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+  <title>Event Interface</title>
+
+  <para>The V4L2 event interface provides a means for a user to get
+  immediately notified on certain conditions taking place on a device.
+  This might include start of frame or loss of signal events, for
+  example. Changes in the value or state of a V4L2 control can also be
+  reported through events.
+  </para>
+
+  <para>To receive events, the events the user is interested in first must
+  be subscribed using the &VIDIOC-SUBSCRIBE-EVENT; ioctl. Once an event is
+  subscribed, the events of subscribed types are dequeueable using the
+  &VIDIOC-DQEVENT; ioctl. Events may be unsubscribed using
+  VIDIOC_UNSUBSCRIBE_EVENT ioctl. The special event type V4L2_EVENT_ALL may
+  be used to unsubscribe all the events the driver supports.</para>
+
+  <para>The event subscriptions and event queues are specific to file
+  handles. Subscribing an event on one file handle does not affect
+  other file handles.</para>
+
+  <para>The information on dequeueable events is obtained by using select or
+  poll system calls on video devices. The V4L2 events use POLLPRI events on
+  poll system call and exceptions on select system call.</para>
+
+  <para>Starting with kernel 3.1 certain guarantees can be given with
+  regards to events:<orderedlist>
+        <listitem>
+          <para>Each subscribed event has its own internal dedicated event queue.
+This means that flooding of one event type will not interfere with other
+event types.</para>
+        </listitem>
+        <listitem>
+          <para>If the internal event queue for a particular subscribed event
+becomes full, then the oldest event in that queue will be dropped.</para>
+        </listitem>
+        <listitem>
+          <para>Where applicable, certain event types can ensure that the payload
+of the oldest event that is about to be dropped will be merged with the payload
+of the next oldest event. Thus ensuring that no information is lost, but only an
+intermediate step leading up to that information. See the documentation for the
+event you want to subscribe to whether this is applicable for that event or not.</para>
+        </listitem>
+      </orderedlist></para>
+
+  <!--
+Local Variables:
+mode: sgml
+sgml-parent-document: "v4l2.sgml"
+indent-tabs-mode: nil
+End:
+  -->