An extensible file system for hydra

An extensible file system has been designed and implemented for Hydra, an advanced capability-based operating system. This system demonstrates three notable contributions to subsystem design: - It provides a protected and efficient implementation via user-level code of functions ordinarily implemented as part of a conventional system's monolithic privileged section, - It provides practical solutions to two protection problems, the Modification Problem and the Confinement Problem, for users of the file system, and - It provides separation of mechanisms for data representation from mechanisms for protection and synchronization, thus allowing an extensible family of subfile systems to evolve. This paper treats the design and implementation of the Hydra File System and reflects on its implications for subsystem design and implementation.