dht: make DHT xattr names configurable

This is necessary to support "DHT over DHT" configurations, so that the
upper and lower instances of DHT don't step all over each other.  Why
would we even consider such a thing?  Because it gives us the ability to
do data tiering and rack-aware placement, either by themselves or as
complements to other functionality such as erasure codes or
deduplication which save space but cost performance.  By setting up the
top-level DHT to place data into one of several lower-level DHT pools
based on policy instead of pure elastic hashing, we get better
performance for 90% of accesses and better storage efficiency for 90% of
data, all for relatively low effort.

Change-Id: I72e65c29edfc80babf39f7a2a00090f4588c4070
BUG: 924265
Signed-off-by: Jeff Darcy <jdarcy@redhat.com>
Reviewed-on: http://review.gluster.org/4694
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>

11 files changed, 192 insertions, 125 deletions

diff --git a/xlators/cluster/dht/src/dht-common.c b/xlators/cluster/dht/src/dht-common.c
index f95bb84e634..74897b95b04 100644
--- a/xlators/cluster/dht/src/dht-common.c
+++ b/xlators/cluster/dht/src/dht-common.c
@@ -226,6 +226,7 @@ dht_discover_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
         int           is_dir                  = 0;
         int           is_linkfile             = 0;
         int           attempt_unwind          = 0;
+        dht_conf_t   *conf                    = 0;
 
         GF_VALIDATE_OR_GOTO ("dht", frame, out);
         GF_VALIDATE_OR_GOTO ("dht", this, out);
@@ -235,6 +236,7 @@ dht_discover_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
 
         local = frame->local;
         prev  = cookie;
+        conf = this->private;
 
         layout = local->layout;
 
@@ -269,7 +271,8 @@ dht_discover_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                         goto unlock;
                 }
 
-                is_linkfile = check_is_linkfile (inode, stbuf, xattr);
+                is_linkfile = check_is_linkfile (inode, stbuf, xattr,
+                                                 conf->link_xattr_name);
                 is_dir = check_is_dir (inode, stbuf, xattr);
 
                 if (is_dir) {
@@ -328,23 +331,20 @@ dht_discover (call_frame_t *frame, xlator_t *this, loc_t *loc)
         int          i = 0;
         call_frame_t *discover_frame = NULL;
 
-
         conf = this->private;
         local = frame->local;
 
-        ret = dict_set_uint32 (local->xattr_req,
-                               "trusted.glusterfs.dht", 4 * 4);
+        ret = dict_set_uint32 (local->xattr_req, conf->xattr_name, 4 * 4);
         if (ret)
                 gf_log (this->name, GF_LOG_WARNING,
-                        "%s: failed to set 'trusted.glusterfs.dht' key",
-                        loc->path);
+                        "%s: failed to set '%s' key",
+                        loc->path, conf->xattr_name);
 
-        ret = dict_set_uint32 (local->xattr_req,
-                               "trusted.glusterfs.dht.linkto", 256);
+        ret = dict_set_uint32 (local->xattr_req, conf->link_xattr_name, 256);
         if (ret)
                 gf_log (this->name, GF_LOG_WARNING,
-                        "%s: failed to set 'trusted.glusterfs.dht.linkto' key",
-                        loc->path);
+                        "%s: failed to set '%s' key",
+                        loc->path, conf->link_xattr_name);
 
         call_cnt        = conf->subvolume_cnt;
         local->call_cnt = call_cnt;
@@ -585,7 +585,8 @@ dht_revalidate_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                 layout = local->layout;
 
                 is_dir = check_is_dir (inode, stbuf, xattr);
-                is_linkfile = check_is_linkfile (inode, stbuf, xattr);
+                is_linkfile = check_is_linkfile (inode, stbuf, xattr,
+                                                 conf->link_xattr_name);
 
                 if (is_linkfile) {
                         gf_log (this->name, GF_LOG_INFO,
@@ -597,7 +598,7 @@ dht_revalidate_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                 }
 
                 if (is_dir) {
-                        ret = dht_dir_has_layout (xattr);
+                        ret = dht_dir_has_layout (xattr, conf->xattr_name);
                         if (ret >= 0) {
                                 if (is_greater_time(local->stbuf.ia_ctime,
                                                     local->stbuf.ia_ctime_nsec,
@@ -886,7 +887,7 @@ dht_lookup_everywhere_done (call_frame_t *frame, xlator_t *this)
                 hashed_subvol->name);
 
         ret = dht_linkfile_create (frame,
-                                   dht_lookup_linkfile_create_cbk,
+                                   dht_lookup_linkfile_create_cbk, this,
                                    cached_subvol, hashed_subvol, &local->loc);
 
         return ret;
@@ -924,8 +925,9 @@ dht_lookup_everywhere_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
         xlator_t     *subvol        = NULL;
         loc_t        *loc           = NULL;
         xlator_t     *link_subvol   = NULL;
-        int           ret = -1;
-        int32_t       fd_count = 0;
+        int           ret           = -1;
+        int32_t       fd_count      = 0;
+        dht_conf_t   *conf          = NULL;
 
         GF_VALIDATE_OR_GOTO ("dht", frame, out);
         GF_VALIDATE_OR_GOTO ("dht", this, out);
@@ -935,6 +937,7 @@ dht_lookup_everywhere_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
 
         local  = frame->local;
         loc    = &local->loc;
+        conf   = this->private;
 
         prev   = cookie;
         subvol = prev->this;
@@ -956,7 +959,8 @@ dht_lookup_everywhere_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                                 loc->path, prev->this->name);
                 }
 
-                is_linkfile = check_is_linkfile (inode, buf, xattr);
+                is_linkfile = check_is_linkfile (inode, buf, xattr,
+                                                 conf->link_xattr_name);
                 is_dir = check_is_dir (inode, buf, xattr);
 
                 if (is_linkfile) {
@@ -1117,7 +1121,7 @@ dht_lookup_linkfile_cbk (call_frame_t *frame, void *cookie,
                 goto err;
         }
 
-        if (check_is_linkfile (inode, stbuf, xattr)) {
+        if (check_is_linkfile (inode, stbuf, xattr, conf->link_xattr_name)) {
                 gf_log (this->name, GF_LOG_INFO,
                         "lookup of %s on %s (following linkfile) reached link",
                         local->loc.path, subvol->name);
@@ -1294,7 +1298,8 @@ dht_lookup_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                 goto out;
         }
 
-        is_linkfile = check_is_linkfile (inode, stbuf, xattr);
+        is_linkfile = check_is_linkfile (inode, stbuf, xattr,
+                                         conf->link_xattr_name);
 
         if (!is_linkfile) {
                 /* non-directory and not a linkfile */
@@ -1474,7 +1479,7 @@ dht_lookup (call_frame_t *frame, xlator_t *this,
                  *       revalidates directly go to the cached-subvolume.
                  */
                 ret = dict_set_uint32 (local->xattr_req,
-                                       "trusted.glusterfs.dht", 4 * 4);
+                                       conf->xattr_name, 4 * 4);
 
                 if (IA_ISDIR (local->inode->ia_type)) {
                         local->call_cnt = call_cnt = conf->subvolume_cnt;
@@ -1509,10 +1514,10 @@ dht_lookup (call_frame_t *frame, xlator_t *this,
         do_fresh_lookup:
                 /* TODO: remove the hard-coding */
                 ret = dict_set_uint32 (local->xattr_req,
-                                       "trusted.glusterfs.dht", 4 * 4);
+                                       conf->xattr_name, 4 * 4);
 
                 ret = dict_set_uint32 (local->xattr_req,
-                                       DHT_LINKFILE_KEY, 256);
+                                       conf->link_xattr_name, 256);
 
                 /* need it for self-healing linkfiles which is
                    'in-migration' state */
@@ -2009,10 +2014,13 @@ dht_getxattr_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
 {
         int             this_call_cnt = 0;
         dht_local_t     *local = NULL;
+        dht_conf_t      *conf = NULL;
 
         VALIDATE_OR_GOTO (frame, out);
         VALIDATE_OR_GOTO (frame->local, out);
+        VALIDATE_OR_GOTO (this->private, out);
 
+        conf = this->private;
         local = frame->local;
 
         this_call_cnt = dht_frame_return (frame);
@@ -2020,8 +2028,8 @@ dht_getxattr_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
         if (!xattr || (op_ret == -1))
                 goto out;
 
-        if (dict_get (xattr, "trusted.glusterfs.dht")) {
-                dict_del (xattr, "trusted.glusterfs.dht");
+        if (dict_get (xattr, conf->xattr_name)) {
+                dict_del (xattr, conf->xattr_name);
         }
         local->op_ret = 0;
 
@@ -2308,13 +2316,17 @@ dht_fsetxattr (call_frame_t *frame, xlator_t *this,
         xlator_t     *subvol   = NULL;
         dht_local_t  *local    = NULL;
         int           op_errno = EINVAL;
+        dht_conf_t   *conf     = NULL;
 
         VALIDATE_OR_GOTO (frame, err);
         VALIDATE_OR_GOTO (this, err);
         VALIDATE_OR_GOTO (fd, err);
         VALIDATE_OR_GOTO (fd->inode, err);
+        VALIDATE_OR_GOTO (this->private, err);
 
-        GF_IF_INTERNAL_XATTR_GOTO ("trusted.glusterfs.dht*", xattr,
+        conf = this->private;
+
+        GF_IF_INTERNAL_XATTR_GOTO (conf->wild_xattr_name, xattr,
                                    op_errno, err);
 
         local = dht_local_init (frame, NULL, fd, GF_FOP_FSETXATTR);
@@ -2420,10 +2432,11 @@ dht_setxattr (call_frame_t *frame, xlator_t *this,
         VALIDATE_OR_GOTO (loc->inode, err);
         VALIDATE_OR_GOTO (loc->path, err);
 
-        GF_IF_INTERNAL_XATTR_GOTO ("trusted.glusterfs.dht*", xattr,
+        conf   = this->private;
+
+        GF_IF_INTERNAL_XATTR_GOTO (conf->wild_xattr_name, xattr,
                                    op_errno, err);
 
-        conf   = this->private;
         local = dht_local_init (frame, loc, NULL, GF_FOP_SETXATTR);
         if (!local) {
                 op_errno = ENOMEM;
@@ -2636,13 +2649,16 @@ dht_removexattr (call_frame_t *frame, xlator_t *this,
         dht_local_t  *local = NULL;
         dht_layout_t *layout = NULL;
         int           call_cnt = 0;
+        dht_conf_t   *conf = NULL;
 
         int i;
 
         VALIDATE_OR_GOTO (this, err);
+        VALIDATE_OR_GOTO (this->private, err);
 
-        GF_IF_NATIVE_XATTR_GOTO ("trusted.glusterfs.dht*",
-                                 key, op_errno, err);
+        conf = this->private;
+
+        GF_IF_NATIVE_XATTR_GOTO (conf->wild_xattr_name, key, op_errno, err);
 
         VALIDATE_OR_GOTO (frame, err);
         VALIDATE_OR_GOTO (loc, err);
@@ -2699,13 +2715,16 @@ dht_fremovexattr (call_frame_t *frame, xlator_t *this,
         dht_local_t  *local = NULL;
         dht_layout_t *layout = NULL;
         int           call_cnt = 0;
+        dht_conf_t   *conf = 0;
 
         int i;
 
         VALIDATE_OR_GOTO (this, err);
+        VALIDATE_OR_GOTO (this->private, err);
 
-        GF_IF_NATIVE_XATTR_GOTO ("trusted.glusterfs.dht*",
-                                 key, op_errno, err);
+        conf = this->private;
+
+        GF_IF_NATIVE_XATTR_GOTO (conf->wild_xattr_name, key, op_errno, err);
 
         VALIDATE_OR_GOTO (frame, err);
 
@@ -2996,10 +3015,13 @@ dht_readdirp_cbk (call_frame_t *frame, void *cookie, xlator_t *this, int op_ret,
 
         list_for_each_entry (orig_entry, (&orig_entries->list), list) {
                 next_offset = orig_entry->d_off;
-                if ((check_is_dir (NULL, (&orig_entry->d_stat), NULL) &&
-                     (prev->this != dht_first_up_subvol (this))) ||
-                    check_is_linkfile (NULL, (&orig_entry->d_stat),
-                                       orig_entry->dict)) {
+                if (check_is_dir (NULL, (&orig_entry->d_stat), NULL) &&
+                    (prev->this != dht_first_up_subvol (this))) {
+                        continue;
+                }
+                if (check_is_linkfile (NULL, (&orig_entry->d_stat),
+                                       orig_entry->dict,
+                                       conf->link_xattr_name)) {
                         continue;
                 }
 
@@ -3215,6 +3237,7 @@ dht_do_readdir (call_frame_t *frame, xlator_t *this, fd_t *fd, size_t size,
         VALIDATE_OR_GOTO (frame, err);
         VALIDATE_OR_GOTO (this, err);
         VALIDATE_OR_GOTO (fd, err);
+        VALIDATE_OR_GOTO (this->private, err);
 
         conf = this->private;
 
@@ -3239,12 +3262,11 @@ dht_do_readdir (call_frame_t *frame, xlator_t *this, fd_t *fd, size_t size,
 
                 if (local->xattr) {
                         ret = dict_set_uint32 (local->xattr,
-                                               "trusted.glusterfs.dht.linkto",
-                                               256);
+                                               conf->link_xattr_name, 256);
                         if (ret)
                                 gf_log (this->name, GF_LOG_WARNING,
-                                        "failed to set 'glusterfs.dht.linkto'"
-                                        " key");
+                                        "failed to set '%s' key",
+                                        conf->link_xattr_name);
 			if (conf->readdir_optimize == _gf_true) {
                                 if (xvol != dht_first_up_subvol (this)) {
 				        ret = dict_set_int32 (local->xattr,
@@ -3522,7 +3544,7 @@ dht_mknod (call_frame_t *frame, xlator_t *this,
                         local->umask = umask;
                         dht_linkfile_create (frame,
                                              dht_mknod_linkfile_create_cbk,
-                                             avail_subvol, subvol, loc);
+                                             this, avail_subvol, subvol, loc);
                 } else {
                         gf_log (this->name, GF_LOG_TRACE,
                                 "creating %s on %s", loc->path, subvol->name);
@@ -3781,7 +3803,7 @@ dht_link (call_frame_t *frame, xlator_t *this,
 
         if (hashed_subvol != cached_subvol) {
                 uuid_copy (local->gfid, oldloc->inode->gfid);
-                dht_linkfile_create (frame, dht_link_linkfile_cbk,
+                dht_linkfile_create (frame, dht_link_linkfile_cbk, this,
                                      cached_subvol, hashed_subvol, newloc);
         } else {
                 STACK_WIND (frame, dht_link_cbk,
@@ -3942,9 +3964,8 @@ dht_create (call_frame_t *frame, xlator_t *this,
                 gf_log (this->name, GF_LOG_TRACE,
                         "creating %s on %s (link at %s)", loc->path,
                         avail_subvol->name, subvol->name);
-                dht_linkfile_create (frame,
-                                     dht_create_linkfile_create_cbk,
-                                     avail_subvol, subvol, loc);
+                dht_linkfile_create (frame, dht_create_linkfile_create_cbk,
+                                     this, avail_subvol, subvol, loc);
                 goto done;
         }
         gf_log (this->name, GF_LOG_TRACE,
@@ -4483,6 +4504,7 @@ dht_rmdir_lookup_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
         call_frame_t   *main_frame = NULL;
         dht_local_t    *main_local = NULL;
         int             this_call_cnt = 0;
+        dht_conf_t     *conf = this->private;
 
         local = frame->local;
         prev  = cookie;
@@ -4494,7 +4516,7 @@ dht_rmdir_lookup_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
         if (op_ret != 0)
                 goto err;
 
-        if (check_is_linkfile (inode, stbuf, xattr) == 0) {
+        if (!check_is_linkfile (inode, stbuf, xattr, conf->link_xattr_name)) {
                 main_local->op_ret  = -1;
                 main_local->op_errno = ENOTEMPTY;
 
@@ -4529,6 +4551,7 @@ dht_rmdir_is_subvol_empty (call_frame_t *frame, xlator_t *this,
         dht_local_t        *lookup_local = NULL;
         dht_local_t        *local = NULL;
         dict_t             *xattrs = NULL;
+        dht_conf_t         *conf = this->private;
 
         local = frame->local;
 
@@ -4537,7 +4560,8 @@ dht_rmdir_is_subvol_empty (call_frame_t *frame, xlator_t *this,
                         continue;
                 if (strcmp (trav->d_name, "..") == 0)
                         continue;
-                if (check_is_linkfile (NULL, (&trav->d_stat), trav->dict)) {
+                if (check_is_linkfile (NULL, (&trav->d_stat), trav->dict,
+                                              conf->link_xattr_name)) {
                         ret++;
                         continue;
                 }
@@ -4555,7 +4579,7 @@ dht_rmdir_is_subvol_empty (call_frame_t *frame, xlator_t *this,
                 return -1;
         }
 
-        ret = dict_set_uint32 (xattrs, DHT_LINKFILE_KEY, 256);
+        ret = dict_set_uint32 (xattrs, conf->link_xattr_name, 256);
         if (ret) {
                 gf_log (this->name, GF_LOG_ERROR, "failed to set linkto key"
                         " in dict");
@@ -4678,6 +4702,7 @@ dht_rmdir_opendir_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
         call_frame_t *prev = NULL;
         dict_t       *dict = NULL;
         int           ret = 0;
+        dht_conf_t   *conf = this->private;
 
         local = frame->local;
         prev  = cookie;
@@ -4701,12 +4726,11 @@ dht_rmdir_opendir_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                 goto err;
         }
 
-        ret = dict_set_uint32 (dict,
-                               "trusted.glusterfs.dht.linkto", 256);
+        ret = dict_set_uint32 (dict, conf->link_xattr_name, 256);
         if (ret)
                 gf_log (this->name, GF_LOG_WARNING,
-                        "%s: failed to set 'trusted.glusterfs.dht.linkto' key",
-                        local->loc.path);
+                        "%s: failed to set '%s' key",
+                        local->loc.path, conf->link_xattr_name);
 
         STACK_WIND (frame, dht_rmdir_readdirp_cbk,
                     prev->this, prev->this->fops->readdirp,
diff --git a/xlators/cluster/dht/src/dht-common.h b/xlators/cluster/dht/src/dht-common.h
index 65983c0c49f..3679918d79f 100644
--- a/xlators/cluster/dht/src/dht-common.h
+++ b/xlators/cluster/dht/src/dht-common.h
@@ -290,6 +290,11 @@ struct dht_conf {
         gf_boolean_t    rsync_regex_valid;
         regex_t         extra_regex;
         gf_boolean_t    extra_regex_valid;
+
+        /* Support variable xattr names. */
+        char            *xattr_name;
+        char            *link_xattr_name;
+        char            *wild_xattr_name;
 };
 typedef struct dht_conf dht_conf_t;
 
@@ -320,13 +325,12 @@ typedef enum {
 #define DHT_MIGRATION_IN_PROGRESS 1
 #define DHT_MIGRATION_COMPLETED   2
 
-#define DHT_LINKFILE_KEY         "trusted.glusterfs.dht.linkto"
 #define DHT_LINKFILE_MODE        (S_ISVTX)
 
-#define check_is_linkfile(i,s,x) (                                      \
+#define check_is_linkfile(i,s,x,n) (                                      \
                 ((st_mode_from_ia ((s)->ia_prot, (s)->ia_type) & ~S_IFMT) \
-                 == DHT_LINKFILE_MODE) &&                               \
-                dict_get (x, DHT_LINKFILE_KEY))
+                 == DHT_LINKFILE_MODE) &&                                 \
+                dict_get (x, n))
 
 #define IS_DHT_MIGRATION_PHASE2(buf)  (                                 \
                 IA_ISREG ((buf)->ia_type) &&                            \
@@ -438,7 +442,8 @@ int       dht_subvol_cnt (xlator_t *this, xlator_t *subvol);
 int dht_hash_compute (xlator_t *this, int type, const char *name, uint32_t *hash_p);
 
 int dht_linkfile_create (call_frame_t    *frame, fop_mknod_cbk_t linkfile_cbk,
-                         xlator_t        *tovol, xlator_t *fromvol, loc_t *loc);
+                         xlator_t        *this, xlator_t *tovol,
+                         xlator_t        *fromvol, loc_t *loc);
 int                                       dht_lookup_directory (call_frame_t *frame, xlator_t *this, loc_t *loc);
 int                                       dht_lookup_everywhere (call_frame_t *frame, xlator_t *this, loc_t *loc);
 int
@@ -740,7 +745,7 @@ dht_dir_attr_heal (void *data);
 int
 dht_dir_attr_heal_done (int ret, call_frame_t *sync_frame, void *data);
 int
-dht_dir_has_layout (dict_t *xattr);
+dht_dir_has_layout (dict_t *xattr, char *name);
 gf_boolean_t
 dht_is_subvol_in_layout (dht_layout_t *layout, xlator_t *xlator);
 xlator_t *
diff --git a/xlators/cluster/dht/src/dht-helper.c b/xlators/cluster/dht/src/dht-helper.c
index ecd06e394da..4f50e214f2b 100644
--- a/xlators/cluster/dht/src/dht-helper.c
+++ b/xlators/cluster/dht/src/dht-helper.c
@@ -620,10 +620,12 @@ dht_migration_complete_check_task (void *data)
         call_frame_t *frame    = NULL;
         loc_t         tmp_loc  = {0,};
         char         *path     = NULL;
+        dht_conf_t   *conf     = NULL;
 
         this  = THIS;
         frame = data;
         local = frame->local;
+        conf = this->private;
 
         src_node = local->cached_subvol;
 
@@ -633,10 +635,10 @@ dht_migration_complete_check_task (void *data)
         /* getxattr on cached_subvol for 'linkto' value */
         if (!local->loc.inode)
                 ret = syncop_fgetxattr (src_node, local->fd, &dict,
-                                        DHT_LINKFILE_KEY);
+                                        conf->link_xattr_name);
         else
                 ret = syncop_getxattr (src_node, &local->loc, &dict,
-                                       DHT_LINKFILE_KEY);
+                                       conf->link_xattr_name);
 
         if (!ret)
                 dst_node = dht_linkfile_subvol (this, NULL, NULL, dict);
@@ -801,10 +803,12 @@ dht_rebalance_inprogress_task (void *data)
         char         *path     = NULL;
         struct iatt   stbuf    = {0,};
         loc_t         tmp_loc  = {0,};
+        dht_conf_t   *conf     = NULL;
 
         this  = THIS;
         frame = data;
         local = frame->local;
+        conf = this->private;
 
         src_node = local->cached_subvol;
 
@@ -814,10 +818,10 @@ dht_rebalance_inprogress_task (void *data)
         /* getxattr on cached_subvol for 'linkto' value */
         if (local->loc.inode)
                 ret = syncop_getxattr (src_node, &local->loc, &dict,
-                                       DHT_LINKFILE_KEY);
+                                       conf->link_xattr_name);
         else
                 ret = syncop_fgetxattr (src_node, local->fd, &dict,
-                                        DHT_LINKFILE_KEY);
+                                        conf->link_xattr_name);
 
         if (ret) {
                 gf_log (this->name, GF_LOG_ERROR,
diff --git a/xlators/cluster/dht/src/dht-layout.c b/xlators/cluster/dht/src/dht-layout.c
index 71aa1b70c97..7d53e3d04e0 100644
--- a/xlators/cluster/dht/src/dht-layout.c
+++ b/xlators/cluster/dht/src/dht-layout.c
@@ -335,11 +335,12 @@ int
 dht_layout_merge (xlator_t *this, dht_layout_t *layout, xlator_t *subvol,
                   int op_ret, int op_errno, dict_t *xattr)
 {
-        int      i     = 0;
-        int      ret   = -1;
-        int      err   = -1;
-        void    *disk_layout_raw = NULL;
-        int      disk_layout_len = 0;
+        int         i     = 0;
+        int         ret   = -1;
+        int         err   = -1;
+        void       *disk_layout_raw = NULL;
+        int         disk_layout_len = 0;
+        dht_conf_t *conf = this->private;
 
         if (op_ret != 0) {
                 err = op_errno;
@@ -360,7 +361,7 @@ dht_layout_merge (xlator_t *this, dht_layout_t *layout, xlator_t *subvol,
 
         if (xattr) {
                 /* during lookup and not mkdir */
-                ret = dict_get_ptr_and_len (xattr, "trusted.glusterfs.dht",
+                ret = dict_get_ptr_and_len (xattr, conf->xattr_name,
 					    &disk_layout_raw, &disk_layout_len);
         }
 
@@ -650,30 +651,29 @@ out:
 }
 
 int
-dht_dir_has_layout (dict_t *xattr)
+dht_dir_has_layout (dict_t *xattr, char *name)
 {
 
         void     *disk_layout_raw = NULL;
 
-        return dict_get_ptr (xattr, "trusted.glusterfs.dht",
-                             &disk_layout_raw);
-
+        return dict_get_ptr (xattr, name, &disk_layout_raw);
 }
 
 int
 dht_layout_dir_mismatch (xlator_t *this, dht_layout_t *layout, xlator_t *subvol,
                          loc_t *loc, dict_t *xattr)
 {
-        int       idx = 0;
-        int       pos = -1;
-        int       ret = 0;
-        int       err = 0;
-        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;
+        int         idx = 0;
+        int         pos = -1;
+        int         ret = 0;
+        int         err = 0;
+        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;
+        dht_conf_t *conf = this->private;
 
 
         for (idx = 0; idx < layout->cnt; idx++) {
@@ -703,7 +703,7 @@ dht_layout_dir_mismatch (xlator_t *this, dht_layout_t *layout, xlator_t *subvol,
                 goto out;
         }
 
-        dict_ret = dict_get_ptr (xattr, "trusted.glusterfs.dht",
+        dict_ret = dict_get_ptr (xattr, conf->xattr_name,
                                  &disk_layout_raw);
 
         if (dict_ret < 0) {
diff --git a/xlators/cluster/dht/src/dht-linkfile.c b/xlators/cluster/dht/src/dht-linkfile.c
index 67d6ce583a9..b4a074b65b2 100644
--- a/xlators/cluster/dht/src/dht-linkfile.c
+++ b/xlators/cluster/dht/src/dht-linkfile.c
@@ -43,12 +43,14 @@ dht_linkfile_create_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
 
 int
 dht_linkfile_create (call_frame_t *frame, fop_mknod_cbk_t linkfile_cbk,
+                     xlator_t *this,
                      xlator_t *tovol, xlator_t *fromvol, loc_t *loc)
 {
         dht_local_t *local = NULL;
         dict_t      *dict = NULL;
         int          need_unref = 0;
         int          ret = 0;
+        dht_conf_t  *conf = this->private;
 
         local = frame->local;
         local->linkfile.linkfile_cbk = linkfile_cbk;
@@ -76,8 +78,7 @@ dht_linkfile_create (call_frame_t *frame, fop_mknod_cbk_t linkfile_cbk,
                 gf_log ("dht-linkfile", GF_LOG_INFO,
                         "%s: internal-fop set failed", loc->path);
 
-        ret = dict_set_str (dict, "trusted.glusterfs.dht.linkto",
-                                   tovol->name);
+        ret = dict_set_str (dict, conf->link_xattr_name, tovol->name);
 
         if (ret < 0) {
                 gf_log (frame->this->name, GF_LOG_INFO,
@@ -179,7 +180,7 @@ dht_linkfile_subvol (xlator_t *this, inode_t *inode, struct iatt *stbuf,
         if (!xattr)
                 goto out;
 
-        ret = dict_get_ptr (xattr, "trusted.glusterfs.dht.linkto", &volname);
+        ret = dict_get_ptr (xattr, conf->link_xattr_name, &volname);
 
         if ((-1 == ret) || !volname)
                 goto out;
diff --git a/xlators/cluster/dht/src/dht-rebalance.c b/xlators/cluster/dht/src/dht-rebalance.c
index af31072aae3..370118f987b 100644
--- a/xlators/cluster/dht/src/dht-rebalance.c
+++ b/xlators/cluster/dht/src/dht-rebalance.c
@@ -102,12 +102,16 @@ gf_defrag_handle_hardlink (xlator_t *this, loc_t *loc, dict_t  *xattrs,
         data_t                 *data            = NULL;
         struct iatt             iatt            = {0,};
         int32_t                 op_errno        = 0;
+        dht_conf_t             *conf            = NULL;
 
         GF_VALIDATE_OR_GOTO ("defrag", loc, out);
         GF_VALIDATE_OR_GOTO ("defrag", loc->name, out);
         GF_VALIDATE_OR_GOTO ("defrag", stbuf, out);
         GF_VALIDATE_OR_GOTO ("defrag", this, out);
         GF_VALIDATE_OR_GOTO ("defrag", xattrs, out);
+        GF_VALIDATE_OR_GOTO ("defrag", this->private, out);
+
+        conf = this->private;
 
         if (uuid_is_null (loc->pargfid)) {
                 gf_log ("", GF_LOG_ERROR, "loc->pargfid is NULL for "
@@ -138,10 +142,10 @@ gf_defrag_handle_hardlink (xlator_t *this, loc_t *loc, dict_t  *xattrs,
         gf_log (this->name, GF_LOG_INFO, "Attempting to migrate hardlink %s "
                 "with gfid %s from %s -> %s", loc->name, uuid_utoa (loc->gfid),
                 cached_subvol->name, hashed_subvol->name);
-        data = dict_get (xattrs, DHT_LINKFILE_KEY);
+        data = dict_get (xattrs, conf->link_xattr_name);
         /* set linkto on cached -> hashed if not present, else link it */
         if (!data) {
-                ret = dict_set_str (xattrs, DHT_LINKFILE_KEY,
+                ret = dict_set_str (xattrs, conf->link_xattr_name,
                                     hashed_subvol->name);
                 if (ret) {
                         gf_log (this->name, GF_LOG_ERROR, "Failed to set "
@@ -241,12 +245,14 @@ static inline int
 __dht_rebalance_create_dst_file (xlator_t *to, xlator_t *from, loc_t *loc, struct iatt *stbuf,
                                  dict_t *dict, fd_t **dst_fd)
 {
-        xlator_t *this = NULL;
-        int       ret  = -1;
-        fd_t     *fd   = NULL;
-        struct iatt new_stbuf = {0,};
+        xlator_t    *this = NULL;
+        int          ret  = -1;
+        fd_t        *fd   = NULL;
+        struct iatt  new_stbuf = {0,};
+        dht_conf_t  *conf = NULL;
 
         this = THIS;
+        conf = this->private;
 
         ret = dict_set_static_bin (dict, "gfid-req", stbuf->ia_gfid, 16);
         if (ret) {
@@ -255,7 +261,7 @@ __dht_rebalance_create_dst_file (xlator_t *to, xlator_t *from, loc_t *loc, struc
                 goto out;
         }
 
-        ret = dict_set_str (dict, DHT_LINKFILE_KEY, from->name);
+        ret = dict_set_str (dict, conf->link_xattr_name, from->name);
         if (ret) {
                 gf_log (this->name, GF_LOG_ERROR,
                         "%s: failed to set gfid in dict for create", loc->path);
@@ -449,8 +455,10 @@ __dht_rebalance_open_src_file (xlator_t *from, xlator_t *to, loc_t *loc,
         dict_t      *dict = NULL;
         xlator_t    *this = NULL;
         struct iatt  iatt = {0,};
+        dht_conf_t  *conf = NULL;
 
         this = THIS;
+        conf = this->private;
 
         fd = fd_create (loc->inode, DHT_REBALANCE_PID);
         if (!fd) {
@@ -473,7 +481,7 @@ __dht_rebalance_open_src_file (xlator_t *from, xlator_t *to, loc_t *loc,
         if (!dict)
                 goto out;
 
-        ret = dict_set_str (dict, DHT_LINKFILE_KEY, to->name);
+        ret = dict_set_str (dict, conf->link_xattr_name, to->name);
         if (ret) {
                 gf_log (this->name, GF_LOG_ERROR,
                         "failed to set xattr in dict for %s (linkto:%s)",
@@ -526,12 +534,13 @@ migrate_special_files (xlator_t *this, xlator_t *from, xlator_t *to, loc_t *loc,
         dict_t      *dict     = NULL;
         char        *link     = NULL;
         struct iatt  stbuf    = {0,};
+        dht_conf_t  *conf     = this->private;
 
         dict = dict_new ();
         if (!dict)
                 goto out;
 
-        ret = dict_set_int32 (dict, DHT_LINKFILE_KEY, 256);
+        ret = dict_set_int32 (dict, conf->link_xattr_name, 256);
         if (ret) {
                 gf_log (this->name, GF_LOG_ERROR,
                         "%s: failed to set 'linkto' key in dict", loc->path);
@@ -547,12 +556,13 @@ migrate_special_files (xlator_t *this, xlator_t *from, xlator_t *to, loc_t *loc,
         }
 
         /* we no more require this key */
-        dict_del (dict, DHT_LINKFILE_KEY);
+        dict_del (dict, conf->link_xattr_name);
 
         /* file exists in target node, only if it is 'linkfile' its valid,
            otherwise, error out */
         if (!ret) {
-                if (!check_is_linkfile (loc->inode, &stbuf, rsp_dict)) {
+                if (!check_is_linkfile (loc->inode, &stbuf, rsp_dict,
+                                        conf->link_xattr_name)) {
                         gf_log (this->name, GF_LOG_WARNING,
                                 "%s: file exists in destination", loc->path);
                         ret = -1;
@@ -647,6 +657,7 @@ dht_migrate_file (xlator_t *this, loc_t *loc, xlator_t *from, xlator_t *to,
         dict_t         *xattr          = NULL;
         dict_t         *xattr_rsp      = NULL;
         int             file_has_holes = 0;
+        dht_conf_t     *conf           = this->private;
 
         gf_log (this->name, GF_LOG_INFO, "%s: attempting to move from %s to %s",
                 loc->path, from->name, to->name);
@@ -655,7 +666,7 @@ dht_migrate_file (xlator_t *this, loc_t *loc, xlator_t *from, xlator_t *to,
         if (!dict)
                 goto out;
 
-        ret = dict_set_int32 (dict, DHT_LINKFILE_KEY, 256);
+        ret = dict_set_int32 (dict, conf->link_xattr_name, 256);
         if (ret) {
                 gf_log (this->name, GF_LOG_ERROR,
                         "%s: failed to set 'linkto' key in dict", loc->path);
@@ -671,7 +682,7 @@ dht_migrate_file (xlator_t *this, loc_t *loc, xlator_t *from, xlator_t *to,
         }
 
         /* we no more require this key */
-        dict_del (dict, DHT_LINKFILE_KEY);
+        dict_del (dict, conf->link_xattr_name);
 
         /* preserve source mode, so set the same to the destination */
         src_ia_prot = stbuf.ia_prot;
@@ -842,7 +853,7 @@ dht_migrate_file (xlator_t *this, loc_t *loc, xlator_t *from, xlator_t *to,
         }
 
         /* remove the 'linkto' xattr from the destination */
-        ret = syncop_fremovexattr (to, dst_fd, DHT_LINKFILE_KEY);
+        ret = syncop_fremovexattr (to, dst_fd, conf->link_xattr_name);
         if (ret) {
                 gf_log (this->name, GF_LOG_WARNING,
                         "%s: failed to perform removexattr on %s (%s)",
diff --git a/xlators/cluster/dht/src/dht-rename.c b/xlators/cluster/dht/src/dht-rename.c
index 35fedeaa7a4..fd0208f7147 100644
--- a/xlators/cluster/dht/src/dht-rename.c
+++ b/xlators/cluster/dht/src/dht-rename.c
@@ -505,7 +505,8 @@ dht_rename_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                 uuid_copy (link_local->gfid, local->loc.inode->gfid);
 
                 dht_linkfile_create (link_frame, dht_rename_links_create_cbk,
-                                     src_cached, dst_hashed, &link_local->loc);
+                                     this, src_cached, dst_hashed,
+                                     &link_local->loc);
         }
 
 err:
@@ -759,7 +760,7 @@ dht_rename_create_links (call_frame_t *frame)
                         "linkfile %s @ %s => %s",
                         local->loc.path, dst_hashed->name, src_cached->name);
                 memcpy (local->gfid, local->loc.inode->gfid, 16);
-		dht_linkfile_create (frame, dht_rename_links_cbk,
+		dht_linkfile_create (frame, dht_rename_links_cbk, this,
 				     src_cached, dst_hashed, &local->loc);
 	}
 
diff --git a/xlators/cluster/dht/src/dht-selfheal.c b/xlators/cluster/dht/src/dht-selfheal.c
index b8d873aac83..e1e962ab92e 100644
--- a/xlators/cluster/dht/src/dht-selfheal.c
+++ b/xlators/cluster/dht/src/dht-selfheal.c
@@ -124,7 +124,7 @@ dht_selfheal_dir_xattr_persubvol (call_frame_t *frame, loc_t *loc,
         xlator_t          *this = NULL;
         int32_t           *disk_layout = NULL;
         dht_local_t       *local = NULL;
-
+        dht_conf_t        *conf = NULL;
 
         local = frame->local;
         if (req_subvol)
@@ -137,6 +137,9 @@ dht_selfheal_dir_xattr_persubvol (call_frame_t *frame, loc_t *loc,
         GF_VALIDATE_OR_GOTO (this->name, layout, err);
         GF_VALIDATE_OR_GOTO (this->name, local, err);
         GF_VALIDATE_OR_GOTO (this->name, subvol, err);
+        VALIDATE_OR_GOTO (this->private, err);
+
+        conf = this->private;
 
         xattr = get_new_dict ();
         if (!xattr) {
@@ -151,8 +154,7 @@ dht_selfheal_dir_xattr_persubvol (call_frame_t *frame, loc_t *loc,
                 goto err;
         }
 
-        ret = dict_set_bin (xattr, "trusted.glusterfs.dht",
-                            disk_layout, 4 * 4);
+        ret = dict_set_bin (xattr, conf->xattr_name, disk_layout, 4 * 4);
         if (ret == -1) {
                 gf_log (this->name, GF_LOG_WARNING,
                         "%s: (subvol %s) failed to set xattr dictionary",
diff --git a/xlators/cluster/dht/src/dht.c b/xlators/cluster/dht/src/dht.c
index 14f3eb1d1ac..777086ab4bc 100644
--- a/xlators/cluster/dht/src/dht.c
+++ b/xlators/cluster/dht/src/dht.c
@@ -489,6 +489,7 @@ init (xlator_t *this)
         if (!conf) {
                 goto err;
         }
+        memset (conf, 0, sizeof(*conf));
 
         ret = dict_get_int32 (this->options, "rebalance-cmd", &cmd);
 
@@ -602,6 +603,13 @@ init (xlator_t *this)
                 goto err;
         }
 
+        GF_OPTION_INIT ("xattr-name", conf->xattr_name, str, err);
+        gf_asprintf (&conf->link_xattr_name, "%s.linkto", conf->xattr_name);
+        gf_asprintf (&conf->wild_xattr_name, "%s*", conf->xattr_name);
+        if (!conf->link_xattr_name || !conf->wild_xattr_name) {
+                goto err;
+        }
+
         this->private = conf;
 
         return 0;
@@ -623,6 +631,10 @@ err:
 
                 GF_FREE (conf->defrag);
 
+                GF_FREE (conf->xattr_name);
+                GF_FREE (conf->link_xattr_name);
+                GF_FREE (conf->wild_xattr_name);
+
                 GF_FREE (conf);
         }
 
@@ -781,6 +793,13 @@ struct volume_options options[] = {
         { .key = {"rebalance-filter"},
           .type = GF_OPTION_TYPE_STR,
         },
+        { .key = {"xattr-name"},
+          .type = GF_OPTION_TYPE_STR,
+          .default_value = "trusted.glusterfs.dht",
+          .description = "Base for extended attributes used by this "
+          "translator instance, to avoid conflicts with others above or "
+          "below it."
+        },
 
         { .key  = {NULL} },
 };
diff --git a/xlators/cluster/dht/src/nufa.c b/xlators/cluster/dht/src/nufa.c
index 52086e268bd..19f16d78a4d 100644
--- a/xlators/cluster/dht/src/nufa.c
+++ b/xlators/cluster/dht/src/nufa.c
@@ -52,7 +52,8 @@ nufa_local_lookup_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
         if (op_ret == -1)
                 goto out;
 
-        is_linkfile = check_is_linkfile (inode, stbuf, xattr);
+        is_linkfile = check_is_linkfile (inode, stbuf, xattr,
+                                         conf->link_xattr_name);
         is_dir      = check_is_dir (inode, stbuf, xattr);
 
         if (!is_dir && !is_linkfile) {
@@ -201,7 +202,7 @@ nufa_lookup (call_frame_t *frame, xlator_t *this,
                  *       revalidates directly go to the cached-subvolume.
                  */
                 ret = dict_set_uint32 (local->xattr_req,
-                                       "trusted.glusterfs.dht", 4 * 4);
+                                       conf->xattr_name, 4 * 4);
                 if (ret < 0) {
                         gf_log (this->name, GF_LOG_ERROR,
                                 "Failed to set dict value.");
@@ -222,7 +223,7 @@ nufa_lookup (call_frame_t *frame, xlator_t *this,
         } else {
         do_fresh_lookup:
                 ret = dict_set_uint32 (local->xattr_req,
-                                       "trusted.glusterfs.dht", 4 * 4);
+                                       conf->xattr_name, 4 * 4);
                 if (ret < 0) {
                         gf_log (this->name, GF_LOG_ERROR,
                                 "Failed to set dict value.");
@@ -231,7 +232,7 @@ nufa_lookup (call_frame_t *frame, xlator_t *this,
                 }
 
                 ret = dict_set_uint32 (local->xattr_req,
-                                       "trusted.glusterfs.dht.linkto", 256);
+                                       conf->link_xattr_name, 256);
                 if (ret < 0) {
                         gf_log (this->name, GF_LOG_ERROR,
                                 "Failed to set dict value.");
@@ -330,9 +331,8 @@ nufa_create (call_frame_t *frame, xlator_t *this,
                 local->flags = flags;
                 local->umask = umask;
                 local->cached_subvol = avail_subvol;
-                dht_linkfile_create (frame,
-                                     nufa_create_linkfile_create_cbk,
-                                     avail_subvol, subvol, loc);
+                dht_linkfile_create (frame, nufa_create_linkfile_create_cbk,
+                                     this, avail_subvol, subvol, loc);
                 return 0;
         }
 
@@ -437,7 +437,7 @@ nufa_mknod (call_frame_t *frame, xlator_t *this,
                 local->rdev = rdev;
                 local->cached_subvol = avail_subvol;
 
-                dht_linkfile_create (frame, nufa_mknod_linkfile_cbk,
+                dht_linkfile_create (frame, nufa_mknod_linkfile_cbk, this,
                                      avail_subvol, subvol, loc);
                 return 0;
         }
diff --git a/xlators/cluster/dht/src/switch.c b/xlators/cluster/dht/src/switch.c
index 6ec343102b6..8e0b69887cf 100644
--- a/xlators/cluster/dht/src/switch.c
+++ b/xlators/cluster/dht/src/switch.c
@@ -135,7 +135,8 @@ switch_local_lookup_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
         if (op_ret == -1)
                 goto out;
 
-        is_linkfile = check_is_linkfile (inode, stbuf, xattr);
+        is_linkfile = check_is_linkfile (inode, stbuf, xattr,
+                                         conf->link_xattr_name);
         is_dir      = check_is_dir (inode, stbuf, xattr);
 
         if (!is_dir && !is_linkfile) {
@@ -289,11 +290,11 @@ switch_lookup (call_frame_t *frame, xlator_t *this,
                  * attribute, revalidates directly go to the cached-subvolume.
                  */
                 ret = dict_set_uint32 (local->xattr_req,
-                                       "trusted.glusterfs.dht", 4 * 4);
+                                       conf->xattr_name, 4 * 4);
                 if (ret < 0)
                         gf_log (this->name, GF_LOG_WARNING,
-                                "failed to set dict value for "
-                                "trusted.glusterfs.dht");
+                                "failed to set dict value for %s",
+                                conf->xattr_name);
 
                 for (i = 0; i < layout->cnt; i++) {
                         subvol = layout->list[i].xlator;
@@ -308,18 +309,18 @@ switch_lookup (call_frame_t *frame, xlator_t *this,
         } else {
         do_fresh_lookup:
                 ret = dict_set_uint32 (local->xattr_req,
-                                       "trusted.glusterfs.dht", 4 * 4);
+                                       conf->xattr_name, 4 * 4);
                 if (ret < 0)
                         gf_log (this->name, GF_LOG_WARNING,
-                                "failed to set dict value for "
-                                "trusted.glusterfs.dht");
+                                "failed to set dict value for %s",
+                                conf->xattr_name);
 
                 ret = dict_set_uint32 (local->xattr_req,
-                                       "trusted.glusterfs.dht.linkto", 256);
+                                       conf->link_xattr_name, 256);
                 if (ret < 0)
                         gf_log (this->name, GF_LOG_WARNING,
-                                "failed to set dict value for "
-                                "trusted.glusterfs.dht.linkto");
+                                "failed to set dict value for %s",
+                                conf->link_xattr_name);
 
                 if (!hashed_subvol) {
                         gf_log (this->name, GF_LOG_DEBUG,
@@ -443,9 +444,8 @@ switch_create (call_frame_t *frame, xlator_t *this,
                 local->flags = flags;
                 local->umask = umask;
                 local->cached_subvol = avail_subvol;
-                dht_linkfile_create (frame,
-                                     switch_create_linkfile_create_cbk,
-                                     avail_subvol, subvol, loc);
+                dht_linkfile_create (frame, switch_create_linkfile_create_cbk,
+                                     this, avail_subvol, subvol, loc);
                 return 0;
         }
 
@@ -547,7 +547,7 @@ switch_mknod (call_frame_t *frame, xlator_t *this, loc_t *loc, mode_t mode,
                 local->cached_subvol = avail_subvol;
 
                 dht_linkfile_create (frame, switch_mknod_linkfile_cbk,
-                                     avail_subvol, subvol, loc);
+                                     this, avail_subvol, subvol, loc);
                 return 0;
         }