.. -*- 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 ======== .. c:function:: int ioctl( int fd, VIDIOC_G_CTRL, struct v4l2_control *argp ) :name: VIDIOC_G_CTRL .. c:function:: int ioctl( int fd, VIDIOC_S_CTRL, struct v4l2_control *argp ) :name: VIDIOC_S_CTRL Arguments ========= ``fd`` File descriptor returned by :ref:`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 ` 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 ` 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 ` 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 `, :ref:`VIDIOC_S_EXT_CTRLS ` or :ref:`VIDIOC_TRY_EXT_CTRLS ` must be used. .. c:type:: v4l2_control .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| .. 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 ` 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 `). 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.