94 lines
2.6 KiB
ReStructuredText
94 lines
2.6 KiB
ReStructuredText
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.. -*- coding: utf-8; mode: rst -*-
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.. _VIDIOC_G_PRIORITY:
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******************************************
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ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY
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******************************************
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Name
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====
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VIDIOC_G_PRIORITY - VIDIOC_S_PRIORITY - Query or request the access priority associated with a file descriptor
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Synopsis
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========
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.. c:function:: int ioctl( int fd, VIDIOC_G_PRIORITY, enum v4l2_priority *argp )
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:name: VIDIOC_G_PRIORITY
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.. c:function:: int ioctl( int fd, VIDIOC_S_PRIORITY, const enum v4l2_priority *argp )
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:name: VIDIOC_S_PRIORITY
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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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``argp``
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Pointer to an enum :c:type:`v4l2_priority` type.
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Description
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===========
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To query the current access priority applications call the
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:ref:`VIDIOC_G_PRIORITY <VIDIOC_G_PRIORITY>` ioctl with a pointer to an enum v4l2_priority
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variable where the driver stores the current priority.
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To request an access priority applications store the desired priority in
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an enum v4l2_priority variable and call :ref:`VIDIOC_S_PRIORITY <VIDIOC_G_PRIORITY>` ioctl
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with a pointer to this variable.
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.. c:type:: v4l2_priority
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.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
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.. flat-table:: enum v4l2_priority
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 4
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* - ``V4L2_PRIORITY_UNSET``
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- 0
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-
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* - ``V4L2_PRIORITY_BACKGROUND``
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- 1
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- Lowest priority, usually applications running in background, for
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example monitoring VBI transmissions. A proxy application running
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in user space will be necessary if multiple applications want to
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read from a device at this priority.
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* - ``V4L2_PRIORITY_INTERACTIVE``
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- 2
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-
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* - ``V4L2_PRIORITY_DEFAULT``
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- 2
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- Medium priority, usually applications started and interactively
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controlled by the user. For example TV viewers, Teletext browsers,
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or just "panel" applications to change the channel or video
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controls. This is the default priority unless an application
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requests another.
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* - ``V4L2_PRIORITY_RECORD``
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- 3
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- Highest priority. Only one file descriptor can have this priority,
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it blocks any other fd from changing device properties. Usually
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applications which must not be interrupted, like video recording.
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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 requested priority value is invalid.
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EBUSY
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Another application already requested higher priority.
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