mirror of https://gitee.com/openkylin/linux.git
108 lines
2.8 KiB
ReStructuredText
108 lines
2.8 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
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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:function:: int ioctl( int fd, int request, 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 :ref:`open() <func-open>`.
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``request``
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VIDIOC_G_CTRL, VIDIOC_S_CTRL
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``argp``
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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 :ref:`struct v4l2_control <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 :ref:`struct v4l2_control <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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.. _v4l2-control:
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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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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- .. row 1
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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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- .. row 2
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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 :ref:`v4l2_control <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 :ref:`v4l2_control <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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