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

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
54	initialize 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
57	structure. To change the value of a control applications initialize
58	the <structfield>id</structfield> and <structfield>value</structfield>
59	fields 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
63	return an &EINVAL;. When the <structfield>value</structfield> is out
64	of bounds drivers can choose to take the closest valid value or return
65	an &ERANGE;, whatever seems more appropriate. However,
66	<constant>VIDIOC_S_CTRL</constant> is a write-only ioctl, it does not
67	return the actual new value. If the <structfield>value</structfield>
68	is inappropriate for the control (e.g. if it refers to an unsupported
69	menu index of a menu control), then &EINVAL; is returned as well.</para>
70	
71	    <para>These ioctls work only with user controls. For other
72	control classes the &VIDIOC-G-EXT-CTRLS;, &VIDIOC-S-EXT-CTRLS; or
73	&VIDIOC-TRY-EXT-CTRLS; must be used.</para>
74	
75	    <table pgwide="1" frame="none" id="v4l2-control">
76	      <title>struct <structname>v4l2_control</structname></title>
77	      <tgroup cols="3">
78		&cs-str;
79		<tbody valign="top">
80		  <row>
81		    <entry>__u32</entry>
82		    <entry><structfield>id</structfield></entry>
83		    <entry>Identifies the control, set by the
84	application.</entry>
85		  </row>
86		  <row>
87		    <entry>__s32</entry>
88		    <entry><structfield>value</structfield></entry>
89		    <entry>New value or current value.</entry>
90		  </row>
91		</tbody>
92	      </tgroup>
93	    </table>
94	  </refsect1>
95	
96	  <refsect1>
97	    &return-value;
98	
99	    <variablelist>
100	      <varlistentry>
101		<term><errorcode>EINVAL</errorcode></term>
102		<listitem>
103		  <para>The &v4l2-control; <structfield>id</structfield> is
104	invalid or the <structfield>value</structfield> is inappropriate for
105	the given control (i.e. if a menu item is selected that is not supported
106	by the driver according to &VIDIOC-QUERYMENU;).</para>
107		</listitem>
108	      </varlistentry>
109	      <varlistentry>
110		<term><errorcode>ERANGE</errorcode></term>
111		<listitem>
112		  <para>The &v4l2-control; <structfield>value</structfield>
113	is out of bounds.</para>
114		</listitem>
115	      </varlistentry>
116	      <varlistentry>
117		<term><errorcode>EBUSY</errorcode></term>
118		<listitem>
119		  <para>The control is temporarily not changeable, possibly
120	because another applications took over control of the device function
121	this control belongs to.</para>
122		</listitem>
123	      </varlistentry>
124	      <varlistentry>
125		<term><errorcode>EACCES</errorcode></term>
126		<listitem>
127		  <para>Attempt to set a read-only control or to get a
128		  write-only control.</para>
129		</listitem>
130	      </varlistentry>
131	    </variablelist>
132	  </refsect1>
133	</refentry>
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