dht: make lookup-unhashed=auto do something actually useful

The key concept here is to determine whether a directory is "clean" by
comparing its last-known-good topology to the current one for the
volume.  These are stored as "commit hashes" on the directory and the
volume root respectively.  The volume's commit hash changes whenever a
brick is added or removed, and a fix-layout is done.  A directory's
commit hash changes only when a full rebalance (not just fix-layout)
is done on it.  If all bricks are present and have a directory
commit hash that matches the volume commit hash, then we can assume
that every file is in its "proper" place. Therefore, if we look for
a file in that proper place and don't find it, we can assume it's not
on any other subvolume and *safely* skip the global (broadcast to all)
lookup.

Change-Id: Id6ce4593ba1f7daffa74cfab591cb45960629ae3
BUG: 1220064
Reviewed-on-master: http://review.gluster.org/#/c/7702/
Signed-off-by: Jeff Darcy <jdarcy@redhat.com>
Signed-off-by: Shyam <srangana@redhat.com>
Reviewed-on: http://review.gluster.org/10729
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/xlators/mgmt/glusterd/src/glusterd.h b/xlators/mgmt/glusterd/src/glusterd.h
index 3f2ff45f1a1..5341192e84a 100644
--- a/xlators/mgmt/glusterd/src/glusterd.h
+++ b/xlators/mgmt/glusterd/src/glusterd.h
@@ -286,6 +286,7 @@ struct glusterd_rebalance_ {
         glusterd_op_t            op;
         dict_t                  *dict; /* Dict to store misc information
                                         * like list of bricks being removed */
+        uint32_t                 commit_hash;
 };
 
 typedef struct glusterd_rebalance_ glusterd_rebalance_t;