vidioc-g-ctrl.rst 2.7 KB
Newer Older
1 2
.. -*- coding: utf-8; mode: rst -*-

3
.. _VIDIOC_G_CTRL:
4 5 6 7 8 9 10 11 12 13 14 15 16 17

**********************************
ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL
**********************************

*man VIDIOC_G_CTRL(2)*

VIDIOC_S_CTRL
Get or set the value of a control


Synopsis
========

18
.. cpp:function:: int ioctl( int fd, int request, struct v4l2_control *argp )
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35

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``
36
field of a struct :ref:`struct v4l2_control <v4l2-control>` and call the
37
:ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl with a pointer to this structure. To change the
38
value of a control applications initialize the ``id`` and ``value``
39
fields of a struct :ref:`struct v4l2_control <v4l2-control>` and call the
40
:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctl.
41

42
When the ``id`` is invalid drivers return an ``EINVAL`` error code. When the
43
``value`` is out of bounds drivers can choose to take the closest valid
44
value or return an ``ERANGE`` error code, whatever seems more appropriate.
45
However, :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` is a write-only ioctl, it does not return the
46 47 48 49 50
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
51
:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
52 53
:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` or
:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` must be used.
54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92


.. _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
93
    to :ref:`VIDIOC_QUERYMENU <VIDIOC_QUERYCTRL>`).
94 95 96 97 98 99 100 101 102 103 104 105

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.