Verifying an AI-Assisted Copy-on-Write Filesystem Through Device-Level Write Comparison

The author of a from-scratch copy-on-write filesystem called singlefs faces the challenge of proving its correctness, since its on-disk format is unique and AI-generated code outpaces human review. Because self-describing headers and a reverse index let each block identify its owner and generation, the design can check where data went, but per-block checks are slow and only verify results rather than the write process. To address this, the team boots a QEMU virtual machine with write-back caching and places a write-logging filter in front of each virtual disk to record every write and flush. The program's own recorder and the externally captured device log are compared, with the rule that the program's log must be an exact prefix of the disk's log and only flushes may follow. The author notes that a check which always passes would be worthless, so the comparison gate must also be shown capable of failing.