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91 lines
2.6 KiB
91 lines
2.6 KiB
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later |
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.. c:namespace:: V4L |
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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:macro:: VIDIOC_G_PRIORITY |
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``int ioctl(int fd, VIDIOC_G_PRIORITY, enum v4l2_priority *argp)`` |
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.. c:macro:: VIDIOC_S_PRIORITY |
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``int ioctl(int fd, VIDIOC_S_PRIORITY, const enum v4l2_priority *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 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{8.5cm}| |
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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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