Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 EST.
1 <refentry id="vidioc-subscribe-event"> 2 <refmeta> 3 <refentrytitle>ioctl VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT</refentrytitle> 4 &manvol; 5 </refmeta> 6 7 <refnamediv> 8 <refname>VIDIOC_SUBSCRIBE_EVENT</refname> 9 <refname>VIDIOC_UNSUBSCRIBE_EVENT</refname> 10 <refpurpose>Subscribe or unsubscribe event</refpurpose> 11 </refnamediv> 12 13 <refsynopsisdiv> 14 <funcsynopsis> 15 <funcprototype> 16 <funcdef>int <function>ioctl</function></funcdef> 17 <paramdef>int <parameter>fd</parameter></paramdef> 18 <paramdef>int <parameter>request</parameter></paramdef> 19 <paramdef>struct v4l2_event_subscription 20 *<parameter>argp</parameter></paramdef> 21 </funcprototype> 22 </funcsynopsis> 23 </refsynopsisdiv> 24 25 <refsect1> 26 <title>Arguments</title> 27 28 <variablelist> 29 <varlistentry> 30 <term><parameter>fd</parameter></term> 31 <listitem> 32 <para>&fd;</para> 33 </listitem> 34 </varlistentry> 35 <varlistentry> 36 <term><parameter>request</parameter></term> 37 <listitem> 38 <para>VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT</para> 39 </listitem> 40 </varlistentry> 41 <varlistentry> 42 <term><parameter>argp</parameter></term> 43 <listitem> 44 <para></para> 45 </listitem> 46 </varlistentry> 47 </variablelist> 48 </refsect1> 49 50 <refsect1> 51 <title>Description</title> 52 53 <para>Subscribe or unsubscribe V4L2 event. Subscribed events are 54 dequeued by using the &VIDIOC-DQEVENT; ioctl.</para> 55 56 <table frame="none" pgwide="1" id="v4l2-event-subscription"> 57 <title>struct <structname>v4l2_event_subscription</structname></title> 58 <tgroup cols="3"> 59 &cs-str; 60 <tbody valign="top"> 61 <row> 62 <entry>__u32</entry> 63 <entry><structfield>type</structfield></entry> 64 <entry>Type of the event, see <xref linkend="event-type" />. Note that 65 <constant>V4L2_EVENT_ALL</constant> can be used with VIDIOC_UNSUBSCRIBE_EVENT 66 for unsubscribing all events at once.</entry> 67 </row> 68 <row> 69 <entry>__u32</entry> 70 <entry><structfield>id</structfield></entry> 71 <entry>ID of the event source. If there is no ID associated with 72 the event source, then set this to 0. Whether or not an event 73 needs an ID depends on the event type.</entry> 74 </row> 75 <row> 76 <entry>__u32</entry> 77 <entry><structfield>flags</structfield></entry> 78 <entry>Event flags, see <xref linkend="event-flags" />.</entry> 79 </row> 80 <row> 81 <entry>__u32</entry> 82 <entry><structfield>reserved</structfield>[5]</entry> 83 <entry>Reserved for future extensions. Drivers and applications 84 must set the array to zero.</entry> 85 </row> 86 </tbody> 87 </tgroup> 88 </table> 89 90 <table pgwide="1" frame="none" id="event-flags"> 91 <title>Event Flags</title> 92 <tgroup cols="3"> 93 &cs-def; 94 <tbody valign="top"> 95 <row> 96 <entry><constant>V4L2_EVENT_SUB_FL_SEND_INITIAL</constant></entry> 97 <entry>0x0001</entry> 98 <entry>When this event is subscribed an initial event will be sent 99 containing the current status. This only makes sense for events 100 that are triggered by a status change such as <constant>V4L2_EVENT_CTRL</constant>. 101 Other events will ignore this flag.</entry> 102 </row> 103 <row> 104 <entry><constant>V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK</constant></entry> 105 <entry>0x0002</entry> 106 <entry><para>If set, then events directly caused by an ioctl will also be sent to 107 the filehandle that called that ioctl. For example, changing a control using 108 &VIDIOC-S-CTRL; will cause a V4L2_EVENT_CTRL to be sent back to that same 109 filehandle. Normally such events are suppressed to prevent feedback loops 110 where an application changes a control to a one value and then another, and 111 then receives an event telling it that that control has changed to the first 112 value.</para> 113 114 <para>Since it can't tell whether that event was caused by another application 115 or by the &VIDIOC-S-CTRL; call it is hard to decide whether to set the 116 control to the value in the event, or ignore it.</para> 117 118 <para>Think carefully when you set this flag so you won't get into situations 119 like that.</para> 120 </entry> 121 </row> 122 </tbody> 123 </tgroup> 124 </table> 125 126 </refsect1> 127 <refsect1> 128 &return-value; 129 </refsect1> 130 </refentry>
