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