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diff --git a/Documentation/userspace-api/media/v4l/vidioc-g-priority.rst b/Documentation/userspace-api/media/v4l/vidioc-g-priority.rst new file mode 100644 index 000000000000..c8add130c7a4 --- /dev/null +++ b/Documentation/userspace-api/media/v4l/vidioc-g-priority.rst @@ -0,0 +1,100 @@ +.. Permission is granted to copy, distribute and/or modify this +.. document under the terms of the GNU Free Documentation License, +.. Version 1.1 or any later version published by the Free Software +.. Foundation, with no Invariant Sections, no Front-Cover Texts +.. and no Back-Cover Texts. A copy of the license is included at +.. Documentation/userspace-api/media/fdl-appendix.rst. +.. +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections + +.. _VIDIOC_G_PRIORITY: + +****************************************** +ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY +****************************************** + +Name +==== + +VIDIOC_G_PRIORITY - VIDIOC_S_PRIORITY - Query or request the access priority associated with a file descriptor + + +Synopsis +======== + +.. c:function:: int ioctl( int fd, VIDIOC_G_PRIORITY, enum v4l2_priority *argp ) + :name: VIDIOC_G_PRIORITY + +.. c:function:: int ioctl( int fd, VIDIOC_S_PRIORITY, const enum v4l2_priority *argp ) + :name: VIDIOC_S_PRIORITY + + +Arguments +========= + +``fd`` + File descriptor returned by :ref:`open() <func-open>`. + +``argp`` + Pointer to an enum :c:type:`v4l2_priority` type. + + +Description +=========== + +To query the current access priority applications call the +:ref:`VIDIOC_G_PRIORITY <VIDIOC_G_PRIORITY>` ioctl with a pointer to an enum v4l2_priority +variable where the driver stores the current priority. + +To request an access priority applications store the desired priority in +an enum v4l2_priority variable and call :ref:`VIDIOC_S_PRIORITY <VIDIOC_G_PRIORITY>` ioctl +with a pointer to this variable. + + +.. c:type:: v4l2_priority + +.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| + +.. flat-table:: enum v4l2_priority + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + * - ``V4L2_PRIORITY_UNSET`` + - 0 + - + * - ``V4L2_PRIORITY_BACKGROUND`` + - 1 + - Lowest priority, usually applications running in background, for + example monitoring VBI transmissions. A proxy application running + in user space will be necessary if multiple applications want to + read from a device at this priority. + * - ``V4L2_PRIORITY_INTERACTIVE`` + - 2 + - + * - ``V4L2_PRIORITY_DEFAULT`` + - 2 + - Medium priority, usually applications started and interactively + controlled by the user. For example TV viewers, Teletext browsers, + or just "panel" applications to change the channel or video + controls. This is the default priority unless an application + requests another. + * - ``V4L2_PRIORITY_RECORD`` + - 3 + - Highest priority. Only one file descriptor can have this priority, + it blocks any other fd from changing device properties. Usually + applications which must not be interrupted, like video recording. + + +Return Value +============ + +On success 0 is returned, on error -1 and the ``errno`` variable is set +appropriately. The generic error codes are described at the +:ref:`Generic Error Codes <gen-errors>` chapter. + +EINVAL + The requested priority value is invalid. + +EBUSY + Another application already requested higher priority. |