diff --git a/fs/ocfs2/Makefile b/fs/ocfs2/Makefile
index d2057e7..3591890 100644
--- a/fs/ocfs2/Makefile
+++ b/fs/ocfs2/Makefile
@@ -21,6 +21,7 @@
 	localalloc.o 		\
 	mmap.o 			\
 	namei.o 		\
+	resize.o		\
 	slot_map.o 		\
 	suballoc.o 		\
 	super.o 		\
diff --git a/fs/ocfs2/buffer_head_io.c b/fs/ocfs2/buffer_head_io.c
index c903741..31aa61d 100644
--- a/fs/ocfs2/buffer_head_io.c
+++ b/fs/ocfs2/buffer_head_io.c
@@ -280,3 +280,64 @@
 	mlog_exit(status);
 	return status;
 }
+
+/* Check whether the blkno is the super block or one of the backups. */
+static void ocfs2_check_super_or_backup(struct super_block *sb,
+					sector_t blkno)
+{
+	int i;
+	u64 backup_blkno;
+
+	if (blkno == OCFS2_SUPER_BLOCK_BLKNO)
+		return;
+
+	for (i = 0; i < OCFS2_MAX_BACKUP_SUPERBLOCKS; i++) {
+		backup_blkno = ocfs2_backup_super_blkno(sb, i);
+		if (backup_blkno == blkno)
+			return;
+	}
+
+	BUG();
+}
+
+/*
+ * Write super block and backups doesn't need to collaborate with journal,
+ * so we don't need to lock ip_io_mutex and inode doesn't need to bea passed
+ * into this function.
+ */
+int ocfs2_write_super_or_backup(struct ocfs2_super *osb,
+				struct buffer_head *bh)
+{
+	int ret = 0;
+
+	mlog_entry_void();
+
+	BUG_ON(buffer_jbd(bh));
+	ocfs2_check_super_or_backup(osb->sb, bh->b_blocknr);
+
+	if (ocfs2_is_hard_readonly(osb) || ocfs2_is_soft_readonly(osb)) {
+		ret = -EROFS;
+		goto out;
+	}
+
+	lock_buffer(bh);
+	set_buffer_uptodate(bh);
+
+	/* remove from dirty list before I/O. */
+	clear_buffer_dirty(bh);
+
+	get_bh(bh); /* for end_buffer_write_sync() */
+	bh->b_end_io = end_buffer_write_sync;
+	submit_bh(WRITE, bh);
+
+	wait_on_buffer(bh);
+
+	if (!buffer_uptodate(bh)) {
+		ret = -EIO;
+		brelse(bh);
+	}
+
+out:
+	mlog_exit(ret);
+	return ret;
+}
diff --git a/fs/ocfs2/buffer_head_io.h b/fs/ocfs2/buffer_head_io.h
index 6cc2093..c2e7861 100644
--- a/fs/ocfs2/buffer_head_io.h
+++ b/fs/ocfs2/buffer_head_io.h
@@ -47,6 +47,8 @@
 		      int                  flags,
 		      struct inode        *inode);
 
+int ocfs2_write_super_or_backup(struct ocfs2_super *osb,
+				struct buffer_head *bh);
 
 #define OCFS2_BH_CACHED            1
 #define OCFS2_BH_READAHEAD         8
diff --git a/fs/ocfs2/ioctl.c b/fs/ocfs2/ioctl.c
index 67c2fb4..b74b24e 100644
--- a/fs/ocfs2/ioctl.c
+++ b/fs/ocfs2/ioctl.c
@@ -20,6 +20,7 @@
 
 #include "ocfs2_fs.h"
 #include "ioctl.h"
+#include "resize.h"
 
 #include <linux/ext2_fs.h>
 
@@ -115,6 +116,7 @@
 	unsigned int cmd, unsigned long arg)
 {
 	unsigned int flags;
+	int new_clusters;
 	int status;
 	struct ocfs2_space_resv sr;
 
@@ -140,6 +142,11 @@
 			return -EFAULT;
 
 		return ocfs2_change_file_space(filp, cmd, &sr);
+	case OCFS2_IOC_GROUP_EXTEND:
+		if (get_user(new_clusters, (int __user *)arg))
+			return -EFAULT;
+
+		return ocfs2_group_extend(inode, new_clusters);
 	default:
 		return -ENOTTY;
 	}
@@ -162,6 +169,7 @@
 	case OCFS2_IOC_RESVSP64:
 	case OCFS2_IOC_UNRESVSP:
 	case OCFS2_IOC_UNRESVSP64:
+	case OCFS2_IOC_GROUP_EXTEND:
 		break;
 	default:
 		return -ENOIOCTLCMD;
diff --git a/fs/ocfs2/journal.h b/fs/ocfs2/journal.h
index 4b32e09..0ba3a42 100644
--- a/fs/ocfs2/journal.h
+++ b/fs/ocfs2/journal.h
@@ -278,6 +278,9 @@
 /* simple file updates like chmod, etc. */
 #define OCFS2_INODE_UPDATE_CREDITS 1
 
+/* group extend. inode update and last group update. */
+#define OCFS2_GROUP_EXTEND_CREDITS	(OCFS2_INODE_UPDATE_CREDITS + 1)
+
 /* get one bit out of a suballocator: dinode + group descriptor +
  * prev. group desc. if we relink. */
 #define OCFS2_SUBALLOC_ALLOC (3)
diff --git a/fs/ocfs2/ocfs2_fs.h b/fs/ocfs2/ocfs2_fs.h
index 6ef8767..19ac421b 100644
--- a/fs/ocfs2/ocfs2_fs.h
+++ b/fs/ocfs2/ocfs2_fs.h
@@ -231,6 +231,8 @@
 #define OCFS2_IOC_RESVSP64	_IOW ('X', 42, struct ocfs2_space_resv)
 #define OCFS2_IOC_UNRESVSP64	_IOW ('X', 43, struct ocfs2_space_resv)
 
+#define OCFS2_IOC_GROUP_EXTEND	_IOW('o', 1, int)
+
 /*
  * Journal Flags (ocfs2_dinode.id1.journal1.i_flags)
  */
diff --git a/fs/ocfs2/resize.c b/fs/ocfs2/resize.c
new file mode 100644
index 0000000..848f729
--- /dev/null
+++ b/fs/ocfs2/resize.c
@@ -0,0 +1,398 @@
+/* -*- mode: c; c-basic-offset: 8; -*-
+ * vim: noexpandtab sw=8 ts=8 sts=0:
+ *
+ * resize.c
+ *
+ * volume resize.
+ * Inspired by ext3/resize.c.
+ *
+ * Copyright (C) 2007 Oracle.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This program 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
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#include <linux/fs.h>
+#include <linux/types.h>
+
+#define MLOG_MASK_PREFIX ML_DISK_ALLOC
+#include <cluster/masklog.h>
+
+#include "ocfs2.h"
+
+#include "alloc.h"
+#include "dlmglue.h"
+#include "inode.h"
+#include "journal.h"
+#include "super.h"
+#include "sysfile.h"
+#include "uptodate.h"
+
+#include "buffer_head_io.h"
+#include "suballoc.h"
+#include "resize.h"
+
+/*
+ * Check whether there are new backup superblocks exist
+ * in the last group. If there are some, mark them or clear
+ * them in the bitmap.
+ *
+ * Return how many backups we find in the last group.
+ */
+static u16 ocfs2_calc_new_backup_super(struct inode *inode,
+				       struct ocfs2_group_desc *gd,
+				       int new_clusters,
+				       u32 first_new_cluster,
+				       u16 cl_cpg,
+				       int set)
+{
+	int i;
+	u16 backups = 0;
+	u32 cluster;
+	u64 blkno, gd_blkno, lgd_blkno = le64_to_cpu(gd->bg_blkno);
+
+	for (i = 0; i < OCFS2_MAX_BACKUP_SUPERBLOCKS; i++) {
+		blkno = ocfs2_backup_super_blkno(inode->i_sb, i);
+		cluster = ocfs2_blocks_to_clusters(inode->i_sb, blkno);
+
+		gd_blkno = ocfs2_which_cluster_group(inode, cluster);
+		if (gd_blkno < lgd_blkno)
+			continue;
+		else if (gd_blkno > lgd_blkno)
+			break;
+
+		if (set)
+			ocfs2_set_bit(cluster % cl_cpg,
+				      (unsigned long *)gd->bg_bitmap);
+		else
+			ocfs2_clear_bit(cluster % cl_cpg,
+					(unsigned long *)gd->bg_bitmap);
+		backups++;
+	}
+
+	mlog_exit_void();
+	return backups;
+}
+
+static int ocfs2_update_last_group_and_inode(handle_t *handle,
+					     struct inode *bm_inode,
+					     struct buffer_head *bm_bh,
+					     struct buffer_head *group_bh,
+					     u32 first_new_cluster,
+					     int new_clusters)
+{
+	int ret = 0;
+	struct ocfs2_super *osb = OCFS2_SB(bm_inode->i_sb);
+	struct ocfs2_dinode *fe = (struct ocfs2_dinode *) bm_bh->b_data;
+	struct ocfs2_chain_list *cl = &fe->id2.i_chain;
+	struct ocfs2_chain_rec *cr;
+	struct ocfs2_group_desc *group;
+	u16 chain, num_bits, backups = 0;
+	u16 cl_bpc = le16_to_cpu(cl->cl_bpc);
+	u16 cl_cpg = le16_to_cpu(cl->cl_cpg);
+
+	mlog_entry("(new_clusters=%d, first_new_cluster = %u)\n",
+		   new_clusters, first_new_cluster);
+
+	ret = ocfs2_journal_access(handle, bm_inode, group_bh,
+				   OCFS2_JOURNAL_ACCESS_WRITE);
+	if (ret < 0) {
+		mlog_errno(ret);
+		goto out;
+	}
+
+	group = (struct ocfs2_group_desc *)group_bh->b_data;
+
+	/* update the group first. */
+	num_bits = new_clusters * cl_bpc;
+	le16_add_cpu(&group->bg_bits, num_bits);
+	le16_add_cpu(&group->bg_free_bits_count, num_bits);
+
+	/*
+	 * check whether there are some new backup superblocks exist in
+	 * this group and update the group bitmap accordingly.
+	 */
+	if (OCFS2_HAS_COMPAT_FEATURE(osb->sb,
+				     OCFS2_FEATURE_COMPAT_BACKUP_SB)) {
+		backups = ocfs2_calc_new_backup_super(bm_inode,
+						     group,
+						     new_clusters,
+						     first_new_cluster,
+						     cl_cpg, 1);
+		le16_add_cpu(&group->bg_free_bits_count, -1 * backups);
+	}
+
+	ret = ocfs2_journal_dirty(handle, group_bh);
+	if (ret < 0) {
+		mlog_errno(ret);
+		goto out_rollback;
+	}
+
+	/* update the inode accordingly. */
+	ret = ocfs2_journal_access(handle, bm_inode, bm_bh,
+				   OCFS2_JOURNAL_ACCESS_WRITE);
+	if (ret < 0) {
+		mlog_errno(ret);
+		goto out_rollback;
+	}
+
+	chain = le16_to_cpu(group->bg_chain);
+	cr = (&cl->cl_recs[chain]);
+	le32_add_cpu(&cr->c_total, num_bits);
+	le32_add_cpu(&cr->c_free, num_bits);
+	le32_add_cpu(&fe->id1.bitmap1.i_total, num_bits);
+	le32_add_cpu(&fe->i_clusters, new_clusters);
+
+	if (backups) {
+		le32_add_cpu(&cr->c_free, -1 * backups);
+		le32_add_cpu(&fe->id1.bitmap1.i_used, backups);
+	}
+
+	spin_lock(&OCFS2_I(bm_inode)->ip_lock);
+	OCFS2_I(bm_inode)->ip_clusters = le32_to_cpu(fe->i_clusters);
+	le64_add_cpu(&fe->i_size, new_clusters << osb->s_clustersize_bits);
+	spin_unlock(&OCFS2_I(bm_inode)->ip_lock);
+	i_size_write(bm_inode, le64_to_cpu(fe->i_size));
+
+	ocfs2_journal_dirty(handle, bm_bh);
+
+out_rollback:
+	if (ret < 0) {
+		ocfs2_calc_new_backup_super(bm_inode,
+					    group,
+					    new_clusters,
+					    first_new_cluster,
+					    cl_cpg, 0);
+		le16_add_cpu(&group->bg_free_bits_count, backups);
+		le16_add_cpu(&group->bg_bits, -1 * num_bits);
+		le16_add_cpu(&group->bg_free_bits_count, -1 * num_bits);
+	}
+out:
+	mlog_exit(ret);
+	return ret;
+}
+
+static int update_backups(struct inode * inode, u32 clusters, char *data)
+{
+	int i, ret = 0;
+	u32 cluster;
+	u64 blkno;
+	struct buffer_head *backup = NULL;
+	struct ocfs2_dinode *backup_di = NULL;
+	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
+
+	/* calculate the real backups we need to update. */
+	for (i = 0; i < OCFS2_MAX_BACKUP_SUPERBLOCKS; i++) {
+		blkno = ocfs2_backup_super_blkno(inode->i_sb, i);
+		cluster = ocfs2_blocks_to_clusters(inode->i_sb, blkno);
+		if (cluster > clusters)
+			break;
+
+		ret = ocfs2_read_block(osb, blkno, &backup, 0, NULL);
+		if (ret < 0) {
+			mlog_errno(ret);
+			break;
+		}
+
+		memcpy(backup->b_data, data, inode->i_sb->s_blocksize);
+
+		backup_di = (struct ocfs2_dinode *)backup->b_data;
+		backup_di->i_blkno = cpu_to_le64(blkno);
+
+		ret = ocfs2_write_super_or_backup(osb, backup);
+		brelse(backup);
+		backup = NULL;
+		if (ret < 0) {
+			mlog_errno(ret);
+			break;
+		}
+	}
+
+	return ret;
+}
+
+static void ocfs2_update_super_and_backups(struct inode *inode,
+					   int new_clusters)
+{
+	int ret;
+	u32 clusters = 0;
+	struct buffer_head *super_bh = NULL;
+	struct ocfs2_dinode *super_di = NULL;
+	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
+
+	/*
+	 * update the superblock last.
+	 * It doesn't matter if the write failed.
+	 */
+	ret = ocfs2_read_block(osb, OCFS2_SUPER_BLOCK_BLKNO,
+			       &super_bh, 0, NULL);
+	if (ret < 0) {
+		mlog_errno(ret);
+		goto out;
+	}
+
+	super_di = (struct ocfs2_dinode *)super_bh->b_data;
+	le32_add_cpu(&super_di->i_clusters, new_clusters);
+	clusters = le32_to_cpu(super_di->i_clusters);
+
+	ret = ocfs2_write_super_or_backup(osb, super_bh);
+	if (ret < 0) {
+		mlog_errno(ret);
+		goto out;
+	}
+
+	if (OCFS2_HAS_COMPAT_FEATURE(osb->sb, OCFS2_FEATURE_COMPAT_BACKUP_SB))
+		ret = update_backups(inode, clusters, super_bh->b_data);
+
+out:
+	if (super_bh)
+		brelse(super_bh);
+	if (ret)
+		printk(KERN_WARNING "ocfs2: Failed to update super blocks on %s"
+			" during fs resize. This condition is not fatal,"
+			" but fsck.ocfs2 should be run to fix it\n",
+			osb->dev_str);
+	return;
+}
+
+/*
+ * Extend the filesystem to the new number of clusters specified.  This entry
+ * point is only used to extend the current filesystem to the end of the last
+ * existing group.
+ */
+int ocfs2_group_extend(struct inode * inode, int new_clusters)
+{
+	int ret;
+	handle_t *handle;
+	struct buffer_head *main_bm_bh = NULL;
+	struct buffer_head *group_bh = NULL;
+	struct inode *main_bm_inode = NULL;
+	struct ocfs2_dinode *fe = NULL;
+	struct ocfs2_group_desc *group = NULL;
+	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
+	u16 cl_bpc;
+	u32 first_new_cluster;
+	u64 lgd_blkno;
+
+	mlog_entry_void();
+
+	if (ocfs2_is_hard_readonly(osb) || ocfs2_is_soft_readonly(osb))
+		return -EROFS;
+
+	if (new_clusters < 0)
+		return -EINVAL;
+	else if (new_clusters == 0)
+		return 0;
+
+	main_bm_inode = ocfs2_get_system_file_inode(osb,
+						    GLOBAL_BITMAP_SYSTEM_INODE,
+						    OCFS2_INVALID_SLOT);
+	if (!main_bm_inode) {
+		ret = -EINVAL;
+		mlog_errno(ret);
+		goto out;
+	}
+
+	mutex_lock(&main_bm_inode->i_mutex);
+
+	ret = ocfs2_inode_lock(main_bm_inode, &main_bm_bh, 1);
+	if (ret < 0) {
+		mlog_errno(ret);
+		goto out_mutex;
+	}
+
+	fe = (struct ocfs2_dinode *)main_bm_bh->b_data;
+
+	if (le16_to_cpu(fe->id2.i_chain.cl_cpg) !=
+				 ocfs2_group_bitmap_size(osb->sb) * 8) {
+		mlog(ML_ERROR, "The disk is too old and small. "
+		     "Force to do offline resize.");
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
+	if (!OCFS2_IS_VALID_DINODE(fe)) {
+		OCFS2_RO_ON_INVALID_DINODE(main_bm_inode->i_sb, fe);
+		ret = -EIO;
+		goto out_unlock;
+	}
+
+	first_new_cluster = le32_to_cpu(fe->i_clusters);
+	lgd_blkno = ocfs2_which_cluster_group(main_bm_inode,
+					      first_new_cluster - 1);
+
+	ret = ocfs2_read_block(osb, lgd_blkno, &group_bh, OCFS2_BH_CACHED,
+			       main_bm_inode);
+	if (ret < 0) {
+		mlog_errno(ret);
+		goto out_unlock;
+	}
+
+	group = (struct ocfs2_group_desc *)group_bh->b_data;
+
+	ret = ocfs2_check_group_descriptor(inode->i_sb, fe, group);
+	if (ret) {
+		mlog_errno(ret);
+		goto out_unlock;
+	}
+
+	cl_bpc = le16_to_cpu(fe->id2.i_chain.cl_bpc);
+	if (le16_to_cpu(group->bg_bits) / cl_bpc + new_clusters >
+		le16_to_cpu(fe->id2.i_chain.cl_cpg)) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
+	mlog(0, "extend the last group at %llu, new clusters = %d\n",
+	     le64_to_cpu(group->bg_blkno), new_clusters);
+
+	handle = ocfs2_start_trans(osb, OCFS2_GROUP_EXTEND_CREDITS);
+	if (IS_ERR(handle)) {
+		mlog_errno(PTR_ERR(handle));
+		ret = -EINVAL;
+		goto out_unlock;
+	}
+
+	/* update the last group descriptor and inode. */
+	ret = ocfs2_update_last_group_and_inode(handle, main_bm_inode,
+						main_bm_bh, group_bh,
+						first_new_cluster,
+						new_clusters);
+	if (ret) {
+		mlog_errno(ret);
+		goto out_commit;
+	}
+
+	ocfs2_update_super_and_backups(main_bm_inode, new_clusters);
+
+out_commit:
+	ocfs2_commit_trans(osb, handle);
+out_unlock:
+	if (group_bh)
+		brelse(group_bh);
+
+	if (main_bm_bh)
+		brelse(main_bm_bh);
+
+	ocfs2_inode_unlock(main_bm_inode, 1);
+
+out_mutex:
+	mutex_unlock(&main_bm_inode->i_mutex);
+	iput(main_bm_inode);
+
+out:
+	mlog_exit_void();
+	return ret;
+}
diff --git a/fs/ocfs2/resize.h b/fs/ocfs2/resize.h
new file mode 100644
index 0000000..3acb79a
--- /dev/null
+++ b/fs/ocfs2/resize.h
@@ -0,0 +1,31 @@
+/* -*- mode: c; c-basic-offset: 8; -*-
+ * vim: noexpandtab sw=8 ts=8 sts=0:
+ *
+ * resize.h
+ *
+ * Function prototypes
+ *
+ * Copyright (C) 2007 Oracle.  All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This program 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
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this program; if not, write to the
+ * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+ * Boston, MA 021110-1307, USA.
+ */
+
+#ifndef OCFS2_RESIZE_H
+#define OCFS2_RESIZE_H
+
+int ocfs2_group_extend(struct inode * inode, int new_clusters);
+
+#endif /* OCFS2_RESIZE_H */
diff --git a/fs/ocfs2/suballoc.c b/fs/ocfs2/suballoc.c
index 6df4dbf..4391744 100644
--- a/fs/ocfs2/suballoc.c
+++ b/fs/ocfs2/suballoc.c
@@ -101,8 +101,6 @@
 static inline u32 ocfs2_desc_bitmap_to_cluster_off(struct inode *inode,
 						   u64 bg_blkno,
 						   u16 bg_bit_off);
-static inline u64 ocfs2_which_cluster_group(struct inode *inode,
-					    u32 cluster);
 static inline void ocfs2_block_to_cluster_group(struct inode *inode,
 						u64 data_blkno,
 						u64 *bg_blkno,
@@ -131,9 +129,9 @@
 }
 
 /* somewhat more expensive than our other checks, so use sparingly. */
-static int ocfs2_check_group_descriptor(struct super_block *sb,
-					struct ocfs2_dinode *di,
-					struct ocfs2_group_desc *gd)
+int ocfs2_check_group_descriptor(struct super_block *sb,
+				 struct ocfs2_dinode *di,
+				 struct ocfs2_group_desc *gd)
 {
 	unsigned int max_bits;
 
@@ -1443,8 +1441,7 @@
 
 /* given a cluster offset, calculate which block group it belongs to
  * and return that block offset. */
-static inline u64 ocfs2_which_cluster_group(struct inode *inode,
-					    u32 cluster)
+u64 ocfs2_which_cluster_group(struct inode *inode, u32 cluster)
 {
 	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
 	u32 group_no;
diff --git a/fs/ocfs2/suballoc.h b/fs/ocfs2/suballoc.h
index cafe937..8799033 100644
--- a/fs/ocfs2/suballoc.h
+++ b/fs/ocfs2/suballoc.h
@@ -147,4 +147,12 @@
 int ocfs2_reserve_cluster_bitmap_bits(struct ocfs2_super *osb,
 				      struct ocfs2_alloc_context *ac);
 
+/* given a cluster offset, calculate which block group it belongs to
+ * and return that block offset. */
+u64 ocfs2_which_cluster_group(struct inode *inode, u32 cluster);
+
+/* somewhat more expensive than our other checks, so use sparingly. */
+int ocfs2_check_group_descriptor(struct super_block *sb,
+				 struct ocfs2_dinode *di,
+				 struct ocfs2_group_desc *gd);
 #endif /* _CHAINALLOC_H_ */