forked from Minki/linux
f1e393de38
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> |
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