BSD provides the flock mechanism for locking file regions as a way to perform atomic modifications to files. POSIX provides this functionality through options to fcntl. Both of these are advisory locks, which means that processes not using the locks can access the file regions.
PVFS2 does not implement a locking infrastructure as part of the file system. At this time there is no add-on advisory locking component either. Thus neither the flock function nor the fcntl advisory locks are supported by PVFS2.