<refentry id="func-ioctl">
  <refmeta>
    <refentrytitle>V4L2 ioctl()</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>v4l2-ioctl</refname>
    <refpurpose>Program a V4L2 device</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcsynopsisinfo>#include &lt;sys/ioctl.h&gt;</funcsynopsisinfo>
      <funcprototype>
	<funcdef>int <function>ioctl</function></funcdef>
	<paramdef>int <parameter>fd</parameter></paramdef>
	<paramdef>int <parameter>request</parameter></paramdef>
	<paramdef>void *<parameter>argp</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Arguments</title>

    <variablelist>
      <varlistentry>
	<term><parameter>fd</parameter></term>
	<listitem>
	  <para>&fd;</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>request</parameter></term>
	<listitem>
	  <para>V4L2 ioctl request code as defined in the <filename>videodev2.h</filename> header file, for example
VIDIOC_QUERYCAP.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para>Pointer to a function parameter, usually a structure.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>The <function>ioctl()</function> function is used to program
V4L2 devices. The argument <parameter>fd</parameter> must be an open
file descriptor. An ioctl <parameter>request</parameter> has encoded
in it whether the argument is an input, output or read/write
parameter, and the size of the argument <parameter>argp</parameter> in
bytes. Macros and defines specifying V4L2 ioctl requests are located
in the <filename>videodev2.h</filename> header file.
Applications should use their own copy, not include the version in the
kernel sources on the system they compile on. All V4L2 ioctl requests,
their respective function and parameters are specified in <xref
	linkend="user-func" />.</para>
  </refsect1>

  <refsect1>
    &return-value;
    <para>When an ioctl that takes an output or read/write parameter fails,
    the parameter remains unmodified.</para>
  </refsect1>
</refentry>
