blob: 6b2b157ba9c7359c695afcde3b1081481a8595b4 [file] [log] [blame]
.. -*- coding: utf-8; mode: rst -*-
.. _VIDIOC_G_CTRL:
**********************************
ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL
**********************************
*man VIDIOC_G_CTRL(2)*
VIDIOC_S_CTRL
Get or set the value of a control
Synopsis
========
.. c:function:: int ioctl( int fd, int request, struct v4l2_control *argp )
Arguments
=========
``fd``
File descriptor returned by :ref:`open() <func-open>`.
``request``
VIDIOC_G_CTRL, VIDIOC_S_CTRL
``argp``
Description
===========
To get the current value of a control applications initialize the ``id``
field of a struct :c:type:`struct v4l2_control` and call the
``VIDIOC_G_CTRL`` ioctl with a pointer to this structure. To change the
value of a control applications initialize the ``id`` and ``value``
fields of a struct :c:type:`struct v4l2_control` and call the
``VIDIOC_S_CTRL`` ioctl.
When the ``id`` is invalid drivers return an EINVAL error code. When the
``value`` is out of bounds drivers can choose to take the closest valid
value or return an ERANGE error code, whatever seems more appropriate.
However, ``VIDIOC_S_CTRL`` is a write-only ioctl, it does not return the
actual new value. If the ``value`` is inappropriate for the control
(e.g. if it refers to an unsupported menu index of a menu control), then
EINVAL error code is returned as well.
These ioctls work only with user controls. For other control classes the
:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` or
:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` must be used.
.. _v4l2-control:
.. flat-table:: struct v4l2_control
:header-rows: 0
:stub-columns: 0
:widths: 1 1 2
- .. row 1
- __u32
- ``id``
- Identifies the control, set by the application.
- .. row 2
- __s32
- ``value``
- New value or current value.
Return Value
============
On success 0 is returned, on error -1 and the ``errno`` variable is set
appropriately. The generic error codes are described at the
:ref:`Generic Error Codes <gen-errors>` chapter.
EINVAL
The struct :ref:`v4l2_control <v4l2-control>` ``id`` is invalid
or the ``value`` is inappropriate for the given control (i.e. if a
menu item is selected that is not supported by the driver according
to :ref:`VIDIOC_QUERYMENU <VIDIOC_QUERYCTRL>`).
ERANGE
The struct :ref:`v4l2_control <v4l2-control>` ``value`` is out of
bounds.
EBUSY
The control is temporarily not changeable, possibly because another
applications took over control of the device function this control
belongs to.
EACCES
Attempt to set a read-only control or to get a write-only control.
.. ------------------------------------------------------------------------------
.. This file was automatically converted from DocBook-XML with the dbxml
.. library (https://github.com/return42/sphkerneldoc). The origin XML comes
.. from the linux kernel, refer to:
..
.. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
.. ------------------------------------------------------------------------------