A Formally Certified Crash-proof File System


FSCQ is the first file system with a machine-checkable proof (using the Coq proof assistant) that its implementation meets its specification and whose specification includes crashes. FSCQ provably avoids bugs that have plagued previous file systems, such as performing disk writes without sufficient barriers or forgetting to zero out directory blocks. If a crash happens at an inopportune time, these bugs can lead to data loss. FSCQ's theorems prove that, under any sequence of crashes followed by reboots, FSCQ will recover the file system correctly without losing data.



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