[deliverable/linux.git] / Documentation / media / uapi / v4l / vidioc-g-ctrl.rst

.. -*- coding: utf-8; mode: rst -*-

.. _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
========

.. cpp: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 :ref:`struct v4l2_control <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 :ref:`struct v4l2_control <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.


.. _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.
Commit	Line	Data
5377d91f MH	1	.. -- coding: utf-8; mode: rst --
5377d91f MH	2
af4a4d0d	3	.. _VIDIOC_G_CTRL:
5377d91f MH	4
	5	**********************************
	6	ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL
	7	**********************************
	8
15e7d615	9	Name
586027ce	10	====
5377d91f	11
586027ce	12	VIDIOC_G_CTRL - VIDIOC_S_CTRL - Get or set the value of a control
5377d91f	13
15e7d615 MCC	14
15e7d615 MCC	15	Synopsis
5377d91f MH	16	========
5377d91f MH	17
b7e67f6c	18	.. cpp:function:: int ioctl( int fd, int request, struct v4l2_control *argp )
5377d91f	19
586027ce	20
15e7d615	21	Arguments
5377d91f MH	22	=========
	23
	24	``fd``
	25	File descriptor returned by :ref:`open() <func-open>`.
	26
	27	``request``
	28	VIDIOC_G_CTRL, VIDIOC_S_CTRL
	29
	30	``argp``
	31
	32
15e7d615	33	Description
5377d91f MH	34	===========
	35
	36	To get the current value of a control applications initialize the ``id``
acf309a2	37	field of a struct :ref:`struct v4l2_control <v4l2-control>` and call the
4e03cb76	38	:ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl with a pointer to this structure. To change the
5377d91f	39	value of a control applications initialize the ``id`` and ``value``
acf309a2	40	fields of a struct :ref:`struct v4l2_control <v4l2-control>` and call the
2212ff25	41	:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctl.
5377d91f	42
cdb4af0f	43	When the ``id`` is invalid drivers return an ``EINVAL`` error code. When the
5377d91f	44	``value`` is out of bounds drivers can choose to take the closest valid
cdb4af0f	45	value or return an ``ERANGE`` error code, whatever seems more appropriate.
2212ff25	46	However, :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` is a write-only ioctl, it does not return the
5377d91f MH	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.
	50
	51	These ioctls work only with user controls. For other control classes the
4e03cb76	52	:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
af4a4d0d MCC	53	:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` or
af4a4d0d MCC	54	:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` must be used.
5377d91f MH	55
	56
	57	.. _v4l2-control:
	58
	59	.. flat-table:: struct v4l2_control
	60	:header-rows: 0
	61	:stub-columns: 0
	62	:widths: 1 1 2
	63
	64
	65	- .. row 1
	66
	67	- __u32
	68
	69	- ``id``
	70
	71	- Identifies the control, set by the application.
	72
	73	- .. row 2
	74
	75	- __s32
	76
	77	- ``value``
	78
	79	- New value or current value.
	80
	81
15e7d615	82	Return Value
5377d91f MH	83	============
	84
	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.
	88
	89	EINVAL
	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
af4a4d0d	93	to :ref:`VIDIOC_QUERYMENU <VIDIOC_QUERYCTRL>`).
5377d91f MH	94
	95	ERANGE
	96	The struct :ref:`v4l2_control <v4l2-control>` ``value`` is out of
	97	bounds.
	98
	99	EBUSY
	100	The control is temporarily not changeable, possibly because another
	101	applications took over control of the device function this control
	102	belongs to.
	103
	104	EACCES
	105	Attempt to set a read-only control or to get a write-only control.