dht: Add lookup-optimize configuration option for DHT

Currently with commit 4eaaf5 a mixed version cluster would
have issues if lookup-uhashed is set to auto, as older clients
would fail to validate the layouts if newer clients (i.e 3.7 or
upwards) create directories. Also, in a mixed version cluster
rebalance daemon would set commit hash for some subvolumes and
not for the others.

This commit fixes this problem by moving the enabling of the
functionality introduced in the above mentioned commit to a
new dht option. This option also has a op_version of 3_7_1
thereby preventing it from being set in a mixed version
cluster. It brings in the following changes,
- Option can be set only if min version of the cluster is
3.7.1 or more
- Rebalance and mkdir update the layout with the commit hashes
only if this option is set, hence ensuring rebalance works in a
mixed version cluster, and also directories created by newer
clients do not cause layout errors when read by older clients
- This option also supersedes lookup-unhased, to enable the
optimization for lookups more deterministic and not conflict
with lookup-unhashed settings.

Option added is cluster.lookup-optimize, which is a boolean.

Usage: # gluster volume set VOLNAME cluster.lookup-optimize on

Change-Id: Ifd1d4ce3f6438fcbcd60ffbfdbfb647355ea1ae0
BUG:  1225940
Signed-off-by: Shyam <srangana@redhat.com>
Reviewed-on: http://review.gluster.org/10976
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: N Balachandran <nbalacha@redhat.com>
Reviewed-by: Raghavendra G <rgowdapp@redhat.com>
Tested-by: Raghavendra G <rgowdapp@redhat.com>

1 files changed, 4 insertions, 2 deletions

diff --git a/xlators/cluster/dht/src/dht-rebalance.c b/xlators/cluster/dht/src/dht-rebalance.c
index 3ab73d4ef5b..89cc3a82f0b 100644
--- a/xlators/cluster/dht/src/dht-rebalance.c
+++ b/xlators/cluster/dht/src/dht-rebalance.c
@@ -2362,8 +2362,10 @@ gf_defrag_settle_hash (xlator_t *this, gf_defrag_info_t *defrag,
                 return -1;
         }
 
-        if (conf->local_subvols_cnt == 0) {
-                /* Commit hash updates are only done on local subvolumes
+        if (conf->local_subvols_cnt == 0 || !conf->lookup_optimize) {
+                /* Commit hash updates are only done on local subvolumes and
+                 * only when lookup optmization is needed (for older client
+                 * support)
                  */
                 return 0;
         }