Mona: an Adaptive, Multiple Level Extensible File System

This paper presents the Modify-on-Access (Mona) le system that provides extensibility through transformations applied to streams of data. Mona is novel in two ways. First, it o ers two levels of extensions (kernel and user). It allows performance-critical operations to execute with little overhead in the kernel and untrusted or more complex operations to execute in user space. Second, a running application can extend Mona dynamically, which allows the application to adapt the le system at runtime. This paper discusses the implementation of the Modify-on-Access le system. In our implementation, extensibility adds only a few microseconds to each le system operation (read, write, open, etc.), which has a negligible e ect on overall system performance. We present applications that achieve 4{5 times speedup by using a simple kernel transformation. This paper also describes several transformations that increase functionality, such as the ftp transformation that allows a user to browse a remote le as though it were local.