* mount: renew POSIX lock leases via keepalive
The mount tracks the inode keys it holds locks on and a background loop
renews its session lease (KEEP_ALIVE) with each key's owner filer every
5s, within the filer's 15s TTL. A live mount is never reaped; a dead one
stops renewing and owners reclaim its locks. Tracking is a superset:
holds are added on grant and dropped only on owner release, so a still
held lock is never under-renewed.
* mount,filer: re-assert held POSIX locks via keepalive
The owner filer holds POSIX advisory locks as in-memory soft state, so a key's
owner change (ring rebalance) or an owner restart lost or stranded them: the new
or restarted owner was blind to existing holders and would double-grant.
Make the keepalive carry the mount's held lock ranges per key. The mount mirrors
its own granted locks (posixOwn), and each tick re-asserts them to the key's
current owner, which rebuilds that session's locks from the assertion — self
-healing after a takeover or restart. The owner arbitrates re-asserted locks
against other sessions so it never double-grants; a lock that lost a migration
race is reported, not forced. A bare keepalive (no ranges) still just renews.
* filer: POSIX advisory lock set primitive (phase 1)
Pure per-inode conflict/coalesce/range-split logic for fcntl byte-range
and flock whole-file locks, extracted from the mount's PosixLockTable
without its wait queue or inode-map concurrency. Owner identity is
(Sid, Owner) so the same FUSE owner on different mounts never aliases,
and ReleaseSession reaps a dead mount's locks. The owner filer will hold
one Set per inode under the per-path lock; no concurrency control here.
* test: tolerate transient FUSE invisibility in ConcurrentReadWrite
A concurrent truncating overwrite leaves a short-lived dentry/cache window
where the file is momentarily ENOENT to another opener. Retry the reads and
writes a few times before failing, as ConcurrentDirectoryOperations does.
Chris Lu