This paper discusses how the Modify-on-Access file system efficiently extends the capabilities of conventional file systems. It demonstrates how an active file system can simplify both applications and system usage by performing computations on behalf of processes. Furthermore, the paper describes the implementation of the MonA file system and the export transformation. Section 5 shows that the overhead of a kernel-resident transformation is very small and that transforming data inline provides performance benefits. Furthermore, it shows that the export transformation provides user extensibility.
The MonA file system is the first component of a suite of system software designed for a collaborative memory system in which intelligent peripheral devices collaborate with a host processor to accomplish tasks. Current projects include a MonA virtual memory system and a MonA peripheral device. These implementations are similar to the Active Page and Active Disk simulations described in related work.
In summary, the MonA file system adds considerable functionality to a file system by transforming data on-the-fly during file accesses. This provides an extensible environment in which a privileged user implements common, time-critical operations within the kernel and an unprivileged user safely implements user-defined operations outside of the kernel. The MonA file system supports these features with minimal overhead.