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1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_G_PRIORITY: |
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4 | |
5 | ****************************************** | |
6 | ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY | |
7 | ****************************************** | |
8 | ||
15e7d615 | 9 | Name |
586027ce | 10 | ==== |
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586027ce | 12 | VIDIOC_G_PRIORITY - VIDIOC_S_PRIORITY - Query or request the access priority associated with a file descriptor |
5377d91f | 13 | |
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14 | |
15 | Synopsis | |
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16 | ======== |
17 | ||
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18 | .. c:function:: int ioctl( int fd, VIDIOC_G_PRIORITY, enum v4l2_priority *argp ) |
19 | :name: VIDIOC_G_PRIORITY | |
5377d91f | 20 | |
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21 | .. c:function:: int ioctl( int fd, VIDIOC_S_PRIORITY, const enum v4l2_priority *argp ) |
22 | :name: VIDIOC_S_PRIORITY | |
5377d91f | 23 | |
586027ce | 24 | |
15e7d615 | 25 | Arguments |
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26 | ========= |
27 | ||
28 | ``fd`` | |
29 | File descriptor returned by :ref:`open() <func-open>`. | |
30 | ||
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31 | ``argp`` |
32 | Pointer to an enum v4l2_priority type. | |
33 | ||
34 | ||
15e7d615 | 35 | Description |
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36 | =========== |
37 | ||
38 | To query the current access priority applications call the | |
4e03cb76 | 39 | :ref:`VIDIOC_G_PRIORITY <VIDIOC_G_PRIORITY>` ioctl with a pointer to an enum v4l2_priority |
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40 | variable where the driver stores the current priority. |
41 | ||
42 | To request an access priority applications store the desired priority in | |
2212ff25 | 43 | an enum v4l2_priority variable and call :ref:`VIDIOC_S_PRIORITY <VIDIOC_G_PRIORITY>` ioctl |
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44 | with a pointer to this variable. |
45 | ||
46 | ||
ffa0441e | 47 | .. c:type:: v4l2_priority |
5377d91f | 48 | |
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49 | .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| |
50 | ||
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51 | .. flat-table:: enum v4l2_priority |
52 | :header-rows: 0 | |
53 | :stub-columns: 0 | |
54 | :widths: 3 1 4 | |
55 | ||
56 | ||
57 | - .. row 1 | |
58 | ||
59 | - ``V4L2_PRIORITY_UNSET`` | |
60 | ||
61 | - 0 | |
62 | ||
0579e6e3 | 63 | - |
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64 | |
65 | - .. row 2 | |
66 | ||
67 | - ``V4L2_PRIORITY_BACKGROUND`` | |
68 | ||
69 | - 1 | |
70 | ||
71 | - Lowest priority, usually applications running in background, for | |
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72 | example monitoring VBI transmissions. A proxy application running |
73 | in user space will be necessary if multiple applications want to | |
74 | read from a device at this priority. | |
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75 | |
76 | - .. row 3 | |
77 | ||
78 | - ``V4L2_PRIORITY_INTERACTIVE`` | |
79 | ||
80 | - 2 | |
81 | ||
0579e6e3 | 82 | - |
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83 | |
84 | - .. row 4 | |
85 | ||
86 | - ``V4L2_PRIORITY_DEFAULT`` | |
87 | ||
88 | - 2 | |
89 | ||
90 | - Medium priority, usually applications started and interactively | |
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91 | controlled by the user. For example TV viewers, Teletext browsers, |
92 | or just "panel" applications to change the channel or video | |
93 | controls. This is the default priority unless an application | |
94 | requests another. | |
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95 | |
96 | - .. row 5 | |
97 | ||
98 | - ``V4L2_PRIORITY_RECORD`` | |
99 | ||
100 | - 3 | |
101 | ||
102 | - Highest priority. Only one file descriptor can have this priority, | |
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103 | it blocks any other fd from changing device properties. Usually |
104 | applications which must not be interrupted, like video recording. | |
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105 | |
106 | ||
15e7d615 | 107 | Return Value |
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108 | ============ |
109 | ||
110 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
111 | appropriately. The generic error codes are described at the | |
112 | :ref:`Generic Error Codes <gen-errors>` chapter. | |
113 | ||
114 | EINVAL | |
115 | The requested priority value is invalid. | |
116 | ||
117 | EBUSY | |
118 | Another application already requested higher priority. |