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 <link 38linkend="videodev">videodev.h</link> header file, for example 39VIDIOC_QUERYCAP.</para> 40 </listitem> 41 </varlistentry> 42 <varlistentry> 43 <term><parameter>argp</parameter></term> 44 <listitem> 45 <para>Pointer to a function parameter, usually a structure.</para> 46 </listitem> 47 </varlistentry> 48 </variablelist> 49 </refsect1> 50 51 <refsect1> 52 <title>Description</title> 53 54 <para>The <function>ioctl()</function> function is used to program 55V4L2 devices. The argument <parameter>fd</parameter> must be an open 56file descriptor. An ioctl <parameter>request</parameter> has encoded 57in it whether the argument is an input, output or read/write 58parameter, and the size of the argument <parameter>argp</parameter> in 59bytes. Macros and defines specifying V4L2 ioctl requests are located 60in the <link linkend="videodev">videodev.h</link> header file. 61Applications should use their own copy, not include the version in the 62kernel sources on the system they compile on. All V4L2 ioctl requests, 63their respective function and parameters are specified in <xref 64 linkend="user-func" />.</para> 65 </refsect1> 66 67 <refsect1> 68 <title>Return Value</title> 69 70 <para>On success the <function>ioctl()</function> function returns 71<returnvalue>0</returnvalue> and does not reset the 72<varname>errno</varname> variable. On failure 73<returnvalue>-1</returnvalue> is returned, when the ioctl takes an 74output or read/write parameter it remains unmodified, and the 75<varname>errno</varname> variable is set appropriately. See below for 76possible error codes. Generic errors like <errorcode>EBADF</errorcode> 77or <errorcode>EFAULT</errorcode> are not listed in the sections 78discussing individual ioctl requests.</para> 79 <para>Note ioctls may return undefined error codes. Since errors 80may have side effects such as a driver reset applications should 81abort on unexpected errors.</para> 82 83 <variablelist> 84 <varlistentry> 85 <term><errorcode>EBADF</errorcode></term> 86 <listitem> 87 <para><parameter>fd</parameter> is not a valid open file 88descriptor.</para> 89 </listitem> 90 </varlistentry> 91 <varlistentry> 92 <term><errorcode>EBUSY</errorcode></term> 93 <listitem> 94 <para>The property cannot be changed right now. Typically 95this error code is returned when I/O is in progress or the driver 96supports multiple opens and another process locked the property.</para> 97 </listitem> 98 </varlistentry> 99 <varlistentry> 100 <term><errorcode>EFAULT</errorcode></term> 101 <listitem> 102 <para><parameter>argp</parameter> references an inaccessible 103memory area.</para> 104 </listitem> 105 </varlistentry> 106 <varlistentry> 107 <term><errorcode>ENOTTY</errorcode></term> 108 <listitem> 109 <para><parameter>fd</parameter> is not associated with a 110character special device.</para> 111 </listitem> 112 </varlistentry> 113 <varlistentry> 114 <term><errorcode>EINVAL</errorcode></term> 115 <listitem> 116 <para>The <parameter>request</parameter> or the data pointed 117to by <parameter>argp</parameter> is not valid. This is a very common 118error code, see the individual ioctl requests listed in <xref 119 linkend="user-func" /> for actual causes.</para> 120 </listitem> 121 </varlistentry> 122 <varlistentry> 123 <term><errorcode>ENOMEM</errorcode></term> 124 <listitem> 125 <para>Not enough physical or virtual memory was available to 126complete the request.</para> 127 </listitem> 128 </varlistentry> 129 <varlistentry> 130 <term><errorcode>ERANGE</errorcode></term> 131 <listitem> 132 <para>The application attempted to set a control with the 133&VIDIOC-S-CTRL; ioctl to a value which is out of bounds.</para> 134 </listitem> 135 </varlistentry> 136 </variablelist> 137 </refsect1> 138</refentry> 139 140<!-- 141Local Variables: 142mode: sgml 143sgml-parent-document: "v4l2.sgml" 144indent-tabs-mode: nil 145End: 146--> 147