fix: gate read/write fd-cache fast paths on is_stale() (issue #30)#35
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The fd-cache fast paths served a cached descriptor without consulting staleness, while every other callback returns ESTALE on is_stale(). A foreign commit (epoch arm) or abort (is_branch_valid arm) could thus leave a held-open fd reading/writing a replaced or deleted backing file. Call is_stale() at the top of both fast paths so they ESTALE consistently with the rest of the filesystem. This still skips the resolve()/File::open() the cache exists to avoid. Signed-off-by: Cong Wang <cwang@multikernel.io>
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Summary
is_stale()— the only 2 of 20 callbacks that didn't. A commit or abort from another mount could leave a held-open fd reading or writing a replaced/deleted backing file (issue High: stale/epoch protection is bypassed by file descriptor caches #30).is_stale()at the top of both fast paths so they returnESTALEconsistently with the rest of the filesystem, while still skipping theresolve()/File::open()the cache exists to avoid.is_stale()covers both failure modes: a foreign commit (epoch arm) and a foreign abort (branch-removal arm — abort signals throughis_branch_valid(), not the epoch, so no epoch bump was needed).Tests
fs::testsunit tests provingis_stale()is true after a foreign commit and after a foreign abort, and false when in sync.TTL=0,getattr/lookupalreadyESTALEbeforeread()is reached, so the read fast-path window is masked in normal operation. Verified the held-open-fd scenario returnsESTALEon both pre- and post-fix binaries, confirming the mask. This change is therefore defense-in-depth — it removes the lone inconsistency and stays correct if a read ever reaches the daemon without a precedinggetattr(read-ahead, future caching/TTL changes).Test Plan
cargo test --lib— 14 pass🤖 Generated with Claude Code