1. A computer-implemented method for providing client applications with access to file data in a distributed file system, each of the client applications coupled to a virtual file system that is coupled to one or more physical file systems, and the virtual file system coupled to a lock agent, which is coupled to a lock server, the method comprising: invoking the virtual file system with file access requests from the client applications, each file access request including an operation code and a data reference; submitting data validation requests to the lock agent by the virtual file system in response to the file access requests; submitting lease requests from the lock agent to the lock server; processing lease requests by the lock server; returning leases from the lock server to the virtual file system via the lock agent in response the lease requests; and for each file access request, submitting the file access request to a selected one of the physical file systems after a lease is granted.