[media] v4l2-event/ctrls/fh: allocate events per fh and per type instead of just per-fh

The driver had to decide how many events to allocate when the v4l2_fh struct
was created. It was possible to add more events afterwards, but there was no
way to ensure that you wouldn't miss important events if the event queue
would fill up for that filehandle.

In addition, once there were no more free events, any new events were simply
dropped on the floor.

For the control event in particular this made life very difficult since
control status/value changes could just be missed if the number of allocated
events and the speed at which the application read events was too low to keep
up with the number of generated events. The application would have no idea
what the latest state was for a control since it could have missed the latest
control change.

So this patch makes some major changes in how events are allocated. Instead
of allocating events per-filehandle they are now allocated when subscribing an
event. So for that particular event type N events (determined by the driver)
are allocated. Those events are reserved for that particular event type.
This ensures that you will not miss events for a particular type altogether.

In addition, if there are N events in use and a new event is raised, then
the oldest event is dropped and the new one is added. So the latest event
is always available.

This can be further improved by adding the ability to merge the state of
two events together, ensuring that no data is lost at all. This will be
added in the next patch.

This also makes it possible to allow the user to determine the number of
events that will be allocated. This is not implemented at the moment, but
would be trivial.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

1 files changed, 0 insertions, 18 deletions

diff --git a/drivers/media/video/v4l2-ctrls.c b/drivers/media/video/v4l2-ctrls.c
index b63fe2a17fce..a37e5bff4342 100644
--- a/drivers/media/video/v4l2-ctrls.c
+++ b/drivers/media/video/v4l2-ctrls.c
@@ -1011,7 +1011,6 @@ static int handler_new_ref(struct v4l2_ctrl_handler *hdl,
 	   insertion is an O(1) operation. */
 	if (list_empty(&hdl->ctrl_refs) || id > node2id(hdl->ctrl_refs.prev)) {
 		list_add_tail(&new_ref->node, &hdl->ctrl_refs);
-		hdl->nr_of_refs++;
 		goto insert_in_hash;
 	}
 
@@ -2051,20 +2050,3 @@ void v4l2_ctrl_del_event(struct v4l2_ctrl *ctrl,
 	v4l2_ctrl_unlock(ctrl);
 }
 EXPORT_SYMBOL(v4l2_ctrl_del_event);
-
-int v4l2_ctrl_subscribe_fh(struct v4l2_fh *fh,
-			struct v4l2_event_subscription *sub, unsigned n)
-{
-	struct v4l2_ctrl_handler *hdl = fh->ctrl_handler;
-	int ret = 0;
-
-	if (!ret) {
-		if (hdl->nr_of_refs * 2 > n)
-			n = hdl->nr_of_refs * 2;
-		ret = v4l2_event_alloc(fh, n);
-	}
-	if (!ret)
-		ret = v4l2_event_subscribe(fh, sub);
-	return ret;
-}
-EXPORT_SYMBOL(v4l2_ctrl_subscribe_fh);