54f38fcae5
Since 2017, there is an space reserved for userspace API,
created by changeset 1d596dee38 ("docs: Create a user-space API guide").
As the media subsystem was one of the first subsystems to use
Sphinx, until this patch, we were keeping things on a separate
place.
Let's just use the new location, as having all uAPI altogether
will likely make things easier for developers.
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
94 lines
2.9 KiB
ReStructuredText
94 lines
2.9 KiB
ReStructuredText
.. Permission is granted to copy, distribute and/or modify this
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.. document under the terms of the GNU Free Documentation License,
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.. Version 1.1 or any later version published by the Free Software
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.. Foundation, with no Invariant Sections, no Front-Cover Texts
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.. and no Back-Cover Texts. A copy of the license is included at
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.. Documentation/userspace-api/media/fdl-appendix.rst.
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..
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.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
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.. _DMX_QBUF:
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*************************
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ioctl DMX_QBUF, DMX_DQBUF
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*************************
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Name
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====
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DMX_QBUF - DMX_DQBUF - Exchange a buffer with the driver
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.. warning:: this API is still experimental
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Synopsis
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========
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.. c:function:: int ioctl( int fd, DMX_QBUF, struct dmx_buffer *argp )
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:name: DMX_QBUF
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.. c:function:: int ioctl( int fd, DMX_DQBUF, struct dmx_buffer *argp )
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:name: DMX_DQBUF
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Arguments
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=========
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``fd``
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File descriptor returned by :ref:`open() <dmx_fopen>`.
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``argp``
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Pointer to struct :c:type:`dmx_buffer`.
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Description
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===========
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Applications call the ``DMX_QBUF`` ioctl to enqueue an empty
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(capturing) or filled (output) buffer in the driver's incoming queue.
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The semantics depend on the selected I/O method.
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To enqueue a buffer applications set the ``index`` field. Valid index
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numbers range from zero to the number of buffers allocated with
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:ref:`DMX_REQBUFS` (struct :c:type:`dmx_requestbuffers` ``count``) minus
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one. The contents of the struct :c:type:`dmx_buffer` returned
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by a :ref:`DMX_QUERYBUF` ioctl will do as well.
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When ``DMX_QBUF`` is called with a pointer to this structure, it locks the
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memory pages of the buffer in physical memory, so they cannot be swapped
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out to disk. Buffers remain locked until dequeued, until the
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the device is closed.
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Applications call the ``DMX_DQBUF`` ioctl to dequeue a filled
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(capturing) buffer from the driver's outgoing queue.
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They just set the ``index`` field with the buffer ID to be queued.
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When ``DMX_DQBUF`` is called with a pointer to struct :c:type:`dmx_buffer`,
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the driver fills the remaining fields or returns an error code.
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By default ``DMX_DQBUF`` blocks when no buffer is in the outgoing
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queue. When the ``O_NONBLOCK`` flag was given to the
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:ref:`open() <dmx_fopen>` function, ``DMX_DQBUF`` returns
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immediately with an ``EAGAIN`` error code when no buffer is available.
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The struct :c:type:`dmx_buffer` structure is specified in
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:ref:`buffer`.
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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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EAGAIN
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Non-blocking I/O has been selected using ``O_NONBLOCK`` and no
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buffer was in the outgoing queue.
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EINVAL
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The ``index`` is out of bounds, or no buffers have been allocated yet.
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EIO
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``DMX_DQBUF`` failed due to an internal error. Can also indicate
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temporary problems like signal loss or CRC errors.
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