I'm trying to integrate a FS supporting async lock (can run callback when a lock is granted) as ganesha FSAL. For the moment I do not make any upcalls to FSAL and the lock still work. I wonder how it can work? may be SAL handles that itself, does it have an internal lock queue and tries/retries the waiting lock by making lock calls again frequently to the FSAL to know when it can grant the lock? 

Can somebody shed some light on that? And if it is the case, I imagine that making the grant_lock upcall will increase the performance? Or there are even more benefits?

Thank you

Viet