Towards verified file systems

The formal methods community aims to provide a stack of verified software to users. Verified software is proven to be reliable. The rigour of mathematical logic makes it possible to prove that software meets the designer expectations. File system software enables organized data storage, and in most software systems this functionality is critical. This work provides the basis on which to build a formally verified file system. Firstly, a formal and mechanized specification of POSIX (and Linux, Mac OS X, FreeBSD) is defined and used as an oracle to test if modern implementations behave correctly; then it is shown how to extend this specification with timestamps and the challenges this extension entails; finally the definition of an immutable B-tree and the mathematical verification of its operations are mechanically formalized. operations are mechanically formalized. These achievements bring the development of a verified file system within reach.