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1<refentry id="func-ioctl">
2 <refmeta>
3 <refentrytitle>V4L2 ioctl()</refentrytitle>
4 &manvol;
5 </refmeta>
6
7 <refnamediv>
8 <refname>v4l2-ioctl</refname>
9 <refpurpose>Program a V4L2 device</refpurpose>
10 </refnamediv>
11
12 <refsynopsisdiv>
13 <funcsynopsis>
14 <funcsynopsisinfo>#include <sys/ioctl.h></funcsynopsisinfo>
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>void *<parameter>argp</parameter></paramdef>
20 </funcprototype>
21 </funcsynopsis>
22 </refsynopsisdiv>
23
24 <refsect1>
25 <title>Arguments</title>
26
27 <variablelist>
28 <varlistentry>
29 <term><parameter>fd</parameter></term>
30 <listitem>
31 <para>&fd;</para>
32 </listitem>
33 </varlistentry>
34 <varlistentry>
35 <term><parameter>request</parameter></term>
36 <listitem>
37 <para>V4L2 ioctl request code as defined in the <filename>videodev2.h</filename> header file, for example
38VIDIOC_QUERYCAP.</para>
39 </listitem>
40 </varlistentry>
41 <varlistentry>
42 <term><parameter>argp</parameter></term>
43 <listitem>
44 <para>Pointer to a function parameter, usually a structure.</para>
45 </listitem>
46 </varlistentry>
47 </variablelist>
48 </refsect1>
49
50 <refsect1>
51 <title>Description</title>
52
53 <para>The <function>ioctl()</function> function is used to program
54V4L2 devices. The argument <parameter>fd</parameter> must be an open
55file descriptor. An ioctl <parameter>request</parameter> has encoded
56in it whether the argument is an input, output or read/write
57parameter, and the size of the argument <parameter>argp</parameter> in
58bytes. Macros and defines specifying V4L2 ioctl requests are located
59in the <filename>videodev2.h</filename> header file.
60Applications should use their own copy, not include the version in the
61kernel sources on the system they compile on. All V4L2 ioctl requests,
62their respective function and parameters are specified in <xref
63 linkend="user-func" />.</para>
64 </refsect1>
65
66 <refsect1>
67 <title>Return Value</title>
68
69 <para>On success the <function>ioctl()</function> function returns
70<returnvalue>0</returnvalue> and does not reset the
71<varname>errno</varname> variable. On failure
72<returnvalue>-1</returnvalue> is returned, when the ioctl takes an
73output or read/write parameter it remains unmodified, and the
74<varname>errno</varname> variable is set appropriately. See below for
75possible error codes. Generic errors like <errorcode>EBADF</errorcode>
76or <errorcode>EFAULT</errorcode> are not listed in the sections
77discussing individual ioctl requests.</para>
78 <para>Note ioctls may return undefined error codes. Since errors
79may have side effects such as a driver reset applications should
80abort on unexpected errors.</para>
81
82 <variablelist>
83 <varlistentry>
84 <term><errorcode>EBADF</errorcode></term>
85 <listitem>
86 <para><parameter>fd</parameter> is not a valid open file
87descriptor.</para>
88 </listitem>
89 </varlistentry>
90 <varlistentry>
91 <term><errorcode>EBUSY</errorcode></term>
92 <listitem>
93 <para>The property cannot be changed right now. Typically
94this error code is returned when I/O is in progress or the driver
95supports multiple opens and another process locked the property.</para>
96 </listitem>
97 </varlistentry>
98 <varlistentry>
99 <term><errorcode>EFAULT</errorcode></term>
100 <listitem>
101 <para><parameter>argp</parameter> references an inaccessible
102memory area.</para>
103 </listitem>
104 </varlistentry>
105 <varlistentry>
106 <term><errorcode>ENOTTY</errorcode></term>
107 <listitem>
108 <para><parameter>fd</parameter> is not associated with a
109character special device.</para>
110 </listitem>
111 </varlistentry>
112 <varlistentry>
113 <term><errorcode>EINVAL</errorcode></term>
114 <listitem>
115 <para>The <parameter>request</parameter> or the data pointed
116to by <parameter>argp</parameter> is not valid. This is a very common
117error code, see the individual ioctl requests listed in <xref
118 linkend="user-func" /> for actual causes.</para>
119 </listitem>
120 </varlistentry>
121 <varlistentry>
122 <term><errorcode>ENOMEM</errorcode></term>
123 <listitem>
124 <para>Not enough physical or virtual memory was available to
125complete the request.</para>
126 </listitem>
127 </varlistentry>
128 <varlistentry>
129 <term><errorcode>ERANGE</errorcode></term>
130 <listitem>
131 <para>The application attempted to set a control with the
132&VIDIOC-S-CTRL; ioctl to a value which is out of bounds.</para>
133 </listitem>
134 </varlistentry>
135 </variablelist>
136 </refsect1>
137</refentry>
138
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