1 .. Permission is granted to copy, distribute and/or modify this
2 .. document under the terms of the GNU Free Documentation License,
3 .. Version 1.1 or any later version published by the Free Software
4 .. Foundation, with no Invariant Sections, no Front-Cover Texts
5 .. and no Back-Cover Texts. A copy of the license is included at
6 .. Documentation/media/uapi/fdl-appendix.rst.
8 .. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
10 .. _VIDIOC_SUBSCRIBE_EVENT:
11 .. _VIDIOC_UNSUBSCRIBE_EVENT:
13 ******************************************************
14 ioctl VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT
15 ******************************************************
20 VIDIOC_SUBSCRIBE_EVENT - VIDIOC_UNSUBSCRIBE_EVENT - Subscribe or unsubscribe event
26 .. c:function:: int ioctl( int fd, VIDIOC_SUBSCRIBE_EVENT, struct v4l2_event_subscription *argp )
27 :name: VIDIOC_SUBSCRIBE_EVENT
29 .. c:function:: int ioctl( int fd, VIDIOC_UNSUBSCRIBE_EVENT, struct v4l2_event_subscription *argp )
30 :name: VIDIOC_UNSUBSCRIBE_EVENT
37 File descriptor returned by :ref:`open() <func-open>`.
40 Pointer to struct :c:type:`v4l2_event_subscription`.
46 Subscribe or unsubscribe V4L2 event. Subscribed events are dequeued by
47 using the :ref:`VIDIOC_DQEVENT` ioctl.
50 .. tabularcolumns:: |p{4.6cm}|p{4.4cm}|p{8.7cm}|
52 .. c:type:: v4l2_event_subscription
54 .. flat-table:: struct v4l2_event_subscription
61 - Type of the event, see :ref:`event-type`.
65 ``V4L2_EVENT_ALL`` can be used with
66 :ref:`VIDIOC_UNSUBSCRIBE_EVENT <VIDIOC_SUBSCRIBE_EVENT>` for
67 unsubscribing all events at once.
70 - ID of the event source. If there is no ID associated with the
71 event source, then set this to 0. Whether or not an event needs an
72 ID depends on the event type.
75 - Event flags, see :ref:`event-flags`.
78 - Reserved for future extensions. Drivers and applications must set
83 .. tabularcolumns:: |p{6.8cm}|p{2.2cm}|p{8.5cm}|
87 .. flat-table:: Event Flags
92 * - ``V4L2_EVENT_SUB_FL_SEND_INITIAL``
94 - When this event is subscribed an initial event will be sent
95 containing the current status. This only makes sense for events
96 that are triggered by a status change such as ``V4L2_EVENT_CTRL``.
97 Other events will ignore this flag.
98 * - ``V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK``
100 - If set, then events directly caused by an ioctl will also be sent
101 to the filehandle that called that ioctl. For example, changing a
102 control using :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` will cause
103 a V4L2_EVENT_CTRL to be sent back to that same filehandle.
104 Normally such events are suppressed to prevent feedback loops
105 where an application changes a control to a one value and then
106 another, and then receives an event telling it that that control
107 has changed to the first value.
109 Since it can't tell whether that event was caused by another
110 application or by the :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>`
111 call it is hard to decide whether to set the control to the value
112 in the event, or ignore it.
114 Think carefully when you set this flag so you won't get into
115 situations like that.
121 On success 0 is returned, on error -1 and the ``errno`` variable is set
122 appropriately. The generic error codes are described at the
123 :ref:`Generic Error Codes <gen-errors>` chapter.