.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. c:namespace:: V4L
.. _VIDIOC_G_CTRL:
**********************************
ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL
**********************************
Name
====
VIDIOC_G_CTRL - VIDIOC_S_CTRL - Get or set the value of a control
Synopsis
========
.. c:macro:: VIDIOC_G_CTRL
``int ioctl(int fd, VIDIOC_G_CTRL, struct v4l2_control *argp)``
.. c:macro:: VIDIOC_S_CTRL
``int ioctl(int fd, VIDIOC_S_CTRL, struct v4l2_control *argp)``
Arguments
=========
``fd``
File descriptor returned by :c:func:`open()`.
``argp``
Pointer to struct :c:type:`v4l2_control`.
Description
===========
To get the current value of a control applications initialize the ``id``
field of a struct :c:type:`v4l2_control` and call the
:ref:`VIDIOC_G_CTRL <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:`v4l2_control` and call the
:ref:`VIDIOC_S_CTRL <VIDIOC_G_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, :ref:`VIDIOC_S_CTRL <VIDIOC_G_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.
.. c:type:: v4l2_control
.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
.. flat-table:: struct v4l2_control
:header-rows: 0
:stub-columns: 0
:widths: 1 1 2
* - __u32
- ``id``
- Identifies the control, set by the application.
* - __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 :c:type:`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 :c:type:`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.
Or if there is an attempt to set an inactive control and the driver is
not capable of caching the new value until the control is active again.
Codebase Browser
linux