101 lines
3.0 KiB
ReStructuredText
101 lines
3.0 KiB
ReStructuredText
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.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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.. c:namespace:: V4L
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.. _VIDIOC_G_CTRL:
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**********************************
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ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL
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**********************************
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Name
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====
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VIDIOC_G_CTRL - VIDIOC_S_CTRL - Get or set the value of a control
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Synopsis
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========
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.. c:macro:: VIDIOC_G_CTRL
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``int ioctl(int fd, VIDIOC_G_CTRL, struct v4l2_control *argp)``
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.. c:macro:: VIDIOC_S_CTRL
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``int ioctl(int fd, VIDIOC_S_CTRL, struct v4l2_control *argp)``
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Arguments
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=========
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``fd``
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File descriptor returned by :c:func:`open()`.
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``argp``
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Pointer to struct :c:type:`v4l2_control`.
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Description
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===========
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To get the current value of a control applications initialize the ``id``
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field of a struct :c:type:`v4l2_control` and call the
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:ref:`VIDIOC_G_CTRL <VIDIOC_G_CTRL>` ioctl with a pointer to this structure. To change the
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value of a control applications initialize the ``id`` and ``value``
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fields of a struct :c:type:`v4l2_control` and call the
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:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` ioctl.
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When the ``id`` is invalid drivers return an ``EINVAL`` error code. When the
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``value`` is out of bounds drivers can choose to take the closest valid
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value or return an ``ERANGE`` error code, whatever seems more appropriate.
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However, :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` is a write-only ioctl, it does not return the
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actual new value. If the ``value`` is inappropriate for the control
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(e.g. if it refers to an unsupported menu index of a menu control), then
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EINVAL error code is returned as well.
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These ioctls work only with user controls. For other control classes the
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:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`,
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:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` or
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:ref:`VIDIOC_TRY_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` must be used.
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.. c:type:: v4l2_control
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
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.. flat-table:: struct v4l2_control
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __u32
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- ``id``
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- Identifies the control, set by the application.
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* - __s32
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- ``value``
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- New value or current value.
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Return Value
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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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EINVAL
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The struct :c:type:`v4l2_control` ``id`` is invalid
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or the ``value`` is inappropriate for the given control (i.e. if a
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menu item is selected that is not supported by the driver according
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to :ref:`VIDIOC_QUERYMENU <VIDIOC_QUERYCTRL>`).
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ERANGE
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The struct :c:type:`v4l2_control` ``value`` is out of
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bounds.
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EBUSY
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The control is temporarily not changeable, possibly because another
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applications took over control of the device function this control
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belongs to.
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EACCES
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Attempt to set a read-only control or to get a write-only control.
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Or if there is an attempt to set an inactive control and the driver is
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not capable of caching the new value until the control is active again.
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