Documentation/DocBook/media/v4l/media-ioc-enum-links.xml

<refentry id="media-ioc-enum-links">
  <refmeta>
    <refentrytitle>ioctl MEDIA_IOC_ENUM_LINKS</refentrytitle>
    &manvol;
  </refmeta>

  <refnamediv>
    <refname>MEDIA_IOC_ENUM_LINKS</refname>
    <refpurpose>Enumerate all pads and links for a given entity</refpurpose>
  </refnamediv>

  <refsynopsisdiv>
    <funcsynopsis>
      <funcprototype>
	<funcdef>int <function>ioctl</function></funcdef>
	<paramdef>int <parameter>fd</parameter></paramdef>
	<paramdef>int <parameter>request</parameter></paramdef>
	<paramdef>struct media_links_enum *<parameter>argp</parameter></paramdef>
      </funcprototype>
    </funcsynopsis>
  </refsynopsisdiv>

  <refsect1>
    <title>Arguments</title>

    <variablelist>
      <varlistentry>
	<term><parameter>fd</parameter></term>
	<listitem>
	  <para>File descriptor returned by
	  <link linkend='media-func-open'><function>open()</function></link>.</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>request</parameter></term>
	<listitem>
	  <para>MEDIA_IOC_ENUM_LINKS</para>
	</listitem>
      </varlistentry>
      <varlistentry>
	<term><parameter>argp</parameter></term>
	<listitem>
	  <para></para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>

  <refsect1>
    <title>Description</title>

    <para>To enumerate pads and/or links for a given entity, applications set
    the entity field of a &media-links-enum; structure and initialize the
    &media-pad-desc; and &media-link-desc; structure arrays pointed by the
    <structfield>pads</structfield> and <structfield>links</structfield> fields.
    They then call the MEDIA_IOC_ENUM_LINKS ioctl with a pointer to this
    structure.</para>
    <para>If the <structfield>pads</structfield> field is not NULL, the driver
    fills the <structfield>pads</structfield> array with information about the
    entity's pads. The array must have enough room to store all the entity's
    pads. The number of pads can be retrieved with the &MEDIA-IOC-ENUM-ENTITIES;
    ioctl.</para>
    <para>If the <structfield>links</structfield> field is not NULL, the driver
    fills the <structfield>links</structfield> array with information about the
    entity's outbound links. The array must have enough room to store all the
    entity's outbound links. The number of outbound links can be retrieved with
    the &MEDIA-IOC-ENUM-ENTITIES; ioctl.</para>
    <para>Only forward links that originate at one of the entity's source pads
    are returned during the enumeration process.</para>

    <table pgwide="1" frame="none" id="media-links-enum">
      <title>struct <structname>media_links_enum</structname></title>
      <tgroup cols="3">
        &cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>entity</structfield></entry>
	    <entry>Entity id, set by the application.</entry>
	  </row>
	  <row>
	    <entry>&media-pad-desc;</entry>
	    <entry>*<structfield>pads</structfield></entry>
	    <entry>Pointer to a pads array allocated by the application. Ignored
	    if NULL.</entry>
	  </row>
	  <row>
	    <entry>&media-link-desc;</entry>
	    <entry>*<structfield>links</structfield></entry>
	    <entry>Pointer to a links array allocated by the application. Ignored
	    if NULL.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="media-pad-desc">
      <title>struct <structname>media_pad_desc</structname></title>
      <tgroup cols="3">
        &cs-str;
	<tbody valign="top">
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>entity</structfield></entry>
	    <entry>ID of the entity this pad belongs to.</entry>
	  </row>
	  <row>
	    <entry>__u16</entry>
	    <entry><structfield>index</structfield></entry>
	    <entry>0-based pad index.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>flags</structfield></entry>
	    <entry>Pad flags, see <xref linkend="media-pad-flag" /> for more details.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

    <table pgwide="1" frame="none" id="media-link-desc">
      <title>struct <structname>media_link_desc</structname></title>
      <tgroup cols="3">
        &cs-str;
	<tbody valign="top">
	  <row>
	    <entry>&media-pad-desc;</entry>
	    <entry><structfield>source</structfield></entry>
	    <entry>Pad at the origin of this link.</entry>
	  </row>
	  <row>
	    <entry>&media-pad-desc;</entry>
	    <entry><structfield>sink</structfield></entry>
	    <entry>Pad at the target of this link.</entry>
	  </row>
	  <row>
	    <entry>__u32</entry>
	    <entry><structfield>flags</structfield></entry>
	    <entry>Link flags, see <xref linkend="media-link-flag" /> for more details.</entry>
	  </row>
	</tbody>
      </tgroup>
    </table>

  </refsect1>

  <refsect1>
    &return-value;

    <variablelist>
      <varlistentry>
	<term><errorcode>EINVAL</errorcode></term>
	<listitem>
	  <para>The &media-links-enum; <structfield>id</structfield> references
	  a non-existing entity.</para>
	</listitem>
      </varlistentry>
    </variablelist>
  </refsect1>
</refentry>