Based on kernel version 6.8. Page generated on 2024-03-11 21:26 EST.
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.. 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.
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