Streaming extensibility in the Modify-on-Access file system

This paper presents the Modify-on-Access (Mona) le system that provides extensibility through transformations applied to streams of data. Mona overcomes two limitations of prior extensible le systems. First, the Mona le system o ers two levels of extensions (kernel and user) that share a common interface. It allows performance-critical operations to execute with modest overhead in the kernel and untrusted or more complex operations to safely execute in user space. Second, Mona enables ne-grained extensions which allow an application to customize the le system at runtime. This paper discusses the implementation of the Modify-on-Access le system. Our implementation adds modest overhead of 0{3% (0.01{0.21 s) to le system operations. This overhead has even less e ect on net system performance for several benchmarks. Moreover, this paper describes applications that achieve 4{5 times speedup using custom transformations. This paper also describes several transformations that increase functionality. Among these are the ftp transformation that allows a user to browse a remote le as though it were local and the command transformation which invokes an arbitrary executable (even a shell script) on a data stream.