Linux 2.3.0

[davej-history.git] / fs / ext2 / balloc.c

/*
 *  linux/fs/ext2/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@dcs.ed.ac.uk), 1993
 *  Big-endian to little-endian byte-swapping/bitmaps by
 *        David S. Miller (davem@caip.rutgers.edu), 1995
 */

/*
 * balloc.c contains the blocks allocation and deallocation routines
 */

/*
 * 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 ext2_read_super).
 */

#include <linux/fs.h>
#include <linux/ext2_fs.h>
#include <linux/stat.h>
#include <linux/sched.h>
#include <linux/string.h>
#include <linux/locks.h>
#include <linux/quotaops.h>

#include <asm/bitops.h>
#include <asm/byteorder.h>

#define in_range(b, first, len)         ((b) >= (first) && (b) <= (first) + (len) - 1)

struct ext2_group_desc * ext2_get_group_desc(struct super_block * sb,
                                             unsigned int block_group,
                                             struct buffer_head ** bh)
{
        unsigned long group_desc;
        unsigned long desc;
        struct ext2_group_desc * gdp;

        if (block_group >= sb->u.ext2_sb.s_groups_count) {
                ext2_error (sb, "ext2_get_group_desc",
                            "block_group >= groups_count - "
                            "block_group = %d, groups_count = %lu",
                            block_group, sb->u.ext2_sb.s_groups_count);

                return NULL;
        }
        
        group_desc = block_group / EXT2_DESC_PER_BLOCK(sb);
        desc = block_group % EXT2_DESC_PER_BLOCK(sb);
        if (!sb->u.ext2_sb.s_group_desc[group_desc]) {
                ext2_error (sb, "ext2_get_group_desc",
                            "Group descriptor not loaded - "
                            "block_group = %d, group_desc = %lu, desc = %lu",
                             block_group, group_desc, desc);
                return NULL;
        }
        
        gdp = (struct ext2_group_desc *) 
              sb->u.ext2_sb.s_group_desc[group_desc]->b_data;
        if (bh)
                *bh = sb->u.ext2_sb.s_group_desc[group_desc];
        return gdp + desc;
}

/*
 * Read the bitmap for a given block_group, reading into the specified 
 * slot in the superblock's bitmap cache.
 *
 * Return >=0 on success or a -ve error code.
 */

static int read_block_bitmap (struct super_block * sb,
                               unsigned int block_group,
                               unsigned long bitmap_nr)
{
        struct ext2_group_desc * gdp;
        struct buffer_head * bh = NULL;
        int retval = -EIO;
        
        gdp = ext2_get_group_desc (sb, block_group, NULL);
        if (!gdp)
                goto error_out;
        retval = 0;
        bh = bread (sb->s_dev, le32_to_cpu(gdp->bg_block_bitmap), sb->s_blocksize);
        if (!bh) {
                ext2_error (sb, "read_block_bitmap",
                            "Cannot read block bitmap - "
                            "block_group = %d, block_bitmap = %lu",
                            block_group, (unsigned long) gdp->bg_block_bitmap);
                retval = -EIO;
        }
        /*
         * On IO error, just leave a zero in the superblock's block pointer for
         * this group.  The IO will be retried next time.
         */
error_out:
        sb->u.ext2_sb.s_block_bitmap_number[bitmap_nr] = block_group;
        sb->u.ext2_sb.s_block_bitmap[bitmap_nr] = bh;
        return retval;
}

/*
 * load_block_bitmap loads the block bitmap for a blocks group
 *
 * It maintains a cache for the last bitmaps loaded.  This cache is managed
 * with a LRU algorithm.
 *
 * Notes:
 * 1/ There is one cache per mounted file system.
 * 2/ If the file system contains less than EXT2_MAX_GROUP_LOADED groups,
 *    this function reads the bitmap without maintaining a LRU cache.
 * 
 * Return the slot used to store the bitmap, or a -ve error code.
 */
static int load__block_bitmap (struct super_block * sb,
                               unsigned int block_group)
{
        int i, j, retval = 0;
        unsigned long block_bitmap_number;
        struct buffer_head * block_bitmap;

        if (block_group >= sb->u.ext2_sb.s_groups_count)
                ext2_panic (sb, "load_block_bitmap",
                            "block_group >= groups_count - "
                            "block_group = %d, groups_count = %lu",
                            block_group, sb->u.ext2_sb.s_groups_count);

        if (sb->u.ext2_sb.s_groups_count <= EXT2_MAX_GROUP_LOADED) {
                if (sb->u.ext2_sb.s_block_bitmap[block_group]) {
                        if (sb->u.ext2_sb.s_block_bitmap_number[block_group] ==
                            block_group)
                                return block_group;
                        ext2_error (sb, "load_block_bitmap",
                                    "block_group != block_bitmap_number");
                }
                retval = read_block_bitmap (sb, block_group, block_group);
                if (retval < 0)
                        return retval;
                return block_group;
        }

        for (i = 0; i < sb->u.ext2_sb.s_loaded_block_bitmaps &&
                    sb->u.ext2_sb.s_block_bitmap_number[i] != block_group; i++)
                ;
        if (i < sb->u.ext2_sb.s_loaded_block_bitmaps &&
            sb->u.ext2_sb.s_block_bitmap_number[i] == block_group) {
                block_bitmap_number = sb->u.ext2_sb.s_block_bitmap_number[i];
                block_bitmap = sb->u.ext2_sb.s_block_bitmap[i];
                for (j = i; j > 0; j--) {
                        sb->u.ext2_sb.s_block_bitmap_number[j] =
                                sb->u.ext2_sb.s_block_bitmap_number[j - 1];
                        sb->u.ext2_sb.s_block_bitmap[j] =
                                sb->u.ext2_sb.s_block_bitmap[j - 1];
                }
                sb->u.ext2_sb.s_block_bitmap_number[0] = block_bitmap_number;
                sb->u.ext2_sb.s_block_bitmap[0] = block_bitmap;

                /*
                 * There's still one special case here --- if block_bitmap == 0
                 * then our last attempt to read the bitmap failed and we have
                 * just ended up caching that failure.  Try again to read it.
                 */
                if (!block_bitmap)
                        retval = read_block_bitmap (sb, block_group, 0);
        } else {
                if (sb->u.ext2_sb.s_loaded_block_bitmaps < EXT2_MAX_GROUP_LOADED)
                        sb->u.ext2_sb.s_loaded_block_bitmaps++;
                else
                        brelse (sb->u.ext2_sb.s_block_bitmap[EXT2_MAX_GROUP_LOADED - 1]);
                for (j = sb->u.ext2_sb.s_loaded_block_bitmaps - 1; j > 0;  j--) {
                        sb->u.ext2_sb.s_block_bitmap_number[j] =
                                sb->u.ext2_sb.s_block_bitmap_number[j - 1];
                        sb->u.ext2_sb.s_block_bitmap[j] =
                                sb->u.ext2_sb.s_block_bitmap[j - 1];
                }
                retval = read_block_bitmap (sb, block_group, 0);
        }
        return retval;
}

/*
 * Load the block bitmap for a given block group.  First of all do a couple
 * of fast lookups for common cases and then pass the request onto the guts
 * of the bitmap loader.
 *
 * Return the slot number of the group in the superblock bitmap cache's on
 * success, or a -ve error code.
 *
 * There is still one inconsistancy here --- if the number of groups in this
 * filesystems is <= EXT2_MAX_GROUP_LOADED, then we have no way of 
 * differentiating between a group for which we have never performed a bitmap
 * IO request, and a group for which the last bitmap read request failed.
 */
static inline int load_block_bitmap (struct super_block * sb,
                                     unsigned int block_group)
{
        int slot;
        
        /*
         * Do the lookup for the slot.  First of all, check if we're asking
         * for the same slot as last time, and did we succeed that last time?
         */
        if (sb->u.ext2_sb.s_loaded_block_bitmaps > 0 &&
            sb->u.ext2_sb.s_block_bitmap_number[0] == block_group &&
            sb->u.ext2_sb.s_block_bitmap[block_group]) {
                return 0;
        }
        /*
         * Or can we do a fast lookup based on a loaded group on a filesystem
         * small enough to be mapped directly into the superblock?
         */
        else if (sb->u.ext2_sb.s_groups_count <= EXT2_MAX_GROUP_LOADED && 
                 sb->u.ext2_sb.s_block_bitmap_number[block_group] == block_group &&
                 sb->u.ext2_sb.s_block_bitmap[block_group]) {
                slot = block_group;
        }
        /*
         * If not, then do a full lookup for this block group.
         */
        else {
                slot = load__block_bitmap (sb, block_group);
        }

        /*
         * <0 means we just got an error
         */
        if (slot < 0)
                return slot;
        
        /*
         * If it's a valid slot, we may still have cached a previous IO error,
         * in which case the bh in the superblock cache will be zero.
         */
        if (!sb->u.ext2_sb.s_block_bitmap[slot])
                return -EIO;
        
        /*
         * Must have been read in OK to get this far.
         */
        return slot;
}

void ext2_free_blocks (const struct inode * inode, unsigned long block,
                       unsigned long count)
{
        struct buffer_head * bh;
        struct buffer_head * bh2;
        unsigned long block_group;
        unsigned long bit;
        unsigned long i;
        int bitmap_nr;
        unsigned long overflow;
        struct super_block * sb;
        struct ext2_group_desc * gdp;
        struct ext2_super_block * es;

        sb = inode->i_sb;
        if (!sb) {
                printk ("ext2_free_blocks: nonexistent device");
                return;
        }
        lock_super (sb);
        es = sb->u.ext2_sb.s_es;
        if (block < le32_to_cpu(es->s_first_data_block) || 
            (block + count) > le32_to_cpu(es->s_blocks_count)) {
                ext2_error (sb, "ext2_free_blocks",
                            "Freeing blocks not in datazone - "
                            "block = %lu, count = %lu", block, count);
                goto error_return;
        }

        ext2_debug ("freeing block %lu\n", block);

do_more:
        overflow = 0;
        block_group = (block - le32_to_cpu(es->s_first_data_block)) /
                      EXT2_BLOCKS_PER_GROUP(sb);
        bit = (block - le32_to_cpu(es->s_first_data_block)) %
                      EXT2_BLOCKS_PER_GROUP(sb);
        /*
         * Check to see if we are freeing blocks across a group
         * boundary.
         */
        if (bit + count > EXT2_BLOCKS_PER_GROUP(sb)) {
                overflow = bit + count - EXT2_BLOCKS_PER_GROUP(sb);
                count -= overflow;
        }
        bitmap_nr = load_block_bitmap (sb, block_group);
        if (bitmap_nr < 0)
                goto error_return;
        
        bh = sb->u.ext2_sb.s_block_bitmap[bitmap_nr];
        gdp = ext2_get_group_desc (sb, block_group, &bh2);
        if (!gdp)
                goto error_return;

        if (test_opt (sb, CHECK_STRICT) &&
            (in_range (le32_to_cpu(gdp->bg_block_bitmap), block, count) ||
             in_range (le32_to_cpu(gdp->bg_inode_bitmap), block, count) ||
             in_range (block, le32_to_cpu(gdp->bg_inode_table),
                       sb->u.ext2_sb.s_itb_per_group) ||
             in_range (block + count - 1, le32_to_cpu(gdp->bg_inode_table),
                       sb->u.ext2_sb.s_itb_per_group)))
                ext2_panic (sb, "ext2_free_blocks",
                            "Freeing blocks in system zones - "
                            "Block = %lu, count = %lu",
                            block, count);

        for (i = 0; i < count; i++) {
                if (!ext2_clear_bit (bit + i, bh->b_data))
                        ext2_warning (sb, "ext2_free_blocks",
                                      "bit already cleared for block %lu", 
                                      block);
                else {
                        DQUOT_FREE_BLOCK(sb, inode, 1);
                        gdp->bg_free_blocks_count =
                                cpu_to_le16(le16_to_cpu(gdp->bg_free_blocks_count)+1);
                        es->s_free_blocks_count =
                                cpu_to_le32(le32_to_cpu(es->s_free_blocks_count)+1);
                }
        }
        
        mark_buffer_dirty(bh2, 1);
        mark_buffer_dirty(sb->u.ext2_sb.s_sbh, 1);

        mark_buffer_dirty(bh, 1);
        if (sb->s_flags & MS_SYNCHRONOUS) {
                ll_rw_block (WRITE, 1, &bh);
                wait_on_buffer (bh);
        }
        if (overflow) {
                block += count;
                count = overflow;
                goto do_more;
        }
        sb->s_dirt = 1;
error_return:
        unlock_super (sb);
        return;
}

/*
 * ext2_new_block uses a goal block to assist allocation.  If the goal is
 * free, or there is a free block within 32 blocks of the goal, that block
 * is allocated.  Otherwise a forward search is made for a free block; within 
 * each block group the search first looks for an entire free byte in the block
 * bitmap, and then for any free bit if that fails.
 */
int ext2_new_block (const struct inode * inode, unsigned long goal,
                    u32 * prealloc_count, u32 * prealloc_block, int * err)
{
        struct buffer_head * bh;
        struct buffer_head * bh2;
        char * p, * r;
        int i, j, k, tmp;
        int bitmap_nr;
        struct super_block * sb;
        struct ext2_group_desc * gdp;
        struct ext2_super_block * es;

        *err = -ENOSPC;
#ifdef EXT2FS_DEBUG
        static int goal_hits = 0, goal_attempts = 0;
#endif
        sb = inode->i_sb;
        if (!sb) {
                printk ("ext2_new_block: nonexistent device");
                return 0;
        }

        lock_super (sb);
        es = sb->u.ext2_sb.s_es;
        if (le32_to_cpu(es->s_free_blocks_count) <= le32_to_cpu(es->s_r_blocks_count) &&
            ((sb->u.ext2_sb.s_resuid != current->fsuid) &&
             (sb->u.ext2_sb.s_resgid == 0 ||
              !in_group_p (sb->u.ext2_sb.s_resgid)) && 
             !capable(CAP_SYS_RESOURCE))) {
                unlock_super (sb);
                return 0;
        }

        ext2_debug ("goal=%lu.\n", goal);

repeat:
        /*
         * First, test whether the goal block is free.
         */
        if (goal < le32_to_cpu(es->s_first_data_block) ||
            goal >= le32_to_cpu(es->s_blocks_count))
                goal = le32_to_cpu(es->s_first_data_block);
        i = (goal - le32_to_cpu(es->s_first_data_block)) / EXT2_BLOCKS_PER_GROUP(sb);
        gdp = ext2_get_group_desc (sb, i, &bh2);
        if (!gdp)
                goto io_error;

        if (le16_to_cpu(gdp->bg_free_blocks_count) > 0) {
                j = ((goal - le32_to_cpu(es->s_first_data_block)) % EXT2_BLOCKS_PER_GROUP(sb));
#ifdef EXT2FS_DEBUG
                if (j)
                        goal_attempts++;
#endif
                bitmap_nr = load_block_bitmap (sb, i);
                if (bitmap_nr < 0)
                        goto io_error;
                
                bh = sb->u.ext2_sb.s_block_bitmap[bitmap_nr];

                ext2_debug ("goal is at %d:%d.\n", i, j);

                if (!ext2_test_bit(j, bh->b_data)) {
#ifdef EXT2FS_DEBUG
                        goal_hits++;
                        ext2_debug ("goal bit allocated.\n");
#endif
                        goto got_block;
                }
                if (j) {
                        /*
                         * The goal was occupied; search forward for a free 
                         * block within the next XX blocks.
                         *
                         * end_goal is more or less random, but it has to be
                         * less than EXT2_BLOCKS_PER_GROUP. Aligning up to the
                         * next 64-bit boundary is simple..
                         */
                        int end_goal = (j + 63) & ~63;
                        j = ext2_find_next_zero_bit(bh->b_data, end_goal, j);
                        if (j < end_goal)
                                goto got_block;
                }
        
                ext2_debug ("Bit not found near goal\n");

                /*
                 * There has been no free block found in the near vicinity
                 * of the goal: do a search forward through the block groups,
                 * searching in each group first for an entire free byte in
                 * the bitmap and then for any free bit.
                 * 
                 * Search first in the remainder of the current group; then,
                 * cyclicly search through the rest of the groups.
                 */
                p = ((char *) bh->b_data) + (j >> 3);
                r = memscan(p, 0, (EXT2_BLOCKS_PER_GROUP(sb) - j + 7) >> 3);
                k = (r - ((char *) bh->b_data)) << 3;
                if (k < EXT2_BLOCKS_PER_GROUP(sb)) {
                        j = k;
                        goto search_back;
                }

                k = ext2_find_next_zero_bit ((unsigned long *) bh->b_data, 
                                        EXT2_BLOCKS_PER_GROUP(sb),
                                        j);
                if (k < EXT2_BLOCKS_PER_GROUP(sb)) {
                        j = k;
                        goto got_block;
                }
        }

        ext2_debug ("Bit not found in block group %d.\n", i);

        /*
         * Now search the rest of the groups.  We assume that 
         * i and gdp correctly point to the last group visited.
         */
        for (k = 0; k < sb->u.ext2_sb.s_groups_count; k++) {
                i++;
                if (i >= sb->u.ext2_sb.s_groups_count)
                        i = 0;
                gdp = ext2_get_group_desc (sb, i, &bh2);
                if (!gdp) {
                        *err = -EIO;
                        unlock_super (sb);
                        return 0;
                }
                if (le16_to_cpu(gdp->bg_free_blocks_count) > 0)
                        break;
        }
        if (k >= sb->u.ext2_sb.s_groups_count) {
                unlock_super (sb);
                return 0;
        }
        bitmap_nr = load_block_bitmap (sb, i);
        if (bitmap_nr < 0)
                goto io_error;
        
        bh = sb->u.ext2_sb.s_block_bitmap[bitmap_nr];
        r = memscan(bh->b_data, 0, EXT2_BLOCKS_PER_GROUP(sb) >> 3);
        j = (r - bh->b_data) << 3;
        if (j < EXT2_BLOCKS_PER_GROUP(sb))
                goto search_back;
        else
                j = ext2_find_first_zero_bit ((unsigned long *) bh->b_data,
                                         EXT2_BLOCKS_PER_GROUP(sb));
        if (j >= EXT2_BLOCKS_PER_GROUP(sb)) {
                ext2_error (sb, "ext2_new_block",
                            "Free blocks count corrupted for block group %d", i);
                unlock_super (sb);
                return 0;
        }

search_back:
        /* 
         * We have succeeded in finding a free byte in the block
         * bitmap.  Now search backwards up to 7 bits to find the
         * start of this group of free blocks.
         */
        for (k = 0; k < 7 && j > 0 && !ext2_test_bit (j - 1, bh->b_data); k++, j--);
        
got_block:

        ext2_debug ("using block group %d(%d)\n", i, gdp->bg_free_blocks_count);

        /*
         * Check quota for allocation of this block.
         */
        if(DQUOT_ALLOC_BLOCK(sb, inode, 1)) {
                unlock_super(sb);
                *err = -EDQUOT;
                return 0;
        }

        tmp = j + i * EXT2_BLOCKS_PER_GROUP(sb) + le32_to_cpu(es->s_first_data_block);

        if (test_opt (sb, CHECK_STRICT) &&
            (tmp == le32_to_cpu(gdp->bg_block_bitmap) ||
             tmp == le32_to_cpu(gdp->bg_inode_bitmap) ||
             in_range (tmp, le32_to_cpu(gdp->bg_inode_table), sb->u.ext2_sb.s_itb_per_group)))
                ext2_panic (sb, "ext2_new_block",
                            "Allocating block in system zone - "
                            "block = %u", tmp);

        if (ext2_set_bit (j, bh->b_data)) {
                ext2_warning (sb, "ext2_new_block",
                              "bit already set for block %d", j);
                DQUOT_FREE_BLOCK(sb, inode, 1);
                goto repeat;
        }

        ext2_debug ("found bit %d\n", j);

        /*
         * Do block preallocation now if required.
         */
#ifdef EXT2_PREALLOCATE
        if (prealloc_block) {
                int     prealloc_goal;

                prealloc_goal = es->s_prealloc_blocks ?
                        es->s_prealloc_blocks : EXT2_DEFAULT_PREALLOC_BLOCKS;

                *prealloc_count = 0;
                *prealloc_block = tmp + 1;
                for (k = 1;
                     k < prealloc_goal && (j + k) < EXT2_BLOCKS_PER_GROUP(sb);
                     k++) {
                        if (DQUOT_PREALLOC_BLOCK(sb, inode, 1))
                                break;
                        if (ext2_set_bit (j + k, bh->b_data)) {
                                DQUOT_FREE_BLOCK(sb, inode, 1);
                                break;
                        }
                        (*prealloc_count)++;
                }       
                gdp->bg_free_blocks_count =
                        cpu_to_le16(le16_to_cpu(gdp->bg_free_blocks_count) -
                               *prealloc_count);
                es->s_free_blocks_count =
                        cpu_to_le32(le32_to_cpu(es->s_free_blocks_count) -
                               *prealloc_count);
                ext2_debug ("Preallocated a further %lu bits.\n",
                            *prealloc_count);
        }
#endif

        j = tmp;

        mark_buffer_dirty(bh, 1);
        if (sb->s_flags & MS_SYNCHRONOUS) {
                ll_rw_block (WRITE, 1, &bh);
                wait_on_buffer (bh);
        }

        if (j >= le32_to_cpu(es->s_blocks_count)) {
                ext2_error (sb, "ext2_new_block",
                            "block >= blocks count - "
                            "block_group = %d, block=%d", i, j);
                unlock_super (sb);
                return 0;
        }
        if (!(bh = getblk (sb->s_dev, j, sb->s_blocksize))) {
                ext2_error (sb, "ext2_new_block", "cannot get block %d", j);
                unlock_super (sb);
                return 0;
        }
        memset(bh->b_data, 0, sb->s_blocksize);
        mark_buffer_uptodate(bh, 1);
        mark_buffer_dirty(bh, 1);
        brelse (bh);

        ext2_debug ("allocating block %d. "
                    "Goal hits %d of %d.\n", j, goal_hits, goal_attempts);

        gdp->bg_free_blocks_count = cpu_to_le16(le16_to_cpu(gdp->bg_free_blocks_count) - 1);
        mark_buffer_dirty(bh2, 1);
        es->s_free_blocks_count = cpu_to_le32(le32_to_cpu(es->s_free_blocks_count) - 1);
        mark_buffer_dirty(sb->u.ext2_sb.s_sbh, 1);
        sb->s_dirt = 1;
        unlock_super (sb);
        *err = 0;
        return j;
        
io_error:
        *err = -EIO;
        unlock_super (sb);
        return 0;
        
}

unsigned long ext2_count_free_blocks (struct super_block * sb)
{
#ifdef EXT2FS_DEBUG
        struct ext2_super_block * es;
        unsigned long desc_count, bitmap_count, x;
        int bitmap_nr;
        struct ext2_group_desc * gdp;
        int i;
        
        lock_super (sb);
        es = sb->u.ext2_sb.s_es;
        desc_count = 0;
        bitmap_count = 0;
        gdp = NULL;
        for (i = 0; i < sb->u.ext2_sb.s_groups_count; i++) {
                gdp = ext2_get_group_desc (sb, i, NULL);
                if (!gdp)
                        continue;
                desc_count += le16_to_cpu(gdp->bg_free_blocks_count);
                bitmap_nr = load_block_bitmap (sb, i);
                if (bitmap_nr < 0)
                        continue;
                
                x = ext2_count_free (sb->u.ext2_sb.s_block_bitmap[bitmap_nr],
                                     sb->s_blocksize);
                printk ("group %d: stored = %d, counted = %lu\n",
                        i, le16_to_cpu(gdp->bg_free_blocks_count), x);
                bitmap_count += x;
        }
        printk("ext2_count_free_blocks: stored = %lu, computed = %lu, %lu\n",
               le32_to_cpu(es->s_free_blocks_count), desc_count, bitmap_count);
        unlock_super (sb);
        return bitmap_count;
#else
        return le32_to_cpu(sb->u.ext2_sb.s_es->s_free_blocks_count);
#endif
}

static inline int block_in_use (unsigned long block,
                                struct super_block * sb,
                                unsigned char * map)
{
        return ext2_test_bit ((block - le32_to_cpu(sb->u.ext2_sb.s_es->s_first_data_block)) %
                         EXT2_BLOCKS_PER_GROUP(sb), map);
}

static int test_root(int a, int b)
{
        if (a == 0)
                return 1;
        while (1) {
                if (a == 1)
                        return 1;
                if (a % b)
                        return 0;
                a = a / b;
        }
}

int ext2_group_sparse(int group)
{
        return (test_root(group, 3) || test_root(group, 5) ||
                test_root(group, 7));
}

void ext2_check_blocks_bitmap (struct super_block * sb)
{
        struct buffer_head * bh;
        struct ext2_super_block * es;
        unsigned long desc_count, bitmap_count, x;
        unsigned long desc_blocks;
        int bitmap_nr;
        struct ext2_group_desc * gdp;
        int i, j;

        lock_super (sb);
        es = sb->u.ext2_sb.s_es;
        desc_count = 0;
        bitmap_count = 0;
        gdp = NULL;
        desc_blocks = (sb->u.ext2_sb.s_groups_count + EXT2_DESC_PER_BLOCK(sb) - 1) /
                      EXT2_DESC_PER_BLOCK(sb);
        for (i = 0; i < sb->u.ext2_sb.s_groups_count; i++) {
                gdp = ext2_get_group_desc (sb, i, NULL);
                if (!gdp)
                        continue;
                desc_count += le16_to_cpu(gdp->bg_free_blocks_count);
                bitmap_nr = load_block_bitmap (sb, i);
                if (bitmap_nr < 0)
                        continue;
                
                bh = sb->u.ext2_sb.s_block_bitmap[bitmap_nr];

                if (!(sb->u.ext2_sb.s_feature_ro_compat &
                     EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER) ||
                    ext2_group_sparse(i)) {
                        if (!ext2_test_bit (0, bh->b_data))
                                ext2_error (sb, "ext2_check_blocks_bitmap",
                                            "Superblock in group %d "
                                            "is marked free", i);

                        for (j = 0; j < desc_blocks; j++)
                                if (!ext2_test_bit (j + 1, bh->b_data))
                                        ext2_error (sb,
                                            "ext2_check_blocks_bitmap",
                                            "Descriptor block #%d in group "
                                            "%d is marked free", j, i);
                }

                if (!block_in_use (le32_to_cpu(gdp->bg_block_bitmap), sb, bh->b_data))
                        ext2_error (sb, "ext2_check_blocks_bitmap",
                                    "Block bitmap for group %d is marked free",
                                    i);

                if (!block_in_use (le32_to_cpu(gdp->bg_inode_bitmap), sb, bh->b_data))
                        ext2_error (sb, "ext2_check_blocks_bitmap",
                                    "Inode bitmap for group %d is marked free",
                                    i);

                for (j = 0; j < sb->u.ext2_sb.s_itb_per_group; j++)
                        if (!block_in_use (le32_to_cpu(gdp->bg_inode_table) + j, sb, bh->b_data))
                                ext2_error (sb, "ext2_check_blocks_bitmap",
                                            "Block #%d of the inode table in "
                                            "group %d is marked free", j, i);

                x = ext2_count_free (bh, sb->s_blocksize);
                if (le16_to_cpu(gdp->bg_free_blocks_count) != x)
                        ext2_error (sb, "ext2_check_blocks_bitmap",
                                    "Wrong free blocks count for group %d, "
                                    "stored = %d, counted = %lu", i,
                                    le16_to_cpu(gdp->bg_free_blocks_count), x);
                bitmap_count += x;
        }
        if (le32_to_cpu(es->s_free_blocks_count) != bitmap_count)
                ext2_error (sb, "ext2_check_blocks_bitmap",
                            "Wrong free blocks count in super block, "
                            "stored = %lu, counted = %lu",
                            (unsigned long) le32_to_cpu(es->s_free_blocks_count), bitmap_count);
        unlock_super (sb);
}