balloc.c

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/*
 *  linux/fs/ext4/balloc.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card ([email protected])
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  Enhanced block allocation by Stephen Tweedie ([email protected]), 1993
 *  Big-endian to little-endian byte-swapping/bitmaps by
 *        David S. Miller ([email protected]), 1995
 */

#include <linux/time.h>
#include <linux/capability.h>
#include <linux/fs.h>
#include <linux/jbd2.h>
#include <linux/quotaops.h>
#include <linux/buffer_head.h>
#include "ext4.h"
#include "ext4_jbd2.h"
#include "mballoc.h"

#include <trace/events/ext4.h>

static unsigned ext4_num_base_meta_clusters(struct super_block *sb,
                        ext4_group_t block_group);
/*
 * balloc.c contains the blocks allocation and deallocation routines
 */

/*
 * Calculate the block group number and offset into the block/cluster
 * allocation bitmap, given a block number
 */
void ext4_get_group_no_and_offset(struct super_block *sb, ext4_fsblk_t blocknr,
        ext4_group_t *blockgrpp, ext4_grpblk_t *offsetp)
{
    struct ext4_super_block *es = EXT4_SB(sb)->s_es;
    ext4_grpblk_t offset;

    blocknr = blocknr - le32_to_cpu(es->s_first_data_block);
    offset = do_div(blocknr, EXT4_BLOCKS_PER_GROUP(sb)) >>
        EXT4_SB(sb)->s_cluster_bits;
    if (offsetp)
        *offsetp = offset;
    if (blockgrpp)
        *blockgrpp = blocknr;

}

static int ext4_block_in_group(struct super_block *sb, ext4_fsblk_t block,
            ext4_group_t block_group)
{
    ext4_group_t actual_group;
    ext4_get_group_no_and_offset(sb, block, &actual_group, NULL);
    if (actual_group == block_group)
        return 1;
    return 0;
}

/* Return the number of clusters used for file system metadata; this
 * represents the overhead needed by the file system.
 */
unsigned ext4_num_overhead_clusters(struct super_block *sb,
                    ext4_group_t block_group,
                    struct ext4_group_desc *gdp)
{
    unsigned num_clusters;
    int block_cluster = -1, inode_cluster = -1, itbl_cluster = -1, i, c;
    ext4_fsblk_t start = ext4_group_first_block_no(sb, block_group);
    ext4_fsblk_t itbl_blk;
    struct ext4_sb_info *sbi = EXT4_SB(sb);

    /* This is the number of clusters used by the superblock,
     * block group descriptors, and reserved block group
     * descriptor blocks */
    num_clusters = ext4_num_base_meta_clusters(sb, block_group);

    /*
     * For the allocation bitmaps and inode table, we first need
     * to check to see if the block is in the block group.  If it
     * is, then check to see if the cluster is already accounted
     * for in the clusters used for the base metadata cluster, or
     * if we can increment the base metadata cluster to include
     * that block.  Otherwise, we will have to track the cluster
     * used for the allocation bitmap or inode table explicitly.
     * Normally all of these blocks are contiguous, so the special
     * case handling shouldn't be necessary except for *very*
     * unusual file system layouts.
     */
    if (ext4_block_in_group(sb, ext4_block_bitmap(sb, gdp), block_group)) {
        block_cluster = EXT4_B2C(sbi,
                     ext4_block_bitmap(sb, gdp) - start);
        if (block_cluster < num_clusters)
            block_cluster = -1;
        else if (block_cluster == num_clusters) {
            num_clusters++;
            block_cluster = -1;
        }
    }

    if (ext4_block_in_group(sb, ext4_inode_bitmap(sb, gdp), block_group)) {
        inode_cluster = EXT4_B2C(sbi,
                     ext4_inode_bitmap(sb, gdp) - start);
        if (inode_cluster < num_clusters)
            inode_cluster = -1;
        else if (inode_cluster == num_clusters) {
            num_clusters++;
            inode_cluster = -1;
        }
    }

    itbl_blk = ext4_inode_table(sb, gdp);
    for (i = 0; i < sbi->s_itb_per_group; i++) {
        if (ext4_block_in_group(sb, itbl_blk + i, block_group)) {
            c = EXT4_B2C(sbi, itbl_blk + i - start);
            if ((c < num_clusters) || (c == inode_cluster) ||
                (c == block_cluster) || (c == itbl_cluster))
                continue;
            if (c == num_clusters) {
                num_clusters++;
                continue;
            }
            num_clusters++;
            itbl_cluster = c;
        }
    }

    if (block_cluster != -1)
        num_clusters++;
    if (inode_cluster != -1)
        num_clusters++;

    return num_clusters;
}

static unsigned int num_clusters_in_group(struct super_block *sb,
                      ext4_group_t block_group)
{
    unsigned int blocks;

    if (block_group == ext4_get_groups_count(sb) - 1) {
        /*
         * Even though mke2fs always initializes the first and
         * last group, just in case some other tool was used,
         * we need to make sure we calculate the right free
         * blocks.
         */
        blocks = ext4_blocks_count(EXT4_SB(sb)->s_es) -
            ext4_group_first_block_no(sb, block_group);
    } else
        blocks = EXT4_BLOCKS_PER_GROUP(sb);
    return EXT4_NUM_B2C(EXT4_SB(sb), blocks);
}

/* Initializes an uninitialized block bitmap */
void ext4_init_block_bitmap(struct super_block *sb, struct buffer_head *bh,
                ext4_group_t block_group,
                struct ext4_group_desc *gdp)
{
    unsigned int bit, bit_max;
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    ext4_fsblk_t start, tmp;
    int flex_bg = 0;

    J_ASSERT_BH(bh, buffer_locked(bh));

    /* If checksum is bad mark all blocks used to prevent allocation
     * essentially implementing a per-group read-only flag. */
    if (!ext4_group_desc_csum_verify(sb, block_group, gdp)) {
        ext4_error(sb, "Checksum bad for group %u", block_group);
        ext4_free_group_clusters_set(sb, gdp, 0);
        ext4_free_inodes_set(sb, gdp, 0);
        ext4_itable_unused_set(sb, gdp, 0);
        memset(bh->b_data, 0xff, sb->s_blocksize);
        ext4_block_bitmap_csum_set(sb, block_group, gdp, bh);
        return;
    }
    memset(bh->b_data, 0, sb->s_blocksize);

    bit_max = ext4_num_base_meta_clusters(sb, block_group);
    for (bit = 0; bit < bit_max; bit++)
        ext4_set_bit(bit, bh->b_data);

    start = ext4_group_first_block_no(sb, block_group);

    if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG))
        flex_bg = 1;

    /* Set bits for block and inode bitmaps, and inode table */
    tmp = ext4_block_bitmap(sb, gdp);
    if (!flex_bg || ext4_block_in_group(sb, tmp, block_group))
        ext4_set_bit(EXT4_B2C(sbi, tmp - start), bh->b_data);

    tmp = ext4_inode_bitmap(sb, gdp);
    if (!flex_bg || ext4_block_in_group(sb, tmp, block_group))
        ext4_set_bit(EXT4_B2C(sbi, tmp - start), bh->b_data);

    tmp = ext4_inode_table(sb, gdp);
    for (; tmp < ext4_inode_table(sb, gdp) +
             sbi->s_itb_per_group; tmp++) {
        if (!flex_bg || ext4_block_in_group(sb, tmp, block_group))
            ext4_set_bit(EXT4_B2C(sbi, tmp - start), bh->b_data);
    }

    /*
     * Also if the number of blocks within the group is less than
     * the blocksize * 8 ( which is the size of bitmap ), set rest
     * of the block bitmap to 1
     */
    ext4_mark_bitmap_end(num_clusters_in_group(sb, block_group),
                 sb->s_blocksize * 8, bh->b_data);
    ext4_block_bitmap_csum_set(sb, block_group, gdp, bh);
    ext4_group_desc_csum_set(sb, block_group, gdp);
}

/* Return the number of free blocks in a block group.  It is used when
 * the block bitmap is uninitialized, so we can't just count the bits
 * in the bitmap. */
unsigned ext4_free_clusters_after_init(struct super_block *sb,
                       ext4_group_t block_group,
                       struct ext4_group_desc *gdp)
{
    return num_clusters_in_group(sb, block_group) - 
        ext4_num_overhead_clusters(sb, block_group, gdp);
}

/*
 * The free blocks are managed by bitmaps.  A file system contains several
 * blocks groups.  Each group contains 1 bitmap block for blocks, 1 bitmap
 * block for inodes, N blocks for the inode table and data blocks.
 *
 * The file system contains group descriptors which are located after the
 * super block.  Each descriptor contains the number of the bitmap block and
 * the free blocks count in the block.  The descriptors are loaded in memory
 * when a file system is mounted (see ext4_fill_super).
 */

struct ext4_group_desc * ext4_get_group_desc(struct super_block *sb,
                         ext4_group_t block_group,
                         struct buffer_head **bh)
{
    unsigned int group_desc;
    unsigned int offset;
    ext4_group_t ngroups = ext4_get_groups_count(sb);
    struct ext4_group_desc *desc;
    struct ext4_sb_info *sbi = EXT4_SB(sb);

    if (block_group >= ngroups) {
        ext4_error(sb, "block_group >= groups_count - block_group = %u,"
               " groups_count = %u", block_group, ngroups);

        return NULL;
    }

    group_desc = block_group >> EXT4_DESC_PER_BLOCK_BITS(sb);
    offset = block_group & (EXT4_DESC_PER_BLOCK(sb) - 1);
    if (!sbi->s_group_desc[group_desc]) {
        ext4_error(sb, "Group descriptor not loaded - "
               "block_group = %u, group_desc = %u, desc = %u",
               block_group, group_desc, offset);
        return NULL;
    }

    desc = (struct ext4_group_desc *)(
        (__u8 *)sbi->s_group_desc[group_desc]->b_data +
        offset * EXT4_DESC_SIZE(sb));
    if (bh)
        *bh = sbi->s_group_desc[group_desc];
    return desc;
}

/*
 * Return the block number which was discovered to be invalid, or 0 if
 * the block bitmap is valid.
 */
static ext4_fsblk_t ext4_valid_block_bitmap(struct super_block *sb,
                        struct ext4_group_desc *desc,
                        unsigned int block_group,
                        struct buffer_head *bh)
{
    ext4_grpblk_t offset;
    ext4_grpblk_t next_zero_bit;
    ext4_fsblk_t blk;
    ext4_fsblk_t group_first_block;

    if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG)) {
        /* with FLEX_BG, the inode/block bitmaps and itable
         * blocks may not be in the group at all
         * so the bitmap validation will be skipped for those groups
         * or it has to also read the block group where the bitmaps
         * are located to verify they are set.
         */
        return 0;
    }
    group_first_block = ext4_group_first_block_no(sb, block_group);

    /* check whether block bitmap block number is set */
    blk = ext4_block_bitmap(sb, desc);
    offset = blk - group_first_block;
    if (!ext4_test_bit(offset, bh->b_data))
        /* bad block bitmap */
        return blk;

    /* check whether the inode bitmap block number is set */
    blk = ext4_inode_bitmap(sb, desc);
    offset = blk - group_first_block;
    if (!ext4_test_bit(offset, bh->b_data))
        /* bad block bitmap */
        return blk;

    /* check whether the inode table block number is set */
    blk = ext4_inode_table(sb, desc);
    offset = blk - group_first_block;
    next_zero_bit = ext4_find_next_zero_bit(bh->b_data,
                offset + EXT4_SB(sb)->s_itb_per_group,
                offset);
    if (next_zero_bit < offset + EXT4_SB(sb)->s_itb_per_group)
        /* bad bitmap for inode tables */
        return blk;
    return 0;
}

void ext4_validate_block_bitmap(struct super_block *sb,
                   struct ext4_group_desc *desc,
                   unsigned int block_group,
                   struct buffer_head *bh)
{
    ext4_fsblk_t    blk;

    if (buffer_verified(bh))
        return;

    ext4_lock_group(sb, block_group);
    blk = ext4_valid_block_bitmap(sb, desc, block_group, bh);
    if (unlikely(blk != 0)) {
        ext4_unlock_group(sb, block_group);
        ext4_error(sb, "bg %u: block %llu: invalid block bitmap",
               block_group, blk);
        return;
    }
    if (unlikely(!ext4_block_bitmap_csum_verify(sb, block_group,
            desc, bh))) {
        ext4_unlock_group(sb, block_group);
        ext4_error(sb, "bg %u: bad block bitmap checksum", block_group);
        return;
    }
    set_buffer_verified(bh);
    ext4_unlock_group(sb, block_group);
}

struct buffer_head *
ext4_read_block_bitmap_nowait(struct super_block *sb, ext4_group_t block_group)
{
    struct ext4_group_desc *desc;
    struct buffer_head *bh;
    ext4_fsblk_t bitmap_blk;

    desc = ext4_get_group_desc(sb, block_group, NULL);
    if (!desc)
        return NULL;
    bitmap_blk = ext4_block_bitmap(sb, desc);
    bh = sb_getblk(sb, bitmap_blk);
    if (unlikely(!bh)) {
        ext4_error(sb, "Cannot get buffer for block bitmap - "
               "block_group = %u, block_bitmap = %llu",
               block_group, bitmap_blk);
        return NULL;
    }

    if (bitmap_uptodate(bh))
        goto verify;

    lock_buffer(bh);
    if (bitmap_uptodate(bh)) {
        unlock_buffer(bh);
        goto verify;
    }
    ext4_lock_group(sb, block_group);
    if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
        ext4_init_block_bitmap(sb, bh, block_group, desc);
        set_bitmap_uptodate(bh);
        set_buffer_uptodate(bh);
        ext4_unlock_group(sb, block_group);
        unlock_buffer(bh);
        return bh;
    }
    ext4_unlock_group(sb, block_group);
    if (buffer_uptodate(bh)) {
        /*
         * if not uninit if bh is uptodate,
         * bitmap is also uptodate
         */
        set_bitmap_uptodate(bh);
        unlock_buffer(bh);
        goto verify;
    }
    /*
     * submit the buffer_head for reading
     */
    set_buffer_new(bh);
    trace_ext4_read_block_bitmap_load(sb, block_group);
    bh->b_end_io = ext4_end_bitmap_read;
    get_bh(bh);
    submit_bh(READ, bh);
    return bh;
verify:
    ext4_validate_block_bitmap(sb, desc, block_group, bh);
    return bh;
}

/* Returns 0 on success, 1 on error */
int ext4_wait_block_bitmap(struct super_block *sb, ext4_group_t block_group,
               struct buffer_head *bh)
{
    struct ext4_group_desc *desc;

    if (!buffer_new(bh))
        return 0;
    desc = ext4_get_group_desc(sb, block_group, NULL);
    if (!desc)
        return 1;
    wait_on_buffer(bh);
    if (!buffer_uptodate(bh)) {
        ext4_error(sb, "Cannot read block bitmap - "
               "block_group = %u, block_bitmap = %llu",
               block_group, (unsigned long long) bh->b_blocknr);
        return 1;
    }
    clear_buffer_new(bh);
    /* Panic or remount fs read-only if block bitmap is invalid */
    ext4_validate_block_bitmap(sb, desc, block_group, bh);
    return 0;
}

struct buffer_head *
ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group)
{
    struct buffer_head *bh;

    bh = ext4_read_block_bitmap_nowait(sb, block_group);
    if (ext4_wait_block_bitmap(sb, block_group, bh)) {
        put_bh(bh);
        return NULL;
    }
    return bh;
}

static int ext4_has_free_clusters(struct ext4_sb_info *sbi,
                  s64 nclusters, unsigned int flags)
{
    s64 free_clusters, dirty_clusters, root_clusters;
    struct percpu_counter *fcc = &sbi->s_freeclusters_counter;
    struct percpu_counter *dcc = &sbi->s_dirtyclusters_counter;

    free_clusters  = percpu_counter_read_positive(fcc);
    dirty_clusters = percpu_counter_read_positive(dcc);
    root_clusters = EXT4_B2C(sbi, ext4_r_blocks_count(sbi->s_es));

    if (free_clusters - (nclusters + root_clusters + dirty_clusters) <
                    EXT4_FREECLUSTERS_WATERMARK) {
        free_clusters  = EXT4_C2B(sbi, percpu_counter_sum_positive(fcc));
        dirty_clusters = percpu_counter_sum_positive(dcc);
    }
    /* Check whether we have space after accounting for current
     * dirty clusters & root reserved clusters.
     */
    if (free_clusters >= ((root_clusters + nclusters) + dirty_clusters))
        return 1;

    /* Hm, nope.  Are (enough) root reserved clusters available? */
    if (uid_eq(sbi->s_resuid, current_fsuid()) ||
        (!gid_eq(sbi->s_resgid, GLOBAL_ROOT_GID) && in_group_p(sbi->s_resgid)) ||
        capable(CAP_SYS_RESOURCE) ||
        (flags & EXT4_MB_USE_ROOT_BLOCKS)) {

        if (free_clusters >= (nclusters + dirty_clusters))
            return 1;
    }

    return 0;
}

int ext4_claim_free_clusters(struct ext4_sb_info *sbi,
                 s64 nclusters, unsigned int flags)
{
    if (ext4_has_free_clusters(sbi, nclusters, flags)) {
        percpu_counter_add(&sbi->s_dirtyclusters_counter, nclusters);
        return 0;
    } else
        return -ENOSPC;
}

int ext4_should_retry_alloc(struct super_block *sb, int *retries)
{
    if (!ext4_has_free_clusters(EXT4_SB(sb), 1, 0) ||
        (*retries)++ > 3 ||
        !EXT4_SB(sb)->s_journal)
        return 0;

    jbd_debug(1, "%s: retrying operation after ENOSPC\n", sb->s_id);

    return jbd2_journal_force_commit_nested(EXT4_SB(sb)->s_journal);
}

/*
 * ext4_new_meta_blocks() -- allocate block for meta data (indexing) blocks
 *
 * @handle:             handle to this transaction
 * @inode:              file inode
 * @goal:               given target block(filesystem wide)
 * @count:      pointer to total number of clusters needed
 * @errp:               error code
 *
 * Return 1st allocated block number on success, *count stores total account
 * error stores in errp pointer
 */
ext4_fsblk_t ext4_new_meta_blocks(handle_t *handle, struct inode *inode,
                  ext4_fsblk_t goal, unsigned int flags,
                  unsigned long *count, int *errp)
{
    struct ext4_allocation_request ar;
    ext4_fsblk_t ret;

    memset(&ar, 0, sizeof(ar));
    /* Fill with neighbour allocated blocks */
    ar.inode = inode;
    ar.goal = goal;
    ar.len = count ? *count : 1;
    ar.flags = flags;

    ret = ext4_mb_new_blocks(handle, &ar, errp);
    if (count)
        *count = ar.len;
    /*
     * Account for the allocated meta blocks.  We will never
     * fail EDQUOT for metdata, but we do account for it.
     */
    if (!(*errp) &&
        ext4_test_inode_state(inode, EXT4_STATE_DELALLOC_RESERVED)) {
        spin_lock(&EXT4_I(inode)->i_block_reservation_lock);
        EXT4_I(inode)->i_allocated_meta_blocks += ar.len;
        spin_unlock(&EXT4_I(inode)->i_block_reservation_lock);
        dquot_alloc_block_nofail(inode,
                EXT4_C2B(EXT4_SB(inode->i_sb), ar.len));
    }
    return ret;
}

ext4_fsblk_t ext4_count_free_clusters(struct super_block *sb)
{
    ext4_fsblk_t desc_count;
    struct ext4_group_desc *gdp;
    ext4_group_t i;
    ext4_group_t ngroups = ext4_get_groups_count(sb);
#ifdef EXT4FS_DEBUG
    struct ext4_super_block *es;
    ext4_fsblk_t bitmap_count;
    unsigned int x;
    struct buffer_head *bitmap_bh = NULL;

    es = EXT4_SB(sb)->s_es;
    desc_count = 0;
    bitmap_count = 0;
    gdp = NULL;

    for (i = 0; i < ngroups; i++) {
        gdp = ext4_get_group_desc(sb, i, NULL);
        if (!gdp)
            continue;
        desc_count += ext4_free_group_clusters(sb, gdp);
        brelse(bitmap_bh);
        bitmap_bh = ext4_read_block_bitmap(sb, i);
        if (bitmap_bh == NULL)
            continue;

        x = ext4_count_free(bitmap_bh->b_data,
                    EXT4_BLOCKS_PER_GROUP(sb) / 8);
        printk(KERN_DEBUG "group %u: stored = %d, counted = %u\n",
            i, ext4_free_group_clusters(sb, gdp), x);
        bitmap_count += x;
    }
    brelse(bitmap_bh);
    printk(KERN_DEBUG "ext4_count_free_clusters: stored = %llu"
           ", computed = %llu, %llu\n",
           EXT4_B2C(EXT4_SB(sb), ext4_free_blocks_count(es)),
           desc_count, bitmap_count);
    return bitmap_count;
#else
    desc_count = 0;
    for (i = 0; i < ngroups; i++) {
        gdp = ext4_get_group_desc(sb, i, NULL);
        if (!gdp)
            continue;
        desc_count += ext4_free_group_clusters(sb, gdp);
    }

    return desc_count;
#endif
}

static inline int test_root(ext4_group_t a, int b)
{
    int num = b;

    while (a > num)
        num *= b;
    return num == a;
}

static int ext4_group_sparse(ext4_group_t group)
{
    if (group <= 1)
        return 1;
    if (!(group & 1))
        return 0;
    return (test_root(group, 7) || test_root(group, 5) ||
        test_root(group, 3));
}

int ext4_bg_has_super(struct super_block *sb, ext4_group_t group)
{
    if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
                EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER) &&
            !ext4_group_sparse(group))
        return 0;
    return 1;
}

static unsigned long ext4_bg_num_gdb_meta(struct super_block *sb,
                    ext4_group_t group)
{
    unsigned long metagroup = group / EXT4_DESC_PER_BLOCK(sb);
    ext4_group_t first = metagroup * EXT4_DESC_PER_BLOCK(sb);
    ext4_group_t last = first + EXT4_DESC_PER_BLOCK(sb) - 1;

    if (group == first || group == first + 1 || group == last)
        return 1;
    return 0;
}

static unsigned long ext4_bg_num_gdb_nometa(struct super_block *sb,
                    ext4_group_t group)
{
    if (!ext4_bg_has_super(sb, group))
        return 0;

    if (EXT4_HAS_INCOMPAT_FEATURE(sb,EXT4_FEATURE_INCOMPAT_META_BG))
        return le32_to_cpu(EXT4_SB(sb)->s_es->s_first_meta_bg);
    else
        return EXT4_SB(sb)->s_gdb_count;
}

unsigned long ext4_bg_num_gdb(struct super_block *sb, ext4_group_t group)
{
    unsigned long first_meta_bg =
            le32_to_cpu(EXT4_SB(sb)->s_es->s_first_meta_bg);
    unsigned long metagroup = group / EXT4_DESC_PER_BLOCK(sb);

    if (!EXT4_HAS_INCOMPAT_FEATURE(sb,EXT4_FEATURE_INCOMPAT_META_BG) ||
            metagroup < first_meta_bg)
        return ext4_bg_num_gdb_nometa(sb, group);

    return ext4_bg_num_gdb_meta(sb,group);

}

/*
 * This function returns the number of file system metadata clusters at
 * the beginning of a block group, including the reserved gdt blocks.
 */
static unsigned ext4_num_base_meta_clusters(struct super_block *sb,
                     ext4_group_t block_group)
{
    struct ext4_sb_info *sbi = EXT4_SB(sb);
    unsigned num;

    /* Check for superblock and gdt backups in this group */
    num = ext4_bg_has_super(sb, block_group);

    if (!EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_META_BG) ||
        block_group < le32_to_cpu(sbi->s_es->s_first_meta_bg) *
              sbi->s_desc_per_block) {
        if (num) {
            num += ext4_bg_num_gdb(sb, block_group);
            num += le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks);
        }
    } else { /* For META_BG_BLOCK_GROUPS */
        num += ext4_bg_num_gdb(sb, block_group);
    }
    return EXT4_NUM_B2C(sbi, num);
}
ext4_fsblk_t ext4_inode_to_goal_block(struct inode *inode)
{
    struct ext4_inode_info *ei = EXT4_I(inode);
    ext4_group_t block_group;
    ext4_grpblk_t colour;
    int flex_size = ext4_flex_bg_size(EXT4_SB(inode->i_sb));
    ext4_fsblk_t bg_start;
    ext4_fsblk_t last_block;

    block_group = ei->i_block_group;
    if (flex_size >= EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME) {
        /*
         * If there are at least EXT4_FLEX_SIZE_DIR_ALLOC_SCHEME
         * block groups per flexgroup, reserve the first block
         * group for directories and special files.  Regular
         * files will start at the second block group.  This
         * tends to speed up directory access and improves
         * fsck times.
         */
        block_group &= ~(flex_size-1);
        if (S_ISREG(inode->i_mode))
            block_group++;
    }
    bg_start = ext4_group_first_block_no(inode->i_sb, block_group);
    last_block = ext4_blocks_count(EXT4_SB(inode->i_sb)->s_es) - 1;

    /*
     * If we are doing delayed allocation, we don't need take
     * colour into account.
     */
    if (test_opt(inode->i_sb, DELALLOC))
        return bg_start;

    if (bg_start + EXT4_BLOCKS_PER_GROUP(inode->i_sb) <= last_block)
        colour = (current->pid % 16) *
            (EXT4_BLOCKS_PER_GROUP(inode->i_sb) / 16);
    else
        colour = (current->pid % 16) * ((last_block - bg_start) / 16);
    return bg_start + colour;
}