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- .. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-no-invariants-or-later
- .. c:namespace:: MC
- .. _media_ioc_request_alloc:
- *****************************
- ioctl MEDIA_IOC_REQUEST_ALLOC
- *****************************
- Name
- ====
- MEDIA_IOC_REQUEST_ALLOC - Allocate a request
- Synopsis
- ========
- .. c:macro:: MEDIA_IOC_REQUEST_ALLOC
- ``int ioctl(int fd, MEDIA_IOC_REQUEST_ALLOC, int *argp)``
- Arguments
- =========
- ``fd``
- File descriptor returned by :c:func:`open()`.
- ``argp``
- Pointer to an integer.
- Description
- ===========
- If the media device supports :ref:`requests <media-request-api>`, then
- this ioctl can be used to allocate a request. If it is not supported, then
- ``errno`` is set to ``ENOTTY``. A request is accessed through a file descriptor
- that is returned in ``*argp``.
- If the request was successfully allocated, then the request file descriptor
- can be passed to the :ref:`VIDIOC_QBUF <VIDIOC_QBUF>`,
- :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
- :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` and
- :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` ioctls.
- In addition, the request can be queued by calling
- :ref:`MEDIA_REQUEST_IOC_QUEUE` and re-initialized by calling
- :ref:`MEDIA_REQUEST_IOC_REINIT`.
- Finally, the file descriptor can be :ref:`polled <request-func-poll>` to wait
- for the request to complete.
- The request will remain allocated until all the file descriptors associated
- with it are closed by :c:func:`close()` and the driver no
- longer uses the request internally. See also
- :ref:`here <media-request-life-time>` for more information.
- Return Value
- ============
- On success 0 is returned, on error -1 and the ``errno`` variable is set
- appropriately. The generic error codes are described at the
- :ref:`Generic Error Codes <gen-errors>` chapter.
- ENOTTY
- The driver has no support for requests.
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