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 // SPDX-License-Identifier: GPL-2.0
 /*
  *  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/slab.h>
 #include <linux/sched.h>
 #include <linux/cred.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) {
         WARN(1, "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]) {
         WARN(1, "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;
 }
 
 static int ext2_valid_block_bitmap(struct super_block *sb,
                     struct ext2_group_desc *desc,
                     unsigned int block_group,
                     struct buffer_head *bh)
 {
     ext2_grpblk_t offset;
     ext2_grpblk_t next_zero_bit;
     ext2_fsblk_t bitmap_blk;
     ext2_fsblk_t group_first_block;
 
     group_first_block = ext2_group_first_block_no(sb, block_group);
 
     /* check whether block bitmap block number is set */
     bitmap_blk = le32_to_cpu(desc->bg_block_bitmap);
     offset = bitmap_blk - group_first_block;
     if (!ext2_test_bit(offset, bh->b_data))
         /* bad block bitmap */
         goto err_out;
 
     /* check whether the inode bitmap block number is set */
     bitmap_blk = le32_to_cpu(desc->bg_inode_bitmap);
     offset = bitmap_blk - group_first_block;
     if (!ext2_test_bit(offset, bh->b_data))
         /* bad block bitmap */
         goto err_out;
 
     /* check whether the inode table block number is set */
     bitmap_blk = le32_to_cpu(desc->bg_inode_table);
     offset = bitmap_blk - group_first_block;
     next_zero_bit = ext2_find_next_zero_bit(bh->b_data,
                 offset + EXT2_SB(sb)->s_itb_per_group,
                 offset);
     if (next_zero_bit >= offset + EXT2_SB(sb)->s_itb_per_group)
         /* good bitmap for inode tables */
         return 1;
 
 err_out:
     ext2_error(sb, __func__,
             "Invalid block bitmap - "
             "block_group = %d, block = %lu",
             block_group, bitmap_blk);
     return 0;
 }
 
 /*
  * Read the bitmap for a given block_group,and validate the
  * bits for block/inode/inode tables are set in the bitmaps
  *
  * Return buffer_head on success or NULL in case of failure.
  */
 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;
     ext2_fsblk_t bitmap_blk;
 
     desc = ext2_get_group_desc(sb, block_group, NULL);
     if (!desc)
         return NULL;
     bitmap_blk = le32_to_cpu(desc->bg_block_bitmap);
     bh = sb_getblk(sb, bitmap_blk);
     if (unlikely(!bh)) {
         ext2_error(sb, __func__,
                 "Cannot read block bitmap - "
                 "block_group = %d, block_bitmap = %u",
                 block_group, le32_to_cpu(desc->bg_block_bitmap));
         return NULL;
     }
     if (likely(bh_uptodate_or_lock(bh)))
         return bh;
 
     if (bh_submit_read(bh) < 0) {
         brelse(bh);
         ext2_error(sb, __func__,
                 "Cannot read block bitmap - "
                 "block_group = %d, block_bitmap = %u",
                 block_group, le32_to_cpu(desc->bg_block_bitmap));
         return NULL;
     }
 
     ext2_valid_block_bitmap(sb, desc, block_group, bh);
     /*
      * file system mounted not to panic on error, continue with corrupt
      * bitmap
      */
     return bh;
 }
 
 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));
         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
  * @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");
     BUG_ON(bad);
 }
 #define rsv_window_dump(root, verbose) \
     __rsv_window_dump((root), (verbose), __func__)
 #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 = ext2_group_last_block_no(sb, group);
 
     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()
  * @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;
     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() -- Free given blocks and update quota and i_blocks
  * @inode:      inode
  * @block:      start physical 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 (!ext2_data_block_valid(sbi, block, 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, __func__,
                 "bit already cleared for block %lu", block + i);
         } else {
             group_freed++;
         }
     }
 
     mark_buffer_dirty(bitmap_bh);
     if (sb->s_flags & SB_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);
     if (freed) {
         percpu_counter_add(&sbi->s_freeblocks_counter, freed);
         dquot_free_block_nodirty(inode, freed);
         mark_inode_dirty(inode);
     }
 }
 
 /**
  * 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
  * @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_group_first_block_no(sb, group);
     ext2_fsblk_t group_last_block = ext2_group_last_block_no(sb, group);
         ext2_grpblk_t start, end;
     unsigned long num = 0;
 
     start = 0;
     end = group_last_block - group_first_block + 1;
     /* we do allocation within the reservation window if we have a window */
     if (my_rsv) {
         if (my_rsv->_rsv_start >= group_first_block)
             start = my_rsv->_rsv_start - group_first_block;
         if (my_rsv->_rsv_end < group_last_block)
             end = my_rsv->_rsv_end - group_first_block + 1;
         if (grp_goal < start || grp_goal >= end)
             grp_goal = -1;
     }
     BUG_ON(start > EXT2_BLOCKS_PER_GROUP(sb));
 
     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--)
                 ;
         }
     }
 
     for (; num < *count && grp_goal < end; grp_goal++) {
         if (ext2_set_bit_atomic(sb_bgl_lock(EXT2_SB(sb), group),
                     grp_goal, bitmap_bh->b_data)) {
             if (num == 0)
                 continue;
             break;
         }
         num++;
     }
 
     if (num == 0)
         goto fail_access;
 
     *count = num;
     return grp_goal - num;
 fail_access:
     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.
  *
  *  @sb: the super block.
  *
  *  @start_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 available 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
  *
  *  @my_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 = ext2_group_last_block_no(sb, group);
 
     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 = ext2_group_last_block_no(sb, group);
 
     /*
      * 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) &&
         !uid_eq(sbi->s_resuid, current_fsuid()) &&
         (gid_eq(sbi->s_resgid, GLOBAL_ROOT_GID) ||
          !in_group_p (sbi->s_resgid))) {
         return 0;
     }
     return 1;
 }
 
 /*
  * Returns 1 if the passed-in block region is valid; 0 if some part overlaps
  * with filesystem metadata blocks.
  */
 int ext2_data_block_valid(struct ext2_sb_info *sbi, ext2_fsblk_t start_blk,
               unsigned int count)
 {
     if ((start_blk <= le32_to_cpu(sbi->s_es->s_first_data_block)) ||
         (start_blk + count - 1 < start_blk) ||
         (start_blk + count - 1 >= le32_to_cpu(sbi->s_es->s_blocks_count)))
         return 0;
 
     /* Ensure we do not step over superblock */
     if ((start_blk <= sbi->s_sb_block) &&
         (start_blk + count - 1 >= sbi->s_sb_block))
         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;
     int ret;
 
     *errp = -ENOSPC;
     sb = inode->i_sb;
 
     /*
      * Check quota for allocation of this block.
      */
     ret = dquot_alloc_block(inode, num);
     if (ret) {
         *errp = ret;
         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)
         && (free_blocks > 0)
         && (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));
         /*
          * In case we retry allocation (due to fs reservation not
          * working out or fs corruption), the bitmap_bh is non-null
          * pointer and we have to release it before calling
          * read_block_bitmap().
          */
         brelse(bitmap_bh);
         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
      * group_no 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 (and avoid loading bitmap) if there
          * are no free blocks
          */
         if (!free_blocks)
             continue;
         /*
          * skip this group if the number of
          * free blocks is less than half of the reservation
          * window size.
          */
         if (my_rsv && (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 earlier ENOSPC error due to
      * filesystem is "full" of reservations, but
      * there maybe indeed free blocks available 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);
         /*
          * ext2_try_to_allocate marked the blocks we allocated as in
          * use.  So we may want to selectively mark some of the blocks
          * as free
          */
         num = *count;
         goto retry_alloc;
     }
 
     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 & SB_SYNCHRONOUS)
         sync_dirty_buffer(bitmap_bh);
 
     *errp = 0;
     brelse(bitmap_bh);
     if (num < *count) {
         dquot_free_block_nodirty(inode, *count-num);
         mark_inode_dirty(inode);
         *count = num;
     }
     return ret_block;
 
 io_error:
     *errp = -EIO;
 out:
     /*
      * Undo the block allocation
      */
     if (!performed_allocation) {
         dquot_free_block_nodirty(inode, *count);
         mark_inode_dirty(inode);
     }
     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
 
 unsigned long ext2_count_free(struct buffer_head *map, unsigned int numchars)
 {
     return numchars * BITS_PER_BYTE - memweight(map->b_data, numchars);
 }
 
 #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)
 {
     return ext2_bg_has_super(sb, group) ? EXT2_SB(sb)->s_gdb_count : 0;
 }
 

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