vidioc-g-priority.rst (2636B)
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _VIDIOC_G_PRIORITY: 5 6****************************************** 7ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY 8****************************************** 9 10Name 11==== 12 13VIDIOC_G_PRIORITY - VIDIOC_S_PRIORITY - Query or request the access priority associated with a file descriptor 14 15Synopsis 16======== 17 18.. c:macro:: VIDIOC_G_PRIORITY 19 20``int ioctl(int fd, VIDIOC_G_PRIORITY, enum v4l2_priority *argp)`` 21 22.. c:macro:: VIDIOC_S_PRIORITY 23 24``int ioctl(int fd, VIDIOC_S_PRIORITY, const enum v4l2_priority *argp)`` 25 26Arguments 27========= 28 29``fd`` 30 File descriptor returned by :c:func:`open()`. 31 32``argp`` 33 Pointer to an enum :c:type:`v4l2_priority` type. 34 35Description 36=========== 37 38To query the current access priority applications call the 39:ref:`VIDIOC_G_PRIORITY <VIDIOC_G_PRIORITY>` ioctl with a pointer to an enum v4l2_priority 40variable where the driver stores the current priority. 41 42To request an access priority applications store the desired priority in 43an enum v4l2_priority variable and call :ref:`VIDIOC_S_PRIORITY <VIDIOC_G_PRIORITY>` ioctl 44with a pointer to this variable. 45 46.. c:type:: v4l2_priority 47 48.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}| 49 50.. flat-table:: enum v4l2_priority 51 :header-rows: 0 52 :stub-columns: 0 53 :widths: 3 1 4 54 55 * - ``V4L2_PRIORITY_UNSET`` 56 - 0 57 - 58 * - ``V4L2_PRIORITY_BACKGROUND`` 59 - 1 60 - Lowest priority, usually applications running in background, for 61 example monitoring VBI transmissions. A proxy application running 62 in user space will be necessary if multiple applications want to 63 read from a device at this priority. 64 * - ``V4L2_PRIORITY_INTERACTIVE`` 65 - 2 66 - 67 * - ``V4L2_PRIORITY_DEFAULT`` 68 - 2 69 - Medium priority, usually applications started and interactively 70 controlled by the user. For example TV viewers, Teletext browsers, 71 or just "panel" applications to change the channel or video 72 controls. This is the default priority unless an application 73 requests another. 74 * - ``V4L2_PRIORITY_RECORD`` 75 - 3 76 - Highest priority. Only one file descriptor can have this priority, 77 it blocks any other fd from changing device properties. Usually 78 applications which must not be interrupted, like video recording. 79 80Return Value 81============ 82 83On success 0 is returned, on error -1 and the ``errno`` variable is set 84appropriately. The generic error codes are described at the 85:ref:`Generic Error Codes <gen-errors>` chapter. 86 87EINVAL 88 The requested priority value is invalid. 89 90EBUSY 91 Another application already requested higher priority.