64e4954619
The conversion script added some comments at the end. They point to the original DocBook files, with will be removed after the manual fixes. So, they'll be pointing to nowere. So, remove those comments. They'll be forever stored at the Kernel tree. So, if someone wants the references, it is just a matter of looking at the backlog. Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
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31 lines
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.. -*- coding: utf-8; mode: rst -*-
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.. _app-pri:
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********************
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Application Priority
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********************
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When multiple applications share a device it may be desirable to assign
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them different priorities. Contrary to the traditional "rm -rf /" school
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of thought a video recording application could for example block other
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applications from changing video controls or switching the current TV
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channel. Another objective is to permit low priority applications
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working in background, which can be preempted by user controlled
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applications and automatically regain control of the device at a later
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time.
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Since these features cannot be implemented entirely in user space V4L2
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defines the :ref:`VIDIOC_G_PRIORITY <VIDIOC_G_PRIORITY>` and
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:ref:`VIDIOC_S_PRIORITY <VIDIOC_G_PRIORITY>` ioctls to request and
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query the access priority associate with a file descriptor. Opening a
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device assigns a medium priority, compatible with earlier versions of
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V4L2 and drivers not supporting these ioctls. Applications requiring a
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different priority will usually call :ref:`VIDIOC_S_PRIORITY
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<VIDIOC_G_PRIORITY>` after verifying the device with the
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:ref:`VIDIOC_QUERYCAP` ioctl.
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Ioctls changing driver properties, such as
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:ref:`VIDIOC_S_INPUT <VIDIOC_G_INPUT>`, return an ``EBUSY`` error code
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after another application obtained higher priority.
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