Adding upstream version 6.1.76.upstream/6.1.76upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2194 insertions, 0 deletions

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
new file mode 100644
index 000000000..9833ab6db
--- /dev/null
+++ b/fs/ext4/resize.c
@@ -0,0 +1,2194 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/ext4/resize.c
+ *
+ * Support for resizing an ext4 filesystem while it is mounted.
+ *
+ * Copyright (C) 2001, 2002 Andreas Dilger <adilger@clusterfs.com>
+ *
+ * This could probably be made into a module, because it is not often in use.
+ */
+
+
+#define EXT4FS_DEBUG
+
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/jiffies.h>
+
+#include "ext4_jbd2.h"
+
+struct ext4_rcu_ptr {
+	struct rcu_head rcu;
+	void *ptr;
+};
+
+static void ext4_rcu_ptr_callback(struct rcu_head *head)
+{
+	struct ext4_rcu_ptr *ptr;
+
+	ptr = container_of(head, struct ext4_rcu_ptr, rcu);
+	kvfree(ptr->ptr);
+	kfree(ptr);
+}
+
+void ext4_kvfree_array_rcu(void *to_free)
+{
+	struct ext4_rcu_ptr *ptr = kzalloc(sizeof(*ptr), GFP_KERNEL);
+
+	if (ptr) {
+		ptr->ptr = to_free;
+		call_rcu(&ptr->rcu, ext4_rcu_ptr_callback);
+		return;
+	}
+	synchronize_rcu();
+	kvfree(to_free);
+}
+
+int ext4_resize_begin(struct super_block *sb)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	int ret = 0;
+
+	if (!capable(CAP_SYS_RESOURCE))
+		return -EPERM;
+
+	/*
+	 * If the reserved GDT blocks is non-zero, the resize_inode feature
+	 * should always be set.
+	 */
+	if (EXT4_SB(sb)->s_es->s_reserved_gdt_blocks &&
+	    !ext4_has_feature_resize_inode(sb)) {
+		ext4_error(sb, "resize_inode disabled but reserved GDT blocks non-zero");
+		return -EFSCORRUPTED;
+	}
+
+	/*
+	 * If we are not using the primary superblock/GDT copy don't resize,
+         * because the user tools have no way of handling this.  Probably a
+         * bad time to do it anyways.
+         */
+	if (EXT4_B2C(sbi, sbi->s_sbh->b_blocknr) !=
+	    le32_to_cpu(EXT4_SB(sb)->s_es->s_first_data_block)) {
+		ext4_warning(sb, "won't resize using backup superblock at %llu",
+			(unsigned long long)EXT4_SB(sb)->s_sbh->b_blocknr);
+		return -EPERM;
+	}
+
+	/*
+	 * We are not allowed to do online-resizing on a filesystem mounted
+	 * with error, because it can destroy the filesystem easily.
+	 */
+	if (EXT4_SB(sb)->s_mount_state & EXT4_ERROR_FS) {
+		ext4_warning(sb, "There are errors in the filesystem, "
+			     "so online resizing is not allowed");
+		return -EPERM;
+	}
+
+	if (ext4_has_feature_sparse_super2(sb)) {
+		ext4_msg(sb, KERN_ERR, "Online resizing not supported with sparse_super2");
+		return -EOPNOTSUPP;
+	}
+
+	if (test_and_set_bit_lock(EXT4_FLAGS_RESIZING,
+				  &EXT4_SB(sb)->s_ext4_flags))
+		ret = -EBUSY;
+
+	return ret;
+}
+
+int ext4_resize_end(struct super_block *sb, bool update_backups)
+{
+	clear_bit_unlock(EXT4_FLAGS_RESIZING, &EXT4_SB(sb)->s_ext4_flags);
+	smp_mb__after_atomic();
+	if (update_backups)
+		return ext4_update_overhead(sb, true);
+	return 0;
+}
+
+static ext4_group_t ext4_meta_bg_first_group(struct super_block *sb,
+					     ext4_group_t group) {
+	return (group >> EXT4_DESC_PER_BLOCK_BITS(sb)) <<
+	       EXT4_DESC_PER_BLOCK_BITS(sb);
+}
+
+static ext4_fsblk_t ext4_meta_bg_first_block_no(struct super_block *sb,
+					     ext4_group_t group) {
+	group = ext4_meta_bg_first_group(sb, group);
+	return ext4_group_first_block_no(sb, group);
+}
+
+static ext4_grpblk_t ext4_group_overhead_blocks(struct super_block *sb,
+						ext4_group_t group) {
+	ext4_grpblk_t overhead;
+	overhead = ext4_bg_num_gdb(sb, group);
+	if (ext4_bg_has_super(sb, group))
+		overhead += 1 +
+			  le16_to_cpu(EXT4_SB(sb)->s_es->s_reserved_gdt_blocks);
+	return overhead;
+}
+
+#define outside(b, first, last)	((b) < (first) || (b) >= (last))
+#define inside(b, first, last)	((b) >= (first) && (b) < (last))
+
+static int verify_group_input(struct super_block *sb,
+			      struct ext4_new_group_data *input)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+	ext4_fsblk_t start = ext4_blocks_count(es);
+	ext4_fsblk_t end = start + input->blocks_count;
+	ext4_group_t group = input->group;
+	ext4_fsblk_t itend = input->inode_table + sbi->s_itb_per_group;
+	unsigned overhead;
+	ext4_fsblk_t metaend;
+	struct buffer_head *bh = NULL;
+	ext4_grpblk_t free_blocks_count, offset;
+	int err = -EINVAL;
+
+	if (group != sbi->s_groups_count) {
+		ext4_warning(sb, "Cannot add at group %u (only %u groups)",
+			     input->group, sbi->s_groups_count);
+		return -EINVAL;
+	}
+
+	overhead = ext4_group_overhead_blocks(sb, group);
+	metaend = start + overhead;
+	input->free_clusters_count = free_blocks_count =
+		input->blocks_count - 2 - overhead - sbi->s_itb_per_group;
+
+	if (test_opt(sb, DEBUG))
+		printk(KERN_DEBUG "EXT4-fs: adding %s group %u: %u blocks "
+		       "(%d free, %u reserved)\n",
+		       ext4_bg_has_super(sb, input->group) ? "normal" :
+		       "no-super", input->group, input->blocks_count,
+		       free_blocks_count, input->reserved_blocks);
+
+	ext4_get_group_no_and_offset(sb, start, NULL, &offset);
+	if (offset != 0)
+			ext4_warning(sb, "Last group not full");
+	else if (input->reserved_blocks > input->blocks_count / 5)
+		ext4_warning(sb, "Reserved blocks too high (%u)",
+			     input->reserved_blocks);
+	else if (free_blocks_count < 0)
+		ext4_warning(sb, "Bad blocks count %u",
+			     input->blocks_count);
+	else if (IS_ERR(bh = ext4_sb_bread(sb, end - 1, 0))) {
+		err = PTR_ERR(bh);
+		bh = NULL;
+		ext4_warning(sb, "Cannot read last block (%llu)",
+			     end - 1);
+	} else if (outside(input->block_bitmap, start, end))
+		ext4_warning(sb, "Block bitmap not in group (block %llu)",
+			     (unsigned long long)input->block_bitmap);
+	else if (outside(input->inode_bitmap, start, end))
+		ext4_warning(sb, "Inode bitmap not in group (block %llu)",
+			     (unsigned long long)input->inode_bitmap);
+	else if (outside(input->inode_table, start, end) ||
+		 outside(itend - 1, start, end))
+		ext4_warning(sb, "Inode table not in group (blocks %llu-%llu)",
+			     (unsigned long long)input->inode_table, itend - 1);
+	else if (input->inode_bitmap == input->block_bitmap)
+		ext4_warning(sb, "Block bitmap same as inode bitmap (%llu)",
+			     (unsigned long long)input->block_bitmap);
+	else if (inside(input->block_bitmap, input->inode_table, itend))
+		ext4_warning(sb, "Block bitmap (%llu) in inode table "
+			     "(%llu-%llu)",
+			     (unsigned long long)input->block_bitmap,
+			     (unsigned long long)input->inode_table, itend - 1);
+	else if (inside(input->inode_bitmap, input->inode_table, itend))
+		ext4_warning(sb, "Inode bitmap (%llu) in inode table "
+			     "(%llu-%llu)",
+			     (unsigned long long)input->inode_bitmap,
+			     (unsigned long long)input->inode_table, itend - 1);
+	else if (inside(input->block_bitmap, start, metaend))
+		ext4_warning(sb, "Block bitmap (%llu) in GDT table (%llu-%llu)",
+			     (unsigned long long)input->block_bitmap,
+			     start, metaend - 1);
+	else if (inside(input->inode_bitmap, start, metaend))
+		ext4_warning(sb, "Inode bitmap (%llu) in GDT table (%llu-%llu)",
+			     (unsigned long long)input->inode_bitmap,
+			     start, metaend - 1);
+	else if (inside(input->inode_table, start, metaend) ||
+		 inside(itend - 1, start, metaend))
+		ext4_warning(sb, "Inode table (%llu-%llu) overlaps GDT table "
+			     "(%llu-%llu)",
+			     (unsigned long long)input->inode_table,
+			     itend - 1, start, metaend - 1);
+	else
+		err = 0;
+	brelse(bh);
+
+	return err;
+}
+
+/*
+ * ext4_new_flex_group_data is used by 64bit-resize interface to add a flex
+ * group each time.
+ */
+struct ext4_new_flex_group_data {
+	struct ext4_new_group_data *groups;	/* new_group_data for groups
+						   in the flex group */
+	__u16 *bg_flags;			/* block group flags of groups
+						   in @groups */
+	ext4_group_t count;			/* number of groups in @groups
+						 */
+};
+
+/*
+ * alloc_flex_gd() allocates a ext4_new_flex_group_data with size of
+ * @flexbg_size.
+ *
+ * Returns NULL on failure otherwise address of the allocated structure.
+ */
+static struct ext4_new_flex_group_data *alloc_flex_gd(unsigned long flexbg_size)
+{
+	struct ext4_new_flex_group_data *flex_gd;
+
+	flex_gd = kmalloc(sizeof(*flex_gd), GFP_NOFS);
+	if (flex_gd == NULL)
+		goto out3;
+
+	if (flexbg_size >= UINT_MAX / sizeof(struct ext4_new_group_data))
+		goto out2;
+	flex_gd->count = flexbg_size;
+
+	flex_gd->groups = kmalloc_array(flexbg_size,
+					sizeof(struct ext4_new_group_data),
+					GFP_NOFS);
+	if (flex_gd->groups == NULL)
+		goto out2;
+
+	flex_gd->bg_flags = kmalloc_array(flexbg_size, sizeof(__u16),
+					  GFP_NOFS);
+	if (flex_gd->bg_flags == NULL)
+		goto out1;
+
+	return flex_gd;
+
+out1:
+	kfree(flex_gd->groups);
+out2:
+	kfree(flex_gd);
+out3:
+	return NULL;
+}
+
+static void free_flex_gd(struct ext4_new_flex_group_data *flex_gd)
+{
+	kfree(flex_gd->bg_flags);
+	kfree(flex_gd->groups);
+	kfree(flex_gd);
+}
+
+/*
+ * ext4_alloc_group_tables() allocates block bitmaps, inode bitmaps
+ * and inode tables for a flex group.
+ *
+ * This function is used by 64bit-resize.  Note that this function allocates
+ * group tables from the 1st group of groups contained by @flexgd, which may
+ * be a partial of a flex group.
+ *
+ * @sb: super block of fs to which the groups belongs
+ *
+ * Returns 0 on a successful allocation of the metadata blocks in the
+ * block group.
+ */
+static int ext4_alloc_group_tables(struct super_block *sb,
+				struct ext4_new_flex_group_data *flex_gd,
+				int flexbg_size)
+{
+	struct ext4_new_group_data *group_data = flex_gd->groups;
+	ext4_fsblk_t start_blk;
+	ext4_fsblk_t last_blk;
+	ext4_group_t src_group;
+	ext4_group_t bb_index = 0;
+	ext4_group_t ib_index = 0;
+	ext4_group_t it_index = 0;
+	ext4_group_t group;
+	ext4_group_t last_group;
+	unsigned overhead;
+	__u16 uninit_mask = (flexbg_size > 1) ? ~EXT4_BG_BLOCK_UNINIT : ~0;
+	int i;
+
+	BUG_ON(flex_gd->count == 0 || group_data == NULL);
+
+	src_group = group_data[0].group;
+	last_group  = src_group + flex_gd->count - 1;
+
+	BUG_ON((flexbg_size > 1) && ((src_group & ~(flexbg_size - 1)) !=
+	       (last_group & ~(flexbg_size - 1))));
+next_group:
+	group = group_data[0].group;
+	if (src_group >= group_data[0].group + flex_gd->count)
+		return -ENOSPC;
+	start_blk = ext4_group_first_block_no(sb, src_group);
+	last_blk = start_blk + group_data[src_group - group].blocks_count;
+
+	overhead = ext4_group_overhead_blocks(sb, src_group);
+
+	start_blk += overhead;
+
+	/* We collect contiguous blocks as much as possible. */
+	src_group++;
+	for (; src_group <= last_group; src_group++) {
+		overhead = ext4_group_overhead_blocks(sb, src_group);
+		if (overhead == 0)
+			last_blk += group_data[src_group - group].blocks_count;
+		else
+			break;
+	}
+
+	/* Allocate block bitmaps */
+	for (; bb_index < flex_gd->count; bb_index++) {
+		if (start_blk >= last_blk)
+			goto next_group;
+		group_data[bb_index].block_bitmap = start_blk++;
+		group = ext4_get_group_number(sb, start_blk - 1);
+		group -= group_data[0].group;
+		group_data[group].mdata_blocks++;
+		flex_gd->bg_flags[group] &= uninit_mask;
+	}
+
+	/* Allocate inode bitmaps */
+	for (; ib_index < flex_gd->count; ib_index++) {
+		if (start_blk >= last_blk)
+			goto next_group;
+		group_data[ib_index].inode_bitmap = start_blk++;
+		group = ext4_get_group_number(sb, start_blk - 1);
+		group -= group_data[0].group;
+		group_data[group].mdata_blocks++;
+		flex_gd->bg_flags[group] &= uninit_mask;
+	}
+
+	/* Allocate inode tables */
+	for (; it_index < flex_gd->count; it_index++) {
+		unsigned int itb = EXT4_SB(sb)->s_itb_per_group;
+		ext4_fsblk_t next_group_start;
+
+		if (start_blk + itb > last_blk)
+			goto next_group;
+		group_data[it_index].inode_table = start_blk;
+		group = ext4_get_group_number(sb, start_blk);
+		next_group_start = ext4_group_first_block_no(sb, group + 1);
+		group -= group_data[0].group;
+
+		if (start_blk + itb > next_group_start) {
+			flex_gd->bg_flags[group + 1] &= uninit_mask;
+			overhead = start_blk + itb - next_group_start;
+			group_data[group + 1].mdata_blocks += overhead;
+			itb -= overhead;
+		}
+
+		group_data[group].mdata_blocks += itb;
+		flex_gd->bg_flags[group] &= uninit_mask;
+		start_blk += EXT4_SB(sb)->s_itb_per_group;
+	}
+
+	/* Update free clusters count to exclude metadata blocks */
+	for (i = 0; i < flex_gd->count; i++) {
+		group_data[i].free_clusters_count -=
+				EXT4_NUM_B2C(EXT4_SB(sb),
+					     group_data[i].mdata_blocks);
+	}
+
+	if (test_opt(sb, DEBUG)) {
+		int i;
+		group = group_data[0].group;
+
+		printk(KERN_DEBUG "EXT4-fs: adding a flex group with "
+		       "%d groups, flexbg size is %d:\n", flex_gd->count,
+		       flexbg_size);
+
+		for (i = 0; i < flex_gd->count; i++) {
+			ext4_debug(
+			       "adding %s group %u: %u blocks (%d free, %d mdata blocks)\n",
+			       ext4_bg_has_super(sb, group + i) ? "normal" :
+			       "no-super", group + i,
+			       group_data[i].blocks_count,
+			       group_data[i].free_clusters_count,
+			       group_data[i].mdata_blocks);
+		}
+	}
+	return 0;
+}
+
+static struct buffer_head *bclean(handle_t *handle, struct super_block *sb,
+				  ext4_fsblk_t blk)
+{
+	struct buffer_head *bh;
+	int err;
+
+	bh = sb_getblk(sb, blk);
+	if (unlikely(!bh))
+		return ERR_PTR(-ENOMEM);
+	BUFFER_TRACE(bh, "get_write_access");
+	err = ext4_journal_get_write_access(handle, sb, bh, EXT4_JTR_NONE);
+	if (err) {
+		brelse(bh);
+		bh = ERR_PTR(err);
+	} else {
+		memset(bh->b_data, 0, sb->s_blocksize);
+		set_buffer_uptodate(bh);
+	}
+
+	return bh;
+}
+
+static int ext4_resize_ensure_credits_batch(handle_t *handle, int credits)
+{
+	return ext4_journal_ensure_credits_fn(handle, credits,
+		EXT4_MAX_TRANS_DATA, 0, 0);
+}
+
+/*
+ * set_flexbg_block_bitmap() mark clusters [@first_cluster, @last_cluster] used.
+ *
+ * Helper function for ext4_setup_new_group_blocks() which set .
+ *
+ * @sb: super block
+ * @handle: journal handle
+ * @flex_gd: flex group data
+ */
+static int set_flexbg_block_bitmap(struct super_block *sb, handle_t *handle,
+			struct ext4_new_flex_group_data *flex_gd,
+			ext4_fsblk_t first_cluster, ext4_fsblk_t last_cluster)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	ext4_group_t count = last_cluster - first_cluster + 1;
+	ext4_group_t count2;
+
+	ext4_debug("mark clusters [%llu-%llu] used\n", first_cluster,
+		   last_cluster);
+	for (count2 = count; count > 0;
+	     count -= count2, first_cluster += count2) {
+		ext4_fsblk_t start;
+		struct buffer_head *bh;
+		ext4_group_t group;
+		int err;
+
+		group = ext4_get_group_number(sb, EXT4_C2B(sbi, first_cluster));
+		start = EXT4_B2C(sbi, ext4_group_first_block_no(sb, group));
+		group -= flex_gd->groups[0].group;
+
+		count2 = EXT4_CLUSTERS_PER_GROUP(sb) - (first_cluster - start);
+		if (count2 > count)
+			count2 = count;
+
+		if (flex_gd->bg_flags[group] & EXT4_BG_BLOCK_UNINIT) {
+			BUG_ON(flex_gd->count > 1);
+			continue;
+		}
+
+		err = ext4_resize_ensure_credits_batch(handle, 1);
+		if (err < 0)
+			return err;
+
+		bh = sb_getblk(sb, flex_gd->groups[group].block_bitmap);
+		if (unlikely(!bh))
+			return -ENOMEM;
+
+		BUFFER_TRACE(bh, "get_write_access");
+		err = ext4_journal_get_write_access(handle, sb, bh,
+						    EXT4_JTR_NONE);
+		if (err) {
+			brelse(bh);
+			return err;
+		}
+		ext4_debug("mark block bitmap %#04llx (+%llu/%u)\n",
+			   first_cluster, first_cluster - start, count2);
+		mb_set_bits(bh->b_data, first_cluster - start, count2);
+
+		err = ext4_handle_dirty_metadata(handle, NULL, bh);
+		brelse(bh);
+		if (unlikely(err))
+			return err;
+	}
+
+	return 0;
+}
+
+/*
+ * Set up the block and inode bitmaps, and the inode table for the new groups.
+ * This doesn't need to be part of the main transaction, since we are only
+ * changing blocks outside the actual filesystem.  We still do journaling to
+ * ensure the recovery is correct in case of a failure just after resize.
+ * If any part of this fails, we simply abort the resize.
+ *
+ * setup_new_flex_group_blocks handles a flex group as follow:
+ *  1. copy super block and GDT, and initialize group tables if necessary.
+ *     In this step, we only set bits in blocks bitmaps for blocks taken by
+ *     super block and GDT.
+ *  2. allocate group tables in block bitmaps, that is, set bits in block
+ *     bitmap for blocks taken by group tables.
+ */
+static int setup_new_flex_group_blocks(struct super_block *sb,
+				struct ext4_new_flex_group_data *flex_gd)
+{
+	int group_table_count[] = {1, 1, EXT4_SB(sb)->s_itb_per_group};
+	ext4_fsblk_t start;
+	ext4_fsblk_t block;
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+	struct ext4_new_group_data *group_data = flex_gd->groups;
+	__u16 *bg_flags = flex_gd->bg_flags;
+	handle_t *handle;
+	ext4_group_t group, count;
+	struct buffer_head *bh = NULL;
+	int reserved_gdb, i, j, err = 0, err2;
+	int meta_bg;
+
+	BUG_ON(!flex_gd->count || !group_data ||
+	       group_data[0].group != sbi->s_groups_count);
+
+	reserved_gdb = le16_to_cpu(es->s_reserved_gdt_blocks);
+	meta_bg = ext4_has_feature_meta_bg(sb);
+
+	/* This transaction may be extended/restarted along the way */
+	handle = ext4_journal_start_sb(sb, EXT4_HT_RESIZE, EXT4_MAX_TRANS_DATA);
+	if (IS_ERR(handle))
+		return PTR_ERR(handle);
+
+	group = group_data[0].group;
+	for (i = 0; i < flex_gd->count; i++, group++) {
+		unsigned long gdblocks;
+		ext4_grpblk_t overhead;
+
+		gdblocks = ext4_bg_num_gdb(sb, group);
+		start = ext4_group_first_block_no(sb, group);
+
+		if (meta_bg == 0 && !ext4_bg_has_super(sb, group))
+			goto handle_itb;
+
+		if (meta_bg == 1)
+			goto handle_itb;
+
+		block = start + ext4_bg_has_super(sb, group);
+		/* Copy all of the GDT blocks into the backup in this group */
+		for (j = 0; j < gdblocks; j++, block++) {
+			struct buffer_head *gdb;
+
+			ext4_debug("update backup group %#04llx\n", block);
+			err = ext4_resize_ensure_credits_batch(handle, 1);
+			if (err < 0)
+				goto out;
+
+			gdb = sb_getblk(sb, block);
+			if (unlikely(!gdb)) {
+				err = -ENOMEM;
+				goto out;
+			}
+
+			BUFFER_TRACE(gdb, "get_write_access");
+			err = ext4_journal_get_write_access(handle, sb, gdb,
+							    EXT4_JTR_NONE);
+			if (err) {
+				brelse(gdb);
+				goto out;
+			}
+			memcpy(gdb->b_data, sbi_array_rcu_deref(sbi,
+				s_group_desc, j)->b_data, gdb->b_size);
+			set_buffer_uptodate(gdb);
+
+			err = ext4_handle_dirty_metadata(handle, NULL, gdb);
+			if (unlikely(err)) {
+				brelse(gdb);
+				goto out;
+			}
+			brelse(gdb);
+		}
+
+		/* Zero out all of the reserved backup group descriptor
+		 * table blocks
+		 */
+		if (ext4_bg_has_super(sb, group)) {
+			err = sb_issue_zeroout(sb, gdblocks + start + 1,
+					reserved_gdb, GFP_NOFS);
+			if (err)
+				goto out;
+		}
+
+handle_itb:
+		/* Initialize group tables of the grop @group */
+		if (!(bg_flags[i] & EXT4_BG_INODE_ZEROED))
+			goto handle_bb;
+
+		/* Zero out all of the inode table blocks */
+		block = group_data[i].inode_table;
+		ext4_debug("clear inode table blocks %#04llx -> %#04lx\n",
+			   block, sbi->s_itb_per_group);
+		err = sb_issue_zeroout(sb, block, sbi->s_itb_per_group,
+				       GFP_NOFS);
+		if (err)
+			goto out;
+
+handle_bb:
+		if (bg_flags[i] & EXT4_BG_BLOCK_UNINIT)
+			goto handle_ib;
+
+		/* Initialize block bitmap of the @group */
+		block = group_data[i].block_bitmap;
+		err = ext4_resize_ensure_credits_batch(handle, 1);
+		if (err < 0)
+			goto out;
+
+		bh = bclean(handle, sb, block);
+		if (IS_ERR(bh)) {
+			err = PTR_ERR(bh);
+			goto out;
+		}
+		overhead = ext4_group_overhead_blocks(sb, group);
+		if (overhead != 0) {
+			ext4_debug("mark backup superblock %#04llx (+0)\n",
+				   start);
+			mb_set_bits(bh->b_data, 0,
+				      EXT4_NUM_B2C(sbi, overhead));
+		}
+		ext4_mark_bitmap_end(EXT4_B2C(sbi, group_data[i].blocks_count),
+				     sb->s_blocksize * 8, bh->b_data);
+		err = ext4_handle_dirty_metadata(handle, NULL, bh);
+		brelse(bh);
+		if (err)
+			goto out;
+
+handle_ib:
+		if (bg_flags[i] & EXT4_BG_INODE_UNINIT)
+			continue;
+
+		/* Initialize inode bitmap of the @group */
+		block = group_data[i].inode_bitmap;
+		err = ext4_resize_ensure_credits_batch(handle, 1);
+		if (err < 0)
+			goto out;
+		/* Mark unused entries in inode bitmap used */
+		bh = bclean(handle, sb, block);
+		if (IS_ERR(bh)) {
+			err = PTR_ERR(bh);
+			goto out;
+		}
+
+		ext4_mark_bitmap_end(EXT4_INODES_PER_GROUP(sb),
+				     sb->s_blocksize * 8, bh->b_data);
+		err = ext4_handle_dirty_metadata(handle, NULL, bh);
+		brelse(bh);
+		if (err)
+			goto out;
+	}
+
+	/* Mark group tables in block bitmap */
+	for (j = 0; j < GROUP_TABLE_COUNT; j++) {
+		count = group_table_count[j];
+		start = (&group_data[0].block_bitmap)[j];
+		block = start;
+		for (i = 1; i < flex_gd->count; i++) {
+			block += group_table_count[j];
+			if (block == (&group_data[i].block_bitmap)[j]) {
+				count += group_table_count[j];
+				continue;
+			}
+			err = set_flexbg_block_bitmap(sb, handle,
+						      flex_gd,
+						      EXT4_B2C(sbi, start),
+						      EXT4_B2C(sbi,
+							       start + count
+							       - 1));
+			if (err)
+				goto out;
+			count = group_table_count[j];
+			start = (&group_data[i].block_bitmap)[j];
+			block = start;
+		}
+
+		if (count) {
+			err = set_flexbg_block_bitmap(sb, handle,
+						      flex_gd,
+						      EXT4_B2C(sbi, start),
+						      EXT4_B2C(sbi,
+							       start + count
+							       - 1));
+			if (err)
+				goto out;
+		}
+	}
+
+out:
+	err2 = ext4_journal_stop(handle);
+	if (err2 && !err)
+		err = err2;
+
+	return err;
+}
+
+/*
+ * Iterate through the groups which hold BACKUP superblock/GDT copies in an
+ * ext4 filesystem.  The counters should be initialized to 1, 5, and 7 before
+ * calling this for the first time.  In a sparse filesystem it will be the
+ * sequence of powers of 3, 5, and 7: 1, 3, 5, 7, 9, 25, 27, 49, 81, ...
+ * For a non-sparse filesystem it will be every group: 1, 2, 3, 4, ...
+ */
+unsigned int ext4_list_backups(struct super_block *sb, unsigned int *three,
+			       unsigned int *five, unsigned int *seven)
+{
+	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
+	unsigned int *min = three;
+	int mult = 3;
+	unsigned int ret;
+
+	if (ext4_has_feature_sparse_super2(sb)) {
+		do {
+			if (*min > 2)
+				return UINT_MAX;
+			ret = le32_to_cpu(es->s_backup_bgs[*min - 1]);
+			*min += 1;
+		} while (!ret);
+		return ret;
+	}
+
+	if (!ext4_has_feature_sparse_super(sb)) {
+		ret = *min;
+		*min += 1;
+		return ret;
+	}
+
+	if (*five < *min) {
+		min = five;
+		mult = 5;
+	}
+	if (*seven < *min) {
+		min = seven;
+		mult = 7;
+	}
+
+	ret = *min;
+	*min *= mult;
+
+	return ret;
+}
+
+/*
+ * Check that all of the backup GDT blocks are held in the primary GDT block.
+ * It is assumed that they are stored in group order.  Returns the number of
+ * groups in current filesystem that have BACKUPS, or -ve error code.
+ */
+static int verify_reserved_gdb(struct super_block *sb,
+			       ext4_group_t end,
+			       struct buffer_head *primary)
+{
+	const ext4_fsblk_t blk = primary->b_blocknr;
+	unsigned three = 1;
+	unsigned five = 5;
+	unsigned seven = 7;
+	unsigned grp;
+	__le32 *p = (__le32 *)primary->b_data;
+	int gdbackups = 0;
+
+	while ((grp = ext4_list_backups(sb, &three, &five, &seven)) < end) {
+		if (le32_to_cpu(*p++) !=
+		    grp * EXT4_BLOCKS_PER_GROUP(sb) + blk){
+			ext4_warning(sb, "reserved GDT %llu"
+				     " missing grp %d (%llu)",
+				     blk, grp,
+				     grp *
+				     (ext4_fsblk_t)EXT4_BLOCKS_PER_GROUP(sb) +
+				     blk);
+			return -EINVAL;
+		}
+		if (++gdbackups > EXT4_ADDR_PER_BLOCK(sb))
+			return -EFBIG;
+	}
+
+	return gdbackups;
+}
+
+/*
+ * Called when we need to bring a reserved group descriptor table block into
+ * use from the resize inode.  The primary copy of the new GDT block currently
+ * is an indirect block (under the double indirect block in the resize inode).
+ * The new backup GDT blocks will be stored as leaf blocks in this indirect
+ * block, in group order.  Even though we know all the block numbers we need,
+ * we check to ensure that the resize inode has actually reserved these blocks.
+ *
+ * Don't need to update the block bitmaps because the blocks are still in use.
+ *
+ * We get all of the error cases out of the way, so that we are sure to not
+ * fail once we start modifying the data on disk, because JBD has no rollback.
+ */
+static int add_new_gdb(handle_t *handle, struct inode *inode,
+		       ext4_group_t group)
+{
+	struct super_block *sb = inode->i_sb;
+	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
+	unsigned long gdb_num = group / EXT4_DESC_PER_BLOCK(sb);
+	ext4_fsblk_t gdblock = EXT4_SB(sb)->s_sbh->b_blocknr + 1 + gdb_num;
+	struct buffer_head **o_group_desc, **n_group_desc = NULL;
+	struct buffer_head *dind = NULL;
+	struct buffer_head *gdb_bh = NULL;
+	int gdbackups;
+	struct ext4_iloc iloc = { .bh = NULL };
+	__le32 *data;
+	int err;
+
+	if (test_opt(sb, DEBUG))
+		printk(KERN_DEBUG
+		       "EXT4-fs: ext4_add_new_gdb: adding group block %lu\n",
+		       gdb_num);
+
+	gdb_bh = ext4_sb_bread(sb, gdblock, 0);
+	if (IS_ERR(gdb_bh))
+		return PTR_ERR(gdb_bh);
+
+	gdbackups = verify_reserved_gdb(sb, group, gdb_bh);
+	if (gdbackups < 0) {
+		err = gdbackups;
+		goto errout;
+	}
+
+	data = EXT4_I(inode)->i_data + EXT4_DIND_BLOCK;
+	dind = ext4_sb_bread(sb, le32_to_cpu(*data), 0);
+	if (IS_ERR(dind)) {
+		err = PTR_ERR(dind);
+		dind = NULL;
+		goto errout;
+	}
+
+	data = (__le32 *)dind->b_data;
+	if (le32_to_cpu(data[gdb_num % EXT4_ADDR_PER_BLOCK(sb)]) != gdblock) {
+		ext4_warning(sb, "new group %u GDT block %llu not reserved",
+			     group, gdblock);
+		err = -EINVAL;
+		goto errout;
+	}
+
+	BUFFER_TRACE(EXT4_SB(sb)->s_sbh, "get_write_access");
+	err = ext4_journal_get_write_access(handle, sb, EXT4_SB(sb)->s_sbh,
+					    EXT4_JTR_NONE);
+	if (unlikely(err))
+		goto errout;
+
+	BUFFER_TRACE(gdb_bh, "get_write_access");
+	err = ext4_journal_get_write_access(handle, sb, gdb_bh, EXT4_JTR_NONE);
+	if (unlikely(err))
+		goto errout;
+
+	BUFFER_TRACE(dind, "get_write_access");
+	err = ext4_journal_get_write_access(handle, sb, dind, EXT4_JTR_NONE);
+	if (unlikely(err)) {
+		ext4_std_error(sb, err);
+		goto errout;
+	}
+
+	/* ext4_reserve_inode_write() gets a reference on the iloc */
+	err = ext4_reserve_inode_write(handle, inode, &iloc);
+	if (unlikely(err))
+		goto errout;
+
+	n_group_desc = kvmalloc((gdb_num + 1) * sizeof(struct buffer_head *),
+				GFP_KERNEL);
+	if (!n_group_desc) {
+		err = -ENOMEM;
+		ext4_warning(sb, "not enough memory for %lu groups",
+			     gdb_num + 1);
+		goto errout;
+	}
+
+	/*
+	 * Finally, we have all of the possible failures behind us...
+	 *
+	 * Remove new GDT block from inode double-indirect block and clear out
+	 * the new GDT block for use (which also "frees" the backup GDT blocks
+	 * from the reserved inode).  We don't need to change the bitmaps for
+	 * these blocks, because they are marked as in-use from being in the
+	 * reserved inode, and will become GDT blocks (primary and backup).
+	 */
+	data[gdb_num % EXT4_ADDR_PER_BLOCK(sb)] = 0;
+	err = ext4_handle_dirty_metadata(handle, NULL, dind);
+	if (unlikely(err)) {
+		ext4_std_error(sb, err);
+		goto errout;
+	}
+	inode->i_blocks -= (gdbackups + 1) * sb->s_blocksize >>
+			   (9 - EXT4_SB(sb)->s_cluster_bits);
+	ext4_mark_iloc_dirty(handle, inode, &iloc);
+	memset(gdb_bh->b_data, 0, sb->s_blocksize);
+	err = ext4_handle_dirty_metadata(handle, NULL, gdb_bh);
+	if (unlikely(err)) {
+		ext4_std_error(sb, err);
+		iloc.bh = NULL;
+		goto errout;
+	}
+	brelse(dind);
+
+	rcu_read_lock();
+	o_group_desc = rcu_dereference(EXT4_SB(sb)->s_group_desc);
+	memcpy(n_group_desc, o_group_desc,
+	       EXT4_SB(sb)->s_gdb_count * sizeof(struct buffer_head *));
+	rcu_read_unlock();
+	n_group_desc[gdb_num] = gdb_bh;
+	rcu_assign_pointer(EXT4_SB(sb)->s_group_desc, n_group_desc);
+	EXT4_SB(sb)->s_gdb_count++;
+	ext4_kvfree_array_rcu(o_group_desc);
+
+	lock_buffer(EXT4_SB(sb)->s_sbh);
+	le16_add_cpu(&es->s_reserved_gdt_blocks, -1);
+	ext4_superblock_csum_set(sb);
+	unlock_buffer(EXT4_SB(sb)->s_sbh);
+	err = ext4_handle_dirty_metadata(handle, NULL, EXT4_SB(sb)->s_sbh);
+	if (err)
+		ext4_std_error(sb, err);
+	return err;
+errout:
+	kvfree(n_group_desc);
+	brelse(iloc.bh);
+	brelse(dind);
+	brelse(gdb_bh);
+
+	ext4_debug("leaving with error %d\n", err);
+	return err;
+}
+
+/*
+ * add_new_gdb_meta_bg is the sister of add_new_gdb.
+ */
+static int add_new_gdb_meta_bg(struct super_block *sb,
+			       handle_t *handle, ext4_group_t group) {
+	ext4_fsblk_t gdblock;
+	struct buffer_head *gdb_bh;
+	struct buffer_head **o_group_desc, **n_group_desc;
+	unsigned long gdb_num = group / EXT4_DESC_PER_BLOCK(sb);
+	int err;
+
+	gdblock = ext4_meta_bg_first_block_no(sb, group) +
+		   ext4_bg_has_super(sb, group);
+	gdb_bh = ext4_sb_bread(sb, gdblock, 0);
+	if (IS_ERR(gdb_bh))
+		return PTR_ERR(gdb_bh);
+	n_group_desc = kvmalloc((gdb_num + 1) * sizeof(struct buffer_head *),
+				GFP_KERNEL);
+	if (!n_group_desc) {
+		brelse(gdb_bh);
+		err = -ENOMEM;
+		ext4_warning(sb, "not enough memory for %lu groups",
+			     gdb_num + 1);
+		return err;
+	}
+
+	rcu_read_lock();
+	o_group_desc = rcu_dereference(EXT4_SB(sb)->s_group_desc);
+	memcpy(n_group_desc, o_group_desc,
+	       EXT4_SB(sb)->s_gdb_count * sizeof(struct buffer_head *));
+	rcu_read_unlock();
+	n_group_desc[gdb_num] = gdb_bh;
+
+	BUFFER_TRACE(gdb_bh, "get_write_access");
+	err = ext4_journal_get_write_access(handle, sb, gdb_bh, EXT4_JTR_NONE);
+	if (err) {
+		kvfree(n_group_desc);
+		brelse(gdb_bh);
+		return err;
+	}
+
+	rcu_assign_pointer(EXT4_SB(sb)->s_group_desc, n_group_desc);
+	EXT4_SB(sb)->s_gdb_count++;
+	ext4_kvfree_array_rcu(o_group_desc);
+	return err;
+}
+
+/*
+ * Called when we are adding a new group which has a backup copy of each of
+ * the GDT blocks (i.e. sparse group) and there are reserved GDT blocks.
+ * We need to add these reserved backup GDT blocks to the resize inode, so
+ * that they are kept for future resizing and not allocated to files.
+ *
+ * Each reserved backup GDT block will go into a different indirect block.
+ * The indirect blocks are actually the primary reserved GDT blocks,
+ * so we know in advance what their block numbers are.  We only get the
+ * double-indirect block to verify it is pointing to the primary reserved
+ * GDT blocks so we don't overwrite a data block by accident.  The reserved
+ * backup GDT blocks are stored in their reserved primary GDT block.
+ */
+static int reserve_backup_gdb(handle_t *handle, struct inode *inode,
+			      ext4_group_t group)
+{
+	struct super_block *sb = inode->i_sb;
+	int reserved_gdb =le16_to_cpu(EXT4_SB(sb)->s_es->s_reserved_gdt_blocks);
+	int cluster_bits = EXT4_SB(sb)->s_cluster_bits;
+	struct buffer_head **primary;
+	struct buffer_head *dind;
+	struct ext4_iloc iloc;
+	ext4_fsblk_t blk;
+	__le32 *data, *end;
+	int gdbackups = 0;
+	int res, i;
+	int err;
+
+	primary = kmalloc_array(reserved_gdb, sizeof(*primary), GFP_NOFS);
+	if (!primary)
+		return -ENOMEM;
+
+	data = EXT4_I(inode)->i_data + EXT4_DIND_BLOCK;
+	dind = ext4_sb_bread(sb, le32_to_cpu(*data), 0);
+	if (IS_ERR(dind)) {
+		err = PTR_ERR(dind);
+		dind = NULL;
+		goto exit_free;
+	}
+
+	blk = EXT4_SB(sb)->s_sbh->b_blocknr + 1 + EXT4_SB(sb)->s_gdb_count;
+	data = (__le32 *)dind->b_data + (EXT4_SB(sb)->s_gdb_count %
+					 EXT4_ADDR_PER_BLOCK(sb));
+	end = (__le32 *)dind->b_data + EXT4_ADDR_PER_BLOCK(sb);
+
+	/* Get each reserved primary GDT block and verify it holds backups */
+	for (res = 0; res < reserved_gdb; res++, blk++) {
+		if (le32_to_cpu(*data) != blk) {
+			ext4_warning(sb, "reserved block %llu"
+				     " not at offset %ld",
+				     blk,
+				     (long)(data - (__le32 *)dind->b_data));
+			err = -EINVAL;
+			goto exit_bh;
+		}
+		primary[res] = ext4_sb_bread(sb, blk, 0);
+		if (IS_ERR(primary[res])) {
+			err = PTR_ERR(primary[res]);
+			primary[res] = NULL;
+			goto exit_bh;
+		}
+		gdbackups = verify_reserved_gdb(sb, group, primary[res]);
+		if (gdbackups < 0) {
+			brelse(primary[res]);
+			err = gdbackups;
+			goto exit_bh;
+		}
+		if (++data >= end)
+			data = (__le32 *)dind->b_data;
+	}
+
+	for (i = 0; i < reserved_gdb; i++) {
+		BUFFER_TRACE(primary[i], "get_write_access");
+		if ((err = ext4_journal_get_write_access(handle, sb, primary[i],
+							 EXT4_JTR_NONE)))
+			goto exit_bh;
+	}
+
+	if ((err = ext4_reserve_inode_write(handle, inode, &iloc)))
+		goto exit_bh;
+
+	/*
+	 * Finally we can add each of the reserved backup GDT blocks from
+	 * the new group to its reserved primary GDT block.
+	 */
+	blk = group * EXT4_BLOCKS_PER_GROUP(sb);
+	for (i = 0; i < reserved_gdb; i++) {
+		int err2;
+		data = (__le32 *)primary[i]->b_data;
+		/* printk("reserving backup %lu[%u] = %lu\n",
+		       primary[i]->b_blocknr, gdbackups,
+		       blk + primary[i]->b_blocknr); */
+		data[gdbackups] = cpu_to_le32(blk + primary[i]->b_blocknr);
+		err2 = ext4_handle_dirty_metadata(handle, NULL, primary[i]);
+		if (!err)
+			err = err2;
+	}
+
+	inode->i_blocks += reserved_gdb * sb->s_blocksize >> (9 - cluster_bits);
+	ext4_mark_iloc_dirty(handle, inode, &iloc);
+
+exit_bh:
+	while (--res >= 0)
+		brelse(primary[res]);
+	brelse(dind);
+
+exit_free:
+	kfree(primary);
+
+	return err;
+}
+
+static inline void ext4_set_block_group_nr(struct super_block *sb, char *data,
+					   ext4_group_t group)
+{
+	struct ext4_super_block *es = (struct ext4_super_block *) data;
+
+	es->s_block_group_nr = cpu_to_le16(group);
+	if (ext4_has_metadata_csum(sb))
+		es->s_checksum = ext4_superblock_csum(sb, es);
+}
+
+/*
+ * Update the backup copies of the ext4 metadata.  These don't need to be part
+ * of the main resize transaction, because e2fsck will re-write them if there
+ * is a problem (basically only OOM will cause a problem).  However, we
+ * _should_ update the backups if possible, in case the primary gets trashed
+ * for some reason and we need to run e2fsck from a backup superblock.  The
+ * important part is that the new block and inode counts are in the backup
+ * superblocks, and the location of the new group metadata in the GDT backups.
+ *
+ * We do not need take the s_resize_lock for this, because these
+ * blocks are not otherwise touched by the filesystem code when it is
+ * mounted.  We don't need to worry about last changing from
+ * sbi->s_groups_count, because the worst that can happen is that we
+ * do not copy the full number of backups at this time.  The resize
+ * which changed s_groups_count will backup again.
+ */
+static void update_backups(struct super_block *sb, sector_t blk_off, char *data,
+			   int size, int meta_bg)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	ext4_group_t last;
+	const int bpg = EXT4_BLOCKS_PER_GROUP(sb);
+	unsigned three = 1;
+	unsigned five = 5;
+	unsigned seven = 7;
+	ext4_group_t group = 0;
+	int rest = sb->s_blocksize - size;
+	handle_t *handle;
+	int err = 0, err2;
+
+	handle = ext4_journal_start_sb(sb, EXT4_HT_RESIZE, EXT4_MAX_TRANS_DATA);
+	if (IS_ERR(handle)) {
+		group = 1;
+		err = PTR_ERR(handle);
+		goto exit_err;
+	}
+
+	if (meta_bg == 0) {
+		group = ext4_list_backups(sb, &three, &five, &seven);
+		last = sbi->s_groups_count;
+	} else {
+		group = ext4_get_group_number(sb, blk_off) + 1;
+		last = (ext4_group_t)(group + EXT4_DESC_PER_BLOCK(sb) - 2);
+	}
+
+	while (group < sbi->s_groups_count) {
+		struct buffer_head *bh;
+		ext4_fsblk_t backup_block;
+		int has_super = ext4_bg_has_super(sb, group);
+		ext4_fsblk_t first_block = ext4_group_first_block_no(sb, group);
+
+		/* Out of journal space, and can't get more - abort - so sad */
+		err = ext4_resize_ensure_credits_batch(handle, 1);
+		if (err < 0)
+			break;
+
+		if (meta_bg == 0)
+			backup_block = ((ext4_fsblk_t)group) * bpg + blk_off;
+		else
+			backup_block = first_block + has_super;
+
+		bh = sb_getblk(sb, backup_block);
+		if (unlikely(!bh)) {
+			err = -ENOMEM;
+			break;
+		}
+		ext4_debug("update metadata backup %llu(+%llu)\n",
+			   backup_block, backup_block -
+			   ext4_group_first_block_no(sb, group));
+		BUFFER_TRACE(bh, "get_write_access");
+		if ((err = ext4_journal_get_write_access(handle, sb, bh,
+							 EXT4_JTR_NONE))) {
+			brelse(bh);
+			break;
+		}
+		lock_buffer(bh);
+		memcpy(bh->b_data, data, size);
+		if (rest)
+			memset(bh->b_data + size, 0, rest);
+		if (has_super && (backup_block == first_block))
+			ext4_set_block_group_nr(sb, bh->b_data, group);
+		set_buffer_uptodate(bh);
+		unlock_buffer(bh);
+		err = ext4_handle_dirty_metadata(handle, NULL, bh);
+		if (unlikely(err))
+			ext4_std_error(sb, err);
+		brelse(bh);
+
+		if (meta_bg == 0)
+			group = ext4_list_backups(sb, &three, &five, &seven);
+		else if (group == last)
+			break;
+		else
+			group = last;
+	}
+	if ((err2 = ext4_journal_stop(handle)) && !err)
+		err = err2;
+
+	/*
+	 * Ugh! Need to have e2fsck write the backup copies.  It is too
+	 * late to revert the resize, we shouldn't fail just because of
+	 * the backup copies (they are only needed in case of corruption).
+	 *
+	 * However, if we got here we have a journal problem too, so we
+	 * can't really start a transaction to mark the superblock.
+	 * Chicken out and just set the flag on the hope it will be written
+	 * to disk, and if not - we will simply wait until next fsck.
+	 */
+exit_err:
+	if (err) {
+		ext4_warning(sb, "can't update backup for group %u (err %d), "
+			     "forcing fsck on next reboot", group, err);
+		sbi->s_mount_state &= ~EXT4_VALID_FS;
+		sbi->s_es->s_state &= cpu_to_le16(~EXT4_VALID_FS);
+		mark_buffer_dirty(sbi->s_sbh);
+	}
+}
+
+/*
+ * ext4_add_new_descs() adds @count group descriptor of groups
+ * starting at @group
+ *
+ * @handle: journal handle
+ * @sb: super block
+ * @group: the group no. of the first group desc to be added
+ * @resize_inode: the resize inode
+ * @count: number of group descriptors to be added
+ */
+static int ext4_add_new_descs(handle_t *handle, struct super_block *sb,
+			      ext4_group_t group, struct inode *resize_inode,
+			      ext4_group_t count)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+	struct buffer_head *gdb_bh;
+	int i, gdb_off, gdb_num, err = 0;
+	int meta_bg;
+
+	meta_bg = ext4_has_feature_meta_bg(sb);
+	for (i = 0; i < count; i++, group++) {
+		int reserved_gdb = ext4_bg_has_super(sb, group) ?
+			le16_to_cpu(es->s_reserved_gdt_blocks) : 0;
+
+		gdb_off = group % EXT4_DESC_PER_BLOCK(sb);
+		gdb_num = group / EXT4_DESC_PER_BLOCK(sb);
+
+		/*
+		 * We will only either add reserved group blocks to a backup group
+		 * or remove reserved blocks for the first group in a new group block.
+		 * Doing both would be mean more complex code, and sane people don't
+		 * use non-sparse filesystems anymore.  This is already checked above.
+		 */
+		if (gdb_off) {
+			gdb_bh = sbi_array_rcu_deref(sbi, s_group_desc,
+						     gdb_num);
+			BUFFER_TRACE(gdb_bh, "get_write_access");
+			err = ext4_journal_get_write_access(handle, sb, gdb_bh,
+							    EXT4_JTR_NONE);
+
+			if (!err && reserved_gdb && ext4_bg_num_gdb(sb, group))
+				err = reserve_backup_gdb(handle, resize_inode, group);
+		} else if (meta_bg != 0) {
+			err = add_new_gdb_meta_bg(sb, handle, group);
+		} else {
+			err = add_new_gdb(handle, resize_inode, group);
+		}
+		if (err)
+			break;
+	}
+	return err;
+}
+
+static struct buffer_head *ext4_get_bitmap(struct super_block *sb, __u64 block)
+{
+	struct buffer_head *bh = sb_getblk(sb, block);
+	if (unlikely(!bh))
+		return NULL;
+	if (!bh_uptodate_or_lock(bh)) {
+		if (ext4_read_bh(bh, 0, NULL) < 0) {
+			brelse(bh);
+			return NULL;
+		}
+	}
+
+	return bh;
+}
+
+static int ext4_set_bitmap_checksums(struct super_block *sb,
+				     ext4_group_t group,
+				     struct ext4_group_desc *gdp,
+				     struct ext4_new_group_data *group_data)
+{
+	struct buffer_head *bh;
+
+	if (!ext4_has_metadata_csum(sb))
+		return 0;
+
+	bh = ext4_get_bitmap(sb, group_data->inode_bitmap);
+	if (!bh)
+		return -EIO;
+	ext4_inode_bitmap_csum_set(sb, group, gdp, bh,
+				   EXT4_INODES_PER_GROUP(sb) / 8);
+	brelse(bh);
+
+	bh = ext4_get_bitmap(sb, group_data->block_bitmap);
+	if (!bh)
+		return -EIO;
+	ext4_block_bitmap_csum_set(sb, group, gdp, bh);
+	brelse(bh);
+
+	return 0;
+}
+
+/*
+ * ext4_setup_new_descs() will set up the group descriptor descriptors of a flex bg
+ */
+static int ext4_setup_new_descs(handle_t *handle, struct super_block *sb,
+				struct ext4_new_flex_group_data *flex_gd)
+{
+	struct ext4_new_group_data	*group_data = flex_gd->groups;
+	struct ext4_group_desc		*gdp;
+	struct ext4_sb_info		*sbi = EXT4_SB(sb);
+	struct buffer_head		*gdb_bh;
+	ext4_group_t			group;
+	__u16				*bg_flags = flex_gd->bg_flags;
+	int				i, gdb_off, gdb_num, err = 0;
+
+
+	for (i = 0; i < flex_gd->count; i++, group_data++, bg_flags++) {
+		group = group_data->group;
+
+		gdb_off = group % EXT4_DESC_PER_BLOCK(sb);
+		gdb_num = group / EXT4_DESC_PER_BLOCK(sb);
+
+		/*
+		 * get_write_access() has been called on gdb_bh by ext4_add_new_desc().
+		 */
+		gdb_bh = sbi_array_rcu_deref(sbi, s_group_desc, gdb_num);
+		/* Update group descriptor block for new group */
+		gdp = (struct ext4_group_desc *)(gdb_bh->b_data +
+						 gdb_off * EXT4_DESC_SIZE(sb));
+
+		memset(gdp, 0, EXT4_DESC_SIZE(sb));
+		ext4_block_bitmap_set(sb, gdp, group_data->block_bitmap);
+		ext4_inode_bitmap_set(sb, gdp, group_data->inode_bitmap);
+		err = ext4_set_bitmap_checksums(sb, group, gdp, group_data);
+		if (err) {
+			ext4_std_error(sb, err);
+			break;
+		}
+
+		ext4_inode_table_set(sb, gdp, group_data->inode_table);
+		ext4_free_group_clusters_set(sb, gdp,
+					     group_data->free_clusters_count);
+		ext4_free_inodes_set(sb, gdp, EXT4_INODES_PER_GROUP(sb));
+		if (ext4_has_group_desc_csum(sb))
+			ext4_itable_unused_set(sb, gdp,
+					       EXT4_INODES_PER_GROUP(sb));
+		gdp->bg_flags = cpu_to_le16(*bg_flags);
+		ext4_group_desc_csum_set(sb, group, gdp);
+
+		err = ext4_handle_dirty_metadata(handle, NULL, gdb_bh);
+		if (unlikely(err)) {
+			ext4_std_error(sb, err);
+			break;
+		}
+
+		/*
+		 * We can allocate memory for mb_alloc based on the new group
+		 * descriptor
+		 */
+		err = ext4_mb_add_groupinfo(sb, group, gdp);
+		if (err)
+			break;
+	}
+	return err;
+}
+
+static void ext4_add_overhead(struct super_block *sb,
+                              const ext4_fsblk_t overhead)
+{
+       struct ext4_sb_info *sbi = EXT4_SB(sb);
+       struct ext4_super_block *es = sbi->s_es;
+
+       sbi->s_overhead += overhead;
+       es->s_overhead_clusters = cpu_to_le32(sbi->s_overhead);
+       smp_wmb();
+}
+
+/*
+ * ext4_update_super() updates the super block so that the newly added
+ * groups can be seen by the filesystem.
+ *
+ * @sb: super block
+ * @flex_gd: new added groups
+ */
+static void ext4_update_super(struct super_block *sb,
+			     struct ext4_new_flex_group_data *flex_gd)
+{
+	ext4_fsblk_t blocks_count = 0;
+	ext4_fsblk_t free_blocks = 0;
+	ext4_fsblk_t reserved_blocks = 0;
+	struct ext4_new_group_data *group_data = flex_gd->groups;
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+	int i;
+
+	BUG_ON(flex_gd->count == 0 || group_data == NULL);
+	/*
+	 * Make the new blocks and inodes valid next.  We do this before
+	 * increasing the group count so that once the group is enabled,
+	 * all of its blocks and inodes are already valid.
+	 *
+	 * We always allocate group-by-group, then block-by-block or
+	 * inode-by-inode within a group, so enabling these
+	 * blocks/inodes before the group is live won't actually let us
+	 * allocate the new space yet.
+	 */
+	for (i = 0; i < flex_gd->count; i++) {
+		blocks_count += group_data[i].blocks_count;
+		free_blocks += EXT4_C2B(sbi, group_data[i].free_clusters_count);
+	}
+
+	reserved_blocks = ext4_r_blocks_count(es) * 100;
+	reserved_blocks = div64_u64(reserved_blocks, ext4_blocks_count(es));
+	reserved_blocks *= blocks_count;
+	do_div(reserved_blocks, 100);
+
+	lock_buffer(sbi->s_sbh);
+	ext4_blocks_count_set(es, ext4_blocks_count(es) + blocks_count);
+	ext4_free_blocks_count_set(es, ext4_free_blocks_count(es) + free_blocks);
+	le32_add_cpu(&es->s_inodes_count, EXT4_INODES_PER_GROUP(sb) *
+		     flex_gd->count);
+	le32_add_cpu(&es->s_free_inodes_count, EXT4_INODES_PER_GROUP(sb) *
+		     flex_gd->count);
+
+	ext4_debug("free blocks count %llu", ext4_free_blocks_count(es));
+	/*
+	 * We need to protect s_groups_count against other CPUs seeing
+	 * inconsistent state in the superblock.
+	 *
+	 * The precise rules we use are:
+	 *
+	 * * Writers must perform a smp_wmb() after updating all
+	 *   dependent data and before modifying the groups count
+	 *
+	 * * Readers must perform an smp_rmb() after reading the groups
+	 *   count and before reading any dependent data.
+	 *
+	 * NB. These rules can be relaxed when checking the group count
+	 * while freeing data, as we can only allocate from a block
+	 * group after serialising against the group count, and we can
+	 * only then free after serialising in turn against that
+	 * allocation.
+	 */
+	smp_wmb();
+
+	/* Update the global fs size fields */
+	sbi->s_groups_count += flex_gd->count;
+	sbi->s_blockfile_groups = min_t(ext4_group_t, sbi->s_groups_count,
+			(EXT4_MAX_BLOCK_FILE_PHYS / EXT4_BLOCKS_PER_GROUP(sb)));
+
+	/* Update the reserved block counts only once the new group is
+	 * active. */
+	ext4_r_blocks_count_set(es, ext4_r_blocks_count(es) +
+				reserved_blocks);
+
+	/* Update the free space counts */
+	percpu_counter_add(&sbi->s_freeclusters_counter,
+			   EXT4_NUM_B2C(sbi, free_blocks));
+	percpu_counter_add(&sbi->s_freeinodes_counter,
+			   EXT4_INODES_PER_GROUP(sb) * flex_gd->count);
+
+	ext4_debug("free blocks count %llu",
+		   percpu_counter_read(&sbi->s_freeclusters_counter));
+	if (ext4_has_feature_flex_bg(sb) && sbi->s_log_groups_per_flex) {
+		ext4_group_t flex_group;
+		struct flex_groups *fg;
+
+		flex_group = ext4_flex_group(sbi, group_data[0].group);
+		fg = sbi_array_rcu_deref(sbi, s_flex_groups, flex_group);
+		atomic64_add(EXT4_NUM_B2C(sbi, free_blocks),
+			     &fg->free_clusters);
+		atomic_add(EXT4_INODES_PER_GROUP(sb) * flex_gd->count,
+			   &fg->free_inodes);
+	}
+
+	/*
+	 * Update the fs overhead information.
+	 *
+	 * For bigalloc, if the superblock already has a properly calculated
+	 * overhead, update it with a value based on numbers already computed
+	 * above for the newly allocated capacity.
+	 */
+	if (ext4_has_feature_bigalloc(sb) && (sbi->s_overhead != 0))
+		ext4_add_overhead(sb,
+			EXT4_NUM_B2C(sbi, blocks_count - free_blocks));
+	else
+		ext4_calculate_overhead(sb);
+	es->s_overhead_clusters = cpu_to_le32(sbi->s_overhead);
+
+	ext4_superblock_csum_set(sb);
+	unlock_buffer(sbi->s_sbh);
+	if (test_opt(sb, DEBUG))
+		printk(KERN_DEBUG "EXT4-fs: added group %u:"
+		       "%llu blocks(%llu free %llu reserved)\n", flex_gd->count,
+		       blocks_count, free_blocks, reserved_blocks);
+}
+
+/* Add a flex group to an fs. Ensure we handle all possible error conditions
+ * _before_ we start modifying the filesystem, because we cannot abort the
+ * transaction and not have it write the data to disk.
+ */
+static int ext4_flex_group_add(struct super_block *sb,
+			       struct inode *resize_inode,
+			       struct ext4_new_flex_group_data *flex_gd)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+	ext4_fsblk_t o_blocks_count;
+	ext4_grpblk_t last;
+	ext4_group_t group;
+	handle_t *handle;
+	unsigned reserved_gdb;
+	int err = 0, err2 = 0, credit;
+
+	BUG_ON(!flex_gd->count || !flex_gd->groups || !flex_gd->bg_flags);
+
+	reserved_gdb = le16_to_cpu(es->s_reserved_gdt_blocks);
+	o_blocks_count = ext4_blocks_count(es);
+	ext4_get_group_no_and_offset(sb, o_blocks_count, &group, &last);
+	BUG_ON(last);
+
+	err = setup_new_flex_group_blocks(sb, flex_gd);
+	if (err)
+		goto exit;
+	/*
+	 * We will always be modifying at least the superblock and  GDT
+	 * blocks.  If we are adding a group past the last current GDT block,
+	 * we will also modify the inode and the dindirect block.  If we
+	 * are adding a group with superblock/GDT backups  we will also
+	 * modify each of the reserved GDT dindirect blocks.
+	 */
+	credit = 3;	/* sb, resize inode, resize inode dindirect */
+	/* GDT blocks */
+	credit += 1 + DIV_ROUND_UP(flex_gd->count, EXT4_DESC_PER_BLOCK(sb));
+	credit += reserved_gdb;	/* Reserved GDT dindirect blocks */
+	handle = ext4_journal_start_sb(sb, EXT4_HT_RESIZE, credit);
+	if (IS_ERR(handle)) {
+		err = PTR_ERR(handle);
+		goto exit;
+	}
+
+	BUFFER_TRACE(sbi->s_sbh, "get_write_access");
+	err = ext4_journal_get_write_access(handle, sb, sbi->s_sbh,
+					    EXT4_JTR_NONE);
+	if (err)
+		goto exit_journal;
+
+	group = flex_gd->groups[0].group;
+	BUG_ON(group != sbi->s_groups_count);
+	err = ext4_add_new_descs(handle, sb, group,
+				resize_inode, flex_gd->count);
+	if (err)
+		goto exit_journal;
+
+	err = ext4_setup_new_descs(handle, sb, flex_gd);
+	if (err)
+		goto exit_journal;
+
+	ext4_update_super(sb, flex_gd);
+
+	err = ext4_handle_dirty_metadata(handle, NULL, sbi->s_sbh);
+
+exit_journal:
+	err2 = ext4_journal_stop(handle);
+	if (!err)
+		err = err2;
+
+	if (!err) {
+		int gdb_num = group / EXT4_DESC_PER_BLOCK(sb);
+		int gdb_num_end = ((group + flex_gd->count - 1) /
+				   EXT4_DESC_PER_BLOCK(sb));
+		int meta_bg = ext4_has_feature_meta_bg(sb);
+		sector_t padding_blocks = meta_bg ? 0 : sbi->s_sbh->b_blocknr -
+					 ext4_group_first_block_no(sb, 0);
+		sector_t old_gdb = 0;
+
+		update_backups(sb, ext4_group_first_block_no(sb, 0),
+			       (char *)es, sizeof(struct ext4_super_block), 0);
+		for (; gdb_num <= gdb_num_end; gdb_num++) {
+			struct buffer_head *gdb_bh;
+
+			gdb_bh = sbi_array_rcu_deref(sbi, s_group_desc,
+						     gdb_num);
+			if (old_gdb == gdb_bh->b_blocknr)
+				continue;
+			update_backups(sb, gdb_bh->b_blocknr - padding_blocks,
+				       gdb_bh->b_data, gdb_bh->b_size, meta_bg);
+			old_gdb = gdb_bh->b_blocknr;
+		}
+	}
+exit:
+	return err;
+}
+
+static int ext4_setup_next_flex_gd(struct super_block *sb,
+				    struct ext4_new_flex_group_data *flex_gd,
+				    ext4_fsblk_t n_blocks_count,
+				    unsigned long flexbg_size)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+	struct ext4_new_group_data *group_data = flex_gd->groups;
+	ext4_fsblk_t o_blocks_count;
+	ext4_group_t n_group;
+	ext4_group_t group;
+	ext4_group_t last_group;
+	ext4_grpblk_t last;
+	ext4_grpblk_t clusters_per_group;
+	unsigned long i;
+
+	clusters_per_group = EXT4_CLUSTERS_PER_GROUP(sb);
+
+	o_blocks_count = ext4_blocks_count(es);
+
+	if (o_blocks_count == n_blocks_count)
+		return 0;
+
+	ext4_get_group_no_and_offset(sb, o_blocks_count, &group, &last);
+	BUG_ON(last);
+	ext4_get_group_no_and_offset(sb, n_blocks_count - 1, &n_group, &last);
+
+	last_group = group | (flexbg_size - 1);
+	if (last_group > n_group)
+		last_group = n_group;
+
+	flex_gd->count = last_group - group + 1;
+
+	for (i = 0; i < flex_gd->count; i++) {
+		int overhead;
+
+		group_data[i].group = group + i;
+		group_data[i].blocks_count = EXT4_BLOCKS_PER_GROUP(sb);
+		overhead = ext4_group_overhead_blocks(sb, group + i);
+		group_data[i].mdata_blocks = overhead;
+		group_data[i].free_clusters_count = EXT4_CLUSTERS_PER_GROUP(sb);
+		if (ext4_has_group_desc_csum(sb)) {
+			flex_gd->bg_flags[i] = EXT4_BG_BLOCK_UNINIT |
+					       EXT4_BG_INODE_UNINIT;
+			if (!test_opt(sb, INIT_INODE_TABLE))
+				flex_gd->bg_flags[i] |= EXT4_BG_INODE_ZEROED;
+		} else
+			flex_gd->bg_flags[i] = EXT4_BG_INODE_ZEROED;
+	}
+
+	if (last_group == n_group && ext4_has_group_desc_csum(sb))
+		/* We need to initialize block bitmap of last group. */
+		flex_gd->bg_flags[i - 1] &= ~EXT4_BG_BLOCK_UNINIT;
+
+	if ((last_group == n_group) && (last != clusters_per_group - 1)) {
+		group_data[i - 1].blocks_count = EXT4_C2B(sbi, last + 1);
+		group_data[i - 1].free_clusters_count -= clusters_per_group -
+						       last - 1;
+	}
+
+	return 1;
+}
+
+/* Add group descriptor data to an existing or new group descriptor block.
+ * Ensure we handle all possible error conditions _before_ we start modifying
+ * the filesystem, because we cannot abort the transaction and not have it
+ * write the data to disk.
+ *
+ * If we are on a GDT block boundary, we need to get the reserved GDT block.
+ * Otherwise, we may need to add backup GDT blocks for a sparse group.
+ *
+ * We only need to hold the superblock lock while we are actually adding
+ * in the new group's counts to the superblock.  Prior to that we have
+ * not really "added" the group at all.  We re-check that we are still
+ * adding in the last group in case things have changed since verifying.
+ */
+int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input)
+{
+	struct ext4_new_flex_group_data flex_gd;
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+	int reserved_gdb = ext4_bg_has_super(sb, input->group) ?
+		le16_to_cpu(es->s_reserved_gdt_blocks) : 0;
+	struct inode *inode = NULL;
+	int gdb_off;
+	int err;
+	__u16 bg_flags = 0;
+
+	gdb_off = input->group % EXT4_DESC_PER_BLOCK(sb);
+
+	if (gdb_off == 0 && !ext4_has_feature_sparse_super(sb)) {
+		ext4_warning(sb, "Can't resize non-sparse filesystem further");
+		return -EPERM;
+	}
+
+	if (ext4_blocks_count(es) + input->blocks_count <
+	    ext4_blocks_count(es)) {
+		ext4_warning(sb, "blocks_count overflow");
+		return -EINVAL;
+	}
+
+	if (le32_to_cpu(es->s_inodes_count) + EXT4_INODES_PER_GROUP(sb) <
+	    le32_to_cpu(es->s_inodes_count)) {
+		ext4_warning(sb, "inodes_count overflow");
+		return -EINVAL;
+	}
+
+	if (reserved_gdb || gdb_off == 0) {
+		if (!ext4_has_feature_resize_inode(sb) ||
+		    !le16_to_cpu(es->s_reserved_gdt_blocks)) {
+			ext4_warning(sb,
+				     "No reserved GDT blocks, can't resize");
+			return -EPERM;
+		}
+		inode = ext4_iget(sb, EXT4_RESIZE_INO, EXT4_IGET_SPECIAL);
+		if (IS_ERR(inode)) {
+			ext4_warning(sb, "Error opening resize inode");
+			return PTR_ERR(inode);
+		}
+	}
+
+
+	err = verify_group_input(sb, input);
+	if (err)
+		goto out;
+
+	err = ext4_alloc_flex_bg_array(sb, input->group + 1);
+	if (err)
+		goto out;
+
+	err = ext4_mb_alloc_groupinfo(sb, input->group + 1);
+	if (err)
+		goto out;
+
+	flex_gd.count = 1;
+	flex_gd.groups = input;
+	flex_gd.bg_flags = &bg_flags;
+	err = ext4_flex_group_add(sb, inode, &flex_gd);
+out:
+	iput(inode);
+	return err;
+} /* ext4_group_add */
+
+/*
+ * extend a group without checking assuming that checking has been done.
+ */
+static int ext4_group_extend_no_check(struct super_block *sb,
+				      ext4_fsblk_t o_blocks_count, ext4_grpblk_t add)
+{
+	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
+	handle_t *handle;
+	int err = 0, err2;
+
+	/* We will update the superblock, one block bitmap, and
+	 * one group descriptor via ext4_group_add_blocks().
+	 */
+	handle = ext4_journal_start_sb(sb, EXT4_HT_RESIZE, 3);
+	if (IS_ERR(handle)) {
+		err = PTR_ERR(handle);
+		ext4_warning(sb, "error %d on journal start", err);
+		return err;
+	}
+
+	BUFFER_TRACE(EXT4_SB(sb)->s_sbh, "get_write_access");
+	err = ext4_journal_get_write_access(handle, sb, EXT4_SB(sb)->s_sbh,
+					    EXT4_JTR_NONE);
+	if (err) {
+		ext4_warning(sb, "error %d on journal write access", err);
+		goto errout;
+	}
+
+	lock_buffer(EXT4_SB(sb)->s_sbh);
+	ext4_blocks_count_set(es, o_blocks_count + add);
+	ext4_free_blocks_count_set(es, ext4_free_blocks_count(es) + add);
+	ext4_superblock_csum_set(sb);
+	unlock_buffer(EXT4_SB(sb)->s_sbh);
+	ext4_debug("freeing blocks %llu through %llu\n", o_blocks_count,
+		   o_blocks_count + add);
+	/* We add the blocks to the bitmap and set the group need init bit */
+	err = ext4_group_add_blocks(handle, sb, o_blocks_count, add);
+	if (err)
+		goto errout;
+	ext4_handle_dirty_metadata(handle, NULL, EXT4_SB(sb)->s_sbh);
+	ext4_debug("freed blocks %llu through %llu\n", o_blocks_count,
+		   o_blocks_count + add);
+errout:
+	err2 = ext4_journal_stop(handle);
+	if (err2 && !err)
+		err = err2;
+
+	if (!err) {
+		if (test_opt(sb, DEBUG))
+			printk(KERN_DEBUG "EXT4-fs: extended group to %llu "
+			       "blocks\n", ext4_blocks_count(es));
+		update_backups(sb, ext4_group_first_block_no(sb, 0),
+			       (char *)es, sizeof(struct ext4_super_block), 0);
+	}
+	return err;
+}
+
+/*
+ * Extend the filesystem to the new number of blocks specified.  This entry
+ * point is only used to extend the current filesystem to the end of the last
+ * existing group.  It can be accessed via ioctl, or by "remount,resize=<size>"
+ * for emergencies (because it has no dependencies on reserved blocks).
+ *
+ * If we _really_ wanted, we could use default values to call ext4_group_add()
+ * allow the "remount" trick to work for arbitrary resizing, assuming enough
+ * GDT blocks are reserved to grow to the desired size.
+ */
+int ext4_group_extend(struct super_block *sb, struct ext4_super_block *es,
+		      ext4_fsblk_t n_blocks_count)
+{
+	ext4_fsblk_t o_blocks_count;
+	ext4_grpblk_t last;
+	ext4_grpblk_t add;
+	struct buffer_head *bh;
+	int err;
+	ext4_group_t group;
+
+	o_blocks_count = ext4_blocks_count(es);
+
+	if (test_opt(sb, DEBUG))
+		ext4_msg(sb, KERN_DEBUG,
+			 "extending last group from %llu to %llu blocks",
+			 o_blocks_count, n_blocks_count);
+
+	if (n_blocks_count == 0 || n_blocks_count == o_blocks_count)
+		return 0;
+
+	if (n_blocks_count > (sector_t)(~0ULL) >> (sb->s_blocksize_bits - 9)) {
+		ext4_msg(sb, KERN_ERR,
+			 "filesystem too large to resize to %llu blocks safely",
+			 n_blocks_count);
+		return -EINVAL;
+	}
+
+	if (n_blocks_count < o_blocks_count) {
+		ext4_warning(sb, "can't shrink FS - resize aborted");
+		return -EINVAL;
+	}
+
+	/* Handle the remaining blocks in the last group only. */
+	ext4_get_group_no_and_offset(sb, o_blocks_count, &group, &last);
+
+	if (last == 0) {
+		ext4_warning(sb, "need to use ext2online to resize further");
+		return -EPERM;
+	}
+
+	add = EXT4_BLOCKS_PER_GROUP(sb) - last;
+
+	if (o_blocks_count + add < o_blocks_count) {
+		ext4_warning(sb, "blocks_count overflow");
+		return -EINVAL;
+	}
+
+	if (o_blocks_count + add > n_blocks_count)
+		add = n_blocks_count - o_blocks_count;
+
+	if (o_blocks_count + add < n_blocks_count)
+		ext4_warning(sb, "will only finish group (%llu blocks, %u new)",
+			     o_blocks_count + add, add);
+
+	/* See if the device is actually as big as what was requested */
+	bh = ext4_sb_bread(sb, o_blocks_count + add - 1, 0);
+	if (IS_ERR(bh)) {
+		ext4_warning(sb, "can't read last block, resize aborted");
+		return -ENOSPC;
+	}
+	brelse(bh);
+
+	err = ext4_group_extend_no_check(sb, o_blocks_count, add);
+	return err;
+} /* ext4_group_extend */
+
+
+static int num_desc_blocks(struct super_block *sb, ext4_group_t groups)
+{
+	return (groups + EXT4_DESC_PER_BLOCK(sb) - 1) / EXT4_DESC_PER_BLOCK(sb);
+}
+
+/*
+ * Release the resize inode and drop the resize_inode feature if there
+ * are no more reserved gdt blocks, and then convert the file system
+ * to enable meta_bg
+ */
+static int ext4_convert_meta_bg(struct super_block *sb, struct inode *inode)
+{
+	handle_t *handle;
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+	struct ext4_inode_info *ei = EXT4_I(inode);
+	ext4_fsblk_t nr;
+	int i, ret, err = 0;
+	int credits = 1;
+
+	ext4_msg(sb, KERN_INFO, "Converting file system to meta_bg");
+	if (inode) {
+		if (es->s_reserved_gdt_blocks) {
+			ext4_error(sb, "Unexpected non-zero "
+				   "s_reserved_gdt_blocks");
+			return -EPERM;
+		}
+
+		/* Do a quick sanity check of the resize inode */
+		if (inode->i_blocks != 1 << (inode->i_blkbits -
+					     (9 - sbi->s_cluster_bits)))
+			goto invalid_resize_inode;
+		for (i = 0; i < EXT4_N_BLOCKS; i++) {
+			if (i == EXT4_DIND_BLOCK) {
+				if (ei->i_data[i])
+					continue;
+				else
+					goto invalid_resize_inode;
+			}
+			if (ei->i_data[i])
+				goto invalid_resize_inode;
+		}
+		credits += 3;	/* block bitmap, bg descriptor, resize inode */
+	}
+
+	handle = ext4_journal_start_sb(sb, EXT4_HT_RESIZE, credits);
+	if (IS_ERR(handle))
+		return PTR_ERR(handle);
+
+	BUFFER_TRACE(sbi->s_sbh, "get_write_access");
+	err = ext4_journal_get_write_access(handle, sb, sbi->s_sbh,
+					    EXT4_JTR_NONE);
+	if (err)
+		goto errout;
+
+	lock_buffer(sbi->s_sbh);
+	ext4_clear_feature_resize_inode(sb);
+	ext4_set_feature_meta_bg(sb);
+	sbi->s_es->s_first_meta_bg =
+		cpu_to_le32(num_desc_blocks(sb, sbi->s_groups_count));
+	ext4_superblock_csum_set(sb);
+	unlock_buffer(sbi->s_sbh);
+
+	err = ext4_handle_dirty_metadata(handle, NULL, sbi->s_sbh);
+	if (err) {
+		ext4_std_error(sb, err);
+		goto errout;
+	}
+
+	if (inode) {
+		nr = le32_to_cpu(ei->i_data[EXT4_DIND_BLOCK]);
+		ext4_free_blocks(handle, inode, NULL, nr, 1,
+				 EXT4_FREE_BLOCKS_METADATA |
+				 EXT4_FREE_BLOCKS_FORGET);
+		ei->i_data[EXT4_DIND_BLOCK] = 0;
+		inode->i_blocks = 0;
+
+		err = ext4_mark_inode_dirty(handle, inode);
+		if (err)
+			ext4_std_error(sb, err);
+	}
+
+errout:
+	ret = ext4_journal_stop(handle);
+	return err ? err : ret;
+
+invalid_resize_inode:
+	ext4_error(sb, "corrupted/inconsistent resize inode");
+	return -EINVAL;
+}
+
+/*
+ * ext4_resize_fs() resizes a fs to new size specified by @n_blocks_count
+ *
+ * @sb: super block of the fs to be resized
+ * @n_blocks_count: the number of blocks resides in the resized fs
+ */
+int ext4_resize_fs(struct super_block *sb, ext4_fsblk_t n_blocks_count)
+{
+	struct ext4_new_flex_group_data *flex_gd = NULL;
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct ext4_super_block *es = sbi->s_es;
+	struct buffer_head *bh;
+	struct inode *resize_inode = NULL;
+	ext4_grpblk_t add, offset;
+	unsigned long n_desc_blocks;
+	unsigned long o_desc_blocks;
+	ext4_group_t o_group;
+	ext4_group_t n_group;
+	ext4_fsblk_t o_blocks_count;
+	ext4_fsblk_t n_blocks_count_retry = 0;
+	unsigned long last_update_time = 0;
+	int err = 0, flexbg_size = 1 << sbi->s_log_groups_per_flex;
+	int meta_bg;
+
+	/* See if the device is actually as big as what was requested */
+	bh = ext4_sb_bread(sb, n_blocks_count - 1, 0);
+	if (IS_ERR(bh)) {
+		ext4_warning(sb, "can't read last block, resize aborted");
+		return -ENOSPC;
+	}
+	brelse(bh);
+
+	/*
+	 * For bigalloc, trim the requested size to the nearest cluster
+	 * boundary to avoid creating an unusable filesystem. We do this
+	 * silently, instead of returning an error, to avoid breaking
+	 * callers that blindly resize the filesystem to the full size of
+	 * the underlying block device.
+	 */
+	if (ext4_has_feature_bigalloc(sb))
+		n_blocks_count &= ~((1 << EXT4_CLUSTER_BITS(sb)) - 1);
+
+retry:
+	o_blocks_count = ext4_blocks_count(es);
+
+	ext4_msg(sb, KERN_INFO, "resizing filesystem from %llu "
+		 "to %llu blocks", o_blocks_count, n_blocks_count);
+
+	if (n_blocks_count < o_blocks_count) {
+		/* On-line shrinking not supported */
+		ext4_warning(sb, "can't shrink FS - resize aborted");
+		return -EINVAL;
+	}
+
+	if (n_blocks_count == o_blocks_count)
+		/* Nothing need to do */
+		return 0;
+
+	n_group = ext4_get_group_number(sb, n_blocks_count - 1);
+	if (n_group >= (0xFFFFFFFFUL / EXT4_INODES_PER_GROUP(sb))) {
+		ext4_warning(sb, "resize would cause inodes_count overflow");
+		return -EINVAL;
+	}
+	ext4_get_group_no_and_offset(sb, o_blocks_count - 1, &o_group, &offset);
+
+	n_desc_blocks = num_desc_blocks(sb, n_group + 1);
+	o_desc_blocks = num_desc_blocks(sb, sbi->s_groups_count);
+
+	meta_bg = ext4_has_feature_meta_bg(sb);
+
+	if (ext4_has_feature_resize_inode(sb)) {
+		if (meta_bg) {
+			ext4_error(sb, "resize_inode and meta_bg enabled "
+				   "simultaneously");
+			return -EINVAL;
+		}
+		if (n_desc_blocks > o_desc_blocks +
+		    le16_to_cpu(es->s_reserved_gdt_blocks)) {
+			n_blocks_count_retry = n_blocks_count;
+			n_desc_blocks = o_desc_blocks +
+				le16_to_cpu(es->s_reserved_gdt_blocks);
+			n_group = n_desc_blocks * EXT4_DESC_PER_BLOCK(sb);
+			n_blocks_count = (ext4_fsblk_t)n_group *
+				EXT4_BLOCKS_PER_GROUP(sb) +
+				le32_to_cpu(es->s_first_data_block);
+			n_group--; /* set to last group number */
+		}
+
+		if (!resize_inode)
+			resize_inode = ext4_iget(sb, EXT4_RESIZE_INO,
+						 EXT4_IGET_SPECIAL);
+		if (IS_ERR(resize_inode)) {
+			ext4_warning(sb, "Error opening resize inode");
+			return PTR_ERR(resize_inode);
+		}
+	}
+
+	if ((!resize_inode && !meta_bg) || n_blocks_count == o_blocks_count) {
+		err = ext4_convert_meta_bg(sb, resize_inode);
+		if (err)
+			goto out;
+		if (resize_inode) {
+			iput(resize_inode);
+			resize_inode = NULL;
+		}
+		if (n_blocks_count_retry) {
+			n_blocks_count = n_blocks_count_retry;
+			n_blocks_count_retry = 0;
+			goto retry;
+		}
+	}
+
+	/*
+	 * Make sure the last group has enough space so that it's
+	 * guaranteed to have enough space for all metadata blocks
+	 * that it might need to hold.  (We might not need to store
+	 * the inode table blocks in the last block group, but there
+	 * will be cases where this might be needed.)
+	 */
+	if ((ext4_group_first_block_no(sb, n_group) +
+	     ext4_group_overhead_blocks(sb, n_group) + 2 +
+	     sbi->s_itb_per_group + sbi->s_cluster_ratio) >= n_blocks_count) {
+		n_blocks_count = ext4_group_first_block_no(sb, n_group);
+		n_group--;
+		n_blocks_count_retry = 0;
+		if (resize_inode) {
+			iput(resize_inode);
+			resize_inode = NULL;
+		}
+		goto retry;
+	}
+
+	/* extend the last group */
+	if (n_group == o_group)
+		add = n_blocks_count - o_blocks_count;
+	else
+		add = EXT4_C2B(sbi, EXT4_CLUSTERS_PER_GROUP(sb) - (offset + 1));
+	if (add > 0) {
+		err = ext4_group_extend_no_check(sb, o_blocks_count, add);
+		if (err)
+			goto out;
+	}
+
+	if (ext4_blocks_count(es) == n_blocks_count && n_blocks_count_retry == 0)
+		goto out;
+
+	err = ext4_alloc_flex_bg_array(sb, n_group + 1);
+	if (err)
+		goto out;
+
+	err = ext4_mb_alloc_groupinfo(sb, n_group + 1);
+	if (err)
+		goto out;
+
+	flex_gd = alloc_flex_gd(flexbg_size);
+	if (flex_gd == NULL) {
+		err = -ENOMEM;
+		goto out;
+	}
+
+	/* Add flex groups. Note that a regular group is a
+	 * flex group with 1 group.
+	 */
+	while (ext4_setup_next_flex_gd(sb, flex_gd, n_blocks_count,
+					      flexbg_size)) {
+		if (time_is_before_jiffies(last_update_time + HZ * 10)) {
+			if (last_update_time)
+				ext4_msg(sb, KERN_INFO,
+					 "resized to %llu blocks",
+					 ext4_blocks_count(es));
+			last_update_time = jiffies;
+		}
+		if (ext4_alloc_group_tables(sb, flex_gd, flexbg_size) != 0)
+			break;
+		err = ext4_flex_group_add(sb, resize_inode, flex_gd);
+		if (unlikely(err))
+			break;
+	}
+
+	if (!err && n_blocks_count_retry) {
+		n_blocks_count = n_blocks_count_retry;
+		n_blocks_count_retry = 0;
+		free_flex_gd(flex_gd);
+		flex_gd = NULL;
+		if (resize_inode) {
+			iput(resize_inode);
+			resize_inode = NULL;
+		}
+		goto retry;
+	}
+
+out:
+	if (flex_gd)
+		free_flex_gd(flex_gd);
+	if (resize_inode != NULL)
+		iput(resize_inode);
+	if (err)
+		ext4_warning(sb, "error (%d) occurred during "
+			     "file system resize", err);
+	ext4_msg(sb, KERN_INFO, "resized filesystem to %llu",
+		 ext4_blocks_count(es));
+	return err;
+}