make srcu_readers_active() static

[pv_ops_mirror.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@redhat.com), 1993
 *  Big-endian to little-endian byte-swapping/bitmaps by
 *        David S. Miller (davem@caip.rutgers.edu), 1995
 */

#include "ext2.h"
#include <linux/quotaops.h>
#include <linux/sched.h>
#include <linux/buffer_head.h>
#include <linux/capability.h>

/*
 * 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_fill_super).
 */


#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 offset;
        struct ext2_group_desc * desc;
        struct ext2_sb_info *sbi = EXT2_SB(sb);

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

                return NULL;
        }

        group_desc = block_group >> EXT2_DESC_PER_BLOCK_BITS(sb);
        offset = block_group & (EXT2_DESC_PER_BLOCK(sb) - 1);
        if (!sbi->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, offset);
                return NULL;
        }

        desc = (struct ext2_group_desc *) sbi->s_group_desc[group_desc]->b_data;
        if (bh)
                *bh = sbi->s_group_desc[group_desc];
        return desc + offset;
}

/*
 * Read the bitmap for a given block_group, reading into the specified 
 * slot in the superblock's bitmap cache.
 *
 * Return buffer_head on success or NULL in case of failure.
 */
static struct buffer_head *
read_block_bitmap(struct super_block *sb, unsigned int block_group)
{
        struct ext2_group_desc * desc;
        struct buffer_head * bh = NULL;
        
        desc = ext2_get_group_desc (sb, block_group, NULL);
        if (!desc)
                goto error_out;
        bh = sb_bread(sb, le32_to_cpu(desc->bg_block_bitmap));
        if (!bh)
                ext2_error (sb, "read_block_bitmap",
                            "Cannot read block bitmap - "
                            "block_group = %d, block_bitmap = %u",
                            block_group, le32_to_cpu(desc->bg_block_bitmap));
error_out:
        return bh;
}

static void release_blocks(struct super_block *sb, int count)
{
        if (count) {
                struct ext2_sb_info *sbi = EXT2_SB(sb);

                percpu_counter_add(&sbi->s_freeblocks_counter, count);
                sb->s_dirt = 1;
        }
}

static void group_adjust_blocks(struct super_block *sb, int group_no,
        struct ext2_group_desc *desc, struct buffer_head *bh, int count)
{
        if (count) {
                struct ext2_sb_info *sbi = EXT2_SB(sb);
                unsigned free_blocks;

                spin_lock(sb_bgl_lock(sbi, group_no));
                free_blocks = le16_to_cpu(desc->bg_free_blocks_count);
                desc->bg_free_blocks_count = cpu_to_le16(free_blocks + count);
                spin_unlock(sb_bgl_lock(sbi, group_no));
                sb->s_dirt = 1;
                mark_buffer_dirty(bh);
        }
}

/*
 * The reservation window structure operations
 * --------------------------------------------
 * Operations include:
 * dump, find, add, remove, is_empty, find_next_reservable_window, etc.
 *
 * We use a red-black tree to represent per-filesystem reservation
 * windows.
 *
 */

/**
 * __rsv_window_dump() -- Dump the filesystem block allocation reservation map
 * @rb_root:            root of per-filesystem reservation rb tree
 * @verbose:            verbose mode
 * @fn:                 function which wishes to dump the reservation map
 *
 * If verbose is turned on, it will print the whole block reservation
 * windows(start, end). Otherwise, it will only print out the "bad" windows,
 * those windows that overlap with their immediate neighbors.
 */
#if 1
static void __rsv_window_dump(struct rb_root *root, int verbose,
                              const char *fn)
{
        struct rb_node *n;
        struct ext2_reserve_window_node *rsv, *prev;
        int bad;

restart:
        n = rb_first(root);
        bad = 0;
        prev = NULL;

        printk("Block Allocation Reservation Windows Map (%s):\n", fn);
        while (n) {
                rsv = rb_entry(n, struct ext2_reserve_window_node, rsv_node);
                if (verbose)
                        printk("reservation window 0x%p "
                                "start: %lu, end: %lu\n",
                                rsv, rsv->rsv_start, rsv->rsv_end);
                if (rsv->rsv_start && rsv->rsv_start >= rsv->rsv_end) {
                        printk("Bad reservation %p (start >= end)\n",
                               rsv);
                        bad = 1;
                }
                if (prev && prev->rsv_end >= rsv->rsv_start) {
                        printk("Bad reservation %p (prev->end >= start)\n",
                               rsv);
                        bad = 1;
                }
                if (bad) {
                        if (!verbose) {
                                printk("Restarting reservation walk in verbose mode\n");
                                verbose = 1;
                                goto restart;
                        }
                }
                n = rb_next(n);
                prev = rsv;
        }
        printk("Window map complete.\n");
        if (bad)
                BUG();
}
#define rsv_window_dump(root, verbose) \
        __rsv_window_dump((root), (verbose), __FUNCTION__)
#else
#define rsv_window_dump(root, verbose) do {} while (0)
#endif

/**
 * goal_in_my_reservation()
 * @rsv:                inode's reservation window
 * @grp_goal:           given goal block relative to the allocation block group
 * @group:              the current allocation block group
 * @sb:                 filesystem super block
 *
 * Test if the given goal block (group relative) is within the file's
 * own block reservation window range.
 *
 * If the reservation window is outside the goal allocation group, return 0;
 * grp_goal (given goal block) could be -1, which means no specific
 * goal block. In this case, always return 1.
 * If the goal block is within the reservation window, return 1;
 * otherwise, return 0;
 */
static int
goal_in_my_reservation(struct ext2_reserve_window *rsv, ext2_grpblk_t grp_goal,
                        unsigned int group, struct super_block * sb)
{
        ext2_fsblk_t group_first_block, group_last_block;

        group_first_block = ext2_group_first_block_no(sb, group);
        group_last_block = group_first_block + EXT2_BLOCKS_PER_GROUP(sb) - 1;

        if ((rsv->_rsv_start > group_last_block) ||
            (rsv->_rsv_end < group_first_block))
                return 0;
        if ((grp_goal >= 0) && ((grp_goal + group_first_block < rsv->_rsv_start)
                || (grp_goal + group_first_block > rsv->_rsv_end)))
                return 0;
        return 1;
}

/**
 * search_reserve_window()
 * @rb_root:            root of reservation tree
 * @goal:               target allocation block
 *
 * Find the reserved window which includes the goal, or the previous one
 * if the goal is not in any window.
 * Returns NULL if there are no windows or if all windows start after the goal.
 */
static struct ext2_reserve_window_node *
search_reserve_window(struct rb_root *root, ext2_fsblk_t goal)
{
        struct rb_node *n = root->rb_node;
        struct ext2_reserve_window_node *rsv;

        if (!n)
                return NULL;

        do {
                rsv = rb_entry(n, struct ext2_reserve_window_node, rsv_node);

                if (goal < rsv->rsv_start)
                        n = n->rb_left;
                else if (goal > rsv->rsv_end)
                        n = n->rb_right;
                else
                        return rsv;
        } while (n);
        /*
         * We've fallen off the end of the tree: the goal wasn't inside
         * any particular node.  OK, the previous node must be to one
         * side of the interval containing the goal.  If it's the RHS,
         * we need to back up one.
         */
        if (rsv->rsv_start > goal) {
                n = rb_prev(&rsv->rsv_node);
                rsv = rb_entry(n, struct ext2_reserve_window_node, rsv_node);
        }
        return rsv;
}

/*
 * ext2_rsv_window_add() -- Insert a window to the block reservation rb tree.
 * @sb:                 super block
 * @rsv:                reservation window to add
 *
 * Must be called with rsv_lock held.
 */
void ext2_rsv_window_add(struct super_block *sb,
                    struct ext2_reserve_window_node *rsv)
{
        struct rb_root *root = &EXT2_SB(sb)->s_rsv_window_root;
        struct rb_node *node = &rsv->rsv_node;
        ext2_fsblk_t start = rsv->rsv_start;

        struct rb_node ** p = &root->rb_node;
        struct rb_node * parent = NULL;
        struct ext2_reserve_window_node *this;

        while (*p)
        {
                parent = *p;
                this = rb_entry(parent, struct ext2_reserve_window_node, rsv_node);

                if (start < this->rsv_start)
                        p = &(*p)->rb_left;
                else if (start > this->rsv_end)
                        p = &(*p)->rb_right;
                else {
                        rsv_window_dump(root, 1);
                        BUG();
                }
        }

        rb_link_node(node, parent, p);
        rb_insert_color(node, root);
}

/**
 * rsv_window_remove() -- unlink a window from the reservation rb tree
 * @sb:                 super block
 * @rsv:                reservation window to remove
 *
 * Mark the block reservation window as not allocated, and unlink it
 * from the filesystem reservation window rb tree. Must be called with
 * rsv_lock held.
 */
static void rsv_window_remove(struct super_block *sb,
                              struct ext2_reserve_window_node *rsv)
{
        rsv->rsv_start = EXT2_RESERVE_WINDOW_NOT_ALLOCATED;
        rsv->rsv_end = EXT2_RESERVE_WINDOW_NOT_ALLOCATED;
        rsv->rsv_alloc_hit = 0;
        rb_erase(&rsv->rsv_node, &EXT2_SB(sb)->s_rsv_window_root);
}

/*
 * rsv_is_empty() -- Check if the reservation window is allocated.
 * @rsv:                given reservation window to check
 *
 * returns 1 if the end block is EXT2_RESERVE_WINDOW_NOT_ALLOCATED.
 */
static inline int rsv_is_empty(struct ext2_reserve_window *rsv)
{
        /* a valid reservation end block could not be 0 */
        return (rsv->_rsv_end == EXT2_RESERVE_WINDOW_NOT_ALLOCATED);
}

/**
 * ext2_init_block_alloc_info()
 * @inode:              file inode structure
 *
 * Allocate and initialize the  reservation window structure, and
 * link the window to the ext2 inode structure at last
 *
 * The reservation window structure is only dynamically allocated
 * and linked to ext2 inode the first time the open file
 * needs a new block. So, before every ext2_new_block(s) call, for
 * regular files, we should check whether the reservation window
 * structure exists or not. In the latter case, this function is called.
 * Fail to do so will result in block reservation being turned off for that
 * open file.
 *
 * This function is called from ext2_get_blocks_handle(), also called
 * when setting the reservation window size through ioctl before the file
 * is open for write (needs block allocation).
 *
 * Needs truncate_mutex protection prior to calling this function.
 */
void ext2_init_block_alloc_info(struct inode *inode)
{
        struct ext2_inode_info *ei = EXT2_I(inode);
        struct ext2_block_alloc_info *block_i = ei->i_block_alloc_info;
        struct super_block *sb = inode->i_sb;

        block_i = kmalloc(sizeof(*block_i), GFP_NOFS);
        if (block_i) {
                struct ext2_reserve_window_node *rsv = &block_i->rsv_window_node;

                rsv->rsv_start = EXT2_RESERVE_WINDOW_NOT_ALLOCATED;
                rsv->rsv_end = EXT2_RESERVE_WINDOW_NOT_ALLOCATED;

                /*
                 * if filesystem is mounted with NORESERVATION, the goal
                 * reservation window size is set to zero to indicate
                 * block reservation is off
                 */
                if (!test_opt(sb, RESERVATION))
                        rsv->rsv_goal_size = 0;
                else
                        rsv->rsv_goal_size = EXT2_DEFAULT_RESERVE_BLOCKS;
                rsv->rsv_alloc_hit = 0;
                block_i->last_alloc_logical_block = 0;
                block_i->last_alloc_physical_block = 0;
        }
        ei->i_block_alloc_info = block_i;
}

/**
 * ext2_discard_reservation()
 * @inode:              inode
 *
 * Discard(free) block reservation window on last file close, or truncate
 * or at last iput().
 *
 * It is being called in three cases:
 *      ext2_release_file(): last writer closes the file
 *      ext2_clear_inode(): last iput(), when nobody links to this file.
 *      ext2_truncate(): when the block indirect map is about to change.
 */
void ext2_discard_reservation(struct inode *inode)
{
        struct ext2_inode_info *ei = EXT2_I(inode);
        struct ext2_block_alloc_info *block_i = ei->i_block_alloc_info;
        struct ext2_reserve_window_node *rsv;
        spinlock_t *rsv_lock = &EXT2_SB(inode->i_sb)->s_rsv_window_lock;

        if (!block_i)
                return;

        rsv = &block_i->rsv_window_node;
        if (!rsv_is_empty(&rsv->rsv_window)) {
                spin_lock(rsv_lock);
                if (!rsv_is_empty(&rsv->rsv_window))
                        rsv_window_remove(inode->i_sb, rsv);
                spin_unlock(rsv_lock);
        }
}

/**
 * ext2_free_blocks_sb() -- Free given blocks and update quota and i_blocks
 * @inode:              inode
 * @block:              start physcial block to free
 * @count:              number of blocks to free
 */
void ext2_free_blocks (struct inode * inode, unsigned long block,
                       unsigned long count)
{
        struct buffer_head *bitmap_bh = NULL;
        struct buffer_head * bh2;
        unsigned long block_group;
        unsigned long bit;
        unsigned long i;
        unsigned long overflow;
        struct super_block * sb = inode->i_sb;
        struct ext2_sb_info * sbi = EXT2_SB(sb);
        struct ext2_group_desc * desc;
        struct ext2_super_block * es = sbi->s_es;
        unsigned freed = 0, group_freed;

        if (block < le32_to_cpu(es->s_first_data_block) ||
            block + count < 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(s) %lu-%lu\n", block, block + count - 1);

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;
        }
        brelse(bitmap_bh);
        bitmap_bh = read_block_bitmap(sb, block_group);
        if (!bitmap_bh)
                goto error_return;

        desc = ext2_get_group_desc (sb, block_group, &bh2);
        if (!desc)
                goto error_return;

        if (in_range (le32_to_cpu(desc->bg_block_bitmap), block, count) ||
            in_range (le32_to_cpu(desc->bg_inode_bitmap), block, count) ||
            in_range (block, le32_to_cpu(desc->bg_inode_table),
                      sbi->s_itb_per_group) ||
            in_range (block + count - 1, le32_to_cpu(desc->bg_inode_table),
                      sbi->s_itb_per_group)) {
                ext2_error (sb, "ext2_free_blocks",
                            "Freeing blocks in system zones - "
                            "Block = %lu, count = %lu",
                            block, count);
                goto error_return;
        }

        for (i = 0, group_freed = 0; i < count; i++) {
                if (!ext2_clear_bit_atomic(sb_bgl_lock(sbi, block_group),
                                                bit + i, bitmap_bh->b_data)) {
                        ext2_error(sb, __FUNCTION__,
                                "bit already cleared for block %lu", block + i);
                } else {
                        group_freed++;
                }
        }

        mark_buffer_dirty(bitmap_bh);
        if (sb->s_flags & MS_SYNCHRONOUS)
                sync_dirty_buffer(bitmap_bh);

        group_adjust_blocks(sb, block_group, desc, bh2, group_freed);
        freed += group_freed;

        if (overflow) {
                block += count;
                count = overflow;
                goto do_more;
        }
error_return:
        brelse(bitmap_bh);
        release_blocks(sb, freed);
        DQUOT_FREE_BLOCK(inode, freed);
}

/**
 * bitmap_search_next_usable_block()
 * @start:              the starting block (group relative) of the search
 * @bh:                 bufferhead contains the block group bitmap
 * @maxblocks:          the ending block (group relative) of the reservation
 *
 * The bitmap search --- search forward through the actual bitmap on disk until
 * we find a bit free.
 */
static ext2_grpblk_t
bitmap_search_next_usable_block(ext2_grpblk_t start, struct buffer_head *bh,
                                        ext2_grpblk_t maxblocks)
{
        ext2_grpblk_t next;

        next = ext2_find_next_zero_bit(bh->b_data, maxblocks, start);
        if (next >= maxblocks)
                return -1;
        return next;
}

/**
 * find_next_usable_block()
 * @start:              the starting block (group relative) to find next
 *                      allocatable block in bitmap.
 * @bh:                 bufferhead contains the block group bitmap
 * @maxblocks:          the ending block (group relative) for the search
 *
 * Find an allocatable block in a bitmap.  We perform the "most
 * appropriate allocation" algorithm of looking for a free block near
 * the initial goal; then for a free byte somewhere in the bitmap;
 * then for any free bit in the bitmap.
 */
static ext2_grpblk_t
find_next_usable_block(int start, struct buffer_head *bh, int maxblocks)
{
        ext2_grpblk_t here, next;
        char *p, *r;

        if (start > 0) {
                /*
                 * 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..
                 */
                ext2_grpblk_t end_goal = (start + 63) & ~63;
                if (end_goal > maxblocks)
                        end_goal = maxblocks;
                here = ext2_find_next_zero_bit(bh->b_data, end_goal, start);
                if (here < end_goal)
                        return here;
                ext2_debug("Bit not found near goal\n");
        }

        here = start;
        if (here < 0)
                here = 0;

        p = ((char *)bh->b_data) + (here >> 3);
        r = memscan(p, 0, ((maxblocks + 7) >> 3) - (here >> 3));
        next = (r - ((char *)bh->b_data)) << 3;

        if (next < maxblocks && next >= here)
                return next;

        here = bitmap_search_next_usable_block(here, bh, maxblocks);
        return here;
}

/*
 * ext2_try_to_allocate()
 * @sb:                 superblock
 * @handle:             handle to this transaction
 * @group:              given allocation block group
 * @bitmap_bh:          bufferhead holds the block bitmap
 * @grp_goal:           given target block within the group
 * @count:              target number of blocks to allocate
 * @my_rsv:             reservation window
 *
 * Attempt to allocate blocks within a give range. Set the range of allocation
 * first, then find the first free bit(s) from the bitmap (within the range),
 * and at last, allocate the blocks by claiming the found free bit as allocated.
 *
 * To set the range of this allocation:
 *      if there is a reservation window, only try to allocate block(s)
 *      from the file's own reservation window;
 *      Otherwise, the allocation range starts from the give goal block,
 *      ends at the block group's last block.
 *
 * If we failed to allocate the desired block then we may end up crossing to a
 * new bitmap.
 */
static int
ext2_try_to_allocate(struct super_block *sb, int group,
                        struct buffer_head *bitmap_bh, ext2_grpblk_t grp_goal,
                        unsigned long *count,
                        struct ext2_reserve_window *my_rsv)
{
        ext2_fsblk_t group_first_block;
        ext2_grpblk_t start, end;
        unsigned long num = 0;

        /* we do allocation within the reservation window if we have a window */
        if (my_rsv) {
                group_first_block = ext2_group_first_block_no(sb, group);
                if (my_rsv->_rsv_start >= group_first_block)
                        start = my_rsv->_rsv_start - group_first_block;
                else
                        /* reservation window cross group boundary */
                        start = 0;
                end = my_rsv->_rsv_end - group_first_block + 1;
                if (end > EXT2_BLOCKS_PER_GROUP(sb))
                        /* reservation window crosses group boundary */
                        end = EXT2_BLOCKS_PER_GROUP(sb);
                if ((start <= grp_goal) && (grp_goal < end))
                        start = grp_goal;
                else
                        grp_goal = -1;
        } else {
                if (grp_goal > 0)
                        start = grp_goal;
                else
                        start = 0;
                end = EXT2_BLOCKS_PER_GROUP(sb);
        }

        BUG_ON(start > EXT2_BLOCKS_PER_GROUP(sb));

repeat:
        if (grp_goal < 0) {
                grp_goal = find_next_usable_block(start, bitmap_bh, end);
                if (grp_goal < 0)
                        goto fail_access;
                if (!my_rsv) {
                        int i;

                        for (i = 0; i < 7 && grp_goal > start &&
                                        !ext2_test_bit(grp_goal - 1,
                                                        bitmap_bh->b_data);
                                        i++, grp_goal--)
                                ;
                }
        }
        start = grp_goal;

        if (ext2_set_bit_atomic(sb_bgl_lock(EXT2_SB(sb), group), grp_goal,
                                                        bitmap_bh->b_data)) {
                /*
                 * The block was allocated by another thread, or it was
                 * allocated and then freed by another thread
                 */
                start++;
                grp_goal++;
                if (start >= end)
                        goto fail_access;
                goto repeat;
        }
        num++;
        grp_goal++;
        while (num < *count && grp_goal < end
                && !ext2_set_bit_atomic(sb_bgl_lock(EXT2_SB(sb), group),
                                        grp_goal, bitmap_bh->b_data)) {
                num++;
                grp_goal++;
        }
        *count = num;
        return grp_goal - num;
fail_access:
        *count = num;
        return -1;
}

/**
 *      find_next_reservable_window():
 *              find a reservable space within the given range.
 *              It does not allocate the reservation window for now:
 *              alloc_new_reservation() will do the work later.
 *
 *      @search_head: the head of the searching list;
 *              This is not necessarily the list head of the whole filesystem
 *
 *              We have both head and start_block to assist the search
 *              for the reservable space. The list starts from head,
 *              but we will shift to the place where start_block is,
 *              then start from there, when looking for a reservable space.
 *
 *      @size: the target new reservation window size
 *
 *      @group_first_block: the first block we consider to start
 *                      the real search from
 *
 *      @last_block:
 *              the maximum block number that our goal reservable space
 *              could start from. This is normally the last block in this
 *              group. The search will end when we found the start of next
 *              possible reservable space is out of this boundary.
 *              This could handle the cross boundary reservation window
 *              request.
 *
 *      basically we search from the given range, rather than the whole
 *      reservation double linked list, (start_block, last_block)
 *      to find a free region that is of my size and has not
 *      been reserved.
 *
 */
static int find_next_reservable_window(
                                struct ext2_reserve_window_node *search_head,
                                struct ext2_reserve_window_node *my_rsv,
                                struct super_block * sb,
                                ext2_fsblk_t start_block,
                                ext2_fsblk_t last_block)
{
        struct rb_node *next;
        struct ext2_reserve_window_node *rsv, *prev;
        ext2_fsblk_t cur;
        int size = my_rsv->rsv_goal_size;

        /* TODO: make the start of the reservation window byte-aligned */
        /* cur = *start_block & ~7;*/
        cur = start_block;
        rsv = search_head;
        if (!rsv)
                return -1;

        while (1) {
                if (cur <= rsv->rsv_end)
                        cur = rsv->rsv_end + 1;

                /* TODO?
                 * in the case we could not find a reservable space
                 * that is what is expected, during the re-search, we could
                 * remember what's the largest reservable space we could have
                 * and return that one.
                 *
                 * For now it will fail if we could not find the reservable
                 * space with expected-size (or more)...
                 */
                if (cur > last_block)
                        return -1;              /* fail */

                prev = rsv;
                next = rb_next(&rsv->rsv_node);
                rsv = rb_entry(next,struct ext2_reserve_window_node,rsv_node);

                /*
                 * Reached the last reservation, we can just append to the
                 * previous one.
                 */
                if (!next)
                        break;

                if (cur + size <= rsv->rsv_start) {
                        /*
                         * Found a reserveable space big enough.  We could
                         * have a reservation across the group boundary here
                         */
                        break;
                }
        }
        /*
         * we come here either :
         * when we reach the end of the whole list,
         * and there is empty reservable space after last entry in the list.
         * append it to the end of the list.
         *
         * or we found one reservable space in the middle of the list,
         * return the reservation window that we could append to.
         * succeed.
         */

        if ((prev != my_rsv) && (!rsv_is_empty(&my_rsv->rsv_window)))
                rsv_window_remove(sb, my_rsv);

        /*
         * Let's book the whole avaliable window for now.  We will check the
         * disk bitmap later and then, if there are free blocks then we adjust
         * the window size if it's larger than requested.
         * Otherwise, we will remove this node from the tree next time
         * call find_next_reservable_window.
         */
        my_rsv->rsv_start = cur;
        my_rsv->rsv_end = cur + size - 1;
        my_rsv->rsv_alloc_hit = 0;

        if (prev != my_rsv)
                ext2_rsv_window_add(sb, my_rsv);

        return 0;
}

/**
 *      alloc_new_reservation()--allocate a new reservation window
 *
 *              To make a new reservation, we search part of the filesystem
 *              reservation list (the list that inside the group). We try to
 *              allocate a new reservation window near the allocation goal,
 *              or the beginning of the group, if there is no goal.
 *
 *              We first find a reservable space after the goal, then from
 *              there, we check the bitmap for the first free block after
 *              it. If there is no free block until the end of group, then the
 *              whole group is full, we failed. Otherwise, check if the free
 *              block is inside the expected reservable space, if so, we
 *              succeed.
 *              If the first free block is outside the reservable space, then
 *              start from the first free block, we search for next available
 *              space, and go on.
 *
 *      on succeed, a new reservation will be found and inserted into the list
 *      It contains at least one free block, and it does not overlap with other
 *      reservation windows.
 *
 *      failed: we failed to find a reservation window in this group
 *
 *      @rsv: the reservation
 *
 *      @grp_goal: The goal (group-relative).  It is where the search for a
 *              free reservable space should start from.
 *              if we have a goal(goal >0 ), then start from there,
 *              no goal(goal = -1), we start from the first block
 *              of the group.
 *
 *      @sb: the super block
 *      @group: the group we are trying to allocate in
 *      @bitmap_bh: the block group block bitmap
 *
 */
static int alloc_new_reservation(struct ext2_reserve_window_node *my_rsv,
                ext2_grpblk_t grp_goal, struct super_block *sb,
                unsigned int group, struct buffer_head *bitmap_bh)
{
        struct ext2_reserve_window_node *search_head;
        ext2_fsblk_t group_first_block, group_end_block, start_block;
        ext2_grpblk_t first_free_block;
        struct rb_root *fs_rsv_root = &EXT2_SB(sb)->s_rsv_window_root;
        unsigned long size;
        int ret;
        spinlock_t *rsv_lock = &EXT2_SB(sb)->s_rsv_window_lock;

        group_first_block = ext2_group_first_block_no(sb, group);
        group_end_block = group_first_block + (EXT2_BLOCKS_PER_GROUP(sb) - 1);

        if (grp_goal < 0)
                start_block = group_first_block;
        else
                start_block = grp_goal + group_first_block;

        size = my_rsv->rsv_goal_size;

        if (!rsv_is_empty(&my_rsv->rsv_window)) {
                /*
                 * if the old reservation is cross group boundary
                 * and if the goal is inside the old reservation window,
                 * we will come here when we just failed to allocate from
                 * the first part of the window. We still have another part
                 * that belongs to the next group. In this case, there is no
                 * point to discard our window and try to allocate a new one
                 * in this group(which will fail). we should
                 * keep the reservation window, just simply move on.
                 *
                 * Maybe we could shift the start block of the reservation
                 * window to the first block of next group.
                 */

                if ((my_rsv->rsv_start <= group_end_block) &&
                                (my_rsv->rsv_end > group_end_block) &&
                                (start_block >= my_rsv->rsv_start))
                        return -1;

                if ((my_rsv->rsv_alloc_hit >
                     (my_rsv->rsv_end - my_rsv->rsv_start + 1) / 2)) {
                        /*
                         * if the previously allocation hit ratio is
                         * greater than 1/2, then we double the size of
                         * the reservation window the next time,
                         * otherwise we keep the same size window
                         */
                        size = size * 2;
                        if (size > EXT2_MAX_RESERVE_BLOCKS)
                                size = EXT2_MAX_RESERVE_BLOCKS;
                        my_rsv->rsv_goal_size= size;
                }
        }

        spin_lock(rsv_lock);
        /*
         * shift the search start to the window near the goal block
         */
        search_head = search_reserve_window(fs_rsv_root, start_block);

        /*
         * find_next_reservable_window() simply finds a reservable window
         * inside the given range(start_block, group_end_block).
         *
         * To make sure the reservation window has a free bit inside it, we
         * need to check the bitmap after we found a reservable window.
         */
retry:
        ret = find_next_reservable_window(search_head, my_rsv, sb,
                                                start_block, group_end_block);

        if (ret == -1) {
                if (!rsv_is_empty(&my_rsv->rsv_window))
                        rsv_window_remove(sb, my_rsv);
                spin_unlock(rsv_lock);
                return -1;
        }

        /*
         * On success, find_next_reservable_window() returns the
         * reservation window where there is a reservable space after it.
         * Before we reserve this reservable space, we need
         * to make sure there is at least a free block inside this region.
         *
         * Search the first free bit on the block bitmap.  Search starts from
         * the start block of the reservable space we just found.
         */
        spin_unlock(rsv_lock);
        first_free_block = bitmap_search_next_usable_block(
                        my_rsv->rsv_start - group_first_block,
                        bitmap_bh, group_end_block - group_first_block + 1);

        if (first_free_block < 0) {
                /*
                 * no free block left on the bitmap, no point
                 * to reserve the space. return failed.
                 */
                spin_lock(rsv_lock);
                if (!rsv_is_empty(&my_rsv->rsv_window))
                        rsv_window_remove(sb, my_rsv);
                spin_unlock(rsv_lock);
                return -1;              /* failed */
        }

        start_block = first_free_block + group_first_block;
        /*
         * check if the first free block is within the
         * free space we just reserved
         */
        if (start_block >= my_rsv->rsv_start && start_block <= my_rsv->rsv_end)
                return 0;               /* success */
        /*
         * if the first free bit we found is out of the reservable space
         * continue search for next reservable space,
         * start from where the free block is,
         * we also shift the list head to where we stopped last time
         */
        search_head = my_rsv;
        spin_lock(rsv_lock);
        goto retry;
}

/**
 * try_to_extend_reservation()
 * @my_rsv:             given reservation window
 * @sb:                 super block
 * @size:               the delta to extend
 *
 * Attempt to expand the reservation window large enough to have
 * required number of free blocks
 *
 * Since ext2_try_to_allocate() will always allocate blocks within
 * the reservation window range, if the window size is too small,
 * multiple blocks allocation has to stop at the end of the reservation
 * window. To make this more efficient, given the total number of
 * blocks needed and the current size of the window, we try to
 * expand the reservation window size if necessary on a best-effort
 * basis before ext2_new_blocks() tries to allocate blocks.
 */
static void try_to_extend_reservation(struct ext2_reserve_window_node *my_rsv,
                        struct super_block *sb, int size)
{
        struct ext2_reserve_window_node *next_rsv;
        struct rb_node *next;
        spinlock_t *rsv_lock = &EXT2_SB(sb)->s_rsv_window_lock;

        if (!spin_trylock(rsv_lock))
                return;

        next = rb_next(&my_rsv->rsv_node);

        if (!next)
                my_rsv->rsv_end += size;
        else {
                next_rsv = rb_entry(next, struct ext2_reserve_window_node, rsv_node);

                if ((next_rsv->rsv_start - my_rsv->rsv_end - 1) >= size)
                        my_rsv->rsv_end += size;
                else
                        my_rsv->rsv_end = next_rsv->rsv_start - 1;
        }
        spin_unlock(rsv_lock);
}

/**
 * ext2_try_to_allocate_with_rsv()
 * @sb:                 superblock
 * @group:              given allocation block group
 * @bitmap_bh:          bufferhead holds the block bitmap
 * @grp_goal:           given target block within the group
 * @count:              target number of blocks to allocate
 * @my_rsv:             reservation window
 *
 * This is the main function used to allocate a new block and its reservation
 * window.
 *
 * Each time when a new block allocation is need, first try to allocate from
 * its own reservation.  If it does not have a reservation window, instead of
 * looking for a free bit on bitmap first, then look up the reservation list to
 * see if it is inside somebody else's reservation window, we try to allocate a
 * reservation window for it starting from the goal first. Then do the block
 * allocation within the reservation window.
 *
 * This will avoid keeping on searching the reservation list again and
 * again when somebody is looking for a free block (without
 * reservation), and there are lots of free blocks, but they are all
 * being reserved.
 *
 * We use a red-black tree for the per-filesystem reservation list.
 */
static ext2_grpblk_t
ext2_try_to_allocate_with_rsv(struct super_block *sb, unsigned int group,
                        struct buffer_head *bitmap_bh, ext2_grpblk_t grp_goal,
                        struct ext2_reserve_window_node * my_rsv,
                        unsigned long *count)
{
        ext2_fsblk_t group_first_block, group_last_block;
        ext2_grpblk_t ret = 0;
        unsigned long num = *count;

        /*
         * we don't deal with reservation when
         * filesystem is mounted without reservation
         * or the file is not a regular file
         * or last attempt to allocate a block with reservation turned on failed
         */
        if (my_rsv == NULL) {
                return ext2_try_to_allocate(sb, group, bitmap_bh,
                                                grp_goal, count, NULL);
        }
        /*
         * grp_goal is a group relative block number (if there is a goal)
         * 0 <= grp_goal < EXT2_BLOCKS_PER_GROUP(sb)
         * first block is a filesystem wide block number
         * first block is the block number of the first block in this group
         */
        group_first_block = ext2_group_first_block_no(sb, group);
        group_last_block = group_first_block + (EXT2_BLOCKS_PER_GROUP(sb) - 1);

        /*
         * Basically we will allocate a new block from inode's reservation
         * window.
         *
         * We need to allocate a new reservation window, if:
         * a) inode does not have a reservation window; or
         * b) last attempt to allocate a block from existing reservation
         *    failed; or
         * c) we come here with a goal and with a reservation window
         *
         * We do not need to allocate a new reservation window if we come here
         * at the beginning with a goal and the goal is inside the window, or
         * we don't have a goal but already have a reservation window.
         * then we could go to allocate from the reservation window directly.
         */
        while (1) {
                if (rsv_is_empty(&my_rsv->rsv_window) || (ret < 0) ||
                        !goal_in_my_reservation(&my_rsv->rsv_window,
                                                grp_goal, group, sb)) {
                        if (my_rsv->rsv_goal_size < *count)
                                my_rsv->rsv_goal_size = *count;
                        ret = alloc_new_reservation(my_rsv, grp_goal, sb,
                                                        group, bitmap_bh);
                        if (ret < 0)
                                break;                  /* failed */

                        if (!goal_in_my_reservation(&my_rsv->rsv_window,
                                                        grp_goal, group, sb))
                                grp_goal = -1;
                } else if (grp_goal >= 0) {
                        int curr = my_rsv->rsv_end -
                                        (grp_goal + group_first_block) + 1;

                        if (curr < *count)
                                try_to_extend_reservation(my_rsv, sb,
                                                        *count - curr);
                }

                if ((my_rsv->rsv_start > group_last_block) ||
                                (my_rsv->rsv_end < group_first_block)) {
                        rsv_window_dump(&EXT2_SB(sb)->s_rsv_window_root, 1);
                        BUG();
                }
                ret = ext2_try_to_allocate(sb, group, bitmap_bh, grp_goal,
                                           &num, &my_rsv->rsv_window);
                if (ret >= 0) {
                        my_rsv->rsv_alloc_hit += num;
                        *count = num;
                        break;                          /* succeed */
                }
                num = *count;
        }
        return ret;
}

/**
 * ext2_has_free_blocks()
 * @sbi:                in-core super block structure.
 *
 * Check if filesystem has at least 1 free block available for allocation.
 */
static int ext2_has_free_blocks(struct ext2_sb_info *sbi)
{
        ext2_fsblk_t free_blocks, root_blocks;

        free_blocks = percpu_counter_read_positive(&sbi->s_freeblocks_counter);
        root_blocks = le32_to_cpu(sbi->s_es->s_r_blocks_count);
        if (free_blocks < root_blocks + 1 && !capable(CAP_SYS_RESOURCE) &&
                sbi->s_resuid != current->fsuid &&
                (sbi->s_resgid == 0 || !in_group_p (sbi->s_resgid))) {
                return 0;
        }
        return 1;
}

/*
 * ext2_new_blocks() -- core block(s) allocation function
 * @inode:              file inode
 * @goal:               given target block(filesystem wide)
 * @count:              target number of blocks to allocate
 * @errp:               error code
 *
 * ext2_new_blocks 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.
 * This function also updates quota and i_blocks field.
 */
ext2_fsblk_t ext2_new_blocks(struct inode *inode, ext2_fsblk_t goal,
                    unsigned long *count, int *errp)
{
        struct buffer_head *bitmap_bh = NULL;
        struct buffer_head *gdp_bh;
        int group_no;
        int goal_group;
        ext2_grpblk_t grp_target_blk;   /* blockgroup relative goal block */
        ext2_grpblk_t grp_alloc_blk;    /* blockgroup-relative allocated block*/
        ext2_fsblk_t ret_block;         /* filesyetem-wide allocated block */
        int bgi;                        /* blockgroup iteration index */
        int performed_allocation = 0;
        ext2_grpblk_t free_blocks;      /* number of free blocks in a group */
        struct super_block *sb;
        struct ext2_group_desc *gdp;
        struct ext2_super_block *es;
        struct ext2_sb_info *sbi;
        struct ext2_reserve_window_node *my_rsv = NULL;
        struct ext2_block_alloc_info *block_i;
        unsigned short windowsz = 0;
        unsigned long ngroups;
        unsigned long num = *count;

        *errp = -ENOSPC;
        sb = inode->i_sb;
        if (!sb) {
                printk("ext2_new_blocks: nonexistent device");
                return 0;
        }

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

        sbi = EXT2_SB(sb);
        es = EXT2_SB(sb)->s_es;
        ext2_debug("goal=%lu.\n", goal);
        /*
         * Allocate a block from reservation only when
         * filesystem is mounted with reservation(default,-o reservation), and
         * it's a regular file, and
         * the desired window size is greater than 0 (One could use ioctl
         * command EXT2_IOC_SETRSVSZ to set the window size to 0 to turn off
         * reservation on that particular file)
         */
        block_i = EXT2_I(inode)->i_block_alloc_info;
        if (block_i) {
                windowsz = block_i->rsv_window_node.rsv_goal_size;
                if (windowsz > 0)
                        my_rsv = &block_i->rsv_window_node;
        }

        if (!ext2_has_free_blocks(sbi)) {
                *errp = -ENOSPC;
                goto out;
        }

        /*
         * 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);
        group_no = (goal - le32_to_cpu(es->s_first_data_block)) /
                        EXT2_BLOCKS_PER_GROUP(sb);
        goal_group = group_no;
retry_alloc:
        gdp = ext2_get_group_desc(sb, group_no, &gdp_bh);
        if (!gdp)
                goto io_error;

        free_blocks = le16_to_cpu(gdp->bg_free_blocks_count);
        /*
         * if there is not enough free blocks to make a new resevation
         * turn off reservation for this allocation
         */
        if (my_rsv && (free_blocks < windowsz)
                && (rsv_is_empty(&my_rsv->rsv_window)))
                my_rsv = NULL;

        if (free_blocks > 0) {
                grp_target_blk = ((goal - le32_to_cpu(es->s_first_data_block)) %
                                EXT2_BLOCKS_PER_GROUP(sb));
                bitmap_bh = read_block_bitmap(sb, group_no);
                if (!bitmap_bh)
                        goto io_error;
                grp_alloc_blk = ext2_try_to_allocate_with_rsv(sb, group_no,
                                        bitmap_bh, grp_target_blk,
                                        my_rsv, &num);
                if (grp_alloc_blk >= 0)
                        goto allocated;
        }

        ngroups = EXT2_SB(sb)->s_groups_count;
        smp_rmb();

        /*
         * Now search the rest of the groups.  We assume that 
         * i and gdp correctly point to the last group visited.
         */
        for (bgi = 0; bgi < ngroups; bgi++) {
                group_no++;
                if (group_no >= ngroups)
                        group_no = 0;
                gdp = ext2_get_group_desc(sb, group_no, &gdp_bh);
                if (!gdp)
                        goto io_error;

                free_blocks = le16_to_cpu(gdp->bg_free_blocks_count);
                /*
                 * skip this group if the number of
                 * free blocks is less than half of the reservation
                 * window size.
                 */
                if (free_blocks <= (windowsz/2))
                        continue;

                brelse(bitmap_bh);
                bitmap_bh = read_block_bitmap(sb, group_no);
                if (!bitmap_bh)
                        goto io_error;
                /*
                 * try to allocate block(s) from this group, without a goal(-1).
                 */
                grp_alloc_blk = ext2_try_to_allocate_with_rsv(sb, group_no,
                                        bitmap_bh, -1, my_rsv, &num);
                if (grp_alloc_blk >= 0)
                        goto allocated;
        }
        /*
         * We may end up a bogus ealier ENOSPC error due to
         * filesystem is "full" of reservations, but
         * there maybe indeed free blocks avaliable on disk
         * In this case, we just forget about the reservations
         * just do block allocation as without reservations.
         */
        if (my_rsv) {
                my_rsv = NULL;
                windowsz = 0;
                group_no = goal_group;
                goto retry_alloc;
        }
        /* No space left on the device */
        *errp = -ENOSPC;
        goto out;

allocated:

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

        ret_block = grp_alloc_blk + ext2_group_first_block_no(sb, group_no);

        if (in_range(le32_to_cpu(gdp->bg_block_bitmap), ret_block, num) ||
            in_range(le32_to_cpu(gdp->bg_inode_bitmap), ret_block, num) ||
            in_range(ret_block, le32_to_cpu(gdp->bg_inode_table),
                      EXT2_SB(sb)->s_itb_per_group) ||
            in_range(ret_block + num - 1, le32_to_cpu(gdp->bg_inode_table),
                      EXT2_SB(sb)->s_itb_per_group)) {
                ext2_error(sb, "ext2_new_blocks",
                            "Allocating block in system zone - "
                            "blocks from "E2FSBLK", length %lu",
                            ret_block, num);
                goto out;
        }

        performed_allocation = 1;

        if (ret_block + num - 1 >= le32_to_cpu(es->s_blocks_count)) {
                ext2_error(sb, "ext2_new_blocks",
                            "block("E2FSBLK") >= blocks count(%d) - "
                            "block_group = %d, es == %p ", ret_block,
                        le32_to_cpu(es->s_blocks_count), group_no, es);
                goto out;
        }

        group_adjust_blocks(sb, group_no, gdp, gdp_bh, -num);
        percpu_counter_sub(&sbi->s_freeblocks_counter, num);

        mark_buffer_dirty(bitmap_bh);
        if (sb->s_flags & MS_SYNCHRONOUS)
                sync_dirty_buffer(bitmap_bh);

        *errp = 0;
        brelse(bitmap_bh);
        DQUOT_FREE_BLOCK(inode, *count-num);
        *count = num;
        return ret_block;

io_error:
        *errp = -EIO;
out:
        /*
         * Undo the block allocation
         */
        if (!performed_allocation)
                DQUOT_FREE_BLOCK(inode, *count);
        brelse(bitmap_bh);
        return 0;
}

ext2_fsblk_t ext2_new_block(struct inode *inode, unsigned long goal, int *errp)
{
        unsigned long count = 1;

        return ext2_new_blocks(inode, goal, &count, errp);
}

#ifdef EXT2FS_DEBUG

static const int nibblemap[] = {4, 3, 3, 2, 3, 2, 2, 1, 3, 2, 2, 1, 2, 1, 1, 0};

unsigned long ext2_count_free (struct buffer_head * map, unsigned int numchars)
{
        unsigned int i;
        unsigned long sum = 0;

        if (!map)
                return (0);
        for (i = 0; i < numchars; i++)
                sum += nibblemap[map->b_data[i] & 0xf] +
                        nibblemap[(map->b_data[i] >> 4) & 0xf];
        return (sum);
}

#endif  /*  EXT2FS_DEBUG  */

unsigned long ext2_count_free_blocks (struct super_block * sb)
{
        struct ext2_group_desc * desc;
        unsigned long desc_count = 0;
        int i;
#ifdef EXT2FS_DEBUG
        unsigned long bitmap_count, x;
        struct ext2_super_block *es;

        es = EXT2_SB(sb)->s_es;
        desc_count = 0;
        bitmap_count = 0;
        desc = NULL;
        for (i = 0; i < EXT2_SB(sb)->s_groups_count; i++) {
                struct buffer_head *bitmap_bh;
                desc = ext2_get_group_desc (sb, i, NULL);
                if (!desc)
                        continue;
                desc_count += le16_to_cpu(desc->bg_free_blocks_count);
                bitmap_bh = read_block_bitmap(sb, i);
                if (!bitmap_bh)
                        continue;
                
                x = ext2_count_free(bitmap_bh, sb->s_blocksize);
                printk ("group %d: stored = %d, counted = %lu\n",
                        i, le16_to_cpu(desc->bg_free_blocks_count), x);
                bitmap_count += x;
                brelse(bitmap_bh);
        }
        printk("ext2_count_free_blocks: stored = %lu, computed = %lu, %lu\n",
                (long)le32_to_cpu(es->s_free_blocks_count),
                desc_count, bitmap_count);
        return bitmap_count;
#else
        for (i = 0; i < EXT2_SB(sb)->s_groups_count; i++) {
                desc = ext2_get_group_desc (sb, i, NULL);
                if (!desc)
                        continue;
                desc_count += le16_to_cpu(desc->bg_free_blocks_count);
        }
        return desc_count;
#endif
}

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

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

static int ext2_group_sparse(int group)
{
        if (group <= 1)
                return 1;
        return (test_root(group, 3) || test_root(group, 5) ||
                test_root(group, 7));
}

/**
 *      ext2_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 ext2_bg_has_super(struct super_block *sb, int group)
{
        if (EXT2_HAS_RO_COMPAT_FEATURE(sb,EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER)&&
            !ext2_group_sparse(group))
                return 0;
        return 1;
}

/**
 *      ext2_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 ext2_bg_num_gdb(struct super_block *sb, int group)
{
        if (EXT2_HAS_RO_COMPAT_FEATURE(sb,EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER)&&
            !ext2_group_sparse(group))
                return 0;
        return EXT2_SB(sb)->s_gdb_count;
}