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Based on kernel version 3.16. Page generated on 2014-08-06 21:38 EST.

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>&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>&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		  <row>
138		    <entry><constant>MEDIA_PAD_FL_MUST_CONNECT</constant></entry>
139		    <entry>If this flag is set and the pad is linked to any other
140		    pad, then at least one of those links must be enabled for the
141		    entity to be able to stream. There could be temporary reasons
142		    (e.g. device configuration dependent) for the pad to need
143		    enabled links even when this flag isn't set; the absence of the
144		    flag doesn't imply there is none.</entry>
145		  </row>
146		</tbody>
147	      </tgroup>
148	    </table>
149	
150	    <table pgwide="1" frame="none" id="media-link-desc">
151	      <title>struct <structname>media_link_desc</structname></title>
152	      <tgroup cols="3">
153	        &cs-str;
154		<tbody valign="top">
155		  <row>
156		    <entry>&media-pad-desc;</entry>
157		    <entry><structfield>source</structfield></entry>
158		    <entry>Pad at the origin of this link.</entry>
159		  </row>
160		  <row>
161		    <entry>&media-pad-desc;</entry>
162		    <entry><structfield>sink</structfield></entry>
163		    <entry>Pad at the target of this link.</entry>
164		  </row>
165		  <row>
166		    <entry>__u32</entry>
167		    <entry><structfield>flags</structfield></entry>
168		    <entry>Link flags, see <xref linkend="media-link-flag" /> for more details.</entry>
169		  </row>
170		</tbody>
171	      </tgroup>
172	    </table>
173	
174	    <table frame="none" pgwide="1" id="media-link-flag">
175	      <title>Media link flags</title>
176	      <tgroup cols="2">
177	        <colspec colname="c1"/>
178	        <colspec colname="c2"/>
179		<tbody valign="top">
180		  <row>
181		    <entry><constant>MEDIA_LNK_FL_ENABLED</constant></entry>
182		    <entry>The link is enabled and can be used to transfer media data.
183		    When two or more links target a sink pad, only one of them can be
184		    enabled at a time.</entry>
185		  </row>
186		  <row>
187		    <entry><constant>MEDIA_LNK_FL_IMMUTABLE</constant></entry>
188		    <entry>The link enabled state can't be modified at runtime. An
189		    immutable link is always enabled.</entry>
190		  </row>
191		  <row>
192		    <entry><constant>MEDIA_LNK_FL_DYNAMIC</constant></entry>
193		    <entry>The link enabled state can be modified during streaming. This
194		    flag is set by drivers and is read-only for applications.</entry>
195		  </row>
196		</tbody>
197	      </tgroup>
198	    </table>
199	    <para>One and only one of <constant>MEDIA_PAD_FL_SINK</constant> and
200	    <constant>MEDIA_PAD_FL_SOURCE</constant> must be set for every pad.</para>
201	  </refsect1>
202	
203	  <refsect1>
204	    &return-value;
205	
206	    <variablelist>
207	      <varlistentry>
208		<term><errorcode>EINVAL</errorcode></term>
209		<listitem>
210		  <para>The &media-links-enum; <structfield>id</structfield> references
211		  a non-existing entity.</para>
212		</listitem>
213	      </varlistentry>
214	    </variablelist>
215	  </refsect1>
216	</refentry>
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