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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>
75 lines
2.3 KiB
ReStructuredText
75 lines
2.3 KiB
ReStructuredText
.. _DMX_REQBUFS:
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*****************
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ioctl DMX_REQBUFS
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*****************
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Name
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====
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DMX_REQBUFS - Initiate Memory Mapping and/or DMA buffer I/O
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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_REQBUFS, struct dmx_requestbuffers *argp )
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:name: DMX_REQBUFS
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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_requestbuffers`.
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Description
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===========
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This ioctl is used to initiate a memory mapped or DMABUF based demux I/O.
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Memory mapped buffers are located in device memory and must be allocated
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with this ioctl before they can be mapped into the application's address
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space. User buffers are allocated by applications themselves, and this
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ioctl is merely used to switch the driver into user pointer I/O mode and
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to setup some internal structures. Similarly, DMABUF buffers are
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allocated by applications through a device driver, and this ioctl only
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configures the driver into DMABUF I/O mode without performing any direct
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allocation.
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To allocate device buffers applications initialize all fields of the
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struct :c:type:`dmx_requestbuffers` structure. They set the ``count`` field
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to the desired number of buffers, and ``size`` to the size of each
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buffer.
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When the ioctl is called with a pointer to this structure, the driver will
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attempt to allocate the requested number of buffers and it stores the actual
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number allocated in the ``count`` field. The ``count`` can be smaller than the number requested, even zero, when the driver runs out of free memory. A larger
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number is also possible when the driver requires more buffers to
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function correctly. The actual allocated buffer size can is returned
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at ``size``, and can be smaller than what's requested.
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When this I/O method is not supported, the ioctl returns an ``EOPNOTSUPP``
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error code.
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Applications can call :ref:`DMX_REQBUFS` again to change the number of
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buffers, however this cannot succeed when any buffers are still mapped.
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A ``count`` value of zero frees all buffers, after aborting or finishing
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any DMA in progress.
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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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EOPNOTSUPP
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The the requested I/O method is not supported.
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