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75 lines
2.4 KiB
75 lines
2.4 KiB
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later |
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.. c:namespace:: DTV.dmx |
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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:macro:: DMX_REQBUFS |
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``int ioctl(int fd, DMX_REQBUFS, struct dmx_requestbuffers *argp)`` |
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Arguments |
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========= |
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``fd`` |
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File descriptor returned by :c:func:`open()`. |
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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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