets and then
* use it on a non-isochronous endpoint. If you do this, ensure that at time
* of submission, num_iso_packets is 0 and that type is set appropriately.
*
* \param iso_packets number of isochronous packet descriptors to allocate
* \returns a newly allocated transfer, or NULL on error
*/
DEFAULT_VISIBILITY
struct libusb_transfer * LIBUSB_CALL libusb_alloc_transfer(
int iso_packets)
{
size_t os_alloc_size = usbi_backend->transfer_priv_size
size_t alloc_size = sizeof(struct usbi_transfer)
+ sizeof(struct libusb_transfer)
+ (sizeof(struct libusb_iso_packet_descriptor) * iso_packets)
+ os_alloc_size;
struct usbi_transfer *itransfer = malloc(alloc_size);
if (!itransfer)
return NULL;

memset(itransfer, 0, alloc_size);
itransfer->num_iso_packets = iso_packets;
usbi_mutex_init(&itransfer->lock, NULL);
return USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
}

/** \ingroup asyncio
* Free a transfer structure. This should be called for all transfers
* allocated with libusb_alloc_transfer().
*
* If the \ref libusb_transfer_flags::LIBUSB_TRANSFER_FREE_BUFFER
* "LIBUSB_TRANSFER_FREE_BUFFER" flag is set and the transfer buffer is
* non-NULL, this function will also free the transfer buffer using the
* standard system memory allocator (e.g. free()).
*
* It is legal to call this function with a NULL transfer. In this case,
* the function will simply return safely.
*
* It is not legal to free an active transfer (one which has been submitted
* and has not yet completed).
*
* \param transfer the transfer to free
*/
void API_EXPORTED libusb_free_transfer(struct libusb_transfer *transfer)
{
struct usbi_transfer *itransfer;
if (!transfer)
return;

if (transfer->flags & LIBUSB_TRANSFER_FREE_BUFFER && transfer->buffer)
free(transfer->buffer);

itransfer = LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
usbi_mutex_destroy(&itransfer->lock);
free(itransfer);
}

/** \ingroup asyncio
* Submit a transfer. This function will fire off the USB transfer and then
* return immediately.
*
* \param transfer the transfer to submit
* \returns 0 on success
* \returns LIBUSB_ERROR_NO_DEVICE if the device has been disconnected
* \returns LIBUSB_ERROR_BUSY if the transfer has already been submitted.
* \returns LIBUSB_ERROR_NOT_SUPPORTED if the transfer flags are not supported
* by the operating system.
* \returns another LIBUSB_ERROR code on other failure
*/
int API_EXPORTED libusb_submit_transfer(struct libusb_transfer *transfer)
{
struct libusb_context *ctx = TRANSFER_CTX(transfer);
struct usbi_transfer *itransfer =
LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
int r;
int first;

usbi_mutex_lock(&itransfer->lock);
itransfer->transferred = 0;
itransfer->flags = 0;
r = calculate_timeout(itransfer);
if (r < 0) {
r = LIBUSB_ERROR_OTHER;
goto out;
}

r = usbi_backend->submit_transfer(itransfer);
if (r) {
usbi_mutex_lock(&ctx->flying_transfers_lock);
list_del(&itransfer->list);
usbi_mutex_unlock(&ctx->flying_transfers_lock);
}
#ifdef USBI_TIMERFD_AVAILABLE
else if (first && usbi_using_timerfd(ctx)) {
/* if this transfer has the lowest timeout of all active transfers,
* rearm the timerfd with this transfer's timeout */
const struct itimerspec it = { {0, 0},
{ itransfer->timeout.tv_sec, itransfer->timeout.tv_usec * 1000 } };
usbi_dbg("arm timerfd for timeout in %dms (first in line)", transfer->timeout);
r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
if (r < 0)
r = LIBUSB_ERROR_OTHER;
}
#else
(void)first;
#endif

out:
usbi_mutex_unlock(&itransfer->lock);
return r;
}

/** \ingroup asyncio
* Asynchronously cancel a previously submitted transfer.
* This function returns immediately, but this does not indicate cancellation
* is complete. Your callback function will be invoked at some later time
* with a transfer status of
* \ref libusb_transfer_status::LIBUSB_TRANSFER_CANCELLED
* "LIBUSB_TRANSFER_CANCELLED."
*
* \param transfer the transfer to cancel
* \returns 0 on success
* \returns LIBUSB_ERROR_NOT_FOUND if the transfer is already complete or
* cancelled.
* \returns a LIBUSB_ERROR code on failure
*/
int API_EXPORTED libusb_cancel_transfer(struct libusb_transfer *transfer)
{
struct usbi_transfer *itransfer =
LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer);
int r;

usbi_dbg("");
usbi_mutex_lock(&itransfer->lock);
r = usbi_backend->cancel_transfer(itransfer);
if (r < 0) {
if (r != LIBUSB_ERROR_NOT_FOUND)
usbi_err(TRANSFER_CTX(transfer),
"cancel transfer failed error %d", r);
else
usbi_dbg("cancel transfer failed error %d", r);

if (r == LIBUSB_ERROR_NO_DEVICE)
itransfer->flags |= USBI_TRANSFER_DEVICE_DISAPPEARED;
}

itransfer->flags |= USBI_TRANSFER_CANCELLING;

usbi_mutex_unlock(&itransfer->lock);
return r;
}

#ifdef USBI_TIMERFD_AVAILABLE
static int disarm_timerfd(struct libusb_context *ctx)
{
const struct itimerspec disarm_timer = { { 0, 0 }, { 0, 0 } };
int r;

usbi_dbg("");
r = timerfd_settime(ctx->timerfd, 0, &disarm_timer, NULL);
if (r < 0)
return LIBUSB_ERROR_OTHER;
else
return 0;
}

/* iterates through the flying transfers, and rearms the timerfd based on the
* next upcoming timeout.
* must be called with flying_list locked.
* returns 0 if there was no timeout to arm, 1 if the next timeout was armed,
* or a LIBUSB_ERROR code on failure.
*/
static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
{
struct usbi_transfer *transfer;

list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
struct timeval *cur_tv = &transfer->timeout;

/* if we've reached transfers of infinite timeout, then we have no
* arming to do */
if (!timerisset(cur_tv))
return 0;

/* act on first transfer that is not already cancelled */
if (!(transfer->flags & USBI_TRANSFER_TIMED_OUT)) {
int r;
const struct itimerspec it = { {0, 0},
{ cur_tv->tv_sec, cur_tv->tv_usec * 1000 } };
usbi_dbg("next timeout originally %dms", USBI_TRANSFER_TO_LIBUSB_TRANSFER(transfer)->timeout);
r = timerfd_settime(ctx->timerfd, TFD_TIMER_ABSTIME, &it, NULL);
if (r < 0)
return LIBUSB_ERROR_OTHER;
return 1;
}
}

return 0;
}
#else
static int disarm_timerfd(struct libusb_context *ctx)
{
(void)ctx;
return 0;
}
static int arm_timerfd_for_next_timeout(struct libusb_context *ctx)
{
(void)ctx;
return 0;
}
#endif

/* Handle completion of a transfer (completion might be an error condition).
* This will invoke the user-supplied callback function, which may end up
* freeing the transfer. Therefore you cannot use the transfer structure
* after calling this function, and you should free all backend-specific
* data before calling it.
* Do not call this function with the usbi_transfer lock held. User-specified
* callback functions may attempt to directly resubmit the transfer, which
* will attempt to take the lock. */
int usbi_handle_transfer_completion(struct usbi_transfer *itransfer,
enum libusb_transfer_status status)
{
struct libusb_transfer *transfer =
USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
struct libusb_context *ctx = TRANSFER_CTX(transfer);
uint8_t flags;
int r = 0;

/* FIXME: could be more intelligent with the timerfd here. we don't need
* to disarm the timerfd if there was no timer running, and we only need
* to rearm the timerfd if the transfer that expired was the one with
* the shortest timeout. */

usbi_mutex_lock(&ctx->flying_transfers_lock);
list_del(&itransfer->list);
if (usbi_using_timerfd(ctx))
r = arm_timerfd_for_next_timeout(ctx);
usbi_mutex_unlock(&ctx->flying_transfers_lock);

if (usbi_using_timerfd(ctx)) {
if (r < 0)
return r;
r = disarm_timerfd(ctx);
if (r < 0)
return r;
}

if (status == LIBUSB_TRANSFER_COMPLETED
&& transfer->flags & LIBUSB_TRANSFER_SHORT_NOT_OK) {
int rqlen = transfer->length;
if (transfer->type == LIBUSB_TRANSFER_TYPE_CONTROL)
rqlen -= LIBUSB_CONTROL_SETUP_SIZE;
if (rqlen != itransfer->transferred) {
usbi_dbg("interpreting short transfer as error");
status = LIBUSB_TRANSFER_ERROR;
}
}

flags = transfer->flags;
transfer->status = status;
transfer->actual_length = itransfer->transferred;
usbi_dbg("transfer %p has callback %p", transfer, transfer->callback);
if (transfer->callback)
transfer->callback(transfer);
/* transfer might have been freed by the above call, do not use from
* this point. */
if (flags & LIBUSB_TRANSFER_FREE_TRANSFER)
libusb_free_transfer(transfer);
usbi_mutex_lock(&ctx->event_waiters_lock);
usbi_mutex_unlock(&ctx->event_waiters_lock);
return 0;
}

/* Similar to usbi_handle_transfer_completion() but exclusively for transfers
* that were asynchronously cancelled. The same concerns w.r.t. freeing of
* transfers exist here.
* Do not call this function with the usbi_transfer lock held. User-specified
* callback functions may attempt to directly resubmit the transfer, which
* will attempt to take the lock. */
int usbi_handle_transfer_cancellation(struct usbi_transfer *transfer)
{
/* if the URB was cancelled due to timeout, report timeout to the user */
if (transfer->flags & USBI_TRANSFER_TIMED_OUT) {
usbi_dbg("detected timeout cancellation");
return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_TIMED_OUT);
}

/* otherwise its a normal async cancel */
return usbi_handle_transfer_completion(transfer, LIBUSB_TRANSFER_CANCELLED);
}

/** \ingroup poll
* Attempt to acquire the event handling lock. This lock is used to ensure that
* only one thread is monitoring libusb event sources at any one time.
*
* You only need to use this lock if you are developing an application
* which calls poll() or select() on libusb's file descriptors directly.
* If you stick to libusb's event handling loop functions (e.g.
* libusb_handle_events()) then you do not need to be concerned with this
* locking.
*
* While holding this lock, you are trusted to actually be handling events.
* If you are no longer handling events, you must call libusb_unlock_events()
* as soon as possible.
*
* \param ctx the context to operate on, or NULL for the default context
* \returns 0 if the lock was obtained successfully
* \returns 1 if the lock was not obtained (i.e. another thread holds the lock)
* \see \ref mtasync
*/
int API_EXPORTED libusb_try_lock_events(libusb_context *ctx)
{
int r;
USBI_GET_CONTEXT(ctx);

/* is someone else waiting to modify poll fds? if so, don't let this thread
* start event handling */
usbi_mutex_lock(&ctx->pollfd_modify_lock);
r = ctx->pollfd_modify;
usbi_mutex_unlock(&ctx->pollfd_modify_lock);
if (r) {
usbi_dbg("someone else is modifying poll fds");
return 1;
}

r = usbi_mutex_trylock(&ctx->events_lock);
if (r)
return 1;

ctx->event_handler_active = 1;
return 0;
}

/** \ingroup poll
* Acquire the event handling lock, blocking until successful acquisition if
* it is contended. This lock is used to ensure that only one thread is
* monitoring libusb event sources at any one time.
*
* You only need to use this lock if you are developing an application
* which calls poll() or select() on libusb's file descriptors directly.
* If you stick to libusb's event handling loop functions (e.g.
* libusb_handle_events()) then you do not need to be concerned with this
* locking.
*
* While holding this lock, you are trusted to actually be handling events.
* If you are no longer handling events, you must call libusb_unlock_events()
* as soon as possible.
*
* \param ctx the context to operate on, or NULL for the default context
* \see \ref mtasync
*/
void API_EXPORTED libusb_lock_events(libusb_context *ctx)
{
USBI_GET_CONTEXT(ctx);
usbi_mutex_lock(&ctx->events_lock);
ctx->event_handler_active = 1;
}

/** \ingroup poll
* Release the lock previously acquired with libusb_try_lock_events() or
* libusb_lock_events(). Releasing this lock will wake up any threads blocked
* on libusb_wait_for_event().
*
* \param ctx the context to operate on, or NULL for the default context
* \see \ref mtasync
*/
void API_EXPORTED libusb_unlock_events(libusb_context *ctx)
{
USBI_GET_CONTEXT(ctx);
ctx->event_handler_active = 0;
usbi_mutex_unlock(&ctx->events_lock);

/* FIXME: perhaps we should be a bit more efficient by not broadcasting
* the availability of the events lock when we are modifying pollfds
* (check ctx->pollfd_modify)? */
usbi_mutex_lock(&ctx->event_waiters_lock);
usbi_mutex_unlock(&ctx->event_waiters_lock);
}

/** \ingroup poll
* Determine if it is still OK for this thread to be doing event handling.
*
* Sometimes, libusb needs to temporarily pause all event handlers, and this
* is the function you should use before polling file descriptors to see if
* this is the case.
*
* If this function instructs your thread to give up the events lock, you
* should just continue the usual logic that is documented in \ref mtasync.
* On the next iteration, your thread will fail to obtain the events lock,
* and will hence become an event waiter.
*
* This function should be called while the events lock is held: you don't
* the current event handler.
*
* \param ctx the context to operate on, or NULL for the default context
* \returns 1 if event handling can start or continue
* \returns 0 if this thread must give up the events lock
* \see \ref fullstory "Multi-threaded I/O: the full story"
*/
int API_EXPORTED libusb_event_handling_ok(libusb_context *ctx)
{
int r;
USBI_GET_CONTEXT(ctx);

/* is someone else waiting to modify poll fds? if so, don't let this thread
* continue event handling */
usbi_mutex_lock(&ctx->pollfd_modify_lock);
r = ctx->pollfd_modify;
usbi_mutex_unlock(&ctx->pollfd_modify_lock);
if (r) {
usbi_dbg("someone else is modifying poll fds");
return 0;
}

return 1;
}

/** \ingroup poll
* Determine if an active thread is handling events (i.e. if anyone is holding
* the event handling lock).
*
* \param ctx the context to operate on, or NULL for the default context
* \returns 1 if a thread is handling events
* \returns 0 if there are no threads currently handling events
* \see \ref mtasync
*/
int API_EXPORTED libusb_event_handler_active(libusb_context *ctx)
{
int r;
USBI_GET_CONTEXT(ctx);

/* is someone else waiting to modify poll fds? if so, don't let this thread
* start event handling -- indicate that event handling is happening */
usbi_mutex_lock(&ctx->pollfd_modify_lock);
r = ctx->pollfd_modify;
usbi_mutex_unlock(&ctx->pollfd_modify_lock);
if (r) {
usbi_dbg("someone else is modifying poll fds");
return 1;
}

return ctx->event_handler_active;
}

/** \ingroup poll
* Acquire the event waiters lock. This lock is designed to be obtained under
* the situation where you want to be aware when events are completed, but
* some other thread is event handling so calling libusb_handle_events() is not
* allowed.
*
* You then obtain this lock, re-check that another thread is still handling
* events, then call libusb_wait_for_event().
*
* You only need to use this lock if you are developing an application
* which calls poll() or select() on libusb's file descriptors directly,
* <b>and</b> may potentially be handling events from 2 threads simultaenously.
* If you stick to libusb's event handling loop functions (e.g.
* libusb_handle_events()) then you do not need to be concerned with this
* locking.
*
* \param ctx the context to operate on, or NULL for the default context
* \see \ref mtasync
*/
void API_EXPORTED libusb_lock_event_waiters(libusb_context *ctx)
{
USBI_GET_CONTEXT(ctx);
usbi_mutex_lock(&ctx->event_waiters_lock);
}

/** \ingroup poll
* Release the event waiters lock.
* \param ctx the context to operate on, or NULL for the default context
* \see \ref mtasync
*/
void API_EXPORTED libusb_unlock_event_waiters(libusb_context *ctx)
{
USBI_GET_CONTEXT(ctx);
usbi_mutex_unlock(&ctx->event_waiters_lock);
}

/** \ingroup poll
* Wait for another thread to signal completion of an event. Must be called
* with the event waiters lock held, see libusb_lock_event_waiters().
*
* This function will block until any of the following conditions are met:
* -# The timeout expires
* -# A transfer completes
* -# A thread releases the event handling lock through libusb_unlock_events()
*
* the callback for the transfer has completed. Condition 3 is important
* because it means that the thread that was previously handling events is no
* longer doing so, so if any events are to complete, another thread needs to
* step up and start event handling.
*
* This function releases the event waiters lock before putting your thread
* to sleep, and reacquires the lock as it is being woken up.
*
* \param ctx the context to operate on, or NULL for the default context
* \param tv maximum timeout for this blocking function. A NULL value
* indicates unlimited timeout.
* \returns 0 after a transfer completes or another thread stops event handling
* \returns 1 if the timeout expired
* \see \ref mtasync
*/
int API_EXPORTED libusb_wait_for_event(libusb_context *ctx, struct timeval *tv)
{
struct timespec timeout;
int r;

USBI_GET_CONTEXT(ctx);
if (tv == NULL) {
usbi_cond_wait(&ctx->event_waiters_cond, &ctx->event_waiters_lock);
return 0;
}

r = usbi_backend->clock_gettime(USBI_CLOCK_REALTIME, &timeout);
if (r < 0) {
usbi_err(ctx, "failed to read realtime clock, error %d", errno);
return LIBUSB_ERROR_OTHER;
}

timeout.tv_sec += tv->tv_sec;
timeout.tv_nsec += tv->tv_usec * 1000;
if (timeout.tv_nsec > 1000000000) {
timeout.tv_nsec -= 1000000000;
timeout.tv_sec++;
}

r = usbi_cond_timedwait(&ctx->event_waiters_cond,
&ctx->event_waiters_lock, &timeout);
return (r == ETIMEDOUT);
}

static void handle_timeout(struct usbi_transfer *itransfer)
{
struct libusb_transfer *transfer =
USBI_TRANSFER_TO_LIBUSB_TRANSFER(itransfer);
int r;

itransfer->flags |= USBI_TRANSFER_TIMED_OUT;
r = libusb_cancel_transfer(transfer);
if (r < 0)
usbi_warn(TRANSFER_CTX(transfer),
"async cancel failed %d errno=%d", r, errno);
}

static int handle_timeouts_locked(struct libusb_context *ctx)
{
int r;
struct timespec systime_ts;
struct timeval systime;
struct usbi_transfer *transfer;

if (list_empty(&ctx->flying_transfers))
return 0;

/* get current time */
r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, &systime_ts);
if (r < 0)
return r;

TIMESPEC_TO_TIMEVAL(&systime, &systime_ts);

/* iterate through flying transfers list, finding all transfers that
* have expired timeouts */
list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
struct timeval *cur_tv = &transfer->timeout;

/* if we've reached transfers of infinite timeout, we're all done */
if (!timerisset(cur_tv))
return 0;

/* ignore timeouts we've already handled */
if (transfer->flags & (USBI_TRANSFER_TIMED_OUT | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
continue;

/* if transfer has non-expired timeout, nothing more to do */
if ((cur_tv->tv_sec > systime.tv_sec) ||
(cur_tv->tv_sec == systime.tv_sec &&
cur_tv->tv_usec > systime.tv_usec))
return 0;

/* otherwise, we've got an expired timeout to handle */
handle_timeout(transfer);
}
return 0;
}

static int handle_timeouts(struct libusb_context *ctx)
{
int r;
USBI_GET_CONTEXT(ctx);
usbi_mutex_lock(&ctx->flying_transfers_lock);
r = handle_timeouts_locked(ctx);
usbi_mutex_unlock(&ctx->flying_transfers_lock);
return r;
}

#ifdef USBI_TIMERFD_AVAILABLE
static int handle_timerfd_trigger(struct libusb_context *ctx)
{
int r;

r = disarm_timerfd(ctx);
if (r < 0)
return r;

usbi_mutex_lock(&ctx->flying_transfers_lock);

/* process the timeout that just happened */
r = handle_timeouts_locked(ctx);
if (r < 0)
goto out;

/* arm for next timeout*/
r = arm_timerfd_for_next_timeout(ctx);

out:
usbi_mutex_unlock(&ctx->flying_transfers_lock);
return r;
}
#endif

/* do the actual event handling. assumes that no other thread is concurrently
* doing the same thing. */
static int handle_events(struct libusb_context *ctx, struct timeval *tv)
{
int r;
struct usbi_pollfd *ipollfd;
POLL_NFDS_TYPE nfds = 0;
struct pollfd *fds;
int i = -1;
int timeout_ms;

usbi_mutex_lock(&ctx->pollfds_lock);
list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
nfds++;

/* TODO: malloc when number of fd's changes, not on every poll */
fds = malloc(sizeof(*fds) * nfds);
if (!fds) {
usbi_mutex_unlock(&ctx->pollfds_lock);
return LIBUSB_ERROR_NO_MEM;
}

list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd) {
struct libusb_pollfd *pollfd = &ipollfd->pollfd;
int fd = pollfd->fd;
i++;
fds[i].fd = fd;
fds[i].events = pollfd->events;
fds[i].revents = 0;
}
usbi_mutex_unlock(&ctx->pollfds_lock);

timeout_ms = (tv->tv_sec * 1000) + (tv->tv_usec / 1000);

/* round up to next millisecond */
if (tv->tv_usec % 1000)
timeout_ms++;

usbi_dbg("poll() %d fds with timeout in %dms", nfds, timeout_ms);
r = usbi_poll(fds, nfds, timeout_ms);
usbi_dbg("poll() returned %d", r);
if (r == 0) {
free(fds);
return handle_timeouts(ctx);
} else if (r == -1 && errno == EINTR) {
free(fds);
return LIBUSB_ERROR_INTERRUPTED;
} else if (r < 0) {
free(fds);
usbi_err(ctx, "poll failed %d err=%d\n", r, errno);
return LIBUSB_ERROR_IO;
}

/* fd[0] is always the ctrl pipe */
if (fds[0].revents) {
/* another thread wanted to interrupt event handling, and it succeeded!
* handle any other events that cropped up at the same time, and
* simply return */
usbi_dbg("caught a fish on the control pipe");

if (r == 1) {
r = 0;
goto handled;
} else {
/* prevent OS backend from trying to handle events on ctrl pipe */
fds[0].revents = 0;
r--;
}
}

#ifdef USBI_TIMERFD_AVAILABLE
/* on timerfd configurations, fds[1] is the timerfd */
if (usbi_using_timerfd(ctx) && fds[1].revents) {
/* timerfd indicates that a timeout has expired */
int ret;
usbi_dbg("timerfd triggered");

ret = handle_timerfd_trigger(ctx);
if (ret < 0) {
/* return error code */
r = ret;
goto handled;
} else if (r == 1) {
/* no more active file descriptors, nothing more to do */
r = 0;
goto handled;
} else {
/* more events pending...
* prevent OS backend from trying to handle events on timerfd */
fds[1].revents = 0;
r--;
}
}
#endif

r = usbi_backend->handle_events(ctx, fds, nfds, r);
if (r)
usbi_err(ctx, "backend handle_events failed with error %d", r);

handled:
free(fds);
return r;
}

/* returns the smallest of:
*  1. timeout of next URB
*  2. user-supplied timeout
* returns 1 if there is an already-expired timeout, otherwise returns 0
* and populates out
*/
static int get_next_timeout(libusb_context *ctx, struct timeval *tv,
struct timeval *out)
{
struct timeval timeout;
int r = libusb_get_next_timeout(ctx, &timeout);
if (r) {
if (!timerisset(&timeout))
return 1;

/* choose the smallest of next URB timeout or user specified timeout */
if (timercmp(&timeout, tv, <))
*out = timeout;
else
*out = *tv;
} else {
*out = *tv;
}
return 0;
}

/** \ingroup poll
* Handle any pending events.
*
* libusb determines "pending events" by checking if any timeouts have expired
* and by checking the set of file descriptors for activity.
*
* If a zero timeval is passed, this function will handle any already-pending
* events and then immediately return in non-blocking style.
*
* If a non-zero timeval is passed and no events are currently pending, this
* function will block waiting for events to handle up until the specified
* timeout. If an event arrives or a signal is raised, this function will
* return early.
*
* If the parameter completed is not NULL then <em>after obtaining the event
* handling lock</em> this function will return immediately if the integer
* pointed to is not 0. This allows for race free waiting for the completion
* of a specific transfer.
*
* \param ctx the context to operate on, or NULL for the default context
* \param tv the maximum time to block waiting for events, or an all zero
* timeval struct for non-blocking mode
* \param completed pointer to completion integer to check, or NULL
* \returns 0 on success, or a LIBUSB_ERROR code on failure
* \see \ref mtasync
*/
int API_EXPORTED libusb_handle_events_timeout_completed(libusb_context *ctx,
struct timeval *tv, int *completed)
{
int r;
struct timeval poll_timeout;

USBI_GET_CONTEXT(ctx);
r = get_next_timeout(ctx, tv, &poll_timeout);
if (r) {
return handle_timeouts(ctx);
}

retry:
if (libusb_try_lock_events(ctx) == 0) {
if (completed == NULL || !*completed) {
/* we obtained the event lock: do our own event handling */
usbi_dbg("doing our own event handling");
r = handle_events(ctx, &poll_timeout);
}
libusb_unlock_events(ctx);
return r;
}

/* another thread is doing event handling. wait for thread events that
* notify event completion. */
libusb_lock_event_waiters(ctx);

if (completed && *completed)

if (!libusb_event_handler_active(ctx)) {
/* we hit a race: whoever was event handling earlier finished in the
* time it took us to reach this point. try the cycle again. */
libusb_unlock_event_waiters(ctx);
usbi_dbg("event handler was active but went away, retrying");
goto retry;
}

usbi_dbg("another thread is doing event handling");
r = libusb_wait_for_event(ctx, &poll_timeout);

libusb_unlock_event_waiters(ctx);

if (r < 0)
return r;
else if (r == 1)
return handle_timeouts(ctx);
else
return 0;
}

/** \ingroup poll
* Handle any pending events
*
* Like libusb_handle_events_timeout_completed(), but without the completed
* parameter, calling this function is equivalent to calling
* libusb_handle_events_timeout_completed() with a NULL completed parameter.
*
* This function is kept primarily for backwards compatibility.
* All new code should call libusb_handle_events_completed() or
* libusb_handle_events_timeout_completed() to avoid race conditions.
*
* \param ctx the context to operate on, or NULL for the default context
* \param tv the maximum time to block waiting for events, or an all zero
* timeval struct for non-blocking mode
* \returns 0 on success, or a LIBUSB_ERROR code on failure
*/
int API_EXPORTED libusb_handle_events_timeout(libusb_context *ctx,
struct timeval *tv)
{
return libusb_handle_events_timeout_completed(ctx, tv, NULL);
}

/** \ingroup poll
* Handle any pending events in blocking mode. There is currently a timeout
* hardcoded at 60 seconds but we plan to make it unlimited in future. For
* finer control over whether this function is blocking or non-blocking, or
* for control over the timeout, use libusb_handle_events_timeout_completed()
*
* This function is kept primarily for backwards compatibility.
* All new code should call libusb_handle_events_completed() or
* libusb_handle_events_timeout_completed() to avoid race conditions.
*
* \param ctx the context to operate on, or NULL for the default context
* \returns 0 on success, or a LIBUSB_ERROR code on failure
*/
int API_EXPORTED libusb_handle_events(libusb_context *ctx)
{
struct timeval tv;
tv.tv_sec = 60;
tv.tv_usec = 0;
return libusb_handle_events_timeout_completed(ctx, &tv, NULL);
}

/** \ingroup poll
* Handle any pending events in blocking mode.
*
* Like libusb_handle_events(), with the addition of a completed parameter
* to allow for race free waiting for the completion of a specific transfer.
*
* See libusb_handle_events_timeout_completed() for details on the completed
* parameter.
*
* \param ctx the context to operate on, or NULL for the default context
* \param completed pointer to completion integer to check, or NULL
* \returns 0 on success, or a LIBUSB_ERROR code on failure
* \see \ref mtasync
*/
int API_EXPORTED libusb_handle_events_completed(libusb_context *ctx,
int *completed)
{
struct timeval tv;
tv.tv_sec = 60;
tv.tv_usec = 0;
return libusb_handle_events_timeout_completed(ctx, &tv, completed);
}

/** \ingroup poll
* Handle any pending events by polling file descriptors, without checking if
* any other threads are already doing so. Must be called with the event lock
* held, see libusb_lock_events().
*
* This function is designed to be called under the situation where you have
* taken the event lock and are calling poll()/select() directly on libusb's
* file descriptors (as opposed to using libusb_handle_events() or similar).
* You detect events on libusb's descriptors, so you then call this function
* with a zero timeout value (while still holding the event lock).
*
* \param ctx the context to operate on, or NULL for the default context
* \param tv the maximum time to block waiting for events, or zero for
* non-blocking mode
* \returns 0 on success, or a LIBUSB_ERROR code on failure
* \see \ref mtasync
*/
int API_EXPORTED libusb_handle_events_locked(libusb_context *ctx,
struct timeval *tv)
{
int r;
struct timeval poll_timeout;

USBI_GET_CONTEXT(ctx);
r = get_next_timeout(ctx, tv, &poll_timeout);
if (r) {
return handle_timeouts(ctx);
}

return handle_events(ctx, &poll_timeout);
}

/** \ingroup poll
* Determines whether your application must apply special timing considerations
* when monitoring libusb's file descriptors.
*
* This function is only useful for applications which retrieve and poll
* libusb's file descriptors in their own main loop (\ref pollmain).
*
* Ordinarily, libusb's event handler needs to be called into at specific
* moments in time (in addition to times when there is activity on the file
* descriptor set). The usual approach is to use libusb_get_next_timeout()
* to learn about when the next timeout occurs, and to adjust your
* poll()/select() timeout accordingly so that you can make a call into the
* library at that time.
*
* Some platforms supported by libusb do not come with this baggage - any
* events relevant to timing will be represented by activity on the file
* descriptor set, and libusb_get_next_timeout() will always return 0.
* This function allows you to detect whether you are running on such a
* platform.
*
* Since v1.0.5.
*
* \param ctx the context to operate on, or NULL for the default context
* \returns 0 if you must call into libusb at times determined by
* libusb_get_next_timeout(), or 1 if all timeout events are handled internally
* or through regular activity on the file descriptors.
* \see \ref pollmain "Polling libusb file descriptors for event handling"
*/
int API_EXPORTED libusb_pollfds_handle_timeouts(libusb_context *ctx)
{
#if defined(USBI_TIMERFD_AVAILABLE)
USBI_GET_CONTEXT(ctx);
return usbi_using_timerfd(ctx);
#else
(void)ctx;
return 0;
#endif
}

/** \ingroup poll
* Determine the next internal timeout that libusb needs to handle. You only
* need to use this function if you are calling poll() or select() or similar
* on libusb's file descriptors yourself - you do not need to use it if you
* are calling libusb_handle_events() or a variant directly.
*
* You should call this function in your main loop in order to determine how
* long to wait for select() or poll() to return results. libusb needs to be
* called into at this timeout, so you should use it as an upper bound on
* your select() or poll() call.
*
* When the timeout has expired, call into libusb_handle_events_timeout()
* (perhaps in non-blocking mode) so that libusb can handle the timeout.
*
* This function may return 1 (success) and an all-zero timeval. If this is
* the case, it indicates that libusb has a timeout that has already expired
* so you should call libusb_handle_events_timeout() or similar immediately.
* A return code of 0 indicates that there are no pending timeouts.
*
* On some platforms, this function will always returns 0 (no pending
* timeouts). See \ref polltime.
*
* \param ctx the context to operate on, or NULL for the default context
* \param tv output location for a relative time against the current
* clock in which libusb must be called into in order to process timeout events
* \returns 0 if there are no pending timeouts, 1 if a timeout was returned,
* or LIBUSB_ERROR_OTHER on failure
*/
int API_EXPORTED libusb_get_next_timeout(libusb_context *ctx,
struct timeval *tv)
{
struct usbi_transfer *transfer;
struct timespec cur_ts;
struct timeval cur_tv;
struct timeval *next_timeout;
int r;
int found = 0;

USBI_GET_CONTEXT(ctx);
if (usbi_using_timerfd(ctx))
return 0;

usbi_mutex_lock(&ctx->flying_transfers_lock);
if (list_empty(&ctx->flying_transfers)) {
usbi_mutex_unlock(&ctx->flying_transfers_lock);
usbi_dbg("no URBs, no timeout!");
return 0;
}

/* find next transfer which hasn't already been processed as timed out */
list_for_each_entry(transfer, &ctx->flying_transfers, list, struct usbi_transfer) {
if (transfer->flags & (USBI_TRANSFER_TIMED_OUT | USBI_TRANSFER_OS_HANDLES_TIMEOUT))
continue;

/* no timeout for this transfer? */
if (!timerisset(&transfer->timeout))
continue;

found = 1;
break;
}
usbi_mutex_unlock(&ctx->flying_transfers_lock);

if (!found) {
usbi_dbg("no URB with timeout or all handled by OS; no timeout!");
return 0;
}

next_timeout = &transfer->timeout;

r = usbi_backend->clock_gettime(USBI_CLOCK_MONOTONIC, &cur_ts);
if (r < 0) {
usbi_err(ctx, "failed to read monotonic clock, errno=%d", errno);
return LIBUSB_ERROR_OTHER;
}
TIMESPEC_TO_TIMEVAL(&cur_tv, &cur_ts);

if (!timercmp(&cur_tv, next_timeout, <)) {
timerclear(tv);
} else {
timersub(next_timeout, &cur_tv, tv);
usbi_dbg("next timeout in %d.%06ds", tv->tv_sec, tv->tv_usec);
}

return 1;
}

/** \ingroup poll
* These functions will be invoked for every new or removed file descriptor
* that libusb uses as an event source.
*
* To remove notifiers, pass NULL values for the function pointers.
*
* Note that file descriptors may have been added even before you register
* these notifiers (e.g. at libusb_init() time).
*
* Additionally, note that the removal notifier may be called during
* libusb_exit() (e.g. when it is closing file descriptors that were opened
* and added to the poll set at libusb_init() time). If you don't want this,
* remove the notifiers immediately before calling libusb_exit().
*
* \param ctx the context to operate on, or NULL for the default context
* \param removed_cb pointer to function for removal notifications
* \param user_data User data to be passed back to callbacks (useful for
* passing context information)
*/
void API_EXPORTED libusb_set_pollfd_notifiers(libusb_context *ctx,
void *user_data)
{
USBI_GET_CONTEXT(ctx);
ctx->fd_removed_cb = removed_cb;
ctx->fd_cb_user_data = user_data;
}

/* Add a file descriptor to the list of file descriptors to be monitored.
* events should be specified as a bitmask of events passed to poll(), e.g.
* POLLIN and/or POLLOUT. */
int usbi_add_pollfd(struct libusb_context *ctx, int fd, short events)
{
struct usbi_pollfd *ipollfd = malloc(sizeof(*ipollfd));
if (!ipollfd)
return LIBUSB_ERROR_NO_MEM;

usbi_dbg("add fd %d events %d", fd, events);
ipollfd->pollfd.fd = fd;
ipollfd->pollfd.events = events;
usbi_mutex_lock(&ctx->pollfds_lock);
usbi_mutex_unlock(&ctx->pollfds_lock);

return 0;
}

/* Remove a file descriptor from the list of file descriptors to be polled. */
void usbi_remove_pollfd(struct libusb_context *ctx, int fd)
{
struct usbi_pollfd *ipollfd;
int found = 0;

usbi_dbg("remove fd %d", fd);
usbi_mutex_lock(&ctx->pollfds_lock);
list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
if (ipollfd->pollfd.fd == fd) {
found = 1;
break;
}

if (!found) {
usbi_dbg("couldn't find fd %d to remove", fd);
usbi_mutex_unlock(&ctx->pollfds_lock);
return;
}

list_del(&ipollfd->list);
usbi_mutex_unlock(&ctx->pollfds_lock);
free(ipollfd);
if (ctx->fd_removed_cb)
ctx->fd_removed_cb(fd, ctx->fd_cb_user_data);
}

/** \ingroup poll
* Retrieve a list of file descriptors that should be polled by your main loop
* as libusb event sources.
*
* The returned list is NULL-terminated and should be freed with free() when
* done. The actual list contents must not be touched.
*
* As file descriptors are a Unix-specific concept, this function is not
* available on Windows and will always return NULL.
*
* \param ctx the context to operate on, or NULL for the default context
* \returns a NULL-terminated list of libusb_pollfd structures
* \returns NULL on error
* \returns NULL on platforms where the functionality is not available
*/
DEFAULT_VISIBILITY
const struct libusb_pollfd ** LIBUSB_CALL libusb_get_pollfds(
libusb_context *ctx)
{
#ifndef OS_WINDOWS
struct libusb_pollfd **ret = NULL;
struct usbi_pollfd *ipollfd;
size_t i = 0;
size_t cnt = 0;
USBI_GET_CONTEXT(ctx);

usbi_mutex_lock(&ctx->pollfds_lock);
list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
cnt++;

ret = calloc(cnt + 1, sizeof(struct libusb_pollfd *));
if (!ret)
goto out;

list_for_each_entry(ipollfd, &ctx->pollfds, list, struct usbi_pollfd)
ret[i++] = (struct libusb_pollfd *) ipollfd;
ret[cnt] = NULL;

out:
usbi_mutex_unlock(&ctx->pollfds_lock);
return (const struct libusb_pollfd **) ret;
#else
usbi_err(ctx, "external polling of libusb's internal descriptors "\
"is not yet supported on Windows platforms");
return NULL;
#endif
}

/* Backends call this from handle_events to report disconnection of a device.
* The transfers get cancelled appropriately.
*/
void usbi_handle_disconnect(struct libusb_device_handle *handle)
{
struct usbi_transfer *cur;
struct usbi_transfer *to_cancel;

usbi_dbg("device %d.%d",

/* terminate all pending transfers with the LIBUSB_TRANSFER_NO_DEVICE
* status code.
*
* this is a bit tricky because:
* 1. we can't do transfer completion while holding flying_transfers_lock
* 2. the transfers list can change underneath us - if we were to build a
*    list of transfers to complete (while holding look), the situation
*    might be different by the time we come to free them
*
* so we resort to a loop-based approach as below
* FIXME: is this still potentially racy?
*/

while (1) {
usbi_mutex_lock(&HANDLE_CTX(handle)->flying_transfers_lock);
to_cancel = NULL;
list_for_each_entry(cur, &HANDLE_CTX(handle)->flying_transfers, list, struct usbi_transfer)
if (USBI_TRANSFER_TO_LIBUSB_TRANSFER(cur)->dev_handle == handle) {
to_cancel = cur;
break;
}
usbi_mutex_unlock(&HANDLE_CTX(handle)->flying_transfers_lock);

if (!to_cancel)
break;

usbi_backend->clear_transfer_priv(to_cancel);
usbi_handle_transfer_completion(to_cancel, LIBUSB_TRANSFER_NO_DEVICE);
}

}