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>

15 files changed, 781 insertions, 91 deletions

diff --git a/libglusterfs/src/glusterfs.h b/libglusterfs/src/glusterfs.h
index b26580f1ec9..3843bb76ed9 100644
--- a/libglusterfs/src/glusterfs.h
+++ b/libglusterfs/src/glusterfs.h
@@ -227,6 +227,7 @@
                                                        (iabuf)->ia_type) & ~S_IFMT)\
                                      == DHT_LINKFILE_MODE)
 #define DHT_LINKFILE_STR "linkto"
+#define DHT_COMMITHASH_STR "commithash"
 
 #define DHT_SKIP_NON_LINKTO_UNLINK "unlink-only-if-dht-linkto-file"
 #define DHT_SKIP_OPEN_FD_UNLINK "dont-unlink-for-open-fd"
diff --git a/tests/bugs/distribute/bug-907072.t b/tests/bugs/distribute/bug-907072.t
index 1e8bd280f32..a4d98831380 100755
--- a/tests/bugs/distribute/bug-907072.t
+++ b/tests/bugs/distribute/bug-907072.t
@@ -17,10 +17,11 @@ TEST glusterfs -s $H0 --volfile-id $V0 $M0;
 
 TEST mkdir $M0/test;
 
-OLD_LAYOUT0=`get_layout $B0/${V0}0/test`;
-OLD_LAYOUT1=`get_layout $B0/${V0}1/test`;
-OLD_LAYOUT2=`get_layout $B0/${V0}2/test`;
-OLD_LAYOUT3=`get_layout $B0/${V0}3/test`;
+# Extract the layout sans the commit hash
+OLD_LAYOUT0=`get_layout $B0/${V0}0/test | cut -c11-34`;
+OLD_LAYOUT1=`get_layout $B0/${V0}1/test | cut -c11-34`;
+OLD_LAYOUT2=`get_layout $B0/${V0}2/test | cut -c11-34`;
+OLD_LAYOUT3=`get_layout $B0/${V0}3/test | cut -c11-34`;
 
 TEST killall glusterfsd;
 
@@ -36,10 +37,11 @@ EXPECT_WITHIN $UMOUNT_TIMEOUT "Y" force_umount $M0
 TEST glusterfs -s $H0 --volfile-id $V0 $M0;
 TEST stat $M0/test;
 
-NEW_LAYOUT0=`get_layout $B0/${V0}0/test`;
-NEW_LAYOUT1=`get_layout $B0/${V0}1/test`;
-NEW_LAYOUT2=`get_layout $B0/${V0}2/test`;
-NEW_LAYOUT3=`get_layout $B0/${V0}3/test`;
+# Extract the layout sans the commit hash
+NEW_LAYOUT0=`get_layout $B0/${V0}0/test | cut -c11-34`;
+NEW_LAYOUT1=`get_layout $B0/${V0}1/test | cut -c11-34`;
+NEW_LAYOUT2=`get_layout $B0/${V0}2/test | cut -c11-34`;
+NEW_LAYOUT3=`get_layout $B0/${V0}3/test | cut -c11-34`;
 
 EXPECT $OLD_LAYOUT0 echo $NEW_LAYOUT0;
 EXPECT $OLD_LAYOUT1 echo $NEW_LAYOUT1;
diff --git a/tests/bugs/distribute/bug-921408.t b/tests/bugs/distribute/bug-921408.t
index b1887f8ae22..559114bb85a 100755
--- a/tests/bugs/distribute/bug-921408.t
+++ b/tests/bugs/distribute/bug-921408.t
@@ -37,7 +37,7 @@ addbr_rebal_till_layout_change()
                 then
                         break
                 fi
-                NEW_LAYOUT=`get_layout $B0/${V0}0`
+                NEW_LAYOUT=`get_layout $B0/${V0}0 | cut -c11-34`
                 if [ $OLD_LAYOUT == $NEW_LAYOUT ]
                 then
                         i=`expr $i + 1`;
@@ -64,7 +64,7 @@ TEST touch $M0/test/test
 fd=`fd_available`
 TEST fd_open $fd "rw" $M0/test/test
 
-OLD_LAYOUT=`get_layout $B0/${V0}0`
+OLD_LAYOUT=`get_layout $B0/${V0}0 | cut -c11-34`
 
 addbr_rebal_till_layout_change 1
 
diff --git a/tests/bugs/glusterd/bug-1070734.t b/tests/bugs/glusterd/bug-1070734.t
index b5a53c24cab..5db60e0cfe6 100755
--- a/tests/bugs/glusterd/bug-1070734.t
+++ b/tests/bugs/glusterd/bug-1070734.t
@@ -65,8 +65,11 @@ TEST [ -f ${OTHERBRICK}/DIR/file ]
 
 #Check the DIR on HASHED should have got zeroed layout and the \
 #OTHERBRICK should have got full layout
-EXPECT "0x00000001000000000000000000000000" dht_get_layout $HASHED/DIR ;
-EXPECT "0x000000010000000000000000ffffffff" dht_get_layout $OTHERBRICK/DIR;
+shorter_layout () {
+	dht_get_layout $1 | cut -c 19-
+}
+EXPECT "0000000000000000" shorter_layout $HASHED/DIR ;
+EXPECT "00000000ffffffff" shorter_layout $OTHERBRICK/DIR;
 
 ## Before killing daemon to avoid deadlocks
 EXPECT_WITHIN $UMOUNT_TIMEOUT "Y" umount_nfs $N0
diff --git a/tests/features/unhashed-auto.t b/tests/features/unhashed-auto.t
new file mode 100755
index 00000000000..97663c20e10
--- /dev/null
+++ b/tests/features/unhashed-auto.t
@@ -0,0 +1,99 @@
+#!/bin/bash
+
+. $(dirname $0)/../include.rc
+. $(dirname $0)/../volume.rc
+. $(dirname $0)/../dht.rc
+
+NFILES=100
+
+touch_files () {
+	for i in $(seq 1 $NFILES); do
+		touch $(printf $M0/dir/file%02d $i)
+	done
+}
+
+count_files () {
+	found=0
+	for i in $(seq 1 $NFILES); do
+		if [ -f $(printf $M0/dir/file%02d $i) ]; then
+			found=$((found+1))
+		fi
+	done
+	echo "found $found files" > /dev/tty
+	echo $found
+}
+
+wait_for_rebalance () {
+	while true; do
+		tmp=$(rebalance_completed)
+		if [ $tmp -eq 1 ]; then
+			sleep 1
+		else
+			break
+		fi
+	done
+}
+
+get_xattr () {
+	cmd="getfattr --absolute-names --only-values -n trusted.glusterfs.dht"
+	$cmd $1 | od -tx1 -An | tr -d ' '
+}
+
+cleanup
+
+TEST glusterd
+TEST pidof glusterd
+TEST $CLI volume info
+
+TEST $CLI volume create $V0 $H0:$B0/${V0}{1,2}
+EXPECT "$V0" volinfo_field $V0 'Volume Name'
+EXPECT 'Created' volinfo_field $V0 'Status'
+
+TEST $CLI volume set $V0 cluster.lookup-unhashed auto
+
+TEST $CLI volume start $V0
+EXPECT 'Started' volinfo_field $V0 'Status'
+
+# Create some files for later tests.
+TEST $GFS -s $H0 --volfile-id $V0 $M0
+TEST mkdir $M0/dir
+TEST touch_files
+TEST umount $M0
+
+# Add a brick and do the fix-layout part of rebalance to update directory layouts
+# (including their directory commit hashes).
+TEST $CLI volume add-brick $V0 $H0:$B0/${V0}3
+EXPECT '3' brick_count $V0
+TEST $CLI volume rebalance $V0 fix-layout start
+TEST wait_for_rebalance
+
+# Now for the sneaky part.  *Undo* the part of rebalance that updated the volume
+# commit hash, forcing a false match between that and the directory commit hashes.
+TEST setfattr -x trusted.glusterfs.dht.commithash $B0/${V0}1
+TEST setfattr -x trusted.glusterfs.dht.commithash $B0/${V0}2
+TEST setfattr -x trusted.glusterfs.dht.commithash $B0/${V0}3
+
+# Mount and check that we do *not* see all of the files.  This indicates that we
+# correctly skipped the broadcast lookup that would have found them.
+TEST $GFS -s $H0 --volfile-id $V0 $M0
+TEST [ $(count_files) -ne 100 ]
+TEST umount $M0
+
+# Do the fix-layout again to generate a new volume commit hash.
+TEST $CLI volume rebalance $V0 fix-layout start
+TEST wait_for_rebalance
+
+# Mount and check that we *do* see all of the files.  This indicates that we saw
+# the mismatch and did the broadcast lookup this time.
+TEST $GFS -s $H0 --volfile-id $V0 $M0
+TEST [ $(count_files) -eq 100 ]
+TEST umount $M0
+
+# Do a *full* rebalance and verify that the directory commit hash changed.
+old_val=$(get_xattr $B0/${V0}1/dir)
+TEST $CLI volume rebalance $V0 start
+TEST wait_for_rebalance
+new_val=$(get_xattr $B0/${V0}1/dir)
+TEST [ ! x"$old_val" = x"$new_val" ]
+
+cleanup
diff --git a/xlators/cluster/dht/src/dht-common.c b/xlators/cluster/dht/src/dht-common.c
index 6c0afdbec90..37e07ad77da 100644
--- a/xlators/cluster/dht/src/dht-common.c
+++ b/xlators/cluster/dht/src/dht-common.c
@@ -210,6 +210,7 @@ dht_discover_complete (xlator_t *this, call_frame_t *discover_frame)
         int              ret = -1;
         dht_layout_t    *layout = NULL;
         dht_conf_t      *conf = NULL;
+        uint32_t         vol_commit_hash = 0;
 
         local = discover_frame->local;
         layout = local->layout;
@@ -279,6 +280,15 @@ dht_discover_complete (xlator_t *this, call_frame_t *discover_frame)
                         dht_layout_set (this, local->inode, layout);
         }
 
+        if (!conf->vch_forced) {
+                ret = dict_get_uint32 (local->xattr,
+                                       conf->commithash_xattr_name,
+                                       &vol_commit_hash);
+                if (ret == 0) {
+                        conf->vol_commit_hash = vol_commit_hash;
+                }
+        }
+
         DHT_STACK_UNWIND (lookup, main_frame, local->op_ret, local->op_errno,
                           local->inode, &local->stbuf, local->xattr,
                           &local->postparent);
@@ -459,6 +469,12 @@ dht_discover (call_frame_t *frame, xlator_t *this, loc_t *loc)
                         "%s: Failed to set dictionary value:key = %s",
                         loc->path, conf->link_xattr_name);
 
+        if (__is_root_gfid(local->loc.gfid)) {
+                ret = dict_set_uint32 (local->xattr_req,
+                                       conf->commithash_xattr_name,
+                                       sizeof(uint32_t));
+        }
+
         call_cnt        = conf->subvolume_cnt;
         local->call_cnt = call_cnt;
 
@@ -655,6 +671,7 @@ dht_revalidate_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
         call_frame_t *copy          = NULL;
         dht_local_t  *copy_local    = NULL;
         char gfid[GF_UUID_BUF_SIZE] = {0};
+        uint32_t      vol_commit_hash = 0;
 
         GF_VALIDATE_OR_GOTO ("dht", frame, err);
         GF_VALIDATE_OR_GOTO ("dht", this, err);
@@ -667,6 +684,14 @@ dht_revalidate_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
         if (!conf)
                 goto out;
 
+        if (!conf->vch_forced) {
+                ret = dict_get_uint32 (xattr, conf->commithash_xattr_name,
+                                       &vol_commit_hash);
+                if (ret == 0) {
+                        conf->vol_commit_hash = vol_commit_hash;
+                }
+        }
+
         gf_uuid_unparse (local->loc.gfid, gfid);
 
         LOCK (&frame->lock);
@@ -1852,6 +1877,7 @@ dht_lookup_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
         call_frame_t *prev          = NULL;
         int           ret           = 0;
         dht_layout_t *parent_layout = NULL;
+        uint32_t      vol_commit_hash = 0;
 
         GF_VALIDATE_OR_GOTO ("dht", frame, err);
         GF_VALIDATE_OR_GOTO ("dht", this, out);
@@ -1875,6 +1901,14 @@ dht_lookup_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                       "fresh_lookup returned for %s with op_ret %d and "
                       "op_errno %d", loc->path, op_ret, op_errno);
 
+        if (!conf->vch_forced) {
+                ret = dict_get_uint32 (xattr, conf->commithash_xattr_name,
+                                       &vol_commit_hash);
+                if (ret == 0) {
+                        conf->vol_commit_hash = vol_commit_hash;
+                }
+        }
+
         if (ENTRY_MISSING (op_ret, op_errno)) {
                 gf_msg_debug (this->name, 0,
                               "Entry %s missing on subvol %s",
@@ -1891,7 +1925,10 @@ dht_lookup_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                                                         &parent_layout);
                         if (ret || !parent_layout)
                                 goto out;
-                        if (parent_layout->search_unhashed) {
+                        if (parent_layout->commit_hash
+                                  != conf->vol_commit_hash) {
+                                gf_log (this->name, GF_LOG_DEBUG,
+                                        "hashes don't match, do global lookup");
                                 local->op_errno = ENOENT;
                                 dht_lookup_everywhere (frame, this, loc);
                                 return 0;
@@ -2078,6 +2115,12 @@ dht_lookup (call_frame_t *frame, xlator_t *this,
                 return 0;
         }
 
+        if (__is_root_gfid(loc->gfid)) {
+                ret = dict_set_uint32 (local->xattr_req,
+                                       conf->commithash_xattr_name,
+                                       sizeof(uint32_t));
+        }
+
         if (!hashed_subvol)
                 hashed_subvol = dht_subvol_get_hashed (this, loc);
         local->hashed_subvol = hashed_subvol;
@@ -3238,8 +3281,9 @@ dht_fsetxattr (call_frame_t *frame, xlator_t *this,
 
         conf = this->private;
 
-        GF_IF_INTERNAL_XATTR_GOTO (conf->wild_xattr_name, xattr,
-                                   op_errno, err);
+        if (!conf->defrag)
+                GF_IF_INTERNAL_XATTR_GOTO (conf->wild_xattr_name, xattr,
+                                           op_errno, err);
 
         local = dht_local_init (frame, NULL, fd, GF_FOP_FSETXATTR);
         if (!local) {
@@ -3338,6 +3382,7 @@ dht_setxattr (call_frame_t *frame, xlator_t *this,
         char          value[4096] = {0,};
         gf_dht_migrate_data_type_t forced_rebalance = GF_DHT_MIGRATE_DATA;
         int           call_cnt = 0;
+        uint32_t      new_hash = 0;
 
         VALIDATE_OR_GOTO (frame, err);
         VALIDATE_OR_GOTO (this, err);
@@ -3350,8 +3395,10 @@ dht_setxattr (call_frame_t *frame, xlator_t *this,
         methods = conf->methods;
         GF_VALIDATE_OR_GOTO (this->name, conf->methods, err);
 
-        GF_IF_INTERNAL_XATTR_GOTO (conf->wild_xattr_name, xattr,
-                                   op_errno, err);
+        /* Rebalance daemon is allowed to set internal keys */
+        if (!conf->defrag)
+                GF_IF_INTERNAL_XATTR_GOTO (conf->wild_xattr_name, xattr,
+                                           op_errno, err);
 
         local = dht_local_init (frame, loc, NULL, GF_FOP_SETXATTR);
         if (!local) {
@@ -3489,6 +3536,22 @@ dht_setxattr (call_frame_t *frame, xlator_t *this,
                 gf_log (this->name, GF_LOG_INFO,
                         "fixing the layout of %s", loc->path);
 
+                ret = dict_get_uint32(xattr, "new-commit-hash", &new_hash);
+                if (ret == 0) {
+                        gf_log (this->name, GF_LOG_DEBUG,
+                                "updating commit hash for %s from %u to %u",
+                                uuid_utoa(loc->gfid),
+                                layout->commit_hash, new_hash);
+                        layout->commit_hash = new_hash;
+
+                        ret = dht_update_commit_hash_for_layout (frame);
+                        if (ret) {
+                                op_errno = ENOTCONN;
+                                goto err;
+                        }
+                        return ret;
+                }
+
                 ret = dht_fix_directory_layout (frame, dht_common_setxattr_cbk,
                                                 layout);
                 if (ret) {
@@ -5377,6 +5440,8 @@ dht_mkdir (call_frame_t *frame, xlator_t *this,
                 goto err;
         }
 
+        local->layout->commit_hash = conf->vol_commit_hash;
+
         STACK_WIND (frame, dht_mkdir_hashed_cbk,
                     hashed_subvol,
                     hashed_subvol->fops->mkdir,
@@ -6570,10 +6635,12 @@ dht_log_new_layout_for_dir_selfheal (xlator_t *this, loc_t *loc,
 
                 ret  = snprintf (string, max_string_len,
                                  "[Subvol_name: %s, Err: %d , Start: "
-                                 "%"PRIu32 " , Stop: %"PRIu32 " ], ",
+                                 "%"PRIu32 " , Stop: %"PRIu32 " , Hash: %"
+                                 PRIu32 " ], ",
                                  layout->list[i].xlator->name,
                                  layout->list[i].err, layout->list[i].start,
-                                 layout->list[i].stop);
+                                 layout->list[i].stop,
+                                 layout->list[i].commit_hash);
 
                 if (ret < 0)
                         return;
@@ -6602,10 +6669,12 @@ dht_log_new_layout_for_dir_selfheal (xlator_t *this, loc_t *loc,
 
                 ret  =  snprintf (output_string + off, len - off,
                                   "[Subvol_name: %s, Err: %d , Start: "
-                                  "%"PRIu32 " , Stop: %"PRIu32 " ], ",
+                                  "%"PRIu32 " , Stop: %"PRIu32 " , Hash: %"
+                                  PRIu32  " ], ",
                                   layout->list[i].xlator->name,
                                   layout->list[i].err, layout->list[i].start,
-                                  layout->list[i].stop);
+                                  layout->list[i].stop,
+                                  layout->list[i].commit_hash);
 
                 if (ret < 0)
                         goto err;
diff --git a/xlators/cluster/dht/src/dht-common.h b/xlators/cluster/dht/src/dht-common.h
index 9a6ed1a889a..45b6cc9e80b 100644
--- a/xlators/cluster/dht/src/dht-common.h
+++ b/xlators/cluster/dht/src/dht-common.h
@@ -31,6 +31,7 @@
 #define DHT_PATHINFO_HEADER         "DISTRIBUTE:"
 #define DHT_FILE_MIGRATE_DOMAIN     "dht.file.migrate"
 #define DHT_LAYOUT_HEAL_DOMAIN      "dht.layout.heal"
+#define DHT_LAYOUT_HASH_INVALID     1
 
 #include <fnmatch.h>
 
@@ -48,6 +49,20 @@ struct dht_layout {
                                            special key */
         int                cnt;
         int                preset;
+        /*
+         * The last *configuration* state for which this directory was known
+         * to be in balance.  The corresponding vol_commit_hash changes
+         * whenever bricks are added or removed.  This value changes when a
+         * (full) rebalance is complete.  If they match, it's safe to assume
+         * that every file is where it should be and there's no need to do
+         * lookups for files elsewhere.  If they don't, then we have to do a
+         * global lookup to be sure.
+         */
+        uint32_t           commit_hash;
+        /*
+         * The *runtime* state of the volume, changes when connections to
+         * bricks are made or lost.
+         */
         int                gen;
         int                type;
         int                ref; /* use with dht_conf_t->layout_lock */
@@ -59,6 +74,7 @@ struct dht_layout {
                                   */
                 uint32_t   start;
                 uint32_t   stop;
+                uint32_t   commit_hash;
                 xlator_t  *xlator;
         } list[];
 };
@@ -325,6 +341,7 @@ struct gf_defrag_info_ {
         uuid_t                       node_uuid;
         struct timeval               start_time;
         gf_boolean_t                 stats;
+        uint32_t                     new_commit_hash;
         gf_defrag_pattern_list_t    *defrag_pattern;
         int                          tier_promote_frequency;
         int                          tier_demote_frequency;
@@ -422,6 +439,7 @@ struct dht_conf {
         /* Support variable xattr names. */
         char            *xattr_name;
         char            *link_xattr_name;
+        char            *commithash_xattr_name;
         char            *wild_xattr_name;
 
         /* Support size-weighted rebalancing (heterogeneous bricks). */
@@ -436,6 +454,13 @@ struct dht_conf {
         /*local subvol storage for rebalance*/
         xlator_t       **local_subvols;
         int32_t          local_subvols_cnt;
+
+        /*
+         * "Commit hash" for this volume topology.  Changed whenever bricks
+         * are added or removed.
+         */
+        uint32_t        vol_commit_hash;
+        gf_boolean_t    vch_forced;
 };
 typedef struct dht_conf dht_conf_t;
 
@@ -576,7 +601,7 @@ int dht_layouts_init (xlator_t *this, dht_conf_t *conf);
 int dht_layout_merge (xlator_t *this, dht_layout_t *layout, xlator_t *subvol,
                       int       op_ret, int op_errno, dict_t *xattr);
 
-int dht_disk_layout_extract (xlator_t *this, dht_layout_t *layout,
+int     dht_disk_layout_extract (xlator_t *this, dht_layout_t *layout,
                              int       pos, int32_t **disk_layout_p);
 int dht_disk_layout_merge (xlator_t   *this, dht_layout_t *layout,
                            int         pos, void *disk_layout_raw, int disk_layout_len);
@@ -631,6 +656,7 @@ xlator_t *dht_free_disk_available_subvol (xlator_t *this, xlator_t *subvol,
 int       dht_get_du_info_for_subvol (xlator_t *this, int subvol_idx);
 
 int dht_layout_preset (xlator_t *this, xlator_t *subvol, inode_t *inode);
+int dht_layout_index_for_subvol (dht_layout_t *layout, xlator_t *subvol);
 int           dht_layout_set (xlator_t *this, inode_t *inode, dht_layout_t *layout);;
 void          dht_layout_unref (xlator_t *this, dht_layout_t *layout);
 dht_layout_t *dht_layout_ref (xlator_t *this, dht_layout_t *layout);
@@ -649,6 +675,7 @@ int dht_rename_link_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                          struct iatt      *preparent, struct iatt *postparent,
                          dict_t *xdata);
 
+int dht_update_commit_hash_for_layout (call_frame_t *frame);
 int dht_fix_directory_layout (call_frame_t *frame,
                               dht_selfheal_dir_cbk_t  dir_cbk,
                               dht_layout_t           *layout);
diff --git a/xlators/cluster/dht/src/dht-layout.c b/xlators/cluster/dht/src/dht-layout.c
index 2ed15c5e43c..f88c786a55b 100644
--- a/xlators/cluster/dht/src/dht-layout.c
+++ b/xlators/cluster/dht/src/dht-layout.c
@@ -267,7 +267,7 @@ dht_disk_layout_extract (xlator_t *this, dht_layout_t *layout,
                 goto out;
         }
 
-        disk_layout[0] = hton32 (1);
+        disk_layout[0] = hton32 (layout->list[pos].commit_hash);
         disk_layout[1] = hton32 (layout->type);
         disk_layout[2] = hton32 (layout->list[pos].start);
         disk_layout[3] = hton32 (layout->list[pos].stop);
@@ -288,10 +288,10 @@ int
 dht_disk_layout_merge (xlator_t *this, dht_layout_t *layout,
 		       int pos, void *disk_layout_raw, int disk_layout_len)
 {
-        int      cnt = 0;
         int      type = 0;
         int      start_off = 0;
         int      stop_off = 0;
+        int      commit_hash = 0;
         int      disk_layout[4];
 
 	if (!disk_layout_raw) {
@@ -305,14 +305,6 @@ dht_disk_layout_merge (xlator_t *this, dht_layout_t *layout,
 
         memcpy (disk_layout, disk_layout_raw, disk_layout_len);
 
-        cnt  = ntoh32 (disk_layout[0]);
-        if (cnt != 1) {
-                gf_msg (this->name, GF_LOG_ERROR, 0,
-                        DHT_MSG_INVALID_DISK_LAYOUT,
-                        "Invalid disk layout: Invalid count %d", cnt);
-                return -1;
-        }
-
         type = ntoh32 (disk_layout[1]);
 	switch (type) {
         case DHT_HASH_TYPE_DM_USER:
@@ -330,21 +322,22 @@ dht_disk_layout_merge (xlator_t *this, dht_layout_t *layout,
 		return -1;
 	}
 
+        commit_hash = ntoh32 (disk_layout[0]);
         start_off = ntoh32 (disk_layout[2]);
         stop_off  = ntoh32 (disk_layout[3]);
 
+        layout->list[pos].commit_hash = commit_hash;
         layout->list[pos].start = start_off;
         layout->list[pos].stop  = stop_off;
 
         gf_msg_trace (this->name, 0,
-                      "merged to layout: %u - %u (type %d) from %s",
-                      start_off, stop_off, type,
+                      "merged to layout: %u - %u (type %d, hash %d) from %s",
+                      start_off, stop_off, commit_hash, type,
                       layout->list[pos].xlator->name);
 
         return 0;
 }
 
-
 int
 dht_layout_merge (xlator_t *this, dht_layout_t *layout, xlator_t *subvol,
                   int op_ret, int op_errno, dict_t *xattr)
@@ -397,6 +390,13 @@ dht_layout_merge (xlator_t *this, dht_layout_t *layout, xlator_t *subvol,
                         subvol->name);
                 goto out;
         }
+
+        if (layout->commit_hash == 0) {
+                layout->commit_hash = layout->list[i].commit_hash;
+        } else if (layout->commit_hash != layout->list[i].commit_hash) {
+                layout->commit_hash = DHT_LAYOUT_HASH_INVALID;
+        }
+
         layout->list[i].err = 0;
 
 out:
@@ -409,6 +409,7 @@ dht_layout_entry_swap (dht_layout_t *layout, int i, int j)
 {
         uint32_t  start_swap = 0;
         uint32_t  stop_swap = 0;
+        uint32_t  commit_hash_swap = 0;
         xlator_t *xlator_swap = 0;
         int       err_swap = 0;
 
@@ -416,16 +417,19 @@ dht_layout_entry_swap (dht_layout_t *layout, int i, int j)
         stop_swap   = layout->list[i].stop;
         xlator_swap = layout->list[i].xlator;
         err_swap    = layout->list[i].err;
+        commit_hash_swap = layout->list[i].commit_hash;
 
         layout->list[i].start  = layout->list[j].start;
         layout->list[i].stop   = layout->list[j].stop;
         layout->list[i].xlator = layout->list[j].xlator;
         layout->list[i].err    = layout->list[j].err;
+        layout->list[i].commit_hash = layout->list[j].commit_hash;
 
         layout->list[j].start  = start_swap;
         layout->list[j].stop   = stop_swap;
         layout->list[j].xlator = xlator_swap;
         layout->list[j].err    = err_swap;
+        layout->list[j].commit_hash = commit_hash_swap;
 }
 
 void
@@ -728,9 +732,9 @@ dht_layout_dir_mismatch (xlator_t *this, dht_layout_t *layout, xlator_t *subvol,
         int         dict_ret = 0;
         int32_t     disk_layout[4];
         void       *disk_layout_raw = NULL;
-        int32_t     count = -1;
         uint32_t    start_off = -1;
         uint32_t    stop_off = -1;
+        uint32_t    commit_hash = -1;
         dht_conf_t *conf = this->private;
         char        gfid[GF_UUID_BUF_SIZE] = {0};
 
@@ -779,27 +783,21 @@ dht_layout_dir_mismatch (xlator_t *this, dht_layout_t *layout, xlator_t *subvol,
 
         memcpy (disk_layout, disk_layout_raw, sizeof (disk_layout));
 
-        count  = ntoh32 (disk_layout[0]);
-        if (count != 1) {
-                gf_msg (this->name, GF_LOG_ERROR, 0,
-                        DHT_MSG_INVALID_DISK_LAYOUT,
-                        "Invalid disk layout: invalid count %d,"
-                        "path = %s, gfid = %s ", count, loc->path, gfid);
-                ret = -1;
-                goto out;
-        }
-
         start_off = ntoh32 (disk_layout[2]);
         stop_off  = ntoh32 (disk_layout[3]);
+        commit_hash = ntoh32 (disk_layout[0]);
 
         if ((layout->list[pos].start != start_off)
-            || (layout->list[pos].stop != stop_off)) {
+            || (layout->list[pos].stop != stop_off)
+            || (layout->list[pos].commit_hash != commit_hash)) {
                 gf_log (this->name, GF_LOG_INFO,
-                        "subvol: %s; inode layout - %"PRIu32" - %"PRIu32"; "
-                        "disk layout - %"PRIu32" - %"PRIu32,
+                        "subvol: %s; inode layout - %"PRIu32" - %"PRIu32
+                        " - %"PRIu32"; "
+                        "disk layout - %"PRIu32" - %"PRIu32" - %"PRIu32,
                         layout->list[pos].xlator->name,
                         layout->list[pos].start, layout->list[pos].stop,
-                        start_off, stop_off);
+                        layout->list[pos].commit_hash,
+                        start_off, stop_off, commit_hash);
                 ret = 1;
         } else {
                 ret = 0;
@@ -839,3 +837,18 @@ dht_layout_preset (xlator_t *this, xlator_t *subvol, inode_t *inode)
 out:
         return ret;
 }
+
+int
+dht_layout_index_for_subvol (dht_layout_t *layout, xlator_t *subvol)
+{
+        int i = 0, ret = -1;
+
+        for (i = 0; i < layout->cnt; i++) {
+                if (layout->list[i].xlator == subvol) {
+                        ret = i;
+                        break;
+                }
+        }
+
+        return ret;
+}
diff --git a/xlators/cluster/dht/src/dht-rebalance.c b/xlators/cluster/dht/src/dht-rebalance.c
index 60f7314efe0..fae856d969f 100644
--- a/xlators/cluster/dht/src/dht-rebalance.c
+++ b/xlators/cluster/dht/src/dht-rebalance.c
@@ -2337,6 +2337,46 @@ out:
 
 }
 int
+gf_defrag_settle_hash (xlator_t *this, gf_defrag_info_t *defrag,
+                       loc_t *loc, dict_t *fix_layout)
+{
+        int     ret;
+
+        /*
+         * Now we're ready to update the directory commit hash for the volume
+         * root, so that hash miscompares and broadcast lookups can stop.
+         * However, we want to skip that if fix-layout is all we did.  In
+         * that case, we want the miscompares etc. to continue until a real
+         * rebalance is complete.
+         */
+        if (defrag->cmd == GF_DEFRAG_CMD_START_LAYOUT_FIX
+            || defrag->cmd == GF_DEFRAG_CMD_START_DETACH_TIER
+            || defrag->cmd == GF_DEFRAG_CMD_START_TIER) {
+                return 0;
+        }
+
+        ret = dict_set_uint32 (fix_layout, "new-commit-hash",
+                               defrag->new_commit_hash);
+        if (ret) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "Failed to set new-commit-hash");
+                return -1;
+        }
+
+        ret = syncop_setxattr (this, loc, fix_layout, 0, NULL, NULL);
+        if (ret) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "fix layout on %s failed", loc->path);
+                return -1;
+        }
+
+        /* TBD: find more efficient solution than adding/deleting every time */
+        dict_del(fix_layout, "new-commit-hash");
+
+        return 0;
+}
+
+int
 gf_defrag_fix_layout (xlator_t *this, gf_defrag_info_t *defrag, loc_t *loc,
                   dict_t *fix_layout, dict_t *migrate_data)
 {
@@ -2422,6 +2462,7 @@ gf_defrag_fix_layout (xlator_t *this, gf_defrag_info_t *defrag, loc_t *loc,
                         if (ret) {
                                 gf_log (this->name, GF_LOG_ERROR, "Child loc"
                                         " build failed");
+                                ret = -1;
                                 goto out;
                         }
 
@@ -2487,9 +2528,16 @@ gf_defrag_fix_layout (xlator_t *this, gf_defrag_info_t *defrag, loc_t *loc,
                                         "Fix layout failed for %s",
                                         entry_loc.path);
                                 defrag->total_failures++;
+                                ret = -1;
                                 goto out;
                         }
 
+                        if (gf_defrag_settle_hash (this, defrag, &entry_loc,
+                            fix_layout) != 0) {
+                                defrag->total_failures++;
+                                ret = -1;
+                                goto out;
+                        }
                 }
                 gf_dirent_free (&entries);
                 free_entries = _gf_false;
@@ -2573,6 +2621,36 @@ gf_defrag_start_crawl (void *data)
                 goto out;
         }
 
+        /*
+         * Unfortunately, we can't do special xattrs (like fix.layout) and
+         * real ones in the same call currently, and changing it seems
+         * riskier than just doing two calls.
+         */
+
+        gf_log (this->name, GF_LOG_INFO, "%s using commit hash %u",
+                __func__, conf->vol_commit_hash);
+
+        ret = dict_set_uint32 (fix_layout, conf->commithash_xattr_name,
+                               conf->vol_commit_hash);
+        if (ret) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "Failed to set %s", conf->commithash_xattr_name);
+                defrag->total_failures++;
+                ret = -1;
+                goto out;
+        }
+
+        ret = syncop_setxattr (this, &loc, fix_layout, 0, NULL, NULL);
+        if (ret) {
+                gf_log (this->name, GF_LOG_ERROR, "fix layout on %s failed",
+                        loc.path);
+                defrag->total_failures++;
+                ret = -1;
+                goto out;
+        }
+
+        /* We now return to our regularly scheduled program. */
+
         ret = dict_set_str (fix_layout, GF_XATTR_FIX_LAYOUT_KEY, "yes");
         if (ret) {
                 gf_msg (this->name, GF_LOG_ERROR, 0,
@@ -2580,10 +2658,13 @@ gf_defrag_start_crawl (void *data)
                         "Failed to start rebalance:"
                         "Failed to set dictionary value: key = %s",
                         GF_XATTR_FIX_LAYOUT_KEY);
+                defrag->total_failures++;
                 ret = -1;
                 goto out;
         }
 
+        defrag->new_commit_hash = conf->vol_commit_hash;
+
         ret = syncop_setxattr (this, &loc, fix_layout, 0, NULL, NULL);
         if (ret) {
                 gf_msg (this->name, GF_LOG_ERROR, 0,
@@ -2599,19 +2680,18 @@ gf_defrag_start_crawl (void *data)
             (defrag->cmd != GF_DEFRAG_CMD_START_LAYOUT_FIX)) {
                 migrate_data = dict_new ();
                 if (!migrate_data) {
+                        defrag->total_failures++;
                         ret = -1;
                         goto out;
                 }
-                if (defrag->cmd == GF_DEFRAG_CMD_START_FORCE)
-                        ret = dict_set_str (migrate_data,
-                                            GF_XATTR_FILE_MIGRATE_KEY,
-                                            "force");
-                else
-                        ret = dict_set_str (migrate_data,
-                                            GF_XATTR_FILE_MIGRATE_KEY,
-                                            "non-force");
-                if (ret)
+                ret = dict_set_str (migrate_data, GF_XATTR_FILE_MIGRATE_KEY,
+                        (defrag->cmd == GF_DEFRAG_CMD_START_FORCE)
+                        ?  "force" : "non-force");
+                if (ret) {
+                        defrag->total_failures++;
+                        ret = -1;
                         goto out;
+                }
 
                 /* Find local subvolumes */
                 ret = syncop_getxattr (this, &loc, &dict,
@@ -2670,6 +2750,17 @@ gf_defrag_start_crawl (void *data)
 
         ret = gf_defrag_fix_layout (this, defrag, &loc, fix_layout,
                                     migrate_data);
+        if (ret) {
+                defrag->total_failures++;
+                ret = -1;
+                goto out;
+        }
+
+        if (gf_defrag_settle_hash (this, defrag, &loc, fix_layout) != 0) {
+                defrag->total_failures++;
+                ret = -1;
+                goto out;
+        }
 
         if (defrag->cmd == GF_DEFRAG_CMD_START_TIER) {
                 methods = conf->methods;
diff --git a/xlators/cluster/dht/src/dht-selfheal.c b/xlators/cluster/dht/src/dht-selfheal.c
index cc093e1199f..c881a361804 100644
--- a/xlators/cluster/dht/src/dht-selfheal.c
+++ b/xlators/cluster/dht/src/dht-selfheal.c
@@ -23,11 +23,14 @@
 #define DHT_SET_LAYOUT_RANGE(layout,i,srt,chunk,path)    do {           \
                 layout->list[i].start = srt;                            \
                 layout->list[i].stop  = srt + chunk - 1;                \
+                layout->list[i].commit_hash = layout->commit_hash;      \
                                                                         \
                 gf_msg_trace (this->name, 0,                            \
-                              "gave fix: %u - %u on %s for %s",         \
+                              "gave fix: %u - %u, with commit-hash %u"  \
+                              " on %s for %s",                          \
                               layout->list[i].start,                    \
                               layout->list[i].stop,                     \
+                              layout->list[i].commit_hash,              \
                               layout->list[i].xlator->name, path);      \
         } while (0)
 
@@ -448,6 +451,7 @@ dht_should_fix_layout (call_frame_t *frame, dht_layout_t **inmem,
                        dht_layout_t **ondisk)
 {
         gf_boolean_t             fixit                 = _gf_true;
+
         dht_local_t             *local                 = NULL;
         int                      layout_span           = 0;
         int                      decommissioned_bricks = 0;
@@ -482,6 +486,10 @@ dht_should_fix_layout (call_frame_t *frame, dht_layout_t **inmem,
         if (local->selfheal.hole_cnt || local->selfheal.overlaps_cnt)
                 goto out;
 
+        /* If commit hashes are being updated, let it through */
+        if ((*inmem)->commit_hash != (*ondisk)->commit_hash)
+                goto out;
+
         layout_span = dht_layout_span (*ondisk);
 
         decommissioned_bricks
@@ -497,6 +505,7 @@ dht_should_fix_layout (call_frame_t *frame, dht_layout_t **inmem,
                 fixit = _gf_false;
 
 out:
+
         return fixit;
 }
 
@@ -756,6 +765,7 @@ dht_fix_dir_xattr (call_frame_t *frame, loc_t *loc, dht_layout_t *layout)
         dummy = dht_layout_new (this, 1);
         if (!dummy)
                 goto out;
+        dummy->commit_hash = layout->commit_hash;
         for (i = 0; i < conf->subvolume_cnt; i++) {
                 if (_gf_false ==
                     dht_is_subvol_in_layout (layout, conf->subvolumes[i])) {
@@ -1474,6 +1484,8 @@ dht_fix_layout_of_directory (call_frame_t *frame, loc_t *loc,
 		new_layout->list[i].xlator = layout->list[i].xlator;
         }
 
+        new_layout->commit_hash = layout->commit_hash;
+
         if (priv->du_stats) {
                 for (i = 0; i < priv->subvolume_cnt; ++i) {
                         gf_log (this->name, GF_LOG_INFO,
@@ -1653,6 +1665,11 @@ dht_selfheal_dir_getafix (call_frame_t *frame, loc_t *loc,
         overlaps = local->selfheal.overlaps_cnt;
 
         if (holes || overlaps) {
+                /* If the layout has anomolies which would change the hash
+                 * ranges, then we need to reset the commit_hash for this
+                 * directory, as the layout would change and things may not
+                 * be in place as expected */
+                layout->commit_hash = DHT_LAYOUT_HASH_INVALID;
                 dht_selfheal_layout_new_directory (frame, loc, layout);
                 ret = 0;
         }
@@ -1934,3 +1951,300 @@ dht_dir_attr_heal_done (int ret, call_frame_t *sync_frame, void *data)
         DHT_STACK_DESTROY (sync_frame);
         return 0;
 }
+
+/* EXIT: dht_update_commit_hash_for_layout */
+int
+dht_update_commit_hash_for_layout_done (call_frame_t *frame, void *cookie,
+                       xlator_t *this, int32_t op_ret, int32_t op_errno,
+                       dict_t *xdata)
+{
+        dht_local_t  *local = NULL;
+
+        local = frame->local;
+
+        /* preserve oldest error */
+        if (op_ret && !local->op_ret) {
+                local->op_ret = op_ret;
+                local->op_errno = op_errno;
+        }
+
+        DHT_STACK_UNWIND (setxattr, frame, local->op_ret,
+                          local->op_errno, NULL);
+
+        return 0;
+}
+
+int
+dht_update_commit_hash_for_layout_unlock (call_frame_t *frame, xlator_t *this)
+{
+        dht_local_t  *local = NULL;
+        int ret = 0;
+
+        local = frame->local;
+
+        ret = dht_unlock_inodelk (frame, local->lock.locks,
+                                  local->lock.lk_count,
+                                  dht_update_commit_hash_for_layout_done);
+        if (ret < 0) {
+                /* preserve oldest error, just ... */
+                if (!local->op_ret) {
+                        local->op_errno = errno;
+                        local->op_ret = -1;
+                }
+
+                gf_msg (this->name, GF_LOG_WARNING, errno,
+                        DHT_MSG_DIR_SELFHEAL_XATTR_FAILED,
+                        "Winding unlock failed: stale locks left on brick"
+                        " %s", local->loc.path);
+
+                dht_update_commit_hash_for_layout_done (frame, NULL, this,
+                                                        0, 0, NULL);
+        }
+
+        return 0;
+}
+
+int
+dht_update_commit_hash_for_layout_cbk (call_frame_t *frame, void *cookie,
+                                       xlator_t *this, int op_ret,
+                                       int op_errno, dict_t *xdata)
+{
+        dht_local_t  *local = NULL;
+        int           this_call_cnt = 0;
+
+        local = frame->local;
+
+        LOCK (&frame->lock);
+        /* store first failure, just because */
+        if (op_ret && !local->op_ret) {
+                local->op_ret = op_ret;
+                local->op_errno = op_errno;
+        }
+        UNLOCK (&frame->lock);
+
+        this_call_cnt = dht_frame_return (frame);
+
+        if (is_last_call (this_call_cnt)) {
+                dht_update_commit_hash_for_layout_unlock (frame, this);
+        }
+
+        return 0;
+}
+
+int
+dht_update_commit_hash_for_layout_resume (call_frame_t *frame, void *cookie,
+                                          xlator_t *this, int32_t op_ret,
+                                          int32_t op_errno, dict_t *xdata)
+{
+        dht_local_t   *local = NULL;
+        int            count = 1, ret = -1, i = 0, j = 0;
+        dht_conf_t    *conf = NULL;
+        dht_layout_t  *layout = NULL;
+        int32_t       *disk_layout = NULL;
+        dict_t        **xattr = NULL;
+
+        local = frame->local;
+        conf = frame->this->private;
+        count = conf->local_subvols_cnt;
+        layout = local->layout;
+
+        if (op_ret < 0) {
+                goto err_done;
+        }
+
+        /* We precreate the xattr list as we cannot change call count post the
+         * first wind as we may never continue from there. So we finish prep
+         * work before winding the setxattrs */
+        xattr = GF_CALLOC (count, sizeof (*xattr), gf_common_mt_char);
+        if (!xattr) {
+                local->op_errno = errno;
+
+                gf_msg (this->name, GF_LOG_WARNING, errno,
+                        DHT_MSG_DIR_SELFHEAL_XATTR_FAILED,
+                        "Directory commit hash update failed:"
+                        " %s: Allocation failed", local->loc.path);
+
+                goto err;
+        }
+
+        for (i = 0; i < count; i++) {
+                /* find the layout index for the subvolume */
+                ret = dht_layout_index_for_subvol (layout,
+                                                   conf->local_subvols[i]);
+                if (ret < 0) {
+                        local->op_errno = ENOENT;
+
+                        gf_msg (this->name, GF_LOG_WARNING, 0,
+                                DHT_MSG_DIR_SELFHEAL_XATTR_FAILED,
+                                "Directory commit hash update failed:"
+                                " %s: (subvol %s) Failed to find disk layout",
+                                local->loc.path, conf->local_subvols[i]->name);
+
+                        goto err;
+                }
+                j = ret;
+
+                /* update the commit hash for the layout */
+                layout->list[j].commit_hash = layout->commit_hash;
+
+                /* extract the current layout */
+                ret = dht_disk_layout_extract (this, layout, j, &disk_layout);
+                if (ret == -1) {
+                        local->op_errno = errno;
+
+                        gf_msg (this->name, GF_LOG_WARNING, errno,
+                                DHT_MSG_DIR_SELFHEAL_XATTR_FAILED,
+                                "Directory commit hash update failed:"
+                                " %s: (subvol %s) Failed to extract disk"
+                                " layout", local->loc.path,
+                                conf->local_subvols[i]->name);
+
+                        goto err;
+                }
+
+                xattr[i] = get_new_dict ();
+                if (!xattr[i]) {
+                        local->op_errno = errno;
+
+                        gf_msg (this->name, GF_LOG_WARNING, errno,
+                                DHT_MSG_DIR_SELFHEAL_XATTR_FAILED,
+                                "Directory commit hash update failed:"
+                                " %s: Allocation failed", local->loc.path);
+
+                        goto err;
+                }
+
+                ret = dict_set_bin (xattr[i], conf->xattr_name,
+                                    disk_layout, 4 * 4);
+                if (ret != 0) {
+                        local->op_errno = ENOMEM;
+
+                        gf_msg (this->name, GF_LOG_WARNING, 0,
+                                DHT_MSG_DIR_SELFHEAL_XATTR_FAILED,
+                                "Directory self heal xattr failed:"
+                                "%s: (subvol %s) Failed to set xattr"
+                                " dictionary,", local->loc.path,
+                                conf->local_subvols[i]->name);
+
+                        goto err;
+                }
+                disk_layout = NULL;
+
+                gf_msg_trace (this->name, 0,
+                              "setting commit hash %u on subvolume %s"
+                              " for %s", layout->list[j].commit_hash,
+                              conf->local_subvols[i]->name, local->loc.path);
+        }
+
+        /* wind the setting of the commit hash across the local subvols */
+        local->call_cnt = count;
+        local->op_ret = 0;
+        local->op_errno = 0;
+        for (i = 0; i < count; i++) {
+                dict_ref (xattr[i]);
+
+                STACK_WIND (frame, dht_update_commit_hash_for_layout_cbk,
+                            conf->local_subvols[i],
+                            conf->local_subvols[i]->fops->setxattr,
+                            &local->loc, xattr[i], 0, NULL);
+
+                dict_unref (xattr[i]);
+        }
+
+        return 0;
+err:
+        if (xattr) {
+                for (i = 0; i < count; i++) {
+                        if (xattr[i])
+                                dict_destroy (xattr[i]);
+                }
+
+                GF_FREE (xattr);
+        }
+
+        GF_FREE (disk_layout);
+
+        local->op_ret = -1;
+
+        dht_update_commit_hash_for_layout_unlock (frame, this);
+
+        return 0;
+err_done:
+        local->op_ret = -1;
+
+        dht_update_commit_hash_for_layout_done (frame, NULL, this, 0, 0, NULL);
+
+        return 0;
+}
+
+/* ENTER: dht_update_commit_hash_for_layout (see EXIT above)
+ * This function is invoked from rebalance only.
+ * As a result, the check here is simple enough to see if defrag is present
+ * in the conf, as other data would be populated appropriately if so.
+ * If ever this was to be used in other code paths, checks would need to
+ * change.
+ *
+ * Functional details:
+ *  - Lock the inodes on the subvols that we want the commit hash updated
+ *  - Update each layout with the inode layout, modified to take in the new
+ *    commit hash.
+ *  - Unlock and return.
+ */
+int
+dht_update_commit_hash_for_layout (call_frame_t *frame)
+{
+        dht_local_t   *local = NULL;
+        int            count = 1, ret = -1, i = 0;
+        dht_lock_t   **lk_array = NULL;
+        dht_conf_t    *conf = NULL;
+
+        GF_VALIDATE_OR_GOTO ("dht", frame, err);
+        GF_VALIDATE_OR_GOTO (frame->this->name, frame->local, err);
+
+        local = frame->local;
+        conf = frame->this->private;
+
+        if (!conf->defrag)
+                goto err;
+
+        count = conf->local_subvols_cnt;
+        lk_array = GF_CALLOC (count, sizeof (*lk_array),
+                              gf_common_mt_char);
+        if (lk_array == NULL)
+                goto err;
+
+        for (i = 0; i < count; i++) {
+                lk_array[i] = dht_lock_new (frame->this,
+                                            conf->local_subvols[i],
+                                            &local->loc, F_WRLCK,
+                                            DHT_LAYOUT_HEAL_DOMAIN);
+                if (lk_array[i] == NULL)
+                        goto err;
+        }
+
+        local->lock.locks = lk_array;
+        local->lock.lk_count = count;
+
+        ret = dht_blocking_inodelk (frame, lk_array, count,
+                                    dht_update_commit_hash_for_layout_resume);
+        if (ret < 0) {
+                local->lock.locks = NULL;
+                local->lock.lk_count = 0;
+                goto err;
+        }
+
+        return 0;
+err:
+        if (lk_array != NULL) {
+                int tmp_count = 0, i = 0;
+
+                for (i = 0; (i < count) && (lk_array[i]); i++, tmp_count++) {
+                        ;
+                }
+
+                dht_lock_array_free (lk_array, tmp_count);
+                GF_FREE (lk_array);
+        }
+
+        return -1;
+}
diff --git a/xlators/cluster/dht/src/dht-shared.c b/xlators/cluster/dht/src/dht-shared.c
index ffabc820d70..a1f72a85112 100644
--- a/xlators/cluster/dht/src/dht-shared.c
+++ b/xlators/cluster/dht/src/dht-shared.c
@@ -569,6 +569,7 @@ dht_init (xlator_t *this)
         int                              cmd            = 0;
         char                            *node_uuid      = NULL;
         int                              throttle_count = 0;
+        uint32_t                         commit_hash    = 0;
 
         GF_VALIDATE_OR_GOTO ("dht", this, err);
 
@@ -590,6 +591,15 @@ dht_init (xlator_t *this)
                 goto err;
         }
 
+        /* We get the commit-hash to set only for rebalance process */
+        if (dict_get_uint32 (this->options,
+                             "commit-hash", &commit_hash) == 0) {
+                gf_log (this->name, GF_LOG_INFO, "%s using commit hash %u",
+                        __func__, commit_hash);
+                conf->vol_commit_hash = commit_hash;
+                conf->vch_forced = _gf_true;
+        }
+
         ret = dict_get_int32 (this->options, "rebalance-cmd", &cmd);
 
         if (cmd) {
@@ -760,6 +770,8 @@ dht_init (xlator_t *this)
         GF_OPTION_INIT ("xattr-name", conf->xattr_name, str, err);
         gf_asprintf (&conf->link_xattr_name, "%s."DHT_LINKFILE_STR,
                      conf->xattr_name);
+        gf_asprintf (&conf->commithash_xattr_name, "%s."DHT_COMMITHASH_STR,
+                     conf->xattr_name);
         gf_asprintf (&conf->wild_xattr_name, "%s*", conf->xattr_name);
         if (!conf->link_xattr_name || !conf->wild_xattr_name) {
                 goto err;
@@ -871,6 +883,9 @@ struct volume_options options[] = {
         { .key  = {"rebalance-cmd"},
           .type = GF_OPTION_TYPE_INT,
         },
+        { .key = {"commit-hash"},
+          .type = GF_OPTION_TYPE_INT,
+        },
         { .key = {"node-uuid"},
           .type = GF_OPTION_TYPE_STR,
         },
diff --git a/xlators/mgmt/glusterd/src/glusterd-brick-ops.c b/xlators/mgmt/glusterd/src/glusterd-brick-ops.c
index 92d15c615be..019766c5d83 100644
--- a/xlators/mgmt/glusterd/src/glusterd-brick-ops.c
+++ b/xlators/mgmt/glusterd/src/glusterd-brick-ops.c
@@ -1997,6 +1997,8 @@ glusterd_op_remove_brick (dict_t *dict, char **op_errstr)
         dict_t                  *bricks_dict   = NULL;
         char                    *brick_tmpstr  = NULL;
         int                      start_remove  = 0;
+        uint32_t                 commit_hash   = 0;
+
         this = THIS;
         GF_ASSERT (this);
 
@@ -2262,6 +2264,9 @@ glusterd_op_remove_brick (dict_t *dict, char **op_errstr)
                 break;
         }
         if (!force && need_rebalance) {
+                if (dict_get_uint32(dict, "commit-hash", &commit_hash) == 0) {
+                        volinfo->rebal.commit_hash = commit_hash;
+                }
                 /* perform the rebalance operations */
                 ret = glusterd_handle_defrag_start
                         (volinfo, err_str, sizeof (err_str),
diff --git a/xlators/mgmt/glusterd/src/glusterd-op-sm.c b/xlators/mgmt/glusterd/src/glusterd-op-sm.c
index 858f0771ca6..bc0763483fd 100644
--- a/xlators/mgmt/glusterd/src/glusterd-op-sm.c
+++ b/xlators/mgmt/glusterd/src/glusterd-op-sm.c
@@ -3404,6 +3404,36 @@ out:
 }
 
 int
+gd_set_commit_hash (dict_t *dict)
+{
+        struct timeval          tv;
+        uint32_t                hash;
+
+        /*
+         * We need a commit hash that won't conflict with others we might have
+         * set, or zero which is the implicit value if we never have.  Using
+         * seconds<<3 like this ensures that we'll only get a collision if two
+         * consecutive rebalances are separated by exactly 2^29 seconds - about
+         * 17 years - and even then there's only a 1/8 chance of a collision in
+         * the low order bits.  It's far more likely that this code will have
+         * changed completely by then.  If not, call me in 2031.
+         *
+         * P.S. Time zone changes?  Yeah, right.
+         */
+        gettimeofday (&tv, NULL);
+        hash = tv.tv_sec << 3;
+
+        /*
+         * Make sure at least one of those low-order bits is set.  The extra
+         * shifting is because not all machines have sub-millisecond time
+         * resolution.
+         */
+        hash |= 1 << ((tv.tv_usec >> 10) % 3);
+
+        return dict_set_uint32 (dict, "commit-hash", hash);
+}
+
+int
 glusterd_op_build_payload (dict_t **req, char **op_errstr, dict_t *op_ctx)
 {
         int                     ret = -1;
@@ -3415,6 +3445,7 @@ glusterd_op_build_payload (dict_t **req, char **op_errstr, dict_t *op_ctx)
         uint32_t                status_cmd = GF_CLI_STATUS_NONE;
         char                    *errstr = NULL;
         xlator_t                *this = NULL;
+        gf_boolean_t            do_common = _gf_false;
 
         GF_ASSERT (req);
 
@@ -3503,12 +3534,6 @@ glusterd_op_build_payload (dict_t **req, char **op_errstr, dict_t *op_ctx)
                         }
                         break;
 
-                case GD_OP_SYNC_VOLUME:
-                        {
-                                dict_copy (dict, req_dict);
-                                break;
-                        }
-
                 case GD_OP_REMOVE_BRICK:
                         {
                                 dict_t *dict = ctx;
@@ -3525,6 +3550,10 @@ glusterd_op_build_payload (dict_t **req, char **op_errstr, dict_t *op_ctx)
                                 if (ret)
                                         goto out;
 
+                                if (gd_set_commit_hash(dict) != 0) {
+                                        goto out;
+                                }
+
                                 dict_destroy (req_dict);
                                 req_dict = dict_ref (dict);
                         }
@@ -3544,8 +3573,10 @@ glusterd_op_build_payload (dict_t **req, char **op_errstr, dict_t *op_ctx)
                                         dict_copy (dict, req_dict);
                                         break;
                                 }
+                                do_common = _gf_true;
                         }
-                        /*fall-through*/
+                        break;
+
                 case GD_OP_DELETE_VOLUME:
                 case GD_OP_START_VOLUME:
                 case GD_OP_STOP_VOLUME:
@@ -3555,7 +3586,6 @@ glusterd_op_build_payload (dict_t **req, char **op_errstr, dict_t *op_ctx)
                 case GD_OP_LOG_ROTATE:
                 case GD_OP_QUOTA:
                 case GD_OP_PROFILE_VOLUME:
-                case GD_OP_REBALANCE:
                 case GD_OP_HEAL_VOLUME:
                 case GD_OP_STATEDUMP_VOLUME:
                 case GD_OP_CLEARLOCKS_VOLUME:
@@ -3563,49 +3593,62 @@ glusterd_op_build_payload (dict_t **req, char **op_errstr, dict_t *op_ctx)
                 case GD_OP_BARRIER:
                 case GD_OP_BITROT:
                         {
-                                ret = dict_get_str (dict, "volname", &volname);
-                                if (ret) {
-                                        gf_log (this->name, GF_LOG_CRITICAL,
-                                                "volname is not present in "
-                                                "operation ctx");
-                                        goto out;
-                                }
-
-                                if (strcasecmp (volname, "all")) {
-                                        ret = glusterd_dict_set_volid (dict,
-                                                                       volname,
-                                                                     op_errstr);
-                                        if (ret)
-                                                goto out;
-                                }
-                                dict_copy (dict, req_dict);
+                                do_common = _gf_true;
                         }
                         break;
 
-                case GD_OP_COPY_FILE:
+                case GD_OP_REBALANCE:
                         {
-                                dict_copy (dict, req_dict);
-                                break;
+                                if (gd_set_commit_hash(dict) != 0) {
+                                        goto out;
+                                }
+                                do_common = _gf_true;
                         }
+                        break;
 
+                case GD_OP_SYNC_VOLUME:
+                case GD_OP_COPY_FILE:
                 case GD_OP_SYS_EXEC:
                         {
                                 dict_copy (dict, req_dict);
-                                break;
                         }
+                        break;
 
                 case GD_OP_GANESHA:
                         {
                                 dict_copy (dict, req_dict);
-                                break;
                         }
+                        break;
 
                 default:
                         break;
         }
 
-        *req = req_dict;
-        ret = 0;
+        /*
+         * This has been moved out of the switch so that multiple ops with
+         * other special needs can all "fall through" to it.
+         */
+        if (do_common) {
+                ret = dict_get_str (dict, "volname", &volname);
+                if (ret) {
+                        gf_log (this->name, GF_LOG_CRITICAL,
+                                "volname is not present in "
+                                "operation ctx");
+                        goto out;
+                }
+
+                if (strcasecmp (volname, "all")) {
+                        ret = glusterd_dict_set_volid (dict,
+                                                       volname,
+                                                     op_errstr);
+                        if (ret)
+                                goto out;
+                }
+                dict_copy (dict, req_dict);
+        }
+
+       *req = req_dict;
+       ret = 0;
 
 out:
         return ret;
diff --git a/xlators/mgmt/glusterd/src/glusterd-rebalance.c b/xlators/mgmt/glusterd/src/glusterd-rebalance.c
index 48d9a706042..cf8ee3a79f7 100644
--- a/xlators/mgmt/glusterd/src/glusterd-rebalance.c
+++ b/xlators/mgmt/glusterd/src/glusterd-rebalance.c
@@ -284,6 +284,9 @@ glusterd_handle_defrag_start (glusterd_volinfo_t *volinfo, char *op_errstr,
         runner_argprintf ( &runner, "*dht.rebalance-cmd=%d",cmd);
         runner_add_arg (&runner, "--xlator-option");
         runner_argprintf (&runner, "*dht.node-uuid=%s", uuid_utoa(MY_UUID));
+        runner_add_arg (&runner, "--xlator-option");
+        runner_argprintf (&runner, "*dht.commit-hash=%u",
+                          volinfo->rebal.commit_hash);
         runner_add_arg (&runner, "--socket-file");
         runner_argprintf (&runner, "%s",sockfile);
         runner_add_arg (&runner, "--pid-file");
@@ -716,6 +719,7 @@ glusterd_op_rebalance (dict_t *dict, char **op_errstr, dict_t *rsp_dict)
         char                    *task_id_str = NULL;
         dict_t                  *ctx = NULL;
         xlator_t                *this = NULL;
+        uint32_t                commit_hash;
 
         this = THIS;
         GF_ASSERT (this);
@@ -804,6 +808,9 @@ glusterd_op_rebalance (dict_t *dict, char **op_errstr, dict_t *rsp_dict)
                         glusterd_store_perform_node_state_store (volinfo);
                         break;
                 }
+                if (dict_get_uint32 (dict, "commit-hash", &commit_hash) == 0) {
+                        volinfo->rebal.commit_hash = commit_hash;
+                }
                 ret = glusterd_handle_defrag_start (volinfo, msg, sizeof (msg),
                                                     cmd, NULL, GD_OP_REBALANCE);
                 break;
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;