When developing file systems, caching is a common technique to achieve a performant implementation. Integrating write-back caches is not primarily a problem for functional correctness, but is critical for proving crash safety. Since parts of written data are stored in volatile memory, special care has to be taken when integrating write-back caches to guarantee that a power cut during a running operation leads to a consistent state. This article shows how non-order-preserving caches can be added to a virtual file system switch (VFS) and gives a novel crash-safety criterion matching the characteristics of such caches. Broken down to individual files, a power cut can be explained by constructing an alternative run, where all writes since the last synchronization of that file have written a prefix. VFS caches have been integrated modularly into Flashix, a verified file system for flash memory, and both functional correctness and crash-safety of this extension have been verified with the interactive theorem prover KIV.

在开发文件系统时，缓存是实现高性能实现的常用技术。集成回写缓存主要不是功能正确性的问题，而是证明碰撞安全性的关键。由于部分写入数据存储在易失性存储器中，因此在集成回写式缓存时必须特别小心，以确保在运行操作期间断电会导致状态一致。本文展示了如何将非顺序保持缓存添加到虚拟文件系统交换机 (VFS) 中，并给出了一种与此类缓存特性相匹配的新崩溃安全标准。分解为单个文件，可以通过构建替代运行来解释断电，其中自上次同步该文件以来的所有写入都写入了前缀。