resize.c

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/*
 *  linux/fs/ext4/resize.c
 *
 * Support for resizing an ext4 filesystem while it is mounted.
 *
 * Copyright (C) 2001, 2002 Andreas Dilger <[email protected]>
 *
 * 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();
}

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_group_overhead_blocks(sb, group);
    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;
    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_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++;
        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;
    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_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_META_BG);

    /* 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;
        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) {
            ext4_group_t first_group;
            first_group = ext4_meta_bg_first_group(sb, group);
            if (first_group != group + 1 &&
                first_group != group + EXT4_DESC_PER_BLOCK(sb) - 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 = 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;
        }
        overhead = ext4_group_overhead_blocks(sb, group);
        if (overhead != 0) {
            ext4_debug("mark backup superblock %#04llx (+0)\n",
                   start);
            ext4_set_bits(bh->b_data, 0, overhead);
        }
        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;
}

/*
 * 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 = sb_bread(sb, gdblock);
    if (!gdb_bh)
        return -EIO;
    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);
        return err;
    }

    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);
    err = ext4_journal_get_write_access(handle, gdb_bh);
    if (unlikely(err))
        brelse(gdb_bh);
    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, 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_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_meta_bg_first_group(sb, group) + 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;

        /* 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;

        if (meta_bg == 0)
            backup_block = group * bpg + blk_off;
        else
            backup_block = (ext4_group_first_block_no(sb, group) +
                    ext4_bg_has_super(sb, group));

        bh = sb_getblk(sb, backup_block);
        if (!bh) {
            err = -EIO;
            break;
        }
        ext4_debug("update metadata backup %llu(+%llu)\n",
               backup_block, backup_block -
               ext4_group_first_block_no(sb, group));
        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 (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_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_META_BG);
    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 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 (!bh)
        return NULL;
    if (!bh_uptodate_or_lock(bh)) {
        if (bh_submit_read(bh) < 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_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);
    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));
        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;
}

/*
 * 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;
    reserved_blocks = div64_u64(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);

    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;

    /* 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);

    ext4_debug("free blocks count %llu",
           percpu_counter_read(&sbi->s_freeclusters_counter));
    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));
        int meta_bg = EXT4_HAS_INCOMPAT_FEATURE(sb,
                EXT4_FEATURE_INCOMPAT_META_BG);
        sector_t old_gdb = 0;

        update_backups(sb, sbi->s_sbh->b_blocknr, (char *)es,
                   sizeof(struct ext4_super_block), 0);
        for (; gdb_num <= gdb_num_end; gdb_num++) {
            struct buffer_head *gdb_bh;

            gdb_bh = sbi->s_group_desc[gdb_num];
            if (old_gdb == gdb_bh->b_blocknr)
                continue;
            update_backups(sb, gdb_bh->b_blocknr, gdb_bh->b_data,
                       gdb_bh->b_size, meta_bg);
            old_gdb = gdb_bh->b_blocknr;
        }
    }
exit:
    return err;
}

static int ext4_setup_next_flex_gd(struct super_block *sb,
                    struct ext4_new_flex_group_data *flex_gd,
                    ext4_fsblk_t n_blocks_count,
                    unsigned long flexbg_size)
{
    struct ext4_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_group_overhead_blocks(sb, group + i);
        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;

    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, 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) {
        ext4_fsblk_t first_block;
        first_block = ext4_group_first_block_no(sb, 0);
        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 - first_block,
                   (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);
        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 */


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))
            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, credits);
    if (IS_ERR(handle))
        return PTR_ERR(handle);

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

    EXT4_CLEAR_COMPAT_FEATURE(sb, EXT4_FEATURE_COMPAT_RESIZE_INODE);
    EXT4_SET_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_META_BG);
    sbi->s_es->s_first_meta_bg =
        cpu_to_le32(num_desc_blocks(sb, sbi->s_groups_count));

    err = ext4_handle_dirty_super(handle, sb);
    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);
    if (!err)
        err = ret;
    return ret;

invalid_resize_inode:
    ext4_error(sb, "corrupted/inconsistent resize inode");
    return -EINVAL;
}

/*
 * ext4_resize_fs() resizes a fs to new size specified by @n_blocks_count
 *
 * @sb: super block of the fs to be resized
 * @n_blocks_count: the number of blocks resides in the resized fs
 */
int ext4_resize_fs(struct super_block *sb, ext4_fsblk_t n_blocks_count)
{
    struct ext4_new_flex_group_data *flex_gd = NULL;
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    struct ext4_super_block *es = sbi->s_es;
    struct buffer_head *bh;
    struct inode *resize_inode = NULL;
    ext4_grpblk_t add, offset;
    unsigned long n_desc_blocks;
    unsigned long o_desc_blocks;
    ext4_group_t o_group;
    ext4_group_t n_group;
    ext4_fsblk_t o_blocks_count;
    ext4_fsblk_t n_blocks_count_retry = 0;
    unsigned long last_update_time = 0;
    int err = 0, flexbg_size = 1 << sbi->s_log_groups_per_flex;
    int meta_bg;

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

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;

    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 = num_desc_blocks(sb, n_group + 1);
    o_desc_blocks = num_desc_blocks(sb, sbi->s_groups_count);

    meta_bg = EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_META_BG);

    if (EXT4_HAS_COMPAT_FEATURE(sb, EXT4_FEATURE_COMPAT_RESIZE_INODE)) {
        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 = n_group * EXT4_BLOCKS_PER_GROUP(sb);
            n_group--; /* set to last group number */
        }

        if (!resize_inode)
            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);
        }
    }

    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;
        }
    }

    /* 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;

    err = ext4_mb_alloc_groupinfo(sb, n_group + 1);
    if (err)
        goto out;

    flex_gd = alloc_flex_gd(flexbg_size);
    if (flex_gd == NULL) {
        err = -ENOMEM;
        goto out;
    }

    /* Add flex groups. Note that a regular group is a
     * flex group with 1 group.
     */
    while (ext4_setup_next_flex_gd(sb, flex_gd, n_blocks_count,
                          flexbg_size)) {
        if (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;
        goto retry;
    }

out:
    if (flex_gd)
        free_flex_gd(flex_gd);
    if (resize_inode != NULL)
        iput(resize_inode);
    ext4_msg(sb, KERN_INFO, "resized filesystem to %llu", n_blocks_count);
    return err;
}