1<refentry id="media-ioc-enum-links">
2  <refmeta>
3    <refentrytitle>ioctl MEDIA_IOC_ENUM_LINKS</refentrytitle>
4    &manvol;
5  </refmeta>
6
7  <refnamediv>
8    <refname>MEDIA_IOC_ENUM_LINKS</refname>
9    <refpurpose>Enumerate all pads and links for a given entity</refpurpose>
10  </refnamediv>
11
12  <refsynopsisdiv>
13    <funcsynopsis>
14      <funcprototype>
15	<funcdef>int <function>ioctl</function></funcdef>
16	<paramdef>int <parameter>fd</parameter></paramdef>
17	<paramdef>int <parameter>request</parameter></paramdef>
18	<paramdef>struct media_links_enum *<parameter>argp</parameter></paramdef>
19      </funcprototype>
20    </funcsynopsis>
21  </refsynopsisdiv>
22
23  <refsect1>
24    <title>Arguments</title>
25
26    <variablelist>
27      <varlistentry>
28	<term><parameter>fd</parameter></term>
29	<listitem>
30	  <para>File descriptor returned by
31	  <link linkend='media-func-open'><function>open()</function></link>.</para>
32	</listitem>
33      </varlistentry>
34      <varlistentry>
35	<term><parameter>request</parameter></term>
36	<listitem>
37	  <para>MEDIA_IOC_ENUM_LINKS</para>
38	</listitem>
39      </varlistentry>
40      <varlistentry>
41	<term><parameter>argp</parameter></term>
42	<listitem>
43	  <para></para>
44	</listitem>
45      </varlistentry>
46    </variablelist>
47  </refsect1>
48
49  <refsect1>
50    <title>Description</title>
51
52    <para>To enumerate pads and/or links for a given entity, applications set
53    the entity field of a &media-links-enum; structure and initialize the
54    &media-pad-desc; and &media-link-desc; structure arrays pointed by the
55    <structfield>pads</structfield> and <structfield>links</structfield> fields.
56    They then call the MEDIA_IOC_ENUM_LINKS ioctl with a pointer to this
57    structure.</para>
58    <para>If the <structfield>pads</structfield> field is not NULL, the driver
59    fills the <structfield>pads</structfield> array with information about the
60    entity's pads. The array must have enough room to store all the entity's
61    pads. The number of pads can be retrieved with the &MEDIA-IOC-ENUM-ENTITIES;
62    ioctl.</para>
63    <para>If the <structfield>links</structfield> field is not NULL, the driver
64    fills the <structfield>links</structfield> array with information about the
65    entity's outbound links. The array must have enough room to store all the
66    entity's outbound links. The number of outbound links can be retrieved with
67    the &MEDIA-IOC-ENUM-ENTITIES; ioctl.</para>
68    <para>Only forward links that originate at one of the entity's source pads
69    are returned during the enumeration process.</para>
70
71    <table pgwide="1" frame="none" id="media-links-enum">
72      <title>struct <structname>media_links_enum</structname></title>
73      <tgroup cols="3">
74        &cs-str;
75	<tbody valign="top">
76	  <row>
77	    <entry>__u32</entry>
78	    <entry><structfield>entity</structfield></entry>
79	    <entry>Entity id, set by the application.</entry>
80	  </row>
81	  <row>
82	    <entry>struct &media-pad-desc;</entry>
83	    <entry>*<structfield>pads</structfield></entry>
84	    <entry>Pointer to a pads array allocated by the application. Ignored
85	    if NULL.</entry>
86	  </row>
87	  <row>
88	    <entry>struct &media-link-desc;</entry>
89	    <entry>*<structfield>links</structfield></entry>
90	    <entry>Pointer to a links array allocated by the application. Ignored
91	    if NULL.</entry>
92	  </row>
93	</tbody>
94      </tgroup>
95    </table>
96
97    <table pgwide="1" frame="none" id="media-pad-desc">
98      <title>struct <structname>media_pad_desc</structname></title>
99      <tgroup cols="3">
100        &cs-str;
101	<tbody valign="top">
102	  <row>
103	    <entry>__u32</entry>
104	    <entry><structfield>entity</structfield></entry>
105	    <entry>ID of the entity this pad belongs to.</entry>
106	  </row>
107	  <row>
108	    <entry>__u16</entry>
109	    <entry><structfield>index</structfield></entry>
110	    <entry>0-based pad index.</entry>
111	  </row>
112	  <row>
113	    <entry>__u32</entry>
114	    <entry><structfield>flags</structfield></entry>
115	    <entry>Pad flags, see <xref linkend="media-pad-flag" /> for more details.</entry>
116	  </row>
117	</tbody>
118      </tgroup>
119    </table>
120
121    <table frame="none" pgwide="1" id="media-pad-flag">
122      <title>Media pad flags</title>
123      <tgroup cols="2">
124        <colspec colname="c1"/>
125        <colspec colname="c2"/>
126	<tbody valign="top">
127	  <row>
128	    <entry><constant>MEDIA_PAD_FL_SINK</constant></entry>
129	    <entry>Input pad, relative to the entity. Input pads sink data and
130	    are targets of links.</entry>
131	  </row>
132	  <row>
133	    <entry><constant>MEDIA_PAD_FL_SOURCE</constant></entry>
134	    <entry>Output pad, relative to the entity. Output pads source data
135	    and are origins of links.</entry>
136	  </row>
137	</tbody>
138      </tgroup>
139    </table>
140
141    <table pgwide="1" frame="none" id="media-link-desc">
142      <title>struct <structname>media_link_desc</structname></title>
143      <tgroup cols="3">
144        &cs-str;
145	<tbody valign="top">
146	  <row>
147	    <entry>struct &media-pad-desc;</entry>
148	    <entry><structfield>source</structfield></entry>
149	    <entry>Pad at the origin of this link.</entry>
150	  </row>
151	  <row>
152	    <entry>struct &media-pad-desc;</entry>
153	    <entry><structfield>sink</structfield></entry>
154	    <entry>Pad at the target of this link.</entry>
155	  </row>
156	  <row>
157	    <entry>__u32</entry>
158	    <entry><structfield>flags</structfield></entry>
159	    <entry>Link flags, see <xref linkend="media-link-flag" /> for more details.</entry>
160	  </row>
161	</tbody>
162      </tgroup>
163    </table>
164
165    <table frame="none" pgwide="1" id="media-link-flag">
166      <title>Media link flags</title>
167      <tgroup cols="2">
168        <colspec colname="c1"/>
169        <colspec colname="c2"/>
170	<tbody valign="top">
171	  <row>
172	    <entry><constant>MEDIA_LNK_FL_ENABLED</constant></entry>
173	    <entry>The link is enabled and can be used to transfer media data.
174	    When two or more links target a sink pad, only one of them can be
175	    enabled at a time.</entry>
176	  </row>
177	  <row>
178	    <entry><constant>MEDIA_LNK_FL_IMMUTABLE</constant></entry>
179	    <entry>The link enabled state can't be modified at runtime. An
180	    immutable link is always enabled.</entry>
181	  </row>
182	  <row>
183	    <entry><constant>MEDIA_LNK_FL_DYNAMIC</constant></entry>
184	    <entry>The link enabled state can be modified during streaming. This
185	    flag is set by drivers and is read-only for applications.</entry>
186	  </row>
187	</tbody>
188      </tgroup>
189    </table>
190    <para>One and only one of <constant>MEDIA_PAD_FL_SINK</constant> and
191    <constant>MEDIA_PAD_FL_SOURCE</constant> must be set for every pad.</para>
192  </refsect1>
193
194  <refsect1>
195    &return-value;
196
197    <variablelist>
198      <varlistentry>
199	<term><errorcode>EINVAL</errorcode></term>
200	<listitem>
201	  <para>The &media-links-enum; <structfield>id</structfield> references
202	  a non-existing entity.</para>
203	</listitem>
204      </varlistentry>
205    </variablelist>
206  </refsect1>
207</refentry>
208