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v4l2-event.h
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1 /*
2  * v4l2-event.h
3  *
4  * V4L2 events.
5  *
6  * Copyright (C) 2009--2010 Nokia Corporation.
7  *
8  * Contact: Sakari Ailus <[email protected]>
9  *
10  * This program is free software; you can redistribute it and/or
11  * modify it under the terms of the GNU General Public License
12  * version 2 as published by the Free Software Foundation.
13  *
14  * This program is distributed in the hope that it will be useful, but
15  * WITHOUT ANY WARRANTY; without even the implied warranty of
16  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
17  * General Public License for more details.
18  *
19  * You should have received a copy of the GNU General Public License
20  * along with this program; if not, write to the Free Software
21  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
22  * 02110-1301 USA
23  */
24 
25 #ifndef V4L2_EVENT_H
26 #define V4L2_EVENT_H
27 
28 #include <linux/types.h>
29 #include <linux/videodev2.h>
30 #include <linux/wait.h>
31 
32 /*
33  * Overview:
34  *
35  * Events are subscribed per-filehandle. An event specification consists of a
36  * type and is optionally associated with an object identified through the
37  * 'id' field. So an event is uniquely identified by the (type, id) tuple.
38  *
39  * The v4l2-fh struct has a list of subscribed events. The v4l2_subscribed_event
40  * struct is added to that list, one for every subscribed event.
41  *
42  * Each v4l2_subscribed_event struct ends with an array of v4l2_kevent structs.
43  * This array (ringbuffer, really) is used to store any events raised by the
44  * driver. The v4l2_kevent struct links into the 'available' list of the
45  * v4l2_fh struct so VIDIOC_DQEVENT will know which event to dequeue first.
46  *
47  * Finally, if the event subscription is associated with a particular object
48  * such as a V4L2 control, then that object needs to know about that as well
49  * so that an event can be raised by that object. So the 'node' field can
50  * be used to link the v4l2_subscribed_event struct into a list of that
51  * object.
52  *
53  * So to summarize:
54  *
55  * struct v4l2_fh has two lists: one of the subscribed events, and one of the
56  * pending events.
57  *
58  * struct v4l2_subscribed_event has a ringbuffer of raised (pending) events of
59  * that particular type.
60  *
61  * If struct v4l2_subscribed_event is associated with a specific object, then
62  * that object will have an internal list of struct v4l2_subscribed_event so
63  * it knows who subscribed an event to that object.
64  */
65 
66 struct v4l2_fh;
68 struct video_device;
69 
75 struct v4l2_kevent {
76  struct list_head list;
78  struct v4l2_event event;
79 };
80 
88  int (*add)(struct v4l2_subscribed_event *sev, unsigned elems);
90  void (*replace)(struct v4l2_event *old, const struct v4l2_event *new);
91  void (*merge)(const struct v4l2_event *old, struct v4l2_event *new);
92 };
93 
108  struct list_head list;
112  struct v4l2_fh *fh;
113  struct list_head node;
115  unsigned elems;
116  unsigned first;
117  unsigned in_use;
118  struct v4l2_kevent events[];
119 };
120 
121 int v4l2_event_dequeue(struct v4l2_fh *fh, struct v4l2_event *event,
122  int nonblocking);
123 void v4l2_event_queue(struct video_device *vdev, const struct v4l2_event *ev);
124 void v4l2_event_queue_fh(struct v4l2_fh *fh, const struct v4l2_event *ev);
125 int v4l2_event_pending(struct v4l2_fh *fh);
126 int v4l2_event_subscribe(struct v4l2_fh *fh,
127  const struct v4l2_event_subscription *sub, unsigned elems,
128  const struct v4l2_subscribed_event_ops *ops);
129 int v4l2_event_unsubscribe(struct v4l2_fh *fh,
130  const struct v4l2_event_subscription *sub);
131 void v4l2_event_unsubscribe_all(struct v4l2_fh *fh);
132 
133 #endif /* V4L2_EVENT_H */