distribute: bring in feature to do rebalance from inside

do the 'rebalance' on a file with 'setxattr()' with
'distribute.migrate-data' key. the valid 'value' is "force" or
anything else.

current implementation of 'rebalance' is same as 'glusterd-rebalance',
and hence comes with limitation of not rebalancing hardlinks, non-regular
files, and files with open-fds.

Signed-off-by: Amar Tumballi <amar@gluster.com>
Signed-off-by: Anand Avati <avati@gluster.com>

BUG: 3070 (After 'rebalance', the gfid of the file gets changed)
URL: http://bugs.gluster.com/cgi-bin/bugzilla3/show_bug.cgi?id=3070

8 files changed, 600 insertions, 15 deletions

diff --git a/xlators/cluster/dht/src/Makefile.am b/xlators/cluster/dht/src/Makefile.am
index 8ebcab04451..cf883a974ca 100644
--- a/xlators/cluster/dht/src/Makefile.am
+++ b/xlators/cluster/dht/src/Makefile.am
@@ -3,11 +3,11 @@ xlator_LTLIBRARIES = dht.la nufa.la switch.la
 xlatordir = $(libdir)/glusterfs/$(PACKAGE_VERSION)/xlator/cluster
 
 
-dht_common_source = dht-layout.c dht-helper.c dht-linkfile.c \
+dht_common_source = dht-layout.c dht-helper.c dht-linkfile.c dht-rebalance.c \
 		dht-selfheal.c dht-rename.c dht-hashfn.c dht-diskusage.c \
 		$(top_builddir)/xlators/lib/src/libxlator.c
 
-dht_la_SOURCES = $(dht_common_source) dht.c 
+dht_la_SOURCES = $(dht_common_source) dht.c
 
 nufa_la_SOURCES = $(dht_common_source) nufa.c
 switch_la_SOURCES = $(dht_common_source) switch.c
@@ -27,7 +27,7 @@ AM_CFLAGS = -fPIC -D_FILE_OFFSET_BITS=64 -D_GNU_SOURCE -Wall -D$(GF_HOST_OS) \
 	-I$(top_srcdir)/libglusterfs/src -shared -nostartfiles $(GF_CFLAGS) \
 	-I$(top_srcdir)/xlators/lib/src
 
-CLEANFILES = 
+CLEANFILES =
 
 uninstall-local:
 	rm -f $(DESTDIR)$(xlatordir)/distribute.so
diff --git a/xlators/cluster/dht/src/dht-common.c b/xlators/cluster/dht/src/dht-common.c
index d5ee7ad1b90..c4bc0b4dfd9 100644
--- a/xlators/cluster/dht/src/dht-common.c
+++ b/xlators/cluster/dht/src/dht-common.c
@@ -2084,6 +2084,7 @@ dht_setxattr (call_frame_t *frame, xlator_t *this,
         data_t       *tmp      = NULL;
         uint32_t      dir_spread = 0;
         char          value[4096] = {0,};
+        int           forced_rebalance = 0;
 
 
         VALIDATE_OR_GOTO (frame, err);
@@ -2115,16 +2116,51 @@ dht_setxattr (call_frame_t *frame, xlator_t *this,
                 goto err;
         }
 
-        tmp = dict_get (xattr, GF_XATTR_FIX_LAYOUT_KEY);
+        ret = loc_dup (loc, &local->loc);
+        if (ret == -1) {
+                op_errno = ENOMEM;
+                goto err;
+        }
+
+        tmp = dict_get (xattr, "distribute.migrate-data");
         if (tmp) {
-                gf_log (this->name, GF_LOG_INFO,
-                        "fixing the layout of %s", loc->path);
+                if (!IA_ISREG (loc->inode->ia_type)) {
+                        op_errno = ENOTSUP;
+                        goto err;
+                }
 
-                ret = loc_dup (loc, &local->loc);
-                if (ret == -1) {
-                        op_errno = ENOMEM;
+                /* TODO: need to interpret the 'value' for more meaning
+                   (ie, 'target' subvolume given there, etc) */
+                memcpy (value, tmp->data, tmp->len);
+                if (strcmp (value, "force") == 0)
+                        forced_rebalance = 1;
+
+                local->to_subvol   = dht_subvol_get_hashed (this, loc);
+                local->from_subvol = dht_subvol_get_cached (this, loc->inode);
+                if (local->to_subvol == local->from_subvol) {
+                        op_errno = ENOTSUP;
                         goto err;
                 }
+                if (local->to_subvol) {
+                        local->flags = forced_rebalance;
+
+                        ret = dht_start_rebalance_task (this, frame);
+                        if (!ret)
+                                return 0;
+
+                        gf_log (this->name, GF_LOG_ERROR,
+                                "%s: failed to create a new synctask",
+                                loc->path);
+                }
+                op_errno = ENOTSUP;
+                goto err;
+
+        }
+
+        tmp = dict_get (xattr, GF_XATTR_FIX_LAYOUT_KEY);
+        if (tmp) {
+                gf_log (this->name, GF_LOG_INFO,
+                        "fixing the layout of %s", loc->path);
 
                 dht_fix_directory_layout (frame, dht_common_setxattr_cbk,
                                           layout);
@@ -2140,11 +2176,6 @@ dht_setxattr (call_frame_t *frame, xlator_t *this,
                              (dir_spread > 0))) {
                         layout->spread_cnt = dir_spread;
 
-                        ret = loc_dup (loc, &local->loc);
-                        if (ret == -1) {
-                                op_errno = ENOMEM;
-                                goto err;
-                        }
                         dht_fix_directory_layout (frame,
                                                   dht_common_setxattr_cbk,
                                                   layout);
@@ -4869,7 +4900,7 @@ dht_forget (xlator_t *this, inode_t *inode)
         uint64_t      tmp_layout = 0;
         dht_layout_t *layout = NULL;
 
-        inode_ctx_get (inode, this, &tmp_layout);
+        inode_ctx_del (inode, this, &tmp_layout);
 
         if (!tmp_layout)
                 return 0;
diff --git a/xlators/cluster/dht/src/dht-common.h b/xlators/cluster/dht/src/dht-common.h
index 43056c78c9f..2fe85d00e5f 100644
--- a/xlators/cluster/dht/src/dht-common.h
+++ b/xlators/cluster/dht/src/dht-common.h
@@ -24,6 +24,7 @@
 
 #include "dht-mem-types.h"
 #include "libxlator.h"
+#include "syncop.h"
 
 #ifndef _DHT_H
 #define _DHT_H
@@ -140,6 +141,10 @@ struct dht_local {
         /* flag used to make sure we need to return estale in
            {lookup,revalidate}_cbk */
         char    return_estale;
+
+        /* rebalance related */
+#define to_subvol    hashed_subvol
+#define from_subvol  cached_subvol
 };
 typedef struct dht_local dht_local_t;
 
@@ -178,6 +183,8 @@ struct dht_conf {
         /* This is the count used as the distribute layout for a directory */
         /* Will be a global flag to control the layout spread count */
         uint32_t       dir_spread_cnt;
+
+	struct syncenv *env; /* The env pointer to the rebalance synctask */
 };
 typedef struct dht_conf dht_conf_t;
 
@@ -330,4 +337,5 @@ int dht_fix_directory_layout (call_frame_t *frame,
                               dht_selfheal_dir_cbk_t dir_cbk,
                               dht_layout_t *layout);
 
+int dht_start_rebalance_task (xlator_t *this, call_frame_t *frame);
 #endif /* _DHT_H */
diff --git a/xlators/cluster/dht/src/dht-mem-types.h b/xlators/cluster/dht/src/dht-mem-types.h
index 38bd3de1581..9dc2648a279 100644
--- a/xlators/cluster/dht/src/dht-mem-types.h
+++ b/xlators/cluster/dht/src/dht-mem-types.h
@@ -36,6 +36,7 @@ enum gf_dht_mem_types_ {
         gf_switch_mt_switch_sched_array,
         gf_switch_mt_switch_struct,
         gf_dht_mt_subvol_time,
+        gf_dht_mt_loc_t,
         gf_dht_mt_end
 };
 #endif
diff --git a/xlators/cluster/dht/src/dht-rebalance.c b/xlators/cluster/dht/src/dht-rebalance.c
new file mode 100644
index 00000000000..6dea40f0b57
--- /dev/null
+++ b/xlators/cluster/dht/src/dht-rebalance.c
@@ -0,0 +1,518 @@
+/*
+  Copyright (c) 2011 Gluster, Inc. <http://www.gluster.com>
+  This file is part of GlusterFS.
+
+  GlusterFS is free software; you can redistribute it and/or modify
+  it under the terms of the GNU Affero General Public License as published
+  by the Free Software Foundation; either version 3 of the License,
+  or (at your option) any later version.
+
+  GlusterFS is distributed in the hope that it will be useful, but
+  WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Affero General Public License for more details.
+
+  You should have received a copy of the GNU Affero General Public License
+  along with this program.  If not, see
+  <http://www.gnu.org/licenses/>.
+*/
+
+
+#ifndef _CONFIG_H
+#define _CONFIG_H
+#include "config.h"
+#endif
+
+#include "dht-common.h"
+
+#define GF_DISK_SECTOR_SIZE             512
+#define DHT_REBALANCE_PID               4242 /* Change it if required */
+#define DHT_REBALANCE_BLKSIZE           (128 * 1024)
+#define DHT_MIGRATE_EVEN_IF_LINK_EXISTS 1
+
+static int
+dht_write_with_holes (xlator_t *to, fd_t *fd, struct iovec *vec, int count,
+                      int32_t size, off_t offset, struct iobref *iobref)
+{
+        int i            = 0;
+        int ret          = -1;
+        int start_idx    = 0;
+        int tmp_offset   = 0;
+        int write_needed = 0;
+        int buf_len      = 0;
+        int size_pending = 0;
+        char *buf        = NULL;
+
+        /* loop through each vector */
+        for (i = 0; i < count; i++) {
+                buf = vec[i].iov_base;
+                buf_len = vec[i].iov_len;
+
+                for (start_idx = 0; (start_idx + GF_DISK_SECTOR_SIZE) <= buf_len;
+                     start_idx += GF_DISK_SECTOR_SIZE) {
+
+                        if (mem_0filled (buf + start_idx, GF_DISK_SECTOR_SIZE) != 0) {
+                                write_needed = 1;
+                                continue;
+                        }
+
+                        if (write_needed) {
+                                ret = syncop_write (to, fd, (buf + tmp_offset),
+                                                    (start_idx - tmp_offset),
+                                                    (offset + tmp_offset),
+                                                    iobref);
+                                if (ret < 0)
+                                        goto out;
+
+                                write_needed = 0;
+                        }
+                        tmp_offset = start_idx + GF_DISK_SECTOR_SIZE;
+                }
+
+                if ((start_idx < buf_len) || write_needed) {
+                        /* This means, last chunk is not yet written.. write it */
+                        ret = syncop_write (to, fd, (buf + tmp_offset),
+                                            (buf_len - tmp_offset),
+                                            (offset + tmp_offset), iobref);
+                        if (ret < 0)
+                                goto out;
+                }
+
+                size_pending = (size - buf_len);
+                if (!size_pending)
+                        break;
+        }
+
+        /* do it regardless of all the above cases as we had to 'write' the
+           given number of bytes */
+        ret = syncop_ftruncate (to, fd, offset + size);
+        if (ret) {
+                gf_log (THIS->name, GF_LOG_WARNING,
+                        "failed to perform truncate on %s", to->name);
+                goto out;
+        }
+
+        ret = size;
+out:
+        return ret;
+
+}
+
+static inline int
+__is_file_migratable (xlator_t *this, loc_t *loc, dict_t *rsp_dict,
+                      struct iatt *stbuf)
+{
+        int ret           = -1;
+        int open_fd_count = 0;
+
+        if (!IA_ISREG (stbuf->ia_type)) {
+                gf_log (this->name, GF_LOG_WARNING,
+                        "%s: migrate-file called on non-regular entry (0%o)",
+                        loc->path, stbuf->ia_type);
+                ret = -1;
+                goto out;
+        }
+
+        if (stbuf->ia_nlink > 1) {
+                /* TODO : support migrating hardlinks */
+                gf_log (this->name, GF_LOG_WARNING, "%s: file has hardlinks",
+                        loc->path);
+                ret = -ENOTSUP;
+                goto out;
+        }
+
+        ret = dict_get_int32 (rsp_dict, GLUSTERFS_OPEN_FD_COUNT, &open_fd_count);
+        if (!ret && (open_fd_count > 0)) {
+                /* TODO: support migration of files with open fds */
+                gf_log (this->name, GF_LOG_WARNING,
+                        "%s: file has open fds, not attempting migration",
+                        loc->path);
+                goto out;
+        }
+        ret = 0;
+
+out:
+        return ret;
+}
+
+static inline int
+__dht_rebalance_create_dst_file (xlator_t *to, loc_t *loc, struct iatt *stbuf,
+                                 dict_t *dict, fd_t **dst_fd, int *need_unlink)
+{
+        xlator_t *this = NULL;
+        int       ret  = -1;
+        mode_t    mode = 0;
+        fd_t     *fd   = NULL;
+        struct iatt new_stbuf = {0,};
+
+        this = THIS;
+
+        ret = dict_set_static_bin (dict, "gfid-req", stbuf->ia_gfid, 16);
+        if (ret) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "%s: failed to set gfid in dict for create", loc->path);
+                goto out;
+        }
+
+        fd = fd_create (loc->inode, DHT_REBALANCE_PID);
+        if (!fd) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "%s: fd create failed (destination)", loc->path);
+                ret = -1;
+                goto out;
+        }
+
+        ret = syncop_lookup (to, loc, NULL, &new_stbuf, NULL, NULL);
+        if (ret) {
+                gf_log (this->name, GF_LOG_DEBUG, "failed to lookup %s on %s",
+                        loc->path, to->name);
+
+                mode = st_mode_from_ia (stbuf->ia_prot, stbuf->ia_type);
+                ret = syncop_create (to, loc, O_WRONLY, mode, fd, dict);
+                if (ret < 0) {
+                        gf_log (this->name, GF_LOG_ERROR,
+                                "failed to create %s on %s", loc->path, to->name);
+                        goto out;
+                }
+
+                *need_unlink = 1;
+                goto done;
+        }
+
+        /* File exits in the destination, just do the open if gfid matches */
+        if (uuid_compare (stbuf->ia_gfid, new_stbuf.ia_gfid) != 0) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "file %s exits in %s with different gfid",
+                        loc->path, to->name);
+                fd_unref (fd);
+                goto out;
+        }
+
+        ret = syncop_open (to, loc, O_WRONLY, fd);
+        if (ret < 0) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "failed to open file %s on %s",
+                        loc->path, to->name);
+                fd_unref (fd);
+                goto out;
+        }
+done:
+        if (dst_fd)
+                *dst_fd = fd;
+
+        /* success */
+        ret = 0;
+
+out:
+        return ret;
+}
+
+static inline int
+__dht_check_free_space (xlator_t *to, xlator_t *from, loc_t *loc,
+                        struct iatt *stbuf)
+{
+        struct statvfs  src_statfs = {0,};
+        struct statvfs  dst_statfs = {0,};
+        int             ret        = -1;
+        xlator_t       *this       = NULL;
+
+        this = THIS;
+
+        ret = syncop_statfs (from, loc, &src_statfs);
+        if (ret) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "failed to get statfs of %s on %s",
+                        loc->path, from->name);
+                goto out;
+        }
+
+        ret = syncop_statfs (to, loc, &dst_statfs);
+        if (ret) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "failed to get statfs of %s on %s",
+                        loc->path, to->name);
+                goto out;
+        }
+        if (((dst_statfs.f_bavail *
+              dst_statfs.f_bsize) / GF_DISK_SECTOR_SIZE) >
+            (((src_statfs.f_bavail * src_statfs.f_bsize) /
+              GF_DISK_SECTOR_SIZE) - stbuf->ia_blocks)) {
+                gf_log (this->name, GF_LOG_WARNING,
+                        "data movement attempted from node (%s) with"
+                        " higher disk space to a node (%s) with "
+                        "lesser disk space (%s)", from->name,
+                        to->name, loc->path);
+
+                ret = -1;
+                goto out;
+        }
+
+        ret = 0;
+out:
+        return ret;
+}
+
+static inline int
+__dht_rebalane_migrate_data (xlator_t *from, xlator_t *to, fd_t *src, fd_t *dst,
+                             int hole_exists)
+{
+        int            ret    = -1;
+        int            count  = 0;
+        off_t          offset = 0;
+        struct iovec  *vector = NULL;
+        struct iobref *iobref = NULL;
+
+        while (1) {
+                ret = syncop_readv (from, src, DHT_REBALANCE_BLKSIZE,
+                                    offset, &vector, &count, &iobref);
+                if (!ret || (ret < 0)) {
+                        break;
+                }
+
+                if (hole_exists)
+                        ret = dht_write_with_holes (to, dst, vector, count,
+                                                    ret, offset, iobref);
+                else
+                        ret = syncop_writev (to, dst, vector, count,
+                                             offset, iobref);
+                if (ret < 0) {
+                        break;
+                }
+                offset += ret;
+
+                if (vector)
+                        GF_FREE (vector);
+                if (iobref)
+                        iobref_unref (iobref);
+                iobref = NULL;
+                vector = NULL;
+        }
+        if (iobref)
+                iobref_unref (iobref);
+        if (vector)
+                GF_FREE (vector);
+
+        if (ret >= 0)
+                ret = 0;
+
+        return ret;
+}
+
+int
+dht_migrate_file (xlator_t *this, loc_t *loc, xlator_t *from, xlator_t *to,
+                  int flag)
+{
+        int             ret            = -1;
+        struct iatt     new_stbuf      = {0,};
+        struct iatt     stbuf          = {0,};
+        fd_t           *src_fd         = NULL;
+        fd_t           *dst_fd         = NULL;
+        dict_t         *dict           = NULL;
+        dict_t         *xattr          = NULL;
+        dict_t         *rsp_dict       = NULL;
+        int             file_has_holes = 0;
+        int             need_unlink    = 0;
+
+        gf_log (this->name, GF_LOG_INFO, "%s: attempting to move from %s to %s",
+                loc->path, from->name, to->name);
+
+        dict = dict_new ();
+        if (!dict)
+                goto out;
+
+        ret = dict_set_int32 (dict, GLUSTERFS_OPEN_FD_COUNT, 4);
+        if (ret)
+                gf_log (this->name, GF_LOG_WARNING,
+                        "%s: failed to set fd-count key in dict, may attempt "
+                        "migration of file which has open fds", loc->path);
+
+        ret = syncop_lookup (from, loc, dict, &stbuf, &rsp_dict, NULL);
+        if (ret) {
+                gf_log (this->name, GF_LOG_ERROR, "failed to lookup %s on %s",
+                        loc->path, from->name);
+                goto out;
+        }
+
+        /* Check if file can be migrated */
+        ret = __is_file_migratable (this, loc, rsp_dict, &stbuf);
+        if (ret)
+                goto out;
+
+        /* create the destination */
+        ret = __dht_rebalance_create_dst_file (to, loc, &stbuf, dict, &dst_fd,
+                                               &need_unlink);
+        if (ret)
+                goto out;
+
+        /* Should happen on all files when 'force' option is not given */
+        if (flag != DHT_MIGRATE_EVEN_IF_LINK_EXISTS) {
+                ret = __dht_check_free_space (to, from, loc, &stbuf);
+                if (ret)
+                        goto out;
+        }
+
+        /* Try to preserve 'holes' while migrating data */
+        if (stbuf.ia_size > (stbuf.ia_blocks * GF_DISK_SECTOR_SIZE))
+                file_has_holes = 1;
+
+        src_fd = fd_create (loc->inode, DHT_REBALANCE_PID);
+        if (!src_fd) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "%s: fd create failed (source)", loc->path);
+                ret = -1;
+                goto out;
+        }
+
+        ret = syncop_open (from, loc, O_RDONLY, src_fd);
+        if (ret == -1) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "failed to open file %s on %s",
+                        loc->path, from->name);
+                goto out;
+        }
+
+        /* All I/O happens in this function */
+        ret = __dht_rebalane_migrate_data (from, to, src_fd, dst_fd,
+                                           file_has_holes);
+        if (ret) {
+                gf_log (this->name, GF_LOG_ERROR, "%s: failed to migrate data",
+                        loc->path);
+                goto out;
+        }
+
+        ret = syncop_lookup (from, loc, NULL, &new_stbuf, NULL, NULL);
+        if (ret < 0) {
+                /* Failed to get the stat info */
+                gf_log (this->name, GF_LOG_ERROR,
+                        "failed to lookup file %s on %s",
+                        loc->path, from->name);
+                need_unlink = 0;
+                goto out;
+        }
+
+        /* No need to rebalance, if there is some
+           activity on source file */
+        if (new_stbuf.ia_mtime != stbuf.ia_mtime) {
+                gf_log (this->name, GF_LOG_WARNING,
+                        "%s: ignoring destination file as source has "
+                        "undergone some changes while migration was happening",
+                        loc->path);
+                ret = -1;
+                goto out;
+        }
+
+        ret = syncop_setattr (to, loc, &new_stbuf,
+                              (GF_SET_ATTR_UID | GF_SET_ATTR_GID |
+                               GF_SET_ATTR_MODE | GF_SET_ATTR_ATIME |
+                               GF_SET_ATTR_MTIME), NULL, NULL);
+        if (ret) {
+                gf_log (this->name, GF_LOG_WARNING,
+                        "%s: failed to perform setattr on %s",
+                        loc->path, to->name);
+        }
+
+        ret = syncop_listxattr (from, loc, &xattr);
+        if (ret == -1)
+                gf_log (this->name, GF_LOG_WARNING,
+                        "%s: failed to get xattr from %s", loc->path, from->name);
+
+        ret = syncop_setxattr (to, loc, xattr, 0);
+        if (ret == -1)
+                gf_log (this->name, GF_LOG_WARNING,
+                        "%s: failed to set xattr on %s", loc->path, to->name);
+
+        /* rebalance complete */
+        syncop_close (dst_fd);
+        syncop_close (src_fd);
+        syncop_unlink (from, loc);
+        need_unlink = 0;
+
+        gf_log (this->name, GF_LOG_INFO,
+                "completed migration of %s from subvolume %s to %s",
+                loc->path, from->name, to->name);
+
+        ret = 0;
+out:
+        if (dict)
+                dict_unref (dict);
+
+        if (ret) {
+                if (dst_fd)
+                        syncop_close (dst_fd);
+                if (src_fd)
+                        syncop_close (src_fd);
+                if (need_unlink)
+                        syncop_unlink (to, loc);
+        }
+
+        return ret;
+}
+
+static int
+rebalance_task (void *data)
+{
+        int           ret   = -1;
+        xlator_t     *this  = NULL;
+        dht_local_t  *local = NULL;
+        call_frame_t *frame = NULL;
+
+        frame = data;
+        this = THIS;
+
+        local = frame->local;
+
+        /* This function is 'synchrounous', hence if it returns,
+           we are done with the task */
+        ret = dht_migrate_file (THIS, &local->loc, local->from_subvol,
+                                local->to_subvol, local->flags);
+
+        return ret;
+}
+
+static int
+rebalance_task_completion (int op_ret, call_frame_t *sync_frame, void *data)
+{
+        int           ret        = -1;
+        uint64_t      layout_int = 0;
+        dht_layout_t *layout     = 0;
+        xlator_t     *this       = NULL;
+        dht_local_t  *local      = NULL;
+
+        this = THIS;
+        local = sync_frame->local;
+
+        if (!op_ret) {
+                /* Make sure we have valid 'layout' in inode ctx
+                   after the operation */
+                ret = inode_ctx_del (local->loc.inode, this, &layout_int);
+                if (!ret && layout_int) {
+                        layout = (dht_layout_t *)(long)layout_int;
+                        dht_layout_unref (this, layout);
+                }
+
+                ret = dht_layout_preset (this, local->to_subvol,
+                                         local->loc.inode);
+                if (ret)
+                        gf_log (this->name, GF_LOG_WARNING,
+                                "%s: failed to set inode ctx", local->loc.path);
+        }
+
+        /* if success, errno is not checked,
+           if ret is -1, then let errno be 'ENOTSUP' */
+        DHT_STACK_UNWIND (setxattr, sync_frame, op_ret, ENOTSUP);
+        return 0;
+}
+
+int
+dht_start_rebalance_task (xlator_t *this, call_frame_t *frame)
+{
+        int         ret     = -1;
+        dht_conf_t *conf    = NULL;
+
+        conf = this->private;
+
+        ret = synctask_new (conf->env, rebalance_task,
+                            rebalance_task_completion,
+                            frame, frame);
+        return ret;
+}
diff --git a/xlators/cluster/dht/src/dht.c b/xlators/cluster/dht/src/dht.c
index 42f0c0d75e8..e78ee1b45e6 100644
--- a/xlators/cluster/dht/src/dht.c
+++ b/xlators/cluster/dht/src/dht.c
@@ -501,6 +501,15 @@ init (xlator_t *this)
 
         conf->gen = 1;
 
+        /* Create 'syncop' environment */
+	conf->env = syncenv_new (0);
+        if (!conf->env) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "failed to create sync environment %s",
+                        strerror (errno));
+                goto err;
+        }
+
         this->private = conf;
 
         return 0;
diff --git a/xlators/cluster/dht/src/nufa.c b/xlators/cluster/dht/src/nufa.c
index 45fea55ae3b..b3d17351a9b 100644
--- a/xlators/cluster/dht/src/nufa.c
+++ b/xlators/cluster/dht/src/nufa.c
@@ -644,6 +644,15 @@ init (xlator_t *this)
                 goto err;
         }
 
+        /* Create 'syncop' environment */
+	conf->env = syncenv_new (0);
+        if (!conf->env) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "failed to create sync environment %s",
+                        strerror (errno));
+                goto err;
+        }
+
         this->private = conf;
 
         return 0;
diff --git a/xlators/cluster/dht/src/switch.c b/xlators/cluster/dht/src/switch.c
index e4bed0dd96e..211834fb5fe 100644
--- a/xlators/cluster/dht/src/switch.c
+++ b/xlators/cluster/dht/src/switch.c
@@ -949,6 +949,15 @@ init (xlator_t *this)
                 goto err;
         }
 
+        /* Create 'syncop' environment */
+	conf->env = syncenv_new (0);
+        if (!conf->env) {
+                gf_log (this->name, GF_LOG_ERROR,
+                        "failed to create sync environment %s",
+                        strerror (errno));
+                goto err;
+        }
+
         this->private = conf;
 
         return 0;