LXR linux/Documentation/userspace-api/media/v4l/vidioc-g-ctrl.rst

   1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
   2.. c:namespace:: V4L
   3
   4.. _VIDIOC_G_CTRL:
   5
   6**********************************
   7ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL
   8**********************************
   9
  10Name
  11====
  12
  13VIDIOC_G_CTRL - VIDIOC_S_CTRL - Get or set the value of a control
  14
  15Synopsis
  16========
  17
  18.. c:macro:: VIDIOC_G_CTRL
  19
  20``int ioctl(int fd, VIDIOC_G_CTRL, struct v4l2_control *argp)``
  21
  22.. c:macro:: VIDIOC_S_CTRL
  23
  24``int ioctl(int fd, VIDIOC_S_CTRL, struct v4l2_control *argp)``
  25
  26Arguments
  27=========
  28
  29``fd``
  30    File descriptor returned by :c:func:`open()`.
  31
  32``argp``
  33    Pointer to struct :c:type:`v4l2_control`.
  34
  35Description
  36===========
  37
  38To get the current value of a control applications initialize the ``id``
  39field of a struct :c:type:`v4l2_control` and call the
  40:ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl with a pointer to this structure. To change the
  41value of a control applications initialize the ``id`` and ``value``
  42fields of a struct :c:type:`v4l2_control` and call the
  43:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctl.
  44
  45When the ``id`` is invalid drivers return an ``EINVAL`` error code. When the
  46``value`` is out of bounds drivers can choose to take the closest valid
  47value or return an ``ERANGE`` error code, whatever seems more appropriate.
  48However, :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` is a write-only ioctl, it does not return the
  49actual new value. If the ``value`` is inappropriate for the control
  50(e.g. if it refers to an unsupported menu index of a menu control), then
  51EINVAL error code is returned as well.
  52
  53These ioctls work only with user controls. For other control classes the
  54:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
  55:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` or
  56:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` must be used.
  57
  58.. c:type:: v4l2_control
  59
  60.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
  61
  62.. flat-table:: struct v4l2_control
  63    :header-rows:  0
  64    :stub-columns: 0
  65    :widths:       1 1 2
  66
  67    * - __u32
  68      - ``id``
  69      - Identifies the control, set by the application.
  70    * - __s32
  71      - ``value``
  72      - New value or current value.
  73
  74Return Value
  75============
  76
  77On success 0 is returned, on error -1 and the ``errno`` variable is set
  78appropriately. The generic error codes are described at the
  79:ref:`Generic Error Codes <gen-errors>` chapter.
  80
  81EINVAL
  82    The struct :c:type:`v4l2_control` ``id`` is invalid
  83    or the ``value`` is inappropriate for the given control (i.e. if a
  84    menu item is selected that is not supported by the driver according
  85    to :ref:`VIDIOC_QUERYMENU <VIDIOC_QUERYCTRL>`).
  86
  87ERANGE
  88    The struct :c:type:`v4l2_control` ``value`` is out of
  89    bounds.
  90
  91EBUSY
  92    The control is temporarily not changeable, possibly because another
  93    applications took over control of the device function this control
  94    belongs to.
  95
  96EACCES
  97    Attempt to set a read-only control or to get a write-only control.
  98
  99    Or if there is an attempt to set an inactive control and the driver is
 100    not capable of caching the new value until the control is active again.
 101