fs/ext2/balloc.c - kernel/msm-4.9 - Gitiles

 /*
  *  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 <linux/config.h>
 #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_read_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;
 }

 /*
  * Set sb->s_dirt here because the superblock was "logically" altered.  We
  * need to recalculate its free blocks count and flush it out.
  */
 static int reserve_blocks(struct super_block *sb, int count)
 {
 	struct ext2_sb_info *sbi = EXT2_SB(sb);
 	struct ext2_super_block *es = sbi->s_es;
 	unsigned free_blocks;
 	unsigned root_blocks;

 	free_blocks = percpu_counter_read_positive(&sbi->s_freeblocks_counter);
 	root_blocks = le32_to_cpu(es->s_r_blocks_count);

 	if (free_blocks < count)
 		count = free_blocks;

 	if (free_blocks < root_blocks + count && !capable(CAP_SYS_RESOURCE) &&
 	    sbi->s_resuid != current->fsuid &&
 	    (sbi->s_resgid == 0 || !in_group_p (sbi->s_resgid))) {
 		/*
 		 * We are too close to reserve and we are not privileged.
 		 * Can we allocate anything at all?
 		 */
 		if (free_blocks > root_blocks)
 			count = free_blocks - root_blocks;
 		else
 			return 0;
 	}

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

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

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

 static int group_reserve_blocks(struct ext2_sb_info *sbi, int group_no,
 	struct ext2_group_desc *desc, struct buffer_head *bh, int count)
 {
 	unsigned free_blocks;

 	if (!desc->bg_free_blocks_count)
 		return 0;

 	spin_lock(sb_bgl_lock(sbi, group_no));
 	free_blocks = le16_to_cpu(desc->bg_free_blocks_count);
 	if (free_blocks < count)
 		count = free_blocks;
 	desc->bg_free_blocks_count = cpu_to_le16(free_blocks - count);
 	spin_unlock(sb_bgl_lock(sbi, group_no));
 	mark_buffer_dirty(bh);
 	return count;
 }

 static void group_release_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);
 	}
 }

 /* Free given blocks, update quota and i_blocks field */
 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_release_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);
 }

 static int grab_block(spinlock_t *lock, char *map, unsigned size, int goal)
 {
 	int k;
 	char *p, *r;

 	if (!ext2_test_bit(goal, map))
 		goto got_it;

 repeat:
 	if (goal) {
 		/*
 		 * 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..
 		 */
 		k = (goal + 63) & ~63;
 		goal = ext2_find_next_zero_bit(map, k, goal);
 		if (goal < k)
 			goto got_it;
 		/*
 		 * Search in the remainder of the current group.
 		 */
 	}

 	p = map + (goal >> 3);
 	r = memscan(p, 0, (size - goal + 7) >> 3);
 	k = (r - map) << 3;
 	if (k < size) {
 		/*
 		 * We have succeeded in finding a free byte in the block
 		 * bitmap.  Now search backwards to find the start of this
 		 * group of free blocks - won't take more than 7 iterations.
 		 */
 		for (goal = k; goal && !ext2_test_bit (goal - 1, map); goal--)
 			;
 		goto got_it;
 	}

 	k = ext2_find_next_zero_bit ((u32 *)map, size, goal);
 	if (k < size) {
 		goal = k;
 		goto got_it;
 	}
 	return -1;
 got_it:
 	if (ext2_set_bit_atomic(lock, goal, (void *) map))
 		goto repeat;
 	return goal;
 }

 /*
  * ext2_new_block uses a goal block to assist allocation.  If the goal is
  * free, or there is a free block within 32 blocks of the goal, that block
  * is allocated.  Otherwise a forward search is made for a free block; within
  * each block group the search first looks for an entire free byte in the block
  * bitmap, and then for any free bit if that fails.
  * This function also updates quota and i_blocks field.
  */
 int ext2_new_block(struct inode *inode, unsigned long goal,
 			u32 *prealloc_count, u32 *prealloc_block, int *err)
 {
 	struct buffer_head *bitmap_bh = NULL;
 	struct buffer_head *gdp_bh;	/* bh2 */
 	struct ext2_group_desc *desc;
 	int group_no;			/* i */
 	int ret_block;			/* j */
 	int group_idx;			/* k */
 	int target_block;		/* tmp */
 	int block = 0;
 	struct super_block *sb = inode->i_sb;
 	struct ext2_sb_info *sbi = EXT2_SB(sb);
 	struct ext2_super_block *es = sbi->s_es;
 	unsigned group_size = EXT2_BLOCKS_PER_GROUP(sb);
 	unsigned prealloc_goal = es->s_prealloc_blocks;
 	unsigned group_alloc = 0, es_alloc, dq_alloc;
 	int nr_scanned_groups;

 	if (!prealloc_goal--)
 		prealloc_goal = EXT2_DEFAULT_PREALLOC_BLOCKS - 1;
 	if (!prealloc_count || *prealloc_count)
 		prealloc_goal = 0;

 	if (DQUOT_ALLOC_BLOCK(inode, 1)) {
 		*err = -EDQUOT;
 		goto out;
 	}

 	while (prealloc_goal && DQUOT_PREALLOC_BLOCK(inode, prealloc_goal))
 		prealloc_goal--;

 	dq_alloc = prealloc_goal + 1;
 	es_alloc = reserve_blocks(sb, dq_alloc);
 	if (!es_alloc) {
 		*err = -ENOSPC;
 		goto out_dquot;
 	}

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

 	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)) / group_size;
 	desc = ext2_get_group_desc (sb, group_no, &gdp_bh);
 	if (!desc) {
 		/*
 		 * gdp_bh may still be uninitialised.  But group_release_blocks
 		 * will not touch it because group_alloc is zero.
 		 */
 		goto io_error;
 	}

 	group_alloc = group_reserve_blocks(sbi, group_no, desc,
 					gdp_bh, es_alloc);
 	if (group_alloc) {
 		ret_block = ((goal - le32_to_cpu(es->s_first_data_block)) %
 					group_size);
 		brelse(bitmap_bh);
 		bitmap_bh = read_block_bitmap(sb, group_no);
 		if (!bitmap_bh)
 			goto io_error;

 		ext2_debug("goal is at %d:%d.\n", group_no, ret_block);

 		ret_block = grab_block(sb_bgl_lock(sbi, group_no),
 				bitmap_bh->b_data, group_size, ret_block);
 		if (ret_block >= 0)
 			goto got_block;
 		group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
 		group_alloc = 0;
 	}

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

 	/*
 	 * Now search the rest of the groups.  We assume that
 	 * i and desc correctly point to the last group visited.
 	 */
 	nr_scanned_groups = 0;
 retry:
 	for (group_idx = 0; !group_alloc &&
 			group_idx < sbi->s_groups_count; group_idx++) {
 		group_no++;
 		if (group_no >= sbi->s_groups_count)
 			group_no = 0;
 		desc = ext2_get_group_desc(sb, group_no, &gdp_bh);
 		if (!desc)
 			goto io_error;
 		group_alloc = group_reserve_blocks(sbi, group_no, desc,
 						gdp_bh, es_alloc);
 	}
 	if (!group_alloc) {
 		*err = -ENOSPC;
 		goto out_release;
 	}
 	brelse(bitmap_bh);
 	bitmap_bh = read_block_bitmap(sb, group_no);
 	if (!bitmap_bh)
 		goto io_error;

 	ret_block = grab_block(sb_bgl_lock(sbi, group_no), bitmap_bh->b_data,
 				group_size, 0);
 	if (ret_block < 0) {
 		/*
 		 * If a free block counter is corrupted we can loop inifintely.
 		 * Detect that here.
 		 */
 		nr_scanned_groups++;
 		if (nr_scanned_groups > 2 * sbi->s_groups_count) {
 			ext2_error(sb, "ext2_new_block",
 				"corrupted free blocks counters");
 			goto io_error;
 		}
 		/*
 		 * Someone else grabbed the last free block in this blockgroup
 		 * before us.  Retry the scan.
 		 */
 		group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
 		group_alloc = 0;
 		goto retry;
 	}

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

 	target_block = ret_block + group_no * group_size +
 			le32_to_cpu(es->s_first_data_block);

 	if (target_block == le32_to_cpu(desc->bg_block_bitmap) ||
 	    target_block == le32_to_cpu(desc->bg_inode_bitmap) ||
 	    in_range(target_block, le32_to_cpu(desc->bg_inode_table),
 		      sbi->s_itb_per_group))
 		ext2_error (sb, "ext2_new_block",
 			    "Allocating block in system zone - "
 			    "block = %u", target_block);

 	if (target_block >= le32_to_cpu(es->s_blocks_count)) {
 		ext2_error (sb, "ext2_new_block",
 			    "block(%d) >= blocks count(%d) - "
 			    "block_group = %d, es == %p ", ret_block,
 			le32_to_cpu(es->s_blocks_count), group_no, es);
 		goto io_error;
 	}
 	block = target_block;

 	/* OK, we _had_ allocated something */
 	ext2_debug("found bit %d\n", ret_block);

 	dq_alloc--;
 	es_alloc--;
 	group_alloc--;

 	/*
 	 * Do block preallocation now if required.
 	 */
 	write_lock(&EXT2_I(inode)->i_meta_lock);
 	if (group_alloc && !*prealloc_count) {
 		unsigned n;

 		for (n = 0; n < group_alloc && ++ret_block < group_size; n++) {
 			if (ext2_set_bit_atomic(sb_bgl_lock(sbi, group_no),
 						ret_block,
 						(void*) bitmap_bh->b_data))
  				break;
 		}
 		*prealloc_block = block + 1;
 		*prealloc_count = n;
 		es_alloc -= n;
 		dq_alloc -= n;
 		group_alloc -= n;
 	}
 	write_unlock(&EXT2_I(inode)->i_meta_lock);

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

 	ext2_debug ("allocating block %d. ", block);

 	*err = 0;
 out_release:
 	group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
 	release_blocks(sb, es_alloc);
 out_dquot:
 	DQUOT_FREE_BLOCK(inode, dq_alloc);
 out:
 	brelse(bitmap_bh);
 	return block;

 io_error:
 	*err = -EIO;
 	goto out_release;
 }

 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;

 	lock_super (sb);
 	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);
 	unlock_super (sb);
 	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
 block_in_use(unsigned long block, struct super_block *sb, unsigned char *map)
 {
 	return ext2_test_bit ((block -
 		le32_to_cpu(EXT2_SB(sb)->s_es->s_first_data_block)) %
 			 EXT2_BLOCKS_PER_GROUP(sb), map);
 }

 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;
 }
	/*
	* 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 <linux/config.h>
	#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_read_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;
	}

	/*
	* Set sb->s_dirt here because the superblock was "logically" altered. We
	* need to recalculate its free blocks count and flush it out.
	*/
	static int reserve_blocks(struct super_block *sb, int count)
	{
	struct ext2_sb_info *sbi = EXT2_SB(sb);
	struct ext2_super_block *es = sbi->s_es;
	unsigned free_blocks;
	unsigned root_blocks;

	free_blocks = percpu_counter_read_positive(&sbi->s_freeblocks_counter);
	root_blocks = le32_to_cpu(es->s_r_blocks_count);

	if (free_blocks < count)
	count = free_blocks;

	if (free_blocks < root_blocks + count && !capable(CAP_SYS_RESOURCE) &&
	sbi->s_resuid != current->fsuid &&
	(sbi->s_resgid == 0 \|\| !in_group_p (sbi->s_resgid))) {
	/*
	* We are too close to reserve and we are not privileged.
	* Can we allocate anything at all?
	*/
	if (free_blocks > root_blocks)
	count = free_blocks - root_blocks;
	else
	return 0;
	}

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

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

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

	static int group_reserve_blocks(struct ext2_sb_info *sbi, int group_no,
	struct ext2_group_desc desc, struct buffer_head bh, int count)
	{
	unsigned free_blocks;

	if (!desc->bg_free_blocks_count)
	return 0;

	spin_lock(sb_bgl_lock(sbi, group_no));
	free_blocks = le16_to_cpu(desc->bg_free_blocks_count);
	if (free_blocks < count)
	count = free_blocks;
	desc->bg_free_blocks_count = cpu_to_le16(free_blocks - count);
	spin_unlock(sb_bgl_lock(sbi, group_no));
	mark_buffer_dirty(bh);
	return count;
	}

	static void group_release_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);
	}
	}

	/* Free given blocks, update quota and i_blocks field */
	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_release_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);
	}

	static int grab_block(spinlock_t lock, char map, unsigned size, int goal)
	{
	int k;
	char p, r;

	if (!ext2_test_bit(goal, map))
	goto got_it;

	repeat:
	if (goal) {
	/*
	* 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..
	*/
	k = (goal + 63) & ~63;
	goal = ext2_find_next_zero_bit(map, k, goal);
	if (goal < k)
	goto got_it;
	/*
	* Search in the remainder of the current group.
	*/
	}

	p = map + (goal >> 3);
	r = memscan(p, 0, (size - goal + 7) >> 3);
	k = (r - map) << 3;
	if (k < size) {
	/*
	* We have succeeded in finding a free byte in the block
	* bitmap. Now search backwards to find the start of this
	* group of free blocks - won't take more than 7 iterations.
	*/
	for (goal = k; goal && !ext2_test_bit (goal - 1, map); goal--)
	;
	goto got_it;
	}

	k = ext2_find_next_zero_bit ((u32 *)map, size, goal);
	if (k < size) {
	goal = k;
	goto got_it;
	}
	return -1;
	got_it:
	if (ext2_set_bit_atomic(lock, goal, (void *) map))
	goto repeat;
	return goal;
	}

	/*
	* ext2_new_block uses a goal block to assist allocation. If the goal is
	* free, or there is a free block within 32 blocks of the goal, that block
	* is allocated. Otherwise a forward search is made for a free block; within
	* each block group the search first looks for an entire free byte in the block
	* bitmap, and then for any free bit if that fails.
	* This function also updates quota and i_blocks field.
	*/
	int ext2_new_block(struct inode *inode, unsigned long goal,
	u32 prealloc_count, u32 prealloc_block, int *err)
	{
	struct buffer_head *bitmap_bh = NULL;
	struct buffer_head gdp_bh; / bh2 */
	struct ext2_group_desc *desc;
	int group_no; /* i */
	int ret_block; /* j */
	int group_idx; /* k */
	int target_block; /* tmp */
	int block = 0;
	struct super_block *sb = inode->i_sb;
	struct ext2_sb_info *sbi = EXT2_SB(sb);
	struct ext2_super_block *es = sbi->s_es;
	unsigned group_size = EXT2_BLOCKS_PER_GROUP(sb);
	unsigned prealloc_goal = es->s_prealloc_blocks;
	unsigned group_alloc = 0, es_alloc, dq_alloc;
	int nr_scanned_groups;

	if (!prealloc_goal--)
	prealloc_goal = EXT2_DEFAULT_PREALLOC_BLOCKS - 1;
	if (!prealloc_count \|\| *prealloc_count)
	prealloc_goal = 0;

	if (DQUOT_ALLOC_BLOCK(inode, 1)) {
	*err = -EDQUOT;
	goto out;
	}

	while (prealloc_goal && DQUOT_PREALLOC_BLOCK(inode, prealloc_goal))
	prealloc_goal--;

	dq_alloc = prealloc_goal + 1;
	es_alloc = reserve_blocks(sb, dq_alloc);
	if (!es_alloc) {
	*err = -ENOSPC;
	goto out_dquot;
	}

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

	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)) / group_size;
	desc = ext2_get_group_desc (sb, group_no, &gdp_bh);
	if (!desc) {
	/*
	* gdp_bh may still be uninitialised. But group_release_blocks
	* will not touch it because group_alloc is zero.
	*/
	goto io_error;
	}

	group_alloc = group_reserve_blocks(sbi, group_no, desc,
	gdp_bh, es_alloc);
	if (group_alloc) {
	ret_block = ((goal - le32_to_cpu(es->s_first_data_block)) %
	group_size);
	brelse(bitmap_bh);
	bitmap_bh = read_block_bitmap(sb, group_no);
	if (!bitmap_bh)
	goto io_error;

	ext2_debug("goal is at %d:%d.\n", group_no, ret_block);

	ret_block = grab_block(sb_bgl_lock(sbi, group_no),
	bitmap_bh->b_data, group_size, ret_block);
	if (ret_block >= 0)
	goto got_block;
	group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
	group_alloc = 0;
	}

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

	/*
	* Now search the rest of the groups. We assume that
	* i and desc correctly point to the last group visited.
	*/
	nr_scanned_groups = 0;
	retry:
	for (group_idx = 0; !group_alloc &&
	group_idx < sbi->s_groups_count; group_idx++) {
	group_no++;
	if (group_no >= sbi->s_groups_count)
	group_no = 0;
	desc = ext2_get_group_desc(sb, group_no, &gdp_bh);
	if (!desc)
	goto io_error;
	group_alloc = group_reserve_blocks(sbi, group_no, desc,
	gdp_bh, es_alloc);
	}
	if (!group_alloc) {
	*err = -ENOSPC;
	goto out_release;
	}
	brelse(bitmap_bh);
	bitmap_bh = read_block_bitmap(sb, group_no);
	if (!bitmap_bh)
	goto io_error;

	ret_block = grab_block(sb_bgl_lock(sbi, group_no), bitmap_bh->b_data,
	group_size, 0);
	if (ret_block < 0) {
	/*
	* If a free block counter is corrupted we can loop inifintely.
	* Detect that here.
	*/
	nr_scanned_groups++;
	if (nr_scanned_groups > 2 * sbi->s_groups_count) {
	ext2_error(sb, "ext2_new_block",
	"corrupted free blocks counters");
	goto io_error;
	}
	/*
	* Someone else grabbed the last free block in this blockgroup
	* before us. Retry the scan.
	*/
	group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
	group_alloc = 0;
	goto retry;
	}

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

	target_block = ret_block + group_no * group_size +
	le32_to_cpu(es->s_first_data_block);

	if (target_block == le32_to_cpu(desc->bg_block_bitmap) \|\|
	target_block == le32_to_cpu(desc->bg_inode_bitmap) \|\|
	in_range(target_block, le32_to_cpu(desc->bg_inode_table),
	sbi->s_itb_per_group))
	ext2_error (sb, "ext2_new_block",
	"Allocating block in system zone - "
	"block = %u", target_block);

	if (target_block >= le32_to_cpu(es->s_blocks_count)) {
	ext2_error (sb, "ext2_new_block",
	"block(%d) >= blocks count(%d) - "
	"block_group = %d, es == %p ", ret_block,
	le32_to_cpu(es->s_blocks_count), group_no, es);
	goto io_error;
	}
	block = target_block;

	/* OK, we _had_ allocated something */
	ext2_debug("found bit %d\n", ret_block);

	dq_alloc--;
	es_alloc--;
	group_alloc--;

	/*
	* Do block preallocation now if required.
	*/
	write_lock(&EXT2_I(inode)->i_meta_lock);
	if (group_alloc && !*prealloc_count) {
	unsigned n;

	for (n = 0; n < group_alloc && ++ret_block < group_size; n++) {
	if (ext2_set_bit_atomic(sb_bgl_lock(sbi, group_no),
	ret_block,
	(void*) bitmap_bh->b_data))
	break;
	}
	*prealloc_block = block + 1;
	*prealloc_count = n;
	es_alloc -= n;
	dq_alloc -= n;
	group_alloc -= n;
	}
	write_unlock(&EXT2_I(inode)->i_meta_lock);

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

	ext2_debug ("allocating block %d. ", block);

	*err = 0;
	out_release:
	group_release_blocks(sb, group_no, desc, gdp_bh, group_alloc);
	release_blocks(sb, es_alloc);
	out_dquot:
	DQUOT_FREE_BLOCK(inode, dq_alloc);
	out:
	brelse(bitmap_bh);
	return block;

	io_error:
	*err = -EIO;
	goto out_release;
	}

	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;

	lock_super (sb);
	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);
	unlock_super (sb);
	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
	block_in_use(unsigned long block, struct super_block sb, unsigned char map)
	{
	return ext2_test_bit ((block -
	le32_to_cpu(EXT2_SB(sb)->s_es->s_first_data_block)) %
	EXT2_BLOCKS_PER_GROUP(sb), map);
	}

	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;
	}