Abstract
File systems not only have to be functionally correct, they also have to be crash-safe: a power cut while an operation is running must be guaranteed to lead to a consistent state after restart that loses as little information as possible. Specification and verification of crash-safety is particularly difficult for non-redundant write-back caches. This paper defines a novel crash-safety criterion that facilitates specification and verification of order-preserving caches. A power cut is basically observationally equivalent to a retraction of a few of the last executed operations. The approach is modular: It gives simple proof obligations for each individual component and for each refinement in the development. The theory is supported by our interactive theorem prover KIV and proof obligations for crash-safety have been verified for the Flashix flash file system.
Supported by the Deutsche Forschungsgemeinschaft (DFG), “Verifikation von Flash-Dateisystemen” (grants RE828/13-1 and RE828/13-2).
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Notes
- 1.
The classification of Bornholt et al. [3] defines sequential crash consistency.
- 2.
- 3.
Note that the POSIX specification [1] explicitly permits such short writes to surface at the system interface.
- 4.
In the actual models recovery is a separate operation that runs directly after a crash and tries to restore the state. To keep the presentation brief, we combine the crash and recovery into one transition here.
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Pfähler, J., Ernst, G., Bodenmüller, S., Schellhorn, G., Reif, W. (2017). Modular Verification of Order-Preserving Write-Back Caches. In: Polikarpova, N., Schneider, S. (eds) Integrated Formal Methods. IFM 2017. Lecture Notes in Computer Science(), vol 10510. Springer, Cham. https://doi.org/10.1007/978-3-319-66845-1_25
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