test: fix bind mount test to work without /dev/shm mounted - #139
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Replace the two /proc/mounts-based bind mount assertions with stat-based device number comparisons. The old tests parsed /proc/mounts entries with sed, which is fragile: /proc/mounts does not distinguish bind mounts from their source mount. The new tests use stat -c %d to compare device numbers: - bind mount: verify /dev/shm and /mnt share the same device - tmpfs mount: verify /dev/shm and /mnt have different devices This works regardless of whether /dev/shm is a separate tmpfs mountpoint or just a subdirectory of /dev.
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Snaipe
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Summary
/proc/mounts-based bind mount assertions with a singlestat -c %ddevice number comparison/proc/mountsentries with sed —/proc/mountsdoes not distinguish bind mounts from their source, making the comparison unreliablestat, which works regardless of whether/dev/shmis a separate tmpfs mountpoint or just a subdirectory of/dev/dev/shmis not mounted as its own filesystemInvestigation
The old test failed in barney because
/dev/shmis not a separate mount — it's a subdirectory of the/devtmpfs. We investigated two approaches:mountinfo(device ID column 3): works when/dev/shmis a mountpoint, but fails when it's a subdirectory because it has no entry in mountinfostat -c %d(device number): works in both cases — stat reports the device of the filesystem the path lives onTested in both GitHub CI (Docker,
/dev/shm= separate tmpfs) and barney (no/dev/shmmount).Supersedes #137 (reverted in #138). Suggested by @Snaipe.
Test plan
mount -t tmpfs tmpfs /dev/shm