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Based on kernel version 3.13. Page generated on 2014-01-20 22:02 EST.

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
11	file 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
62	applications call the <constant>VIDIOC_G_PRIORITY</constant> ioctl
63	with a pointer to an enum v4l2_priority variable where the driver stores
64	the current priority.</para>
65	
66	    <para>To request an access priority applications store the
67	desired priority in an enum v4l2_priority variable and call
68	<constant>VIDIOC_S_PRIORITY</constant> ioctl with a pointer to this
69	variable.</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
85	background, for example monitoring VBI transmissions. A proxy
86	application running in user space will be necessary if multiple
87	applications 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
98	interactively controlled by the user. For example TV viewers, Teletext
99	browsers, or just "panel" applications to change the channel or video
100	controls. This is the default priority unless an application requests
101	another.</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
107	this priority, it blocks any other fd from changing device properties.
108	Usually applications which must not be interrupted, like video
109	recording.</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.</para>
124		</listitem>
125	      </varlistentry>
126	      <varlistentry>
127		<term><errorcode>EBUSY</errorcode></term>
128		<listitem>
129		  <para>Another application already requested higher
130	priority.</para>
131		</listitem>
132	      </varlistentry>
133	    </variablelist>
134	  </refsect1>
135	</refentry>
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