* Add FUSE integration tests for POSIX file locking
Test flock() and fcntl() advisory locks over the FUSE mount:
- Exclusive and shared flock with conflict detection
- flock upgrade (shared to exclusive) and release on close
- fcntl F_SETLK write lock conflicts and shared read locks
- fcntl F_GETLK conflict reporting on overlapping byte ranges
- Non-overlapping byte-range locks held independently
- F_SETLKW blocking until conflicting lock is released
- Lock release on file descriptor close
- Concurrent lock contention with multiple workers
* Fix review feedback in POSIX lock integration tests
- Assert specific EAGAIN error on fcntl lock conflicts instead of generic Error
- Use O_APPEND in concurrent contention test so workers append rather than overwrite
- Verify exact line count (numWorkers * writesPerWorker) after concurrent test
- Check unlock error in F_SETLKW blocking test goroutine
* Refactor fcntl tests to use subprocesses for inter-process semantics
POSIX fcntl locks use the process's files_struct as lock owner, so all
fds in the same process share the same owner and never conflict. This
caused the fcntl tests to silently pass without exercising lock conflicts.
Changes:
- Add TestFcntlLockHelper subprocess entry point with hold/try/getlk actions
- Add lockHolder with channel-based coordination (no scanner race)
- Rewrite all fcntl tests to run contenders in separate subprocesses
- Fix F_UNLCK int16 cast in GetLk assertion for type-safe comparison
- Fix concurrent test: use non-blocking flock with retry to avoid
exhausting go-fuse server reader goroutines (blocking FUSE SETLKW
can starve unlock request processing, causing deadlock)
flock tests remain same-process since flock uses per-struct-file owners.
* Fix misleading comment and error handling in lock test subprocess
- Fix comment: tryLockInSubprocess tests a subprocess, not the test process
- Distinguish EAGAIN/EACCES from unexpected errors in subprocess try mode
so real failures aren't silently masked as lock conflicts
* Fix CI race in FcntlReleaseOnClose and increase flock retry budget
- FcntlReleaseOnClose: retry lock acquisition after subprocess exits
since the FUSE server may not process Release immediately
- ConcurrentLockContention: increase retry limit from 500 to 3000
(5s → 30s budget) to handle CI load
* separating flock and fcntl in the in-memory lock table and cleaning them up through the right release path: PID for POSIX locks, lock owner for flock
* ReleasePosixOwner
* weed/mount: flush before releasing posix close owner
* weed/mount: keep woken lock waiters from losing inode state
* test/fuse: make blocking fcntl helper state explicit
* test/fuse: assert flock contention never overlaps
* test/fuse: stabilize concurrent lock contention check
* test/fuse: make concurrent contention writes deterministic
* weed/mount: retry synchronous metadata flushes
Chris Lu