mirror of https://gitee.com/openkylin/linux.git
217 lines
7.1 KiB
XML
217 lines
7.1 KiB
XML
<refentry id="media-ioc-enum-links">
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<refmeta>
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<refentrytitle>ioctl MEDIA_IOC_ENUM_LINKS</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>MEDIA_IOC_ENUM_LINKS</refname>
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<refpurpose>Enumerate all pads and links for a given entity</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct media_links_enum *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>File descriptor returned by
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<link linkend='media-func-open'><function>open()</function></link>.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>MEDIA_IOC_ENUM_LINKS</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>To enumerate pads and/or links for a given entity, applications set
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the entity field of a &media-links-enum; structure and initialize the
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&media-pad-desc; and &media-link-desc; structure arrays pointed by the
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<structfield>pads</structfield> and <structfield>links</structfield> fields.
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They then call the MEDIA_IOC_ENUM_LINKS ioctl with a pointer to this
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structure.</para>
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<para>If the <structfield>pads</structfield> field is not NULL, the driver
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fills the <structfield>pads</structfield> array with information about the
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entity's pads. The array must have enough room to store all the entity's
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pads. The number of pads can be retrieved with the &MEDIA-IOC-ENUM-ENTITIES;
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ioctl.</para>
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<para>If the <structfield>links</structfield> field is not NULL, the driver
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fills the <structfield>links</structfield> array with information about the
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entity's outbound links. The array must have enough room to store all the
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entity's outbound links. The number of outbound links can be retrieved with
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the &MEDIA-IOC-ENUM-ENTITIES; ioctl.</para>
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<para>Only forward links that originate at one of the entity's source pads
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are returned during the enumeration process.</para>
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<table pgwide="1" frame="none" id="media-links-enum">
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<title>struct <structname>media_links_enum</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>entity</structfield></entry>
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<entry>Entity id, set by the application.</entry>
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</row>
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<row>
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<entry>struct &media-pad-desc;</entry>
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<entry>*<structfield>pads</structfield></entry>
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<entry>Pointer to a pads array allocated by the application. Ignored
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if NULL.</entry>
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</row>
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<row>
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<entry>struct &media-link-desc;</entry>
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<entry>*<structfield>links</structfield></entry>
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<entry>Pointer to a links array allocated by the application. Ignored
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if NULL.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="media-pad-desc">
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<title>struct <structname>media_pad_desc</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>entity</structfield></entry>
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<entry>ID of the entity this pad belongs to.</entry>
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</row>
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<row>
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<entry>__u16</entry>
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<entry><structfield>index</structfield></entry>
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<entry>0-based pad index.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>flags</structfield></entry>
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<entry>Pad flags, see <xref linkend="media-pad-flag" /> for more details.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table frame="none" pgwide="1" id="media-pad-flag">
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<title>Media pad flags</title>
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<tgroup cols="2">
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<colspec colname="c1"/>
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<colspec colname="c2"/>
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<tbody valign="top">
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<row>
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<entry><constant>MEDIA_PAD_FL_SINK</constant></entry>
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<entry>Input pad, relative to the entity. Input pads sink data and
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are targets of links.</entry>
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</row>
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<row>
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<entry><constant>MEDIA_PAD_FL_SOURCE</constant></entry>
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<entry>Output pad, relative to the entity. Output pads source data
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and are origins of links.</entry>
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</row>
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<row>
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<entry><constant>MEDIA_PAD_FL_MUST_CONNECT</constant></entry>
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<entry>If this flag is set and the pad is linked to any other
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pad, then at least one of those links must be enabled for the
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entity to be able to stream. There could be temporary reasons
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(e.g. device configuration dependent) for the pad to need
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enabled links even when this flag isn't set; the absence of the
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flag doesn't imply there is none.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="media-link-desc">
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<title>struct <structname>media_link_desc</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>struct &media-pad-desc;</entry>
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<entry><structfield>source</structfield></entry>
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<entry>Pad at the origin of this link.</entry>
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</row>
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<row>
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<entry>struct &media-pad-desc;</entry>
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<entry><structfield>sink</structfield></entry>
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<entry>Pad at the target of this link.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>flags</structfield></entry>
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<entry>Link flags, see <xref linkend="media-link-flag" /> for more details.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table frame="none" pgwide="1" id="media-link-flag">
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<title>Media link flags</title>
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<tgroup cols="2">
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<colspec colname="c1"/>
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<colspec colname="c2"/>
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<tbody valign="top">
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<row>
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<entry><constant>MEDIA_LNK_FL_ENABLED</constant></entry>
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<entry>The link is enabled and can be used to transfer media data.
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When two or more links target a sink pad, only one of them can be
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enabled at a time.</entry>
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</row>
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<row>
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<entry><constant>MEDIA_LNK_FL_IMMUTABLE</constant></entry>
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<entry>The link enabled state can't be modified at runtime. An
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immutable link is always enabled.</entry>
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</row>
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<row>
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<entry><constant>MEDIA_LNK_FL_DYNAMIC</constant></entry>
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<entry>The link enabled state can be modified during streaming. This
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flag is set by drivers and is read-only for applications.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>One and only one of <constant>MEDIA_PAD_FL_SINK</constant> and
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<constant>MEDIA_PAD_FL_SOURCE</constant> must be set for every pad.</para>
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</refsect1>
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<refsect1>
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&return-value;
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<variablelist>
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<varlistentry>
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<term><errorcode>EINVAL</errorcode></term>
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<listitem>
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<para>The &media-links-enum; <structfield>id</structfield> references
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a non-existing entity.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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</refentry>
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