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Abstract:

In a UNIX file system, metadata for the file objects must be updated in a specific order such that the file system can be recovered after a crash. Metadata update usually involves several atomic actions and thus a crash can happen in between these atomic actions before the whole update is completed. This paper investigates formally specifying a UNIX file system and these metadata updating operations using the software specification language Alcoa [2]. Alcoa comes with a tool which along with helping to debug the specification, proved useful in investigating various invariants of the system. 2 Introduction to Alcoa Alcoa is a predicate logic based language with quantifiers and relations. It comes with a tool which finds instances of the specification written. This helps in finding contradictions in the specification because then the tool will notify the user that no instance can be found

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