a114a585be
The "reserved" field was a way, used at V4L2 API, to add new data to existing structs without breaking userspace. However, there are now clever ways of doing that, without needing to add an uneeded overhead. So, get rid of them. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
84 lines
2.4 KiB
ReStructuredText
84 lines
2.4 KiB
ReStructuredText
.. _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. They just set the ``reserved`` field array to zero. When ``DMX_DQBUF`` is called with a
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pointer to this structure, the driver fills the remaining fields or
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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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