tjh.dev
Linux kernel mirror (for testing)
git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
kernel
os
linux
1<refentry id="vidioc-g-priority">
2 <refmeta>
3 <refentrytitle>ioctl VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY</refentrytitle>
4 &manvol;
5 </refmeta>
6
7 <refnamediv>
8 <refname>VIDIOC_G_PRIORITY</refname>
9 <refname>VIDIOC_S_PRIORITY</refname>
10 <refpurpose>Query or request the access priority associated with a
11file descriptor</refpurpose>
12 </refnamediv>
13
14 <refsynopsisdiv>
15 <funcsynopsis>
16 <funcprototype>
17 <funcdef>int <function>ioctl</function></funcdef>
18 <paramdef>int <parameter>fd</parameter></paramdef>
19 <paramdef>int <parameter>request</parameter></paramdef>
20 <paramdef>enum v4l2_priority *<parameter>argp</parameter></paramdef>
21 </funcprototype>
22 </funcsynopsis>
23 <funcsynopsis>
24 <funcprototype>
25 <funcdef>int <function>ioctl</function></funcdef>
26 <paramdef>int <parameter>fd</parameter></paramdef>
27 <paramdef>int <parameter>request</parameter></paramdef>
28 <paramdef>const enum v4l2_priority *<parameter>argp</parameter></paramdef>
29 </funcprototype>
30 </funcsynopsis>
31 </refsynopsisdiv>
32
33 <refsect1>
34 <title>Arguments</title>
35
36 <variablelist>
37 <varlistentry>
38 <term><parameter>fd</parameter></term>
39 <listitem>
40 <para>&fd;</para>
41 </listitem>
42 </varlistentry>
43 <varlistentry>
44 <term><parameter>request</parameter></term>
45 <listitem>
46 <para>VIDIOC_G_PRIORITY, VIDIOC_S_PRIORITY</para>
47 </listitem>
48 </varlistentry>
49 <varlistentry>
50 <term><parameter>argp</parameter></term>
51 <listitem>
52 <para>Pointer to an enum v4l2_priority type.</para>
53 </listitem>
54 </varlistentry>
55 </variablelist>
56 </refsect1>
57
58 <refsect1>
59 <title>Description</title>
60
61 <para>To query the current access priority
62applications call the <constant>VIDIOC_G_PRIORITY</constant> ioctl
63with a pointer to an enum v4l2_priority variable where the driver stores
64the current priority.</para>
65
66 <para>To request an access priority applications store the
67desired priority in an enum v4l2_priority variable and call
68<constant>VIDIOC_S_PRIORITY</constant> ioctl with a pointer to this
69variable.</para>
70
71 <table frame="none" pgwide="1" id="v4l2-priority">
72 <title>enum v4l2_priority</title>
73 <tgroup cols="3">
74 &cs-def;
75 <tbody valign="top">
76 <row>
77 <entry><constant>V4L2_PRIORITY_UNSET</constant></entry>
78 <entry>0</entry>
79 <entry></entry>
80 </row>
81 <row>
82 <entry><constant>V4L2_PRIORITY_BACKGROUND</constant></entry>
83 <entry>1</entry>
84 <entry>Lowest priority, usually applications running in
85background, for example monitoring VBI transmissions. A proxy
86application running in user space will be necessary if multiple
87applications want to read from a device at this priority.</entry>
88 </row>
89 <row>
90 <entry><constant>V4L2_PRIORITY_INTERACTIVE</constant></entry>
91 <entry>2</entry>
92 <entry></entry>
93 </row>
94 <row>
95 <entry><constant>V4L2_PRIORITY_DEFAULT</constant></entry>
96 <entry>2</entry>
97 <entry>Medium priority, usually applications started and
98interactively controlled by the user. For example TV viewers, Teletext
99browsers, or just "panel" applications to change the channel or video
100controls. This is the default priority unless an application requests
101another.</entry>
102 </row>
103 <row>
104 <entry><constant>V4L2_PRIORITY_RECORD</constant></entry>
105 <entry>3</entry>
106 <entry>Highest priority. Only one file descriptor can have
107this priority, it blocks any other fd from changing device properties.
108Usually applications which must not be interrupted, like video
109recording.</entry>
110 </row>
111 </tbody>
112 </tgroup>
113 </table>
114 </refsect1>
115
116 <refsect1>
117 &return-value;
118
119 <variablelist>
120 <varlistentry>
121 <term><errorcode>EINVAL</errorcode></term>
122 <listitem>
123 <para>The requested priority value is invalid, or the
124driver does not support access priorities.</para>
125 </listitem>
126 </varlistentry>
127 <varlistentry>
128 <term><errorcode>EBUSY</errorcode></term>
129 <listitem>
130 <para>Another application already requested higher
131priority.</para>
132 </listitem>
133 </varlistentry>
134 </variablelist>
135 </refsect1>
136</refentry>
137
138<!--
139Local Variables:
140mode: sgml
141sgml-parent-document: "v4l2.sgml"
142indent-tabs-mode: nil
143End:
144-->