Fix "failed to create hardlink" error due to multiple mounts on the same device (Cherry-pick of #19894) - #19914
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…ame device (pantsbuild#19894) As described in pantsbuild#18757, the "check that source and dest are on same device" strategy that was introduced in pantsbuild#18153 to decide whether we could hardlink when materializing files was not robust when faced with the same device being mounted in multiple locations. This change moves to a "create a canary" strategy for deciding when hardlinking between two destinations is legal. Hardlinks are canaried and memoized on a per-destination-root basis, so this strategy might actually be slightly cheaper than the previous one. Fixes pantsbuild#18757.
thejcannon
approved these changes
Sep 22, 2023
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As described in #18757, the "check that source and dest are on same device" strategy that was introduced in #18153 to decide whether we could hardlink when materializing files was not robust when faced with the same device being mounted in multiple locations.
This change moves to a "create a canary" strategy for deciding when hardlinking between two destinations is legal. Hardlinks are canaried and memoized on a per-destination-root basis, so this strategy might actually be slightly cheaper than the previous one.
Fixes #18757.