Commit | Line | Data |
---|---|---|
5377d91f MH |
1 | .. -*- coding: utf-8; mode: rst -*- |
2 | ||
af4a4d0d | 3 | .. _VIDIOC_SUBSCRIBE_EVENT: |
6710ea47 | 4 | .. _VIDIOC_UNSUBSCRIBE_EVENT: |
5377d91f MH |
5 | |
6 | ****************************************************** | |
7 | ioctl VIDIOC_SUBSCRIBE_EVENT, VIDIOC_UNSUBSCRIBE_EVENT | |
8 | ****************************************************** | |
9 | ||
15e7d615 | 10 | Name |
586027ce | 11 | ==== |
5377d91f | 12 | |
586027ce | 13 | VIDIOC_SUBSCRIBE_EVENT - VIDIOC_UNSUBSCRIBE_EVENT - Subscribe or unsubscribe event |
5377d91f | 14 | |
15e7d615 MCC |
15 | |
16 | Synopsis | |
5377d91f MH |
17 | ======== |
18 | ||
41d80465 MCC |
19 | .. c:function:: int ioctl( int fd, VIDIOC_SUBSCRIBE_EVENT, struct v4l2_event_subscription *argp ) |
20 | :name: VIDIOC_SUBSCRIBE_EVENT | |
21 | ||
22 | .. c:function:: int ioctl( int fd, VIDIOC_UNSUBSCRIBE_EVENT, struct v4l2_event_subscription *argp ) | |
23 | :name: VIDIOC_UNSUBSCRIBE_EVENT | |
5377d91f | 24 | |
586027ce | 25 | |
15e7d615 | 26 | Arguments |
5377d91f MH |
27 | ========= |
28 | ||
29 | ``fd`` | |
30 | File descriptor returned by :ref:`open() <func-open>`. | |
31 | ||
5377d91f MH |
32 | ``argp`` |
33 | ||
34 | ||
15e7d615 | 35 | Description |
5377d91f MH |
36 | =========== |
37 | ||
38 | Subscribe or unsubscribe V4L2 event. Subscribed events are dequeued by | |
7347081e | 39 | using the :ref:`VIDIOC_DQEVENT` ioctl. |
5377d91f MH |
40 | |
41 | ||
5bd4bb78 MCC |
42 | .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| |
43 | ||
e8be7e97 | 44 | .. c:type:: v4l2_event_subscription |
fa92b04d | 45 | |
5377d91f MH |
46 | .. flat-table:: struct v4l2_event_subscription |
47 | :header-rows: 0 | |
48 | :stub-columns: 0 | |
49 | :widths: 1 1 2 | |
50 | ||
51 | ||
52 | - .. row 1 | |
53 | ||
54 | - __u32 | |
55 | ||
56 | - ``type`` | |
57 | ||
706f8a99 MCC |
58 | - Type of the event, see :ref:`event-type`. |
59 | ||
b6b6e678 MCC |
60 | .. note:: |
61 | ||
62 | ``V4L2_EVENT_ALL`` can be used with | |
6710ea47 MCC |
63 | :ref:`VIDIOC_UNSUBSCRIBE_EVENT <VIDIOC_SUBSCRIBE_EVENT>` for |
64 | unsubscribing all events at once. | |
5377d91f MH |
65 | |
66 | - .. row 2 | |
67 | ||
68 | - __u32 | |
69 | ||
70 | - ``id`` | |
71 | ||
72 | - ID of the event source. If there is no ID associated with the | |
0579e6e3 MCC |
73 | event source, then set this to 0. Whether or not an event needs an |
74 | ID depends on the event type. | |
5377d91f MH |
75 | |
76 | - .. row 3 | |
77 | ||
78 | - __u32 | |
79 | ||
80 | - ``flags`` | |
81 | ||
82 | - Event flags, see :ref:`event-flags`. | |
83 | ||
84 | - .. row 4 | |
85 | ||
86 | - __u32 | |
87 | ||
8968da9b | 88 | - ``reserved``\ [5] |
5377d91f MH |
89 | |
90 | - Reserved for future extensions. Drivers and applications must set | |
0579e6e3 | 91 | the array to zero. |
5377d91f MH |
92 | |
93 | ||
94 | ||
5bd4bb78 MCC |
95 | .. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| |
96 | ||
fa92b04d MCC |
97 | .. _event-flags: |
98 | ||
5377d91f MH |
99 | .. flat-table:: Event Flags |
100 | :header-rows: 0 | |
101 | :stub-columns: 0 | |
102 | :widths: 3 1 4 | |
103 | ||
104 | ||
105 | - .. row 1 | |
106 | ||
107 | - ``V4L2_EVENT_SUB_FL_SEND_INITIAL`` | |
108 | ||
109 | - 0x0001 | |
110 | ||
111 | - When this event is subscribed an initial event will be sent | |
0579e6e3 MCC |
112 | containing the current status. This only makes sense for events |
113 | that are triggered by a status change such as ``V4L2_EVENT_CTRL``. | |
114 | Other events will ignore this flag. | |
5377d91f MH |
115 | |
116 | - .. row 2 | |
117 | ||
118 | - ``V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK`` | |
119 | ||
120 | - 0x0002 | |
121 | ||
122 | - If set, then events directly caused by an ioctl will also be sent | |
0579e6e3 MCC |
123 | to the filehandle that called that ioctl. For example, changing a |
124 | control using :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` will cause | |
125 | a V4L2_EVENT_CTRL to be sent back to that same filehandle. | |
126 | Normally such events are suppressed to prevent feedback loops | |
127 | where an application changes a control to a one value and then | |
128 | another, and then receives an event telling it that that control | |
129 | has changed to the first value. | |
130 | ||
131 | Since it can't tell whether that event was caused by another | |
132 | application or by the :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` | |
133 | call it is hard to decide whether to set the control to the value | |
134 | in the event, or ignore it. | |
135 | ||
136 | Think carefully when you set this flag so you won't get into | |
137 | situations like that. | |
5377d91f MH |
138 | |
139 | ||
15e7d615 | 140 | Return Value |
5377d91f MH |
141 | ============ |
142 | ||
143 | On success 0 is returned, on error -1 and the ``errno`` variable is set | |
144 | appropriately. The generic error codes are described at the | |
145 | :ref:`Generic Error Codes <gen-errors>` chapter. |