Documentation/linux_tv/media/v4l/vidioc-g-priority.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 .. _VIDIOC_G_PRIORITY:
   4
   5 ******************************************
   6 ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY
   7 ******************************************
   8
   9 *man VIDIOC_G_PRIORITY(2)*
  10
  11 VIDIOC_S_PRIORITY
  12 Query or request the access priority associated with a file descriptor
  13
  14
  15 Synopsis
  16 ========
  17
  18 .. c:function:: int ioctl( int fd, int request, enum v4l2_priority *argp )
  19
  20 .. c:function:: int ioctl( int fd, int request, const enum v4l2_priority *argp )
  21
  22 Arguments
  23 =========
  24
  25 ``fd``
  26     File descriptor returned by :ref:`open() <func-open>`.
  27
  28 ``request``
  29     VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY
  30
  31 ``argp``
  32     Pointer to an enum v4l2_priority type.
  33
  34
  35 Description
  36 ===========
  37
  38 To 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
  40 variable where the driver stores the current priority.
  41
  42 To request an access priority applications store the desired priority in
  43 an enum v4l2_priority variable and call :ref:`VIDIOC_S_PRIORITY <VIDIOC_G_PRIORITY>` ioctl
  44 with a pointer to this variable.
  45
  46
  47 .. _v4l2-priority:
  48
  49 .. flat-table:: enum v4l2_priority
  50     :header-rows:  0
  51     :stub-columns: 0
  52     :widths:       3 1 4
  53
  54
  55     -  .. row 1
  56
  57        -  ``V4L2_PRIORITY_UNSET``
  58
  59        -  0
  60
  61        -
  62
  63     -  .. row 2
  64
  65        -  ``V4L2_PRIORITY_BACKGROUND``
  66
  67        -  1
  68
  69        -  Lowest priority, usually applications running in background, for
  70           example monitoring VBI transmissions. A proxy application running
  71           in user space will be necessary if multiple applications want to
  72           read from a device at this priority.
  73
  74     -  .. row 3
  75
  76        -  ``V4L2_PRIORITY_INTERACTIVE``
  77
  78        -  2
  79
  80        -
  81
  82     -  .. row 4
  83
  84        -  ``V4L2_PRIORITY_DEFAULT``
  85
  86        -  2
  87
  88        -  Medium priority, usually applications started and interactively
  89           controlled by the user. For example TV viewers, Teletext browsers,
  90           or just "panel" applications to change the channel or video
  91           controls. This is the default priority unless an application
  92           requests another.
  93
  94     -  .. row 5
  95
  96        -  ``V4L2_PRIORITY_RECORD``
  97
  98        -  3
  99
 100        -  Highest priority. Only one file descriptor can have this priority,
 101           it blocks any other fd from changing device properties. Usually
 102           applications which must not be interrupted, like video recording.
 103
 104
 105
 106 Return Value
 107 ============
 108
 109 On success 0 is returned, on error -1 and the ``errno`` variable is set
 110 appropriately. The generic error codes are described at the
 111 :ref:`Generic Error Codes <gen-errors>` chapter.
 112
 113 EINVAL
 114     The requested priority value is invalid.
 115
 116 EBUSY
 117     Another application already requested higher priority.
 118
 119
 120 .. ------------------------------------------------------------------------------
 121 .. This file was automatically converted from DocBook-XML with the dbxml
 122 .. library (https://github.com/return42/sphkerneldoc). The origin XML comes
 123 .. from the linux kernel, refer to:
 124 ..
 125 .. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
 126 .. ------------------------------------------------------------------------------