#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 {
- /* list node for the v4l2_fh->available list */
struct list_head list;
- /* pointer to parent v4l2_subscribed_event */
struct v4l2_subscribed_event *sev;
- /* event itself */
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 {
- /* list node for the v4l2_fh->subscribed list */
struct list_head list;
- /* event type */
u32 type;
- /* associated object ID (e.g. control ID) */
u32 id;
- /* copy of v4l2_event_subscription->flags */
u32 flags;
- /* filehandle that subscribed to this event */
struct v4l2_fh *fh;
- /* list node that hooks into the object's event list (if there is one) */
struct list_head node;
- /* Optional callback that can replace event 'old' with event 'new'. */
void (*replace)(struct v4l2_event *old,
const struct v4l2_event *new);
- /* Optional callback that can merge event 'old' into event 'new'. */
void (*merge)(const struct v4l2_event *old,
struct v4l2_event *new);
- /* the number of elements in the events array */
unsigned elems;
- /* the index of the events containing the oldest available event */
unsigned first;
- /* the number of queued events */
unsigned in_use;
- /* an array of elems events */
struct v4l2_kevent events[];
};