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* v4l2-event.h
* V4L2 events.
* Copyright (C) 2009--2010 Nokia Corporation.
* Contact: Sakari Ailus <>
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* version 2 as published by the Free Software Foundation.
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* General Public License for more details.
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
* 02110-1301 USA
#ifndef V4L2_EVENT_H
#define V4L2_EVENT_H
#include <linux/types.h>
#include <linux/videodev2.h>
#include <linux/wait.h>
* Overview:
* Events are subscribed per-filehandle. An event specification consists of a
* type and is optionally associated with an object identified through the
* 'id' field. So an event is uniquely identified by the (type, id) tuple.
* The v4l2-fh struct has a list of subscribed events. The v4l2_subscribed_event
* struct is added to that list, one for every subscribed event.
* Each v4l2_subscribed_event struct ends with an array of v4l2_kevent structs.
* This array (ringbuffer, really) is used to store any events raised by the
* driver. The v4l2_kevent struct links into the 'available' list of the
* v4l2_fh struct so VIDIOC_DQEVENT will know which event to dequeue first.
* Finally, if the event subscription is associated with a particular object
* such as a V4L2 control, then that object needs to know about that as well
* so that an event can be raised by that object. So the 'node' field can
* be used to link the v4l2_subscribed_event struct into a list of that
* object.
* So to summarize:
* struct v4l2_fh has two lists: one of the subscribed events, and one of the
* pending events.
* struct v4l2_subscribed_event has a ringbuffer of raised (pending) events of
* that particular type.
* If struct v4l2_subscribed_event is associated with a specific object, then
* that object will have an internal list of struct v4l2_subscribed_event so
* it knows who subscribed an event to that object.
struct v4l2_fh;
struct v4l2_subscribed_event;
struct video_device;
/** struct v4l2_kevent - Internal kernel event struct.
* @list: List node for the v4l2_fh->available list.
* @sev: Pointer to parent v4l2_subscribed_event.
* @event: The event itself.
struct v4l2_kevent {
struct list_head list;
struct v4l2_subscribed_event *sev;
struct v4l2_event event;
/** struct v4l2_subscribed_event - Internal struct representing a subscribed event.
* @list: List node for the v4l2_fh->subscribed list.
* @type: Event type.
* @id: Associated object ID (e.g. control ID). 0 if there isn't any.
* @flags: Copy of v4l2_event_subscription->flags.
* @fh: Filehandle that subscribed to this event.
* @node: List node that hooks into the object's event list (if there is one).
* @replace: Optional callback that can replace event 'old' with event 'new'.
* @merge: Optional callback that can merge event 'old' into event 'new'.
* @elems: The number of elements in the events array.
* @first: The index of the events containing the oldest available event.
* @in_use: The number of queued events.
* @events: An array of @elems events.
struct v4l2_subscribed_event {
struct list_head list;
u32 type;
u32 id;
u32 flags;
struct v4l2_fh *fh;
struct list_head node;
void (*replace)(struct v4l2_event *old,
const struct v4l2_event *new);
void (*merge)(const struct v4l2_event *old,
struct v4l2_event *new);
unsigned elems;
unsigned first;
unsigned in_use;
struct v4l2_kevent events[];
int v4l2_event_dequeue(struct v4l2_fh *fh, struct v4l2_event *event,
int nonblocking);
void v4l2_event_queue(struct video_device *vdev, const struct v4l2_event *ev);
void v4l2_event_queue_fh(struct v4l2_fh *fh, const struct v4l2_event *ev);
int v4l2_event_pending(struct v4l2_fh *fh);
int v4l2_event_subscribe(struct v4l2_fh *fh,
struct v4l2_event_subscription *sub, unsigned elems);
int v4l2_event_unsubscribe(struct v4l2_fh *fh,
struct v4l2_event_subscription *sub);
void v4l2_event_unsubscribe_all(struct v4l2_fh *fh);
#endif /* V4L2_EVENT_H */