The invention provides a method and 
system for correct 
interoperation of multiple diverse 
file server or 
file locking protocols, using a uniform multi-protocol lock 
management system. A 
file server determines, before allowing any 
client device to access data or to obtain a lock, whether that would be inconsistent with existing locks, regardless of originating 
client device or originating protocol for those existing locks. A first protocol enforces mandatory file-open and file-locking together with an opportunistic file-locking technique, while a second protocol lacks file-open 
semantics and provides only for advisory 
byte-range and 
file locking. Enforcing file-locking protects file data against corruption by NFS 
client devices. A CIFS client device, upon opening a file, can obtain an "oplock" (an opportunistic lock). When a client device issues a non-CIFS protocol request for the oplocked file, the 
file server sends an oplock-break message to the CIFS client device, giving the CIFS client device the opportunity to flush any cached write operations and possibly close the file. Allowing NFS and NLM requests to break oplocks ensures that file data remains available to NFS client devices simultaneously with protecting integrity of that file data. A CIFS client device can obtain a "change-monitoring" lock for a 
directory in the 
file system, so as to be notified by the file 
server whenever there is a change to that 
directory. The file 
server notes changes to the 
directory by both CIFS and non-CIFS client devices, and notifies those CIFS client devices with "change-monitoring" locks of those changes.