[deliverable/linux.git] / fs / ext4 / balloc.c

/*
 *  linux/fs/ext4/balloc.c
 *
 * Copyright (C) 1992, 1993, 1994, 1995
 * Remy Card (card@masi.ibp.fr)
 * Laboratoire MASI - Institut Blaise Pascal
 * Universite Pierre et Marie Curie (Paris VI)
 *
 *  Enhanced block allocation by Stephen Tweedie (sct@redhat.com), 1993
 *  Big-endian to little-endian byte-swapping/bitmaps by
 *        David S. Miller (davem@caip.rutgers.edu), 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>

/*
 * 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, (start -
                                               ext4_block_bitmap(sb, gdp)));
                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,
                                         start - ext4_inode_bitmap(sb, gdp));
                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, start - itbl_blk + i);
                        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(sbi, block_group, gdp)) {
                ext4_error(sb, "Checksum bad for group %u", block_group);
                ext4_free_blks_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);
                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);
}

/* 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_blocks_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).
 */

/**
 * ext4_get_group_desc() -- load group descriptor from disk
 * @sb:                 super block
 * @block_group:        given block group
 * @bh:                 pointer to the buffer head to store the block
 *                      group descriptor
 */
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;
}

static int 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 bitmap_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 1;
        }
        group_first_block = ext4_group_first_block_no(sb, block_group);

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

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

        /* check whether the inode table block number is set */
        bitmap_blk = ext4_inode_table(sb, desc);
        offset = bitmap_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)
                /* good bitmap for inode tables */
                return 1;

err_out:
        ext4_error(sb, "Invalid block bitmap - block_group = %d, block = %llu",
                        block_group, bitmap_blk);
        return 0;
}
/**
 * ext4_read_block_bitmap()
 * @sb:                 super block
 * @block_group:        given block group
 *
 * Read the bitmap for a given block_group,and validate the
 * bits for block/inode/inode tables are set in the bitmaps
 *
 * Return buffer_head on success or NULL in case of failure.
 */
struct buffer_head *
ext4_read_block_bitmap(struct super_block *sb, ext4_group_t block_group)
{
        struct ext4_group_desc *desc;
        struct buffer_head *bh = NULL;
        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 read block bitmap - "
                            "block_group = %u, block_bitmap = %llu",
                            block_group, bitmap_blk);
                return NULL;
        }

        if (bitmap_uptodate(bh))
                return bh;

        lock_buffer(bh);
        if (bitmap_uptodate(bh)) {
                unlock_buffer(bh);
                return bh;
        }
        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);
                return bh;
        }
        /*
         * submit the buffer_head for read. We can
         * safely mark the bitmap as uptodate now.
         * We do it here so the bitmap uptodate bit
         * get set with buffer lock held.
         */
        trace_ext4_read_block_bitmap_load(sb, block_group);
        set_bitmap_uptodate(bh);
        if (bh_submit_read(bh) < 0) {
                put_bh(bh);
                ext4_error(sb, "Cannot read block bitmap - "
                            "block_group = %u, block_bitmap = %llu",
                            block_group, bitmap_blk);
                return NULL;
        }
        ext4_valid_block_bitmap(sb, desc, block_group, bh);
        /*
         * file system mounted not to panic on error,
         * continue with corrupt bitmap
         */
        return bh;
}

/**
 * ext4_has_free_blocks()
 * @sbi:        in-core super block structure.
 * @nblocks:    number of needed blocks
 *
 * Check if filesystem has nblocks free & available for allocation.
 * On success return 1, return 0 on failure.
 */
static int ext4_has_free_blocks(struct ext4_sb_info *sbi,
                                s64 nblocks, unsigned int flags)
{
        s64 free_blocks, dirty_blocks, root_blocks;
        struct percpu_counter *fcc = &sbi->s_freeclusters_counter;
        struct percpu_counter *dbc = &sbi->s_dirtyclusters_counter;

        free_blocks  = percpu_counter_read_positive(fcc);
        dirty_blocks = percpu_counter_read_positive(dbc);
        root_blocks = ext4_r_blocks_count(sbi->s_es);

        if (free_blocks - (nblocks + root_blocks + dirty_blocks) <
                                                EXT4_FREEBLOCKS_WATERMARK) {
                free_blocks  = EXT4_C2B(sbi, percpu_counter_sum_positive(fcc));
                dirty_blocks = percpu_counter_sum_positive(dbc);
        }
        /* Check whether we have space after
         * accounting for current dirty blocks & root reserved blocks.
         */
        if (free_blocks >= ((root_blocks + nblocks) + dirty_blocks))
                return 1;

        /* Hm, nope.  Are (enough) root reserved blocks available? */
        if (sbi->s_resuid == current_fsuid() ||
            ((sbi->s_resgid != 0) && in_group_p(sbi->s_resgid)) ||
            capable(CAP_SYS_RESOURCE) ||
                (flags & EXT4_MB_USE_ROOT_BLOCKS)) {

                if (free_blocks >= (nblocks + dirty_blocks))
                        return 1;
        }

        return 0;
}

int ext4_claim_free_blocks(struct ext4_sb_info *sbi,
                           s64 nblocks, unsigned int flags)
{
        if (ext4_has_free_blocks(sbi, nblocks, flags)) {
                percpu_counter_add(&sbi->s_dirtyclusters_counter, nblocks);
                return 0;
        } else
                return -ENOSPC;
}

/**
 * ext4_should_retry_alloc()
 * @sb:                 super block
 * @retries             number of attemps has been made
 *
 * ext4_should_retry_alloc() is called when ENOSPC is returned, and if
 * it is profitable to retry the operation, this function will wait
 * for the current or committing transaction to complete, and then
 * return TRUE.
 *
 * if the total number of retries exceed three times, return FALSE.
 */
int ext4_should_retry_alloc(struct super_block *sb, int *retries)
{
        if (!ext4_has_free_blocks(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 blocks 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, ar.len);
        }
        return ret;
}

/**
 * ext4_count_free_blocks() -- count filesystem free blocks
 * @sb:         superblock
 *
 * Adds up the number of free blocks from each block group.
 */
ext4_fsblk_t ext4_count_free_blocks(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_blks_count(sb, gdp);
                brelse(bitmap_bh);
                bitmap_bh = ext4_read_block_bitmap(sb, i);
                if (bitmap_bh == NULL)
                        continue;

                x = ext4_count_free(bitmap_bh, sb->s_blocksize);
                printk(KERN_DEBUG "group %u: stored = %d, counted = %u\n",
                        i, ext4_free_blks_count(sb, gdp), x);
                bitmap_count += x;
        }
        brelse(bitmap_bh);
        printk(KERN_DEBUG "ext4_count_free_blocks: stored = %llu"
                ", computed = %llu, %llu\n", 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_blks_count(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));
}

/**
 *      ext4_bg_has_super - number of blocks used by the superblock in group
 *      @sb: superblock for filesystem
 *      @group: group number to check
 *
 *      Return the number of blocks used by the superblock (primary or backup)
 *      in this group.  Currently this will be only 0 or 1.
 */
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;
}

/**
 *      ext4_bg_num_gdb - number of blocks used by the group table in group
 *      @sb: superblock for filesystem
 *      @group: group number to check
 *
 *      Return the number of blocks used by the group descriptor table
 *      (primary or backup) in this group.  In the future there may be a
 *      different number of descriptor blocks in each group.
 */
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.
 */
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_inode_to_goal_block - return a hint for block allocation
 *      @inode: inode for block allocation
 *
 *      Return the ideal location to start allocating blocks for a
 *      newly created inode.
 */
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;
}