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- .. -*- 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() <func-open>`.
- ``argp``
- 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 <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 <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.
- .. 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 <gen-errors>` 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 <VIDIOC_QUERYCTRL>`).
- 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.
|
