1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2 .. c:namespace:: DTV.dmx 3 4 .. _DMX_REQBUFS: 5 6 ***************** 7 ioctl DMX_REQBUFS 8 ***************** 9 10 Name 11 ==== 12 13 DMX_REQBUFS - Initiate Memory Mapping and/or DMA buffer I/O 14 15 .. warning:: this API is still experimental 16 17 Synopsis 18 ======== 19 20 .. c:macro:: DMX_REQBUFS 21 22 ``int ioctl(int fd, DMX_REQBUFS, struct dmx_requestbuffers *argp)`` 23 24 Arguments 25 ========= 26 27 ``fd`` 28 File descriptor returned by :c:func:`open()`. 29 30 ``argp`` 31 Pointer to struct :c:type:`dmx_requestbuffers`. 32 33 Description 34 =========== 35 36 This ioctl is used to initiate a memory mapped or DMABUF based demux I/O. 37 38 Memory mapped buffers are located in device memory and must be allocated 39 with this ioctl before they can be mapped into the application's address 40 space. User buffers are allocated by applications themselves, and this 41 ioctl is merely used to switch the driver into user pointer I/O mode and 42 to setup some internal structures. Similarly, DMABUF buffers are 43 allocated by applications through a device driver, and this ioctl only 44 configures the driver into DMABUF I/O mode without performing any direct 45 allocation. 46 47 To allocate device buffers applications initialize all fields of the 48 struct :c:type:`dmx_requestbuffers` structure. They set the ``count`` field 49 to the desired number of buffers, and ``size`` to the size of each 50 buffer. 51 52 When the ioctl is called with a pointer to this structure, the driver will 53 attempt to allocate the requested number of buffers and it stores the actual 54 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 55 number is also possible when the driver requires more buffers to 56 function correctly. The actual allocated buffer size can is returned 57 at ``size``, and can be smaller than what's requested. 58 59 When this I/O method is not supported, the ioctl returns an ``EOPNOTSUPP`` 60 error code. 61 62 Applications can call :ref:`DMX_REQBUFS` again to change the number of 63 buffers, however this cannot succeed when any buffers are still mapped. 64 A ``count`` value of zero frees all buffers, after aborting or finishing 65 any DMA in progress. 66 67 Return Value 68 ============ 69 70 On success 0 is returned, on error -1 and the ``errno`` variable is set 71 appropriately. The generic error codes are described at the 72 :ref:`Generic Error Codes <gen-errors>` chapter. 73 74 EOPNOTSUPP 75 The the requested I/O method is not supported.
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