Rapid file system development using ptrace

Developing kernel-level file systems is a difficult task that requires a significant time investment. For experimental file systems, it is desirable to develop a prototype before investing the time required to develop a kernel-level file system. We have built a ptrace monitoring infrastructure for file system development. Because our system runs entirely in user-space, debugging is made easier and it is possible to leverage existing tested user-level libraries. Because our monitor intercepts all OS entry points (system calls and signals) it is able to provide more functionality than other prototyping techniques, which are limited by the VFS interface (FUSE) or network protocols (user-level NFS servers). We have developed several example file systems using our framework, including a pass-through layered file system, a layered encryption file system, and a user-level ISO9660 file system. We analyzed the complexity of our code using cyclomatic complexity and other metrics. We show savings for a pass-through file system of 53% compared to existing user-level pass-through file systems and a factor of 4.7 reduction for an in-kernel pass-through file system. Our performance evaluation demonstrates that our infrastructure has an acceptable overhead of 18.4% for a pass-through file system.