1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: DTV.dmx 3 4.. _DMX_REQBUFS: 5 6***************** 7ioctl DMX_REQBUFS 8***************** 9 10Name 11==== 12 13DMX_REQBUFS - Initiate Memory Mapping and/or DMA buffer I/O 14 15.. warning:: this API is still experimental 16 17Synopsis 18======== 19 20.. c:macro:: DMX_REQBUFS 21 22``int ioctl(int fd, DMX_REQBUFS, struct dmx_requestbuffers *argp)`` 23 24Arguments 25========= 26 27``fd`` 28 File descriptor returned by :c:func:`open()`. 29 30``argp`` 31 Pointer to struct :c:type:`dmx_requestbuffers`. 32 33Description 34=========== 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 allocated 39with this ioctl before they can be mapped into the application's address 40space. User buffers are allocated by applications themselves, and this 41ioctl is merely used to switch the driver into user pointer I/O mode and 42to setup some internal structures. Similarly, DMABUF buffers are 43allocated by applications through a device driver, and this ioctl only 44configures the driver into DMABUF I/O mode without performing any direct 45allocation. 46 47To allocate device buffers applications initialize all fields of the 48struct :c:type:`dmx_requestbuffers` structure. They set the ``count`` field 49to the desired number of buffers, and ``size`` to the size of each 50buffer. 51 52When the ioctl is called with a pointer to this structure, the driver will 53attempt to allocate the requested number of buffers and it stores the actual 54number 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 55number is also possible when the driver requires more buffers to 56function correctly. The actual allocated buffer size can is returned 57at ``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 of 63buffers, however this cannot succeed when any buffers are still mapped. 64A ``count`` value of zero frees all buffers, after aborting or finishing 65any DMA in progress. 66 67Return Value 68============ 69 70On success 0 is returned, on error -1 and the ``errno`` variable is set 71appropriately. The generic error codes are described at the 72:ref:`Generic Error Codes <gen-errors>` chapter. 73 74EOPNOTSUPP 75 The the requested I/O method is not supported. 76