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