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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);

      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);

      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;
}


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