Hi! I am Arvind Raghavan, an undergraduate student at the Unversity of Texas at Austin, working with Prof. Vijay Chidambaram. I've been working on the Crashmonkey [1] project, which is a test harness for file system crash consistency checks. Specifically, we've been working on making a fuzzer to find new bugs, and we discovered some weird behavior. Given the following workload: mkdir A mkdir B mkdir A/C creat B/foo sync (1) link B/foo A/C/foo fsync A (2) <crash> Running on Linux 5.5.2, upon recovering the filesystem, the hard linked file A/C/foo is not present. However, if we replace (1) with "fsync B/foo", then upon recovery the link persists. This behavior seems strange, as intuitively it seems that sync should have at least as strong effect as fsync. In addition, it seems that Chris Mason's definition of fsync guarantees here [2] might require this workload to pass. It is important to note that even if we skip the final fsync (2), the result is the same. Thus, the behavior is coming only from the syncing operation at line (1). However, we were also curious to know whether an fsync of the directory A here (2) should persist the file A/C/foo. Chris mentions [2] that an fsync of a directory means that "all the files/subdirs will exist". Should this apply to files created in subdirectories? Thanks! Arvind [1] https://www.github.com/utsaslab/crashmonkey [2] https://www.spinics.net/lists/linux-btrfs/msg77330.html
