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+.. -*- coding: utf-8; mode: rst -*-
+
+.. _VIDIOC_SUBSCRIBE_EVENT:
+.. _VIDIOC_UNSUBSCRIBE_EVENT:
+
+******************************************************
+ioctl VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT
+******************************************************
+
+Name
+====
+
+VIDIOC_SUBSCRIBE_EVENT - VIDIOC_UNSUBSCRIBE_EVENT - Subscribe or unsubscribe event
+
+
+Synopsis
+========
+
+.. cpp:function:: int ioctl( int fd, int request, struct v4l2_event_subscription *argp )
+
+
+Arguments
+=========
+
+``fd``
+    File descriptor returned by :ref:`open() <func-open>`.
+
+``request``
+    VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT
+
+``argp``
+
+
+Description
+===========
+
+Subscribe or unsubscribe V4L2 event. Subscribed events are dequeued by
+using the :ref:`VIDIOC_DQEVENT` ioctl.
+
+
+.. _v4l2-event-subscription:
+
+.. flat-table:: struct v4l2_event_subscription
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       1 1 2
+
+
+    -  .. row 1
+
+       -  __u32
+
+       -  ``type``
+
+       -  Type of the event, see :ref:`event-type`.
+
+	  .. note:: ``V4L2_EVENT_ALL`` can be used with
+	     :ref:`VIDIOC_UNSUBSCRIBE_EVENT <VIDIOC_SUBSCRIBE_EVENT>` for
+	     unsubscribing all events at once.
+
+    -  .. row 2
+
+       -  __u32
+
+       -  ``id``
+
+       -  ID of the event source. If there is no ID associated with the
+	  event source, then set this to 0. Whether or not an event needs an
+	  ID depends on the event type.
+
+    -  .. row 3
+
+       -  __u32
+
+       -  ``flags``
+
+       -  Event flags, see :ref:`event-flags`.
+
+    -  .. row 4
+
+       -  __u32
+
+       -  ``reserved``\ [5]
+
+       -  Reserved for future extensions. Drivers and applications must set
+	  the array to zero.
+
+
+
+.. _event-flags:
+
+.. flat-table:: Event Flags
+    :header-rows:  0
+    :stub-columns: 0
+    :widths:       3 1 4
+
+
+    -  .. row 1
+
+       -  ``V4L2_EVENT_SUB_FL_SEND_INITIAL``
+
+       -  0x0001
+
+       -  When this event is subscribed an initial event will be sent
+	  containing the current status. This only makes sense for events
+	  that are triggered by a status change such as ``V4L2_EVENT_CTRL``.
+	  Other events will ignore this flag.
+
+    -  .. row 2
+
+       -  ``V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK``
+
+       -  0x0002
+
+       -  If set, then events directly caused by an ioctl will also be sent
+	  to the filehandle that called that ioctl. For example, changing a
+	  control using :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` will cause
+	  a V4L2_EVENT_CTRL to be sent back to that same filehandle.
+	  Normally such events are suppressed to prevent feedback loops
+	  where an application changes a control to a one value and then
+	  another, and then receives an event telling it that that control
+	  has changed to the first value.
+
+	  Since it can't tell whether that event was caused by another
+	  application or by the :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>`
+	  call it is hard to decide whether to set the control to the value
+	  in the event, or ignore it.
+
+	  Think carefully when you set this flag so you won't get into
+	  situations like that.
+
+
+Return Value
+============
+
+On success 0 is returned, on error -1 and the ``errno`` variable is set
+appropriately. The generic error codes are described at the
+:ref:`Generic Error Codes <gen-errors>` chapter.