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1<refentry id="vidioc-g-ctrl">
2 <refmeta>
3 <refentrytitle>ioctl VIDIOC_G_CTRL, VIDIOC_S_CTRL</refentrytitle>
4 &manvol;
5 </refmeta>
6
7 <refnamediv>
8 <refname>VIDIOC_G_CTRL</refname>
9 <refname>VIDIOC_S_CTRL</refname>
10 <refpurpose>Get or set the value of a control</refpurpose>
11 </refnamediv>
12
13 <refsynopsisdiv>
14 <funcsynopsis>
15 <funcprototype>
16 <funcdef>int <function>ioctl</function></funcdef>
17 <paramdef>int <parameter>fd</parameter></paramdef>
18 <paramdef>int <parameter>request</parameter></paramdef>
19 <paramdef>struct v4l2_control
20*<parameter>argp</parameter></paramdef>
21 </funcprototype>
22 </funcsynopsis>
23 </refsynopsisdiv>
24
25 <refsect1>
26 <title>Arguments</title>
27
28 <variablelist>
29 <varlistentry>
30 <term><parameter>fd</parameter></term>
31 <listitem>
32 <para>&fd;</para>
33 </listitem>
34 </varlistentry>
35 <varlistentry>
36 <term><parameter>request</parameter></term>
37 <listitem>
38 <para>VIDIOC_G_CTRL, VIDIOC_S_CTRL</para>
39 </listitem>
40 </varlistentry>
41 <varlistentry>
42 <term><parameter>argp</parameter></term>
43 <listitem>
44 <para></para>
45 </listitem>
46 </varlistentry>
47 </variablelist>
48 </refsect1>
49
50 <refsect1>
51 <title>Description</title>
52
53 <para>To get the current value of a control applications
54initialize the <structfield>id</structfield> field of a struct
55<structname>v4l2_control</structname> and call the
56<constant>VIDIOC_G_CTRL</constant> ioctl with a pointer to this
57structure. To change the value of a control applications initialize
58the <structfield>id</structfield> and <structfield>value</structfield>
59fields of a struct <structname>v4l2_control</structname> and call the
60<constant>VIDIOC_S_CTRL</constant> ioctl.</para>
61
62 <para>When the <structfield>id</structfield> is invalid drivers
63return an &EINVAL;. When the <structfield>value</structfield> is out
64of bounds drivers can choose to take the closest valid value or return
65an &ERANGE;, whatever seems more appropriate. However,
66<constant>VIDIOC_S_CTRL</constant> is a write-only ioctl, it does not
67return the actual new value.</para>
68
69 <para>These ioctls work only with user controls. For other
70control classes the &VIDIOC-G-EXT-CTRLS;, &VIDIOC-S-EXT-CTRLS; or
71&VIDIOC-TRY-EXT-CTRLS; must be used.</para>
72
73 <table pgwide="1" frame="none" id="v4l2-control">
74 <title>struct <structname>v4l2_control</structname></title>
75 <tgroup cols="3">
76 &cs-str;
77 <tbody valign="top">
78 <row>
79 <entry>__u32</entry>
80 <entry><structfield>id</structfield></entry>
81 <entry>Identifies the control, set by the
82application.</entry>
83 </row>
84 <row>
85 <entry>__s32</entry>
86 <entry><structfield>value</structfield></entry>
87 <entry>New value or current value.</entry>
88 </row>
89 </tbody>
90 </tgroup>
91 </table>
92 </refsect1>
93
94 <refsect1>
95 &return-value;
96
97 <variablelist>
98 <varlistentry>
99 <term><errorcode>EINVAL</errorcode></term>
100 <listitem>
101 <para>The &v4l2-control; <structfield>id</structfield> is
102invalid.</para>
103 </listitem>
104 </varlistentry>
105 <varlistentry>
106 <term><errorcode>ERANGE</errorcode></term>
107 <listitem>
108 <para>The &v4l2-control; <structfield>value</structfield>
109is out of bounds.</para>
110 </listitem>
111 </varlistentry>
112 <varlistentry>
113 <term><errorcode>EBUSY</errorcode></term>
114 <listitem>
115 <para>The control is temporarily not changeable, possibly
116because another applications took over control of the device function
117this control belongs to.</para>
118 </listitem>
119 </varlistentry>
120 </variablelist>
121 </refsect1>
122</refentry>
123
124<!--
125Local Variables:
126mode: sgml
127sgml-parent-document: "v4l2.sgml"
128indent-tabs-mode: nil
129End:
130-->