From: Hans Verkuil <hans.verkuil@xxxxxxxxx> It's getting confusing who is linking to what, so add an overview at the start of the header. Signed-off-by: Hans Verkuil <hans.verkuil@xxxxxxxxx> --- include/media/v4l2-event.h | 34 ++++++++++++++++++++++++++++++++++ 1 files changed, 34 insertions(+), 0 deletions(-) diff --git a/include/media/v4l2-event.h b/include/media/v4l2-event.h index 7abeb39..5f14e88 100644 --- a/include/media/v4l2-event.h +++ b/include/media/v4l2-event.h @@ -29,6 +29,40 @@ #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; -- 1.7.1 -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
