[releases.git] / resize.c

// 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 resize_bg;                 /* number of allocated
                                                   new_group_data */
        ext4_group_t count;                     /* number of groups in @groups
                                                 */
};

/*
 * Avoiding memory allocation failures due to too many groups added each time.
 */
#define MAX_RESIZE_BG                           16384

/*
 * 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 int 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 (unlikely(flexbg_size > MAX_RESIZE_BG))
                flex_gd->resize_bg = MAX_RESIZE_BG;
        else
                flex_gd->resize_bg = flexbg_size;

        flex_gd->groups = kmalloc_array(flex_gd->resize_bg,
                                        sizeof(struct ext4_new_group_data),
                                        GFP_NOFS);
        if (flex_gd->groups == NULL)
                goto out2;

        flex_gd->bg_flags = kmalloc_array(flex_gd->resize_bg, 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,
                                unsigned 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 "
                       "%u groups, flexbg size is %u:\n", flex_gd->count,
                       flexbg_size);

                for (i = 0; i < flex_gd->count; i++) {
                        ext4_debug(
                               "adding %s group %u: %u blocks (%u free, %u 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) &&
                              gdb_num >= le32_to_cpu(es->s_first_meta_bg);
                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)
{
        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 | (flex_gd->resize_bg - 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;
        int meta_bg;
        unsigned int flexbg_size = ext4_flex_bg_size(sbi);

        /* 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)) {
                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;
}