media-ioc-request-alloc.rst (1826B)
1.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-no-invariants-or-later 2.. c:namespace:: MC 3 4.. _media_ioc_request_alloc: 5 6***************************** 7ioctl MEDIA_IOC_REQUEST_ALLOC 8***************************** 9 10Name 11==== 12 13MEDIA_IOC_REQUEST_ALLOC - Allocate a request 14 15Synopsis 16======== 17 18.. c:macro:: MEDIA_IOC_REQUEST_ALLOC 19 20``int ioctl(int fd, MEDIA_IOC_REQUEST_ALLOC, int *argp)`` 21 22Arguments 23========= 24 25``fd`` 26 File descriptor returned by :c:func:`open()`. 27 28``argp`` 29 Pointer to an integer. 30 31Description 32=========== 33 34If the media device supports :ref:`requests <media-request-api>`, then 35this ioctl can be used to allocate a request. If it is not supported, then 36``errno`` is set to ``ENOTTY``. A request is accessed through a file descriptor 37that is returned in ``*argp``. 38 39If the request was successfully allocated, then the request file descriptor 40can be passed to the :ref:`VIDIOC_QBUF <VIDIOC_QBUF>`, 41:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`, 42:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and 43:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls. 44 45In addition, the request can be queued by calling 46:ref:`MEDIA_REQUEST_IOC_QUEUE` and re-initialized by calling 47:ref:`MEDIA_REQUEST_IOC_REINIT`. 48 49Finally, the file descriptor can be :ref:`polled <request-func-poll>` to wait 50for the request to complete. 51 52The request will remain allocated until all the file descriptors associated 53with it are closed by :c:func:`close()` and the driver no 54longer uses the request internally. See also 55:ref:`here <media-request-life-time>` for more information. 56 57Return Value 58============ 59 60On success 0 is returned, on error -1 and the ``errno`` variable is set 61appropriately. The generic error codes are described at the 62:ref:`Generic Error Codes <gen-errors>` chapter. 63 64ENOTTY 65 The driver has no support for requests.