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