Direct-FUSE: Removing the Middleman for High-Performance FUSE File System Support

Developing a file system is a challenging task, especially a kernel-level file system. User-level file systems alleviate the burden and development complexity associated with kernel-level implementations. The Filesystem in Userspace (FUSE) is a widely used tool that allows non-privileged users to develop file systems in user space. When a FUSE file system is mounted, it runs as a user-level process. Application programs and FUSE file system processes are bridged through FUSE kernel module. However, as the FUSE kernel module transfers requests between an application program and a file system process, the overheads in a FUSE file system call from crossing the user-kernel boundary is non-trivial. The overheads contain user-kernel mode switches, context switches, and additional memory copies. In this paper, we describe our Direct-FUSE framework that supports multiple FUSE file systems as well as other, custom user-level file systems in user space without the need to cross the user/kernel boundary into the FUSE kernel module. All layers of Direct-FUSE are in user space, and applications can directly use pre-defined unified file system calls to interact with different user-defined file systems. Our performance results show that Direct-FUSE can outperform some native FUSE file systems by 11.9% on average and does not add significant overhead over backend file systems.