Merge PR #16779 into master

Merge PR #16779 into master

* refs/pull/16779/head:
	mds: cleanup MDCache::open_snaprealms()
	mds: make sure snaptable version > 0
	mds: don't consider CEPH_INO_LOST_AND_FOUND as base inode
	mds: replace MAX() with std::max()
	tools/cephfs: make cephfs-data-scan create snaprealm for base inodes
	qa/cephfs: don't run TestSnapshots.test_kill_mdstable on kclient
	qa/cephfs: adjust check of 'cephfs-table-tool all show snap' output
	mds: don't warn unconnected snaplrealms in cluster log
	mds: update CInode/CDentry's first according to global snapshot seq
	qa/cephfs: add tests for snapclient cache
	qa/cephfs: add tests for snaptable transaction
	mds: add asok command that dumps cached snap infos
	qa/cephfs: add tests for multimds snapshot
	client: don't mark snap directory complete when its dirstat is empty
	qa/workunits/snaps: add snaprealm split test
	mds: make sure mds has uptodate mdsmap before checking 'allows_snaps'
	client: fix incorrect snaprealm when adding caps
	qa/workunits/snaps: add hardlink snapshot test
	mds: add incompat feature and bump protocol for snapshot changes
	mds: detach inode with single hardlink from global snaprealm
	mds: record hardlink snaps in inode's snaprealm
	mds: attach inode with multiple hardlinks to dummy global snaprealm
	mds: cleanup rename code
	mds: ensure xlocker has uptodate lock state
	mds: simplify SnapRealm::build_snap_{set,trace}
	mds: record global last_created/last_destroyed in snaptable
	mds: pop projected snaprealm before inode's parent changes
	mds: keep isnap lock in sync state
	mds: handle mksnap vs resolve_snapname race
	mds: cleanup snaprealm past parents open check
	mds: rollback snaprealms when rolling back slave request
	mds: send updated snaprealms along with slave requests
	mds: explict notification for snap update
	mds: send snap related messages centrally during mds recovery
	mds: synchronize snaptable caches when mds recovers
	mds: introduce MDCache::maybe_finish_slave_resolve()
	mds: notify all mds about prepared snaptable update
	mds: record snaps in old snaprealm when moving inode into new snaprealm
	mds: cache snaptable in snapclient
	mds: recover snaptable client when mds enters resolve state

Reviewed-by: Patrick Donnelly <pdonnell@redhat.com>