Performance and Security in Userspace NVM File Systems through State Separation

Userspace library file systems (LibFSes) promise to unleash the performance potential of non-volatile memory (NVM) by directly accessing it and enabling unprivileged applications to customize their LibFSes. Unfortunately, such benefits pose a significant challenge to ensuring metadata integrity. Existing works either underutilize NVM’s performance or forgo security guarantees. We present Trio , a userspace file system architecture that resolves this inherent tension. Our key insight is that other state ( i . e ., auxiliary state) in a file system can be regenerated from its “ground truth” state ( i . e ., core state). Trio explicitly defines the data structure of a single core state and shares it as common knowledge among its LibFSes and the trusted entity. A LibFS directly accesses NVM without involving the trusted entity and can be customized with its private auxiliary state. The trusted entity enforces metadata integrity by verifying the core state of a file when its write access is transferred from one LibFS to another. We design a generic POSIX-like file system called ArckFS and two customized file systems based on Trio . Our evaluation shows that ArckFS outperforms existing NVM file systems by 3.1 × to 17 × on LevelDB while the customized file systems further outperform ArckFS by 1.3 ×.