With -dlm, GetLk/SetLk/SetLkw and the flush/release cleanup paths go to
the inode's owner filer via the PosixLock RPC instead of the local table,
so flock/fcntl are honored across mounts. Advisory locking rides the same
switch as whole-file write coordination — and is therefore off under
writeback cache, which implies single-writer. Keys are the inode identity
(HardLinkId else path); SetLkw is client-side polling with the FUSE cancel
channel (no server wait queue); a per-mount session id namespaces owners;
a local hint avoids a release RPC on every close. Background unlock/release
RPCs are bounded so a stuck filer can't hang close().
Chris Lu
3481f13f54