1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2.. c:namespace:: V4L
3
4.. _VIDIOC_G_CTRL:
5
6**********************************
7ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL
8**********************************
9
10Name
11====
12
13VIDIOC_G_CTRL - VIDIOC_S_CTRL - Get or set the value of a control
14
15Synopsis
16========
17
18.. c:macro:: VIDIOC_G_CTRL
19
20``int ioctl(int fd, VIDIOC_G_CTRL, struct v4l2_control *argp)``
21
22.. c:macro:: VIDIOC_S_CTRL
23
24``int ioctl(int fd, VIDIOC_S_CTRL, struct v4l2_control *argp)``
25
26Arguments
27=========
28
29``fd``
30    File descriptor returned by :c:func:`open()`.
31
32``argp``
33    Pointer to struct :c:type:`v4l2_control`.
34
35Description
36===========
37
38To get the current value of a control applications initialize the ``id``
39field of a struct :c:type:`v4l2_control` and call the
40:ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl with a pointer to this structure. To change the
41value of a control applications initialize the ``id`` and ``value``
42fields of a struct :c:type:`v4l2_control` and call the
43:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctl.
44
45When the ``id`` is invalid drivers return an ``EINVAL`` error code. When the
46``value`` is out of bounds drivers can choose to take the closest valid
47value or return an ``ERANGE`` error code, whatever seems more appropriate.
48However, :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` is a write-only ioctl, it does not return the
49actual new value. If the ``value`` is inappropriate for the control
50(e.g. if it refers to an unsupported menu index of a menu control), then
51EINVAL error code is returned as well.
52
53These ioctls work only with user controls. For other control classes the
54:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
55:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` or
56:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` must be used.
57
58.. c:type:: v4l2_control
59
60.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
61
62.. flat-table:: struct v4l2_control
63    :header-rows:  0
64    :stub-columns: 0
65    :widths:       1 1 2
66
67    * - __u32
68      - ``id``
69      - Identifies the control, set by the application.
70    * - __s32
71      - ``value``
72      - New value or current value.
73
74Return Value
75============
76
77On success 0 is returned, on error -1 and the ``errno`` variable is set
78appropriately. The generic error codes are described at the
79:ref:`Generic Error Codes <gen-errors>` chapter.
80
81EINVAL
82    The struct :c:type:`v4l2_control` ``id`` is invalid
83    or the ``value`` is inappropriate for the given control (i.e. if a
84    menu item is selected that is not supported by the driver according
85    to :ref:`VIDIOC_QUERYMENU <VIDIOC_QUERYCTRL>`).
86
87ERANGE
88    The struct :c:type:`v4l2_control` ``value`` is out of
89    bounds.
90
91EBUSY
92    The control is temporarily not changeable, possibly because another
93    applications took over control of the device function this control
94    belongs to.
95
96EACCES
97    Attempt to set a read-only control or to get a write-only control.
98
99    Or if there is an attempt to set an inactive control and the driver is
100    not capable of caching the new value until the control is active again.
101