Get the first lock that blocks the lock description pointed to by the third argument, arg, taken as a reference to a Mono.Unix.Native.Flock. The information retrieved overwrites the information passed to Syscall.fcntl in the flock structure. If no lock is found that would prevent this lock from being created, the structure is left unchanged by this system call except for the lock type which is set to LockType.F_UNLCK.