75 lines
2.3 KiB
ReStructuredText
75 lines
2.3 KiB
ReStructuredText
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.. _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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