resize.c

/*
 *  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 "ext4_jbd2.h"

int ext4_resize_begin(struct super_block *sb)
{
	int ret = 0;

	if (!capable(CAP_SYS_RESOURCE))
		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\n");
		return -EPERM;
	}

	if (test_and_set_bit_lock(EXT4_RESIZING, &EXT4_SB(sb)->s_resize_flags))
		ret = -EBUSY;

	return ret;
}

void ext4_resize_end(struct super_block *sb)
{
	clear_bit_unlock(EXT4_RESIZING, &EXT4_SB(sb)->s_resize_flags);
	smp_mb__after_clear_bit();
}

#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_bg_has_super(sb, group) ?
		(1 + ext4_bg_num_gdb(sb, group) +
		 le16_to_cpu(es->s_reserved_gdt_blocks)) : 0;
	ext4_fsblk_t metaend = start + overhead;
	struct buffer_head *bh = NULL;
	ext4_grpblk_t free_blocks_count, offset;
	int err = -EINVAL;

	input->free_blocks_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 (group != sbi->s_groups_count)
		ext4_warning(sb, "Cannot add at group %u (only %u groups)",
			     input->group, sbi->s_groups_count);
	else 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 (!(bh = sb_bread(sb, end - 1)))
		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_flex_group_data))
		goto out2;
	flex_gd->count = flexbg_size;

	flex_gd->groups = kmalloc(sizeof(struct ext4_new_group_data) *
				  flexbg_size, GFP_NOFS);
	if (flex_gd->groups == NULL)
		goto out2;

	flex_gd->bg_flags = kmalloc(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;
	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
	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;

	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_bg_has_super(sb, src_group) ?
		   (1 + ext4_bg_num_gdb(sb, src_group) +
		    le16_to_cpu(es->s_reserved_gdt_blocks)) : 0;

	start_blk += overhead;

	/* We collect contiguous blocks as much as possible. */
	src_group++;
	for (; src_group <= last_group; src_group++)
		if (!ext4_bg_has_super(sb, src_group))
			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++;
		ext4_get_group_no_and_offset(sb, start_blk - 1, &group, NULL);
		group -= group_data[0].group;
		group_data[group].free_blocks_count--;
		if (flexbg_size > 1)
			flex_gd->bg_flags[group] &= ~EXT4_BG_BLOCK_UNINIT;
	}

	/* 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++;
		ext4_get_group_no_and_offset(sb, start_blk - 1, &group, NULL);
		group -= group_data[0].group;
		group_data[group].free_blocks_count--;
		if (flexbg_size > 1)
			flex_gd->bg_flags[group] &= ~EXT4_BG_BLOCK_UNINIT;
	}

	/* Allocate inode tables */
	for (; it_index < flex_gd->count; it_index++) {
		if (start_blk + EXT4_SB(sb)->s_itb_per_group > last_blk)
			goto next_group;
		group_data[it_index].inode_table = start_blk;
		ext4_get_group_no_and_offset(sb, start_blk, &group, NULL);
		group -= group_data[0].group;
		group_data[group].free_blocks_count -=
					EXT4_SB(sb)->s_itb_per_group;
		if (flexbg_size > 1)
			flex_gd->bg_flags[group] &= ~EXT4_BG_BLOCK_UNINIT;

		start_blk += EXT4_SB(sb)->s_itb_per_group;
	}

	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++) {
			printk(KERN_DEBUG "adding %s group %u: %u "
			       "blocks (%d free)\n",
			       ext4_bg_has_super(sb, group + i) ? "normal" :
			       "no-super", group + i,
			       group_data[i].blocks_count,
			       group_data[i].free_blocks_count);
		}
	}
	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 (!bh)
		return ERR_PTR(-EIO);
	if ((err = ext4_journal_get_write_access(handle, bh))) {
		brelse(bh);
		bh = ERR_PTR(err);
	} else {
		memset(bh->b_data, 0, sb->s_blocksize);
		set_buffer_uptodate(bh);
	}

	return bh;
}

/*
 * If we have fewer than thresh credits, extend by EXT4_MAX_TRANS_DATA.
 * If that fails, restart the transaction & regain write access for the
 * buffer head which is used for block_bitmap modifications.
 */
static int extend_or_restart_transaction(handle_t *handle, int thresh)
{
	int err;

	if (ext4_handle_has_enough_credits(handle, thresh))
		return 0;

	err = ext4_journal_extend(handle, EXT4_MAX_TRANS_DATA);
	if (err < 0)
		return err;
	if (err) {
		err = ext4_journal_restart(handle, EXT4_MAX_TRANS_DATA);
		if (err)
			return err;
	}

	return 0;
}

/*
 * set_flexbg_block_bitmap() mark @count blocks starting from @block 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 block, ext4_group_t count)
{
	ext4_group_t count2;

	ext4_debug("mark blocks [%llu/%u] used\n", block, count);
	for (count2 = count; count > 0; count -= count2, block += count2) {
		ext4_fsblk_t start;
		struct buffer_head *bh;
		ext4_group_t group;
		int err;

		ext4_get_group_no_and_offset(sb, block, &group, NULL);
		start = ext4_group_first_block_no(sb, group);
		group -= flex_gd->groups[0].group;

		count2 = sb->s_blocksize * 8 - (block - start);
		if (count2 > count)
			count2 = count;

		if (flex_gd->bg_flags[group] & EXT4_BG_BLOCK_UNINIT) {
			BUG_ON(flex_gd->count > 1);
			continue;
		}

		err = extend_or_restart_transaction(handle, 1);
		if (err)
			return err;

		bh = sb_getblk(sb, flex_gd->groups[group].block_bitmap);
		if (!bh)
			return -EIO;

		err = ext4_journal_get_write_access(handle, bh);
		if (err)
			return err;
		ext4_debug("mark block bitmap %#04llx (+%llu/%u)\n", block,
			   block - start, count2);
		ext4_set_bits(bh->b_data, block - start, count2);

		err = ext4_handle_dirty_metadata(handle, NULL, bh);
		if (unlikely(err))
			return err;
		brelse(bh);
	}

	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;

	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);

	/* This transaction may be extended/restarted along the way */
	handle = ext4_journal_start_sb(sb, 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;

		gdblocks = ext4_bg_num_gdb(sb, group);
		start = ext4_group_first_block_no(sb, group);

		if (!ext4_bg_has_super(sb, group))
			goto handle_itb;

		/* Copy all of the GDT blocks into the backup in this group */
		for (j = 0, block = start + 1; j < gdblocks; j++, block++) {
			struct buffer_head *gdb;

			ext4_debug("update backup group %#04llx\n", block);
			err = extend_or_restart_transaction(handle, 1);
			if (err)
				goto out;

			gdb = sb_getblk(sb, block);
			if (!gdb) {
				err = -EIO;
				goto out;
			}

			err = ext4_journal_get_write_access(handle, gdb);
			if (err) {
				brelse(gdb);
				goto out;
			}
			memcpy(gdb->b_data, 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 = extend_or_restart_transaction(handle, 1);
		if (err)
			goto out;

		bh = bclean(handle, sb, block);
		if (IS_ERR(bh)) {
			err = PTR_ERR(bh);
			goto out;
		}
		if (ext4_bg_has_super(sb, group)) {
			ext4_debug("mark backup superblock %#04llx (+0)\n",
				   start);
			ext4_set_bits(bh->b_data, 0, gdblocks + reserved_gdb +
						     1);
		}
		ext4_mark_bitmap_end(group_data[i].blocks_count,
				     sb->s_blocksize * 8, bh->b_data);
		err = ext4_handle_dirty_metadata(handle, NULL, bh);
		if (err)
			goto out;
		brelse(bh);

handle_ib:
		if (bg_flags[i] & EXT4_BG_INODE_UNINIT)
			continue;

		/* Initialize inode bitmap of the @group */
		block = group_data[i].inode_bitmap;
		err = extend_or_restart_transaction(handle, 1);
		if (err)
			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);
		if (err)
			goto out;
		brelse(bh);
	}
	bh = NULL;

	/* 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, start, count);
			if (err)
				goto out;
			count = group_table_count[j];
			start = group_data[i].block_bitmap;
			block = start;
		}

		if (count) {
			err = set_flexbg_block_bitmap(sb, handle,
						flex_gd, start, count);
			if (err)
				goto out;
		}
	}

out:
	brelse(bh);
	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, ...
 */
static unsigned ext4_list_backups(struct super_block *sb, unsigned *three,
				  unsigned *five, unsigned *seven)
{
	unsigned *min = three;
	int mult = 3;
	unsigned ret;

	if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
					EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER)) {
		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;
	struct buffer_head *dind;
	struct buffer_head *gdb_bh;
	int gdbackups;
	struct ext4_iloc iloc;
	__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);

	/*
	 * 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_SB(sb)->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;
	}

	gdb_bh = sb_bread(sb, gdblock);
	if (!gdb_bh)
		return -EIO;

	gdbackups = verify_reserved_gdb(sb, group, gdb_bh);
	if (gdbackups < 0) {
		err = gdbackups;
		goto exit_bh;
	}

	data = EXT4_I(inode)->i_data + EXT4_DIND_BLOCK;
	dind = sb_bread(sb, le32_to_cpu(*data));
	if (!dind) {
		err = -EIO;
		goto exit_bh;
	}

	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 exit_dind;
	}

	err = ext4_journal_get_write_access(handle, EXT4_SB(sb)->s_sbh);
	if (unlikely(err))
		goto exit_dind;

	err = ext4_journal_get_write_access(handle, gdb_bh);
	if (unlikely(err))
		goto exit_sbh;

	err = ext4_journal_get_write_access(handle, dind);
	if (unlikely(err))
		ext4_std_error(sb, err);

	/* ext4_reserve_inode_write() gets a reference on the iloc */
	err = ext4_reserve_inode_write(handle, inode, &iloc);
	if (unlikely(err))
		goto exit_dindj;

	n_group_desc = ext4_kvmalloc((gdb_num + 1) *
				     sizeof(struct buffer_head *),
				     GFP_NOFS);
	if (!n_group_desc) {
		err = -ENOMEM;
		ext4_warning(sb, "not enough memory for %lu groups",
			     gdb_num + 1);
		goto exit_inode;
	}

	/*
	 * 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 exit_inode;
	}
	inode->i_blocks -= (gdbackups + 1) * sb->s_blocksize >> 9;
	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);
		goto exit_inode;
	}
	brelse(dind);

	o_group_desc = EXT4_SB(sb)->s_group_desc;
	memcpy(n_group_desc, o_group_desc,
	       EXT4_SB(sb)->s_gdb_count * sizeof(struct buffer_head *));
	n_group_desc[gdb_num] = gdb_bh;
	EXT4_SB(sb)->s_group_desc = n_group_desc;
	EXT4_SB(sb)->s_gdb_count++;
	ext4_kvfree(o_group_desc);

	le16_add_cpu(&es->s_reserved_gdt_blocks, -1);
	err = ext4_handle_dirty_super(handle, sb);
	if (err)
		ext4_std_error(sb, err);

	return err;

exit_inode:
	ext4_kvfree(n_group_desc);
	/* ext4_handle_release_buffer(handle, iloc.bh); */
	brelse(iloc.bh);
exit_dindj:
	/* ext4_handle_release_buffer(handle, dind); */
exit_sbh:
	/* ext4_handle_release_buffer(handle, EXT4_SB(sb)->s_sbh); */
exit_dind:
	brelse(dind);
exit_bh:
	brelse(gdb_bh);

	ext4_debug("leaving with error %d\n", err);
	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);
	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(reserved_gdb * sizeof(*primary), GFP_NOFS);
	if (!primary)
		return -ENOMEM;

	data = EXT4_I(inode)->i_data + EXT4_DIND_BLOCK;
	dind = sb_bread(sb, le32_to_cpu(*data));
	if (!dind) {
		err = -EIO;
		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] = sb_bread(sb, blk);
		if (!primary[res]) {
			err = -EIO;
			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++) {
		if ((err = ext4_journal_get_write_access(handle, primary[i]))) {
			/*
			int j;
			for (j = 0; j < i; j++)
				ext4_handle_release_buffer(handle, primary[j]);
			 */
			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;
	ext4_mark_iloc_dirty(handle, inode, &iloc);

exit_bh:
	while (--res >= 0)
		brelse(primary[res]);
	brelse(dind);

exit_free:
	kfree(primary);

	return err;
}

/*
 * 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,
			   int blk_off, char *data, int size)
{
	struct ext4_sb_info *sbi = EXT4_SB(sb);
	const ext4_group_t last = sbi->s_groups_count;
	const int bpg = EXT4_BLOCKS_PER_GROUP(sb);
	unsigned three = 1;
	unsigned five = 5;
	unsigned seven = 7;
	ext4_group_t group;
	int rest = sb->s_blocksize - size;
	handle_t *handle;
	int err = 0, err2;

	handle = ext4_journal_start_sb(sb, EXT4_MAX_TRANS_DATA);
	if (IS_ERR(handle)) {
		group = 1;
		err = PTR_ERR(handle);
		goto exit_err;
	}

	ext4_superblock_csum_set(sb, (struct ext4_super_block *)data);

	while ((group = ext4_list_backups(sb, &three, &five, &seven)) < last) {
		struct buffer_head *bh;

		/* Out of journal space, and can't get more - abort - so sad */
		if (ext4_handle_valid(handle) &&
		    handle->h_buffer_credits == 0 &&
		    ext4_journal_extend(handle, EXT4_MAX_TRANS_DATA) &&
		    (err = ext4_journal_restart(handle, EXT4_MAX_TRANS_DATA)))
			break;

		bh = sb_getblk(sb, group * bpg + blk_off);
		if (!bh) {
			err = -EIO;
			break;
		}
		ext4_debug("update metadata backup %#04lx\n",
			  (unsigned long)bh->b_blocknr);
		if ((err = ext4_journal_get_write_access(handle, bh)))
			break;
		lock_buffer(bh);
		memcpy(bh->b_data, data, size);
		if (rest)
			memset(bh->b_data + size, 0, rest);
		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 ((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;

	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->s_group_desc[gdb_num];
			err = ext4_journal_get_write_access(handle, gdb_bh);

			if (!err && reserved_gdb && ext4_bg_num_gdb(sb, group))
				err = reserve_backup_gdb(handle, resize_inode, 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 (!bh)
		return NULL;

	if (bitmap_uptodate(bh))
		return bh;

	lock_buffer(bh);
	if (bh_submit_read(bh) < 0) {
		unlock_buffer(bh);
		brelse(bh);
		return NULL;
	}
	unlock_buffer(bh);

	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_RO_COMPAT_FEATURE(sb,
					EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
		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,
				   EXT4_BLOCKS_PER_GROUP(sb) / 8);
	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->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,
					     EXT4_B2C(sbi, group_data->free_blocks_count));
		ext4_free_inodes_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;
}

/*
 * 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 += group_data[i].free_blocks_count;
	}

	reserved_blocks = ext4_r_blocks_count(es) * 100;
	do_div(reserved_blocks, ext4_blocks_count(es));
	reserved_blocks *= blocks_count;
	do_div(reserved_blocks, 100);

	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);

	/*
	 * 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;

	/* 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_B2C(sbi, free_blocks));
	percpu_counter_add(&sbi->s_freeinodes_counter,
			   EXT4_INODES_PER_GROUP(sb) * flex_gd->count);

	if (EXT4_HAS_INCOMPAT_FEATURE(sb,
				      EXT4_FEATURE_INCOMPAT_FLEX_BG) &&
	    sbi->s_log_groups_per_flex) {
		ext4_group_t flex_group;
		flex_group = ext4_flex_group(sbi, group_data[0].group);
		atomic_add(EXT4_B2C(sbi, free_blocks),
			   &sbi->s_flex_groups[flex_group].free_clusters);
		atomic_add(EXT4_INODES_PER_GROUP(sb) * flex_gd->count,
			   &sbi->s_flex_groups[flex_group].free_inodes);
	}

	/*
	 * Update the fs overhead information
	 */
	ext4_calculate_overhead(sb);

	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
	 * block.  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 = flex_gd->count * 4 + reserved_gdb;
	handle = ext4_journal_start_sb(sb, credit);
	if (IS_ERR(handle)) {
		err = PTR_ERR(handle);
		goto exit;
	}

	err = ext4_journal_get_write_access(handle, sbi->s_sbh);
	if (err)
		goto exit_journal;

	group = flex_gd->groups[0].group;
	BUG_ON(group != EXT4_SB(sb)->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_super(handle, sb);

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));

		update_backups(sb, sbi->s_sbh->b_blocknr, (char *)es,
			       sizeof(struct ext4_super_block));
		for (; gdb_num <= gdb_num_end; gdb_num++) {
			struct buffer_head *gdb_bh;

			gdb_bh = sbi->s_group_desc[gdb_num];
			update_backups(sb, gdb_bh->b_blocknr, gdb_bh->b_data,
				       gdb_bh->b_size);
		}
	}
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_super_block *es = EXT4_SB(sb)->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 blocks_per_group;
	unsigned long i;

	blocks_per_group = EXT4_BLOCKS_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 = blocks_per_group;
		overhead = ext4_bg_has_super(sb, group + i) ?
			   (1 + ext4_bg_num_gdb(sb, group + i) +
			    le16_to_cpu(es->s_reserved_gdt_blocks)) : 0;
		group_data[i].free_blocks_count = blocks_per_group - overhead;
		if (ext4_has_group_desc_csum(sb))
			flex_gd->bg_flags[i] = EXT4_BG_BLOCK_UNINIT |
					       EXT4_BG_INODE_UNINIT;
		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 != blocks_per_group - 1)) {
		group_data[i - 1].blocks_count = last + 1;
		group_data[i - 1].free_blocks_count -= blocks_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, gdb_num;
	int err;
	__u16 bg_flags = 0;

	gdb_num = input->group / EXT4_DESC_PER_BLOCK(sb);
	gdb_off = input->group % EXT4_DESC_PER_BLOCK(sb);

	if (gdb_off == 0 && !EXT4_HAS_RO_COMPAT_FEATURE(sb,
					EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER)) {
		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_COMPAT_FEATURE(sb,
					     EXT4_FEATURE_COMPAT_RESIZE_INODE)
		    || !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);
		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)
		return err;

	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, 3);
	if (IS_ERR(handle)) {
		err = PTR_ERR(handle);
		ext4_warning(sb, "error %d on journal start", err);
		return err;
	}

	err = ext4_journal_get_write_access(handle, EXT4_SB(sb)->s_sbh);
	if (err) {
		ext4_warning(sb, "error %d on journal write access", err);
		goto errout;
	}

	ext4_blocks_count_set(es, o_blocks_count + add);
	ext4_free_blocks_count_set(es, ext4_free_blocks_count(es) + add);
	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_super(handle, sb);
	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_SB(sb)->s_sbh->b_blocknr, (char *)es,
			       sizeof(struct ext4_super_block));
	}
	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);
		if (sizeof(sector_t) < 8)
			ext4_warning(sb, "CONFIG_LBDAF not enabled");
		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 = sb_bread(sb, o_blocks_count + add - 1);
	if (!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 */

/*
 * 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;
	ext4_fsblk_t o_blocks_count;
	ext4_group_t o_group;
	ext4_group_t n_group;
	ext4_grpblk_t offset, add;
	unsigned long n_desc_blocks;
	unsigned long o_desc_blocks;
	unsigned long desc_blocks;
	int err = 0, flexbg_size = 1 << sbi->s_log_groups_per_flex;

	o_blocks_count = ext4_blocks_count(es);

	if (test_opt(sb, DEBUG))
		ext4_msg(sb, KERN_DEBUG, "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;

	ext4_get_group_no_and_offset(sb, n_blocks_count - 1, &n_group, &offset);
	ext4_get_group_no_and_offset(sb, o_blocks_count - 1, &o_group, &offset);

	n_desc_blocks = (n_group + EXT4_DESC_PER_BLOCK(sb)) /
			EXT4_DESC_PER_BLOCK(sb);
	o_desc_blocks = (sbi->s_groups_count + EXT4_DESC_PER_BLOCK(sb) - 1) /
			EXT4_DESC_PER_BLOCK(sb);
	desc_blocks = n_desc_blocks - o_desc_blocks;

	if (desc_blocks &&
	    (!EXT4_HAS_COMPAT_FEATURE(sb, EXT4_FEATURE_COMPAT_RESIZE_INODE) ||
	     le16_to_cpu(es->s_reserved_gdt_blocks) < desc_blocks)) {
		ext4_warning(sb, "No reserved GDT blocks, can't resize");
		return -EPERM;
	}

	resize_inode = ext4_iget(sb, EXT4_RESIZE_INO);
	if (IS_ERR(resize_inode)) {
		ext4_warning(sb, "Error opening resize inode");
		return PTR_ERR(resize_inode);
	}

	/* See if the device is actually as big as what was requested */
	bh = sb_bread(sb, n_blocks_count - 1);
	if (!bh) {
		ext4_warning(sb, "can't read last block, resize aborted");
		return -ENOSPC;
	}
	brelse(bh);

	/* extend the last group */
	if (n_group == o_group)
		add = n_blocks_count - o_blocks_count;
	else
		add = EXT4_BLOCKS_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)
		goto out;

	err = ext4_alloc_flex_bg_array(sb, n_group + 1);
	if (err)
		return err;

	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 (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;
	}

out:
	if (flex_gd)
		free_flex_gd(flex_gd);

	iput(resize_inode);
	if (test_opt(sb, DEBUG))
		ext4_msg(sb, KERN_DEBUG, "resized filesystem from %llu "
		       "upto %llu blocks", o_blocks_count, n_blocks_count);
	return err;
}