1 .. -*- coding: utf-8; mode: rst -*-
5 **********************************
6 ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL
7 **********************************
12 VIDIOC_G_CTRL - VIDIOC_S_CTRL - Get or set the value of a control
18 .. cpp:function:: int ioctl( int fd, int request, struct v4l2_control *argp )
25 File descriptor returned by :ref:`open() <func-open>`.
28 VIDIOC_G_CTRL, VIDIOC_S_CTRL
36 To get the current value of a control applications initialize the ``id``
37 field of a struct :ref:`struct v4l2_control <v4l2-control>` and call the
38 :ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl with a pointer to this structure. To change the
39 value of a control applications initialize the ``id`` and ``value``
40 fields of a struct :ref:`struct v4l2_control <v4l2-control>` and call the
41 :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctl.
43 When the ``id`` is invalid drivers return an ``EINVAL`` error code. When the
44 ``value`` is out of bounds drivers can choose to take the closest valid
45 value or return an ``ERANGE`` error code, whatever seems more appropriate.
46 However, :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` is a write-only ioctl, it does not return the
47 actual new value. If the ``value`` is inappropriate for the control
48 (e.g. if it refers to an unsupported menu index of a menu control), then
49 EINVAL error code is returned as well.
51 These ioctls work only with user controls. For other control classes the
52 :ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
53 :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` or
54 :ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` must be used.
59 .. flat-table:: struct v4l2_control
71 - Identifies the control, set by the application.
79 - New value or current value.
85 On success 0 is returned, on error -1 and the ``errno`` variable is set
86 appropriately. The generic error codes are described at the
87 :ref:`Generic Error Codes <gen-errors>` chapter.
90 The struct :ref:`v4l2_control <v4l2-control>` ``id`` is invalid
91 or the ``value`` is inappropriate for the given control (i.e. if a
92 menu item is selected that is not supported by the driver according
93 to :ref:`VIDIOC_QUERYMENU <VIDIOC_QUERYCTRL>`).
96 The struct :ref:`v4l2_control <v4l2-control>` ``value`` is out of
100 The control is temporarily not changeable, possibly because another
101 applications took over control of the device function this control
105 Attempt to set a read-only control or to get a write-only control.