Commit | Line | Data |
---|---|---|
5377d91f MH |
1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_SUBSCRIBE_EVENT: |
5377d91f MH |
4 | |
5 | ****************************************************** | |
6 | ioctl VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT | |
7 | ****************************************************** | |
8 | ||
586027ce MCC |
9 | NAME |
10 | ==== | |
5377d91f | 11 | |
586027ce | 12 | VIDIOC_SUBSCRIBE_EVENT - VIDIOC_UNSUBSCRIBE_EVENT - Subscribe or unsubscribe event |
5377d91f | 13 | |
586027ce | 14 | SYNOPSIS |
5377d91f MH |
15 | ======== |
16 | ||
b7e67f6c | 17 | .. cpp:function:: int ioctl( int fd, int request, struct v4l2_event_subscription *argp ) |
5377d91f | 18 | |
586027ce MCC |
19 | |
20 | ARGUMENTS | |
5377d91f MH |
21 | ========= |
22 | ||
23 | ``fd`` | |
24 | File descriptor returned by :ref:`open() <func-open>`. | |
25 | ||
26 | ``request`` | |
27 | VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT | |
28 | ||
29 | ``argp`` | |
30 | ||
31 | ||
586027ce | 32 | DESCRIPTION |
5377d91f MH |
33 | =========== |
34 | ||
35 | Subscribe or unsubscribe V4L2 event. Subscribed events are dequeued by | |
7347081e | 36 | using the :ref:`VIDIOC_DQEVENT` ioctl. |
5377d91f MH |
37 | |
38 | ||
39 | .. _v4l2-event-subscription: | |
40 | ||
41 | .. flat-table:: struct v4l2_event_subscription | |
42 | :header-rows: 0 | |
43 | :stub-columns: 0 | |
44 | :widths: 1 1 2 | |
45 | ||
46 | ||
47 | - .. row 1 | |
48 | ||
49 | - __u32 | |
50 | ||
51 | - ``type`` | |
52 | ||
53 | - Type of the event, see :ref:`event-type`. Note that | |
0579e6e3 MCC |
54 | ``V4L2_EVENT_ALL`` can be used with VIDIOC_UNSUBSCRIBE_EVENT for |
55 | unsubscribing all events at once. | |
5377d91f MH |
56 | |
57 | - .. row 2 | |
58 | ||
59 | - __u32 | |
60 | ||
61 | - ``id`` | |
62 | ||
63 | - ID of the event source. If there is no ID associated with the | |
0579e6e3 MCC |
64 | event source, then set this to 0. Whether or not an event needs an |
65 | ID depends on the event type. | |
5377d91f MH |
66 | |
67 | - .. row 3 | |
68 | ||
69 | - __u32 | |
70 | ||
71 | - ``flags`` | |
72 | ||
73 | - Event flags, see :ref:`event-flags`. | |
74 | ||
75 | - .. row 4 | |
76 | ||
77 | - __u32 | |
78 | ||
79 | - ``reserved``\ [5] | |
80 | ||
81 | - Reserved for future extensions. Drivers and applications must set | |
0579e6e3 | 82 | the array to zero. |
5377d91f MH |
83 | |
84 | ||
85 | ||
86 | .. _event-flags: | |
87 | ||
88 | .. flat-table:: Event Flags | |
89 | :header-rows: 0 | |
90 | :stub-columns: 0 | |
91 | :widths: 3 1 4 | |
92 | ||
93 | ||
94 | - .. row 1 | |
95 | ||
96 | - ``V4L2_EVENT_SUB_FL_SEND_INITIAL`` | |
97 | ||
98 | - 0x0001 | |
99 | ||
100 | - When this event is subscribed an initial event will be sent | |
0579e6e3 MCC |
101 | containing the current status. This only makes sense for events |
102 | that are triggered by a status change such as ``V4L2_EVENT_CTRL``. | |
103 | Other events will ignore this flag. | |
5377d91f MH |
104 | |
105 | - .. row 2 | |
106 | ||
107 | - ``V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK`` | |
108 | ||
109 | - 0x0002 | |
110 | ||
111 | - If set, then events directly caused by an ioctl will also be sent | |
0579e6e3 MCC |
112 | to the filehandle that called that ioctl. For example, changing a |
113 | control using :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` will cause | |
114 | a V4L2_EVENT_CTRL to be sent back to that same filehandle. | |
115 | Normally such events are suppressed to prevent feedback loops | |
116 | where an application changes a control to a one value and then | |
117 | another, and then receives an event telling it that that control | |
118 | has changed to the first value. | |
119 | ||
120 | Since it can't tell whether that event was caused by another | |
121 | application or by the :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` | |
122 | call it is hard to decide whether to set the control to the value | |
123 | in the event, or ignore it. | |
124 | ||
125 | Think carefully when you set this flag so you won't get into | |
126 | situations like that. | |
5377d91f MH |
127 | |
128 | ||
586027ce | 129 | RETURN VALUE |
5377d91f MH |
130 | ============ |
131 | ||
132 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
133 | appropriately. The generic error codes are described at the | |
134 | :ref:`Generic Error Codes <gen-errors>` chapter. |