The main contribution of this paper is GoJournal, a verified, concurrent journaling system that provides atomicity for storage applications, together with Perennial 2.0, a framework for formally specifying and verifying concurrent crash-safe systems. GoJournal’s goal is to bring the advantages of journaling for code to specs and proofs. Perennial 2.0 makes this possible by introducing several techniques to formalize GoJournal’s specification and to manage the complexity in the proof of GoJournal’s implementation. Lifting predicates and crash framing make the specification easy to use for developers, and logically atomic crash specifications allow for modular reasoning in GoJournal, making the proof tractable despite complex concurrency and crash interleavings.
GoJournal is implemented in Go, and Perennial is implemented in the Coq proof assistant. While verifying GoJournal, we found one serious concurrency bug, even though GoJournal has many unit tests. We built a functional NFSv3 server, called GoNFS, to use GoJournal. Performance experiments show that GoNFS provides similar performance (e.g., at least 90% throughput across several benchmarks on an NVMe disk) to Linux’s NFS server exporting an ext4 file system, suggesting that GoJournal is a competitive journaling system. We also verified a simple NFS server using GoJournal’s specs, which confirms that they are helpful for application verification: a significant part of the proof doesn’t have to consider concurrency and crashes.
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Argosy: verifying layered storage systems with recovery refinement
Reasoning about storage systems is challenging because these
systems make persistence guarantees even if the system crashes at
any point. To achieve these crash-safety guarantees, storage systems
include recovery procedures to restore the system to a consistent
state after a crash. Moreover, large-scale systems are structured as
multiple stacked layers and can require recovery at multiple layers
of abstraction.
Formal verification can ensure that crash-safety guarantees
hold regardless of when the system crashes. To make verification
tractable, large-scale systems should be verified in a modular fashion,
layer-by-layer in the software stack. Layered recovery makes modularity
challenging because the system can crash in the middle of a high-level
recovery procedure and must start over from the low-level recovery
procedure.
We present Argosy, a framework for machine-checked proofs of storage
systems that supports layered recovery implementations with modular
proofs. The framework is based on combinators for transition
relations that are inspired by Kleene algebra, which provides a
convenient formalism for specifying and reasoning about crashes and
recovery. On top of this framework, we implement Crash Hoare Logic
(CHL), the program logic used by FSCQ. Using the logic, we have
verified an example of layered recovery featuring a write-ahead log on
top of a disk, which itself runs by replicating over two unreliable
disks. The metatheory of the framework, the soundness of the program
logic, and these examples are all verified in the Coq theorem prover.
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- NSF-PAR ID:
- 10115002
- Date Published:
- Journal Name:
- Proceedings of the 40th ACM SIGPLAN Conference on Programming Language Design and Implementation (PLDI ’19)
- Page Range / eLocation ID:
- 1054 to 1068
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1145/3314221.3314585
