1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: V4L
3
4.. _VIDIOC_G_PRIORITY:
5
6******************************************
7ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY
8******************************************
9
10Name
11====
12
13VIDIOC_G_PRIORITY - VIDIOC_S_PRIORITY - Query or request the access priority associated with a file descriptor
14
15Synopsis
16========
17
18.. c:macro:: VIDIOC_G_PRIORITY
19
20``int ioctl(int fd, VIDIOC_G_PRIORITY, enum v4l2_priority *argp)``
21
22.. c:macro:: VIDIOC_S_PRIORITY
23
24``int ioctl(int fd, VIDIOC_S_PRIORITY, const enum v4l2_priority *argp)``
25
26Arguments
27=========
28
29``fd``
30    File descriptor returned by :c:func:`open()`.
31
32``argp``
33    Pointer to an enum :c:type:`v4l2_priority` type.
34
35Description
36===========
37
38To query the current access priority applications call the
39:ref:`VIDIOC_G_PRIORITY <VIDIOC_G_PRIORITY>` ioctl with a pointer to an enum v4l2_priority
40variable where the driver stores the current priority.
41
42To request an access priority applications store the desired priority in
43an enum v4l2_priority variable and call :ref:`VIDIOC_S_PRIORITY <VIDIOC_G_PRIORITY>` ioctl
44with a pointer to this variable.
45
46.. c:type:: v4l2_priority
47
48.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|
49
50.. flat-table:: enum v4l2_priority
51    :header-rows:  0
52    :stub-columns: 0
53    :widths:       3 1 4
54
55    * - ``V4L2_PRIORITY_UNSET``
56      - 0
57      -
58    * - ``V4L2_PRIORITY_BACKGROUND``
59      - 1
60      - Lowest priority, usually applications running in background, for
61	example monitoring VBI transmissions. A proxy application running
62	in user space will be necessary if multiple applications want to
63	read from a device at this priority.
64    * - ``V4L2_PRIORITY_INTERACTIVE``
65      - 2
66      -
67    * - ``V4L2_PRIORITY_DEFAULT``
68      - 2
69      - Medium priority, usually applications started and interactively
70	controlled by the user. For example TV viewers, Teletext browsers,
71	or just "panel" applications to change the channel or video
72	controls. This is the default priority unless an application
73	requests another.
74    * - ``V4L2_PRIORITY_RECORD``
75      - 3
76      - Highest priority. Only one file descriptor can have this priority,
77	it blocks any other fd from changing device properties. Usually
78	applications which must not be interrupted, like video recording.
79
80Return Value
81============
82
83On success 0 is returned, on error -1 and the ``errno`` variable is set
84appropriately. The generic error codes are described at the
85:ref:`Generic Error Codes <gen-errors>` chapter.
86
87EINVAL
88    The requested priority value is invalid.
89
90EBUSY
91    Another application already requested higher priority.
92