1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
|
.. -*- coding: utf-8; mode: rst -*-
.. _vidioc-subscribe-event:
******************************************************
ioctl VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT
******************************************************
*man VIDIOC_SUBSCRIBE_EVENT(2)*
VIDIOC_UNSUBSCRIBE_EVENT
Subscribe or unsubscribe event
Synopsis
========
.. c: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 <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 that
``V4L2_EVENT_ALL`` can be used with VIDIOC_UNSUBSCRIBE_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.
.. ------------------------------------------------------------------------------
.. This file was automatically converted from DocBook-XML with the dbxml
.. library (https://github.com/return42/sphkerneldoc). The origin XML comes
.. from the linux kernel, refer to:
..
.. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
.. ------------------------------------------------------------------------------
|
