A Toolkit for User-Level File Systems

This paper describes a C++ toolkit for easily extending the Unix file system. The toolkit exposes the NFS interface, allowing new file systems to be implemented portably at user level. A number of programs have implemented portable, user-level file systems. However, they have been plagued by low-performance, deadlock, restrictions on file system structure, and the need to reboot after software errors. The toolkit makes it easy to avoid the vast majority of these problems. Moreover, the toolkit also supports user-level access to existing file systems through the NFS interface—a heretofore rarely employed technique. NFS gives software an asynchronous, low-level interface to the file system that can greatly benefit the performance, security, and scalability of certain applications. The toolkit uses a new asynchronous I/O library that makes it tractable to build large, event-driven programs that never block.