linux-vybrid_public/Documentation/DocBook/v4l/media-func-ioctl.xml

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

  <refnamediv>
    <refname>media-ioctl</refname>
    <refpurpose>Control a media 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>Media ioctl request code as defined in the media.h header file,
	  for example MEDIA_IOC_SETUP_LINK.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para>Pointer to a request-specific structure.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>
    <para>The <function>ioctl()</function> function manipulates media device
    parameters. The argument <parameter>fd</parameter> must be an open file
    descriptor.</para>
    <para>The ioctl <parameter>request</parameter> code specifies the media
    function to be called. It 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.</para>
    <para>Macros and structures definitions specifying media ioctl requests and
    their parameters are located in the media.h header file. All media ioctl
    requests, their respective function and parameters are specified in
    <xref linkend="media-user-func" />.</para>
  </refsect1>

  <refsect1>
    <title>Return Value</title>

    <para><function>ioctl()</function> returns <returnvalue>0</returnvalue> on
    success. On failure, <returnvalue>-1</returnvalue> is returned, and the
    <varname>errno</varname> variable is set appropriately. Generic error codes
    are listed below, and request-specific error codes are listed in the
    individual requests descriptions.</para>
    <para>When an ioctl that takes an output or read/write parameter fails,
    the parameter remains unmodified.</para>

    <variablelist>
      <varlistentry>
	<term><errorcode>EBADF</errorcode></term>
	<listitem>
	  <para><parameter>fd</parameter> is not a valid open file descriptor.
	  </para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><errorcode>EFAULT</errorcode></term>
	<listitem>
	  <para><parameter>argp</parameter> references an inaccessible memory
	  area.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	  <para>The <parameter>request</parameter> or the data pointed to by
	  <parameter>argp</parameter> is not valid. This is a very common error
	  code, see the individual ioctl requests listed in
	  <xref linkend="media-user-func" /> for actual causes.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><errorcode>ENOMEM</errorcode></term>
	<listitem>
	  <para>Insufficient kernel memory was available to complete the
	  request.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><errorcode>ENOTTY</errorcode></term>
	<listitem>
	  <para><parameter>fd</parameter> is  not  associated  with  a character
	  special device.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>