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1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later2.. c:namespace:: DTV.dmx3 4.. _DMX_REQBUFS:5 6*****************7ioctl DMX_REQBUFS8*****************9 10Name11====12 13DMX_REQBUFS - Initiate Memory Mapping and/or DMA buffer I/O14 15.. warning:: this API is still experimental16 17Synopsis18========19 20.. c:macro:: DMX_REQBUFS21 22``int ioctl(int fd, DMX_REQBUFS, struct dmx_requestbuffers *argp)``23 24Arguments25=========26 27``fd``28 File descriptor returned by :c:func:`open()`.29 30``argp``31 Pointer to struct :c:type:`dmx_requestbuffers`.32 33Description34===========35 36This ioctl is used to initiate a memory mapped or DMABUF based demux I/O.37 38Memory mapped buffers are located in device memory and must be allocated39with this ioctl before they can be mapped into the application's address40space. User buffers are allocated by applications themselves, and this41ioctl is merely used to switch the driver into user pointer I/O mode and42to setup some internal structures. Similarly, DMABUF buffers are43allocated by applications through a device driver, and this ioctl only44configures the driver into DMABUF I/O mode without performing any direct45allocation.46 47To allocate device buffers applications initialize all fields of the48struct :c:type:`dmx_requestbuffers` structure. They set the ``count`` field49to the desired number of buffers, and ``size`` to the size of each50buffer.51 52When the ioctl is called with a pointer to this structure, the driver will53attempt to allocate the requested number of buffers and it stores the actual54number 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 larger55number is also possible when the driver requires more buffers to56function correctly. The actual allocated buffer size can is returned57at ``size``, and can be smaller than what's requested.58 59When this I/O method is not supported, the ioctl returns an ``EOPNOTSUPP``60error code.61 62Applications can call :ref:`DMX_REQBUFS` again to change the number of63buffers, however this cannot succeed when any buffers are still mapped.64A ``count`` value of zero frees all buffers, after aborting or finishing65any DMA in progress.66 67Return Value68============69 70On success 0 is returned, on error -1 and the ``errno`` variable is set71appropriately. The generic error codes are described at the72:ref:`Generic Error Codes <gen-errors>` chapter.73 74EOPNOTSUPP75 The the requested I/O method is not supported.76