/*
   * Copyright (C) 2004, OGAWA Hirofumi
   * Released under GPL v2.
   */
  
  #include <linux/module.h>
  #include <linux/fs.h>
  #include <linux/msdos_fs.h>
  #include <linux/blkdev.h>
  #include "fat.h"
  
  struct fatent_operations {
  	void (*ent_blocknr)(struct super_block *, int, int *, sector_t *);
  	void (*ent_set_ptr)(struct fat_entry *, int);
  	int (*ent_bread)(struct super_block *, struct fat_entry *,
  			 int, sector_t);
  	int (*ent_get)(struct fat_entry *);
  	void (*ent_put)(struct fat_entry *, int);
  	int (*ent_next)(struct fat_entry *);
  };
  
  static DEFINE_SPINLOCK(fat12_entry_lock);
  
  static void fat12_ent_blocknr(struct super_block *sb, int entry,
  			      int *offset, sector_t *blocknr)
  {
  	struct msdos_sb_info *sbi = MSDOS_SB(sb);
  	int bytes = entry + (entry >> 1);
  	WARN_ON(entry < FAT_START_ENT || sbi->max_cluster <= entry);
  	*offset = bytes & (sb->s_blocksize - 1);
  	*blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
  }
  
  static void fat_ent_blocknr(struct super_block *sb, int entry,
  			    int *offset, sector_t *blocknr)
  {
  	struct msdos_sb_info *sbi = MSDOS_SB(sb);
  	int bytes = (entry << sbi->fatent_shift);
  	WARN_ON(entry < FAT_START_ENT || sbi->max_cluster <= entry);
  	*offset = bytes & (sb->s_blocksize - 1);
  	*blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
  }
  
  static void fat12_ent_set_ptr(struct fat_entry *fatent, int offset)
  {
  	struct buffer_head **bhs = fatent->bhs;
  	if (fatent->nr_bhs == 1) {
  		WARN_ON(offset >= (bhs[0]->b_size - 1));
  		fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
  		fatent->u.ent12_p[1] = bhs[0]->b_data + (offset + 1);
  	} else {
  		WARN_ON(offset != (bhs[0]->b_size - 1));
  		fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
  		fatent->u.ent12_p[1] = bhs[1]->b_data;
  	}
  }
  
  static void fat16_ent_set_ptr(struct fat_entry *fatent, int offset)
  {
  	WARN_ON(offset & (2 - 1));
  	fatent->u.ent16_p = (__le16 *)(fatent->bhs[0]->b_data + offset);
  }
  
  static void fat32_ent_set_ptr(struct fat_entry *fatent, int offset)
  {
  	WARN_ON(offset & (4 - 1));
  	fatent->u.ent32_p = (__le32 *)(fatent->bhs[0]->b_data + offset);
  }
  
  static int fat12_ent_bread(struct super_block *sb, struct fat_entry *fatent,
  			   int offset, sector_t blocknr)
  {
  	struct buffer_head **bhs = fatent->bhs;
  
  	WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
  	fatent->fat_inode = MSDOS_SB(sb)->fat_inode;
  
  	bhs[0] = sb_bread(sb, blocknr);
  	if (!bhs[0])
  		goto err;
  
  	if ((offset + 1) < sb->s_blocksize)
  		fatent->nr_bhs = 1;
  	else {
  		/* This entry is block boundary, it needs the next block */
  		blocknr++;
  		bhs[1] = sb_bread(sb, blocknr);
  		if (!bhs[1])
  			goto err_brelse;
  		fatent->nr_bhs = 2;
  	}
  	fat12_ent_set_ptr(fatent, offset);
  	return 0;
  
  err_brelse:
  	brelse(bhs[0]);
  err:
  	fat_msg(sb, KERN_ERR, "FAT read failed (blocknr %llu)", (llu)blocknr);
  	return -EIO;
  }
  
  static int fat_ent_bread(struct super_block *sb, struct fat_entry *fatent,
  			 int offset, sector_t blocknr)
  {
  	struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
  
  	WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
  	fatent->fat_inode = MSDOS_SB(sb)->fat_inode;
  	fatent->bhs[0] = sb_bread(sb, blocknr);
  	if (!fatent->bhs[0]) {
  		fat_msg(sb, KERN_ERR, "FAT read failed (blocknr %llu)",
  		       (llu)blocknr);
  		return -EIO;
  	}
  	fatent->nr_bhs = 1;
  	ops->ent_set_ptr(fatent, offset);
  	return 0;
  }
  
  static int fat12_ent_get(struct fat_entry *fatent)
  {
  	u8 **ent12_p = fatent->u.ent12_p;
  	int next;
  
  	spin_lock(&fat12_entry_lock);
  	if (fatent->entry & 1)
  		next = (*ent12_p[0] >> 4) | (*ent12_p[1] << 4);
  	else
  		next = (*ent12_p[1] << 8) | *ent12_p[0];
  	spin_unlock(&fat12_entry_lock);
  
  	next &= 0x0fff;
  	if (next >= BAD_FAT12)
  		next = FAT_ENT_EOF;
  	return next;
  }
  
  static int fat16_ent_get(struct fat_entry *fatent)
  {
  	int next = le16_to_cpu(*fatent->u.ent16_p);
  	WARN_ON((unsigned long)fatent->u.ent16_p & (2 - 1));
  	if (next >= BAD_FAT16)
  		next = FAT_ENT_EOF;
  	return next;
  }
  
  static int fat32_ent_get(struct fat_entry *fatent)
  {
  	int next = le32_to_cpu(*fatent->u.ent32_p) & 0x0fffffff;
  	WARN_ON((unsigned long)fatent->u.ent32_p & (4 - 1));
  	if (next >= BAD_FAT32)
  		next = FAT_ENT_EOF;
  	return next;
  }
  
  static void fat12_ent_put(struct fat_entry *fatent, int new)
  {
  	u8 **ent12_p = fatent->u.ent12_p;
  
  	if (new == FAT_ENT_EOF)
  		new = EOF_FAT12;
  
  	spin_lock(&fat12_entry_lock);
  	if (fatent->entry & 1) {
  		*ent12_p[0] = (new << 4) | (*ent12_p[0] & 0x0f);
  		*ent12_p[1] = new >> 4;
  	} else {
  		*ent12_p[0] = new & 0xff;
  		*ent12_p[1] = (*ent12_p[1] & 0xf0) | (new >> 8);
  	}
  	spin_unlock(&fat12_entry_lock);
  
  	mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
  	if (fatent->nr_bhs == 2)
  		mark_buffer_dirty_inode(fatent->bhs[1], fatent->fat_inode);
  }
  
  static void fat16_ent_put(struct fat_entry *fatent, int new)
  {
  	if (new == FAT_ENT_EOF)
  		new = EOF_FAT16;
  
  	*fatent->u.ent16_p = cpu_to_le16(new);
  	mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
  }
  
  static void fat32_ent_put(struct fat_entry *fatent, int new)
  {
  	WARN_ON(new & 0xf0000000);
  	new |= le32_to_cpu(*fatent->u.ent32_p) & ~0x0fffffff;
  	*fatent->u.ent32_p = cpu_to_le32(new);
  	mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
  }
  
  static int fat12_ent_next(struct fat_entry *fatent)
  {
  	u8 **ent12_p = fatent->u.ent12_p;
  	struct buffer_head **bhs = fatent->bhs;
  	u8 *nextp = ent12_p[1] + 1 + (fatent->entry & 1);
  
  	fatent->entry++;
  	if (fatent->nr_bhs == 1) {
  		WARN_ON(ent12_p[0] > (u8 *)(bhs[0]->b_data +
  							(bhs[0]->b_size - 2)));
  		WARN_ON(ent12_p[1] > (u8 *)(bhs[0]->b_data +
  							(bhs[0]->b_size - 1)));
  		if (nextp < (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1))) {
  			ent12_p[0] = nextp - 1;
  			ent12_p[1] = nextp;
  			return 1;
  		}
  	} else {
  		WARN_ON(ent12_p[0] != (u8 *)(bhs[0]->b_data +
  							(bhs[0]->b_size - 1)));
  		WARN_ON(ent12_p[1] != (u8 *)bhs[1]->b_data);
  		ent12_p[0] = nextp - 1;
  		ent12_p[1] = nextp;
  		brelse(bhs[0]);
  		bhs[0] = bhs[1];
  		fatent->nr_bhs = 1;
  		return 1;
  	}
  	ent12_p[0] = NULL;
  	ent12_p[1] = NULL;
  	return 0;
  }
  
  static int fat16_ent_next(struct fat_entry *fatent)
  {
  	const struct buffer_head *bh = fatent->bhs[0];
  	fatent->entry++;
  	if (fatent->u.ent16_p < (__le16 *)(bh->b_data + (bh->b_size - 2))) {
  		fatent->u.ent16_p++;
  		return 1;
  	}
  	fatent->u.ent16_p = NULL;
  	return 0;
  }
  
  static int fat32_ent_next(struct fat_entry *fatent)
  {
  	const struct buffer_head *bh = fatent->bhs[0];
  	fatent->entry++;
  	if (fatent->u.ent32_p < (__le32 *)(bh->b_data + (bh->b_size - 4))) {
  		fatent->u.ent32_p++;
  		return 1;
  	}
  	fatent->u.ent32_p = NULL;
  	return 0;
  }
  
  static struct fatent_operations fat12_ops = {
  	.ent_blocknr	= fat12_ent_blocknr,
  	.ent_set_ptr	= fat12_ent_set_ptr,
  	.ent_bread	= fat12_ent_bread,
  	.ent_get	= fat12_ent_get,
  	.ent_put	= fat12_ent_put,
  	.ent_next	= fat12_ent_next,
  };
  
  static struct fatent_operations fat16_ops = {
  	.ent_blocknr	= fat_ent_blocknr,
  	.ent_set_ptr	= fat16_ent_set_ptr,
  	.ent_bread	= fat_ent_bread,
  	.ent_get	= fat16_ent_get,
  	.ent_put	= fat16_ent_put,
  	.ent_next	= fat16_ent_next,
  };
  
  static struct fatent_operations fat32_ops = {
  	.ent_blocknr	= fat_ent_blocknr,
  	.ent_set_ptr	= fat32_ent_set_ptr,
  	.ent_bread	= fat_ent_bread,
  	.ent_get	= fat32_ent_get,
  	.ent_put	= fat32_ent_put,
  	.ent_next	= fat32_ent_next,
  };
  
  static inline void lock_fat(struct msdos_sb_info *sbi)
  {
  	mutex_lock(&sbi->fat_lock);
  }
  
  static inline void unlock_fat(struct msdos_sb_info *sbi)
  {
  	mutex_unlock(&sbi->fat_lock);
  }
  
  void fat_ent_access_init(struct super_block *sb)
  {
  	struct msdos_sb_info *sbi = MSDOS_SB(sb);
  
  	mutex_init(&sbi->fat_lock);
  
  	switch (sbi->fat_bits) {
  	case 32:
  		sbi->fatent_shift = 2;
  		sbi->fatent_ops = &fat32_ops;
  		break;
  	case 16:
  		sbi->fatent_shift = 1;
  		sbi->fatent_ops = &fat16_ops;
  		break;
  	case 12:
  		sbi->fatent_shift = -1;
  		sbi->fatent_ops = &fat12_ops;
  		break;
  	}
  }
  
  static void mark_fsinfo_dirty(struct super_block *sb)
  {
  	struct msdos_sb_info *sbi = MSDOS_SB(sb);
  
  	if (sb->s_flags & MS_RDONLY || sbi->fat_bits != 32)
  		return;
  
  	__mark_inode_dirty(sbi->fsinfo_inode, I_DIRTY_SYNC);
  }
  
  static inline int fat_ent_update_ptr(struct super_block *sb,
  				     struct fat_entry *fatent,
  				     int offset, sector_t blocknr)
  {
  	struct msdos_sb_info *sbi = MSDOS_SB(sb);
  	struct fatent_operations *ops = sbi->fatent_ops;
  	struct buffer_head **bhs = fatent->bhs;
  
  	/* Is this fatent's blocks including this entry? */
  	if (!fatent->nr_bhs || bhs[0]->b_blocknr != blocknr)
  		return 0;
  	if (sbi->fat_bits == 12) {
  		if ((offset + 1) < sb->s_blocksize) {
  			/* This entry is on bhs[0]. */
  			if (fatent->nr_bhs == 2) {
  				brelse(bhs[1]);
  				fatent->nr_bhs = 1;
  			}
  		} else {
  			/* This entry needs the next block. */
  			if (fatent->nr_bhs != 2)
  				return 0;
  			if (bhs[1]->b_blocknr != (blocknr + 1))
  				return 0;
  		}
  	}
  	ops->ent_set_ptr(fatent, offset);
  	return 1;
  }
  
  int fat_ent_read(struct inode *inode, struct fat_entry *fatent, int entry)
  {
  	struct super_block *sb = inode->i_sb;
  	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
  	struct fatent_operations *ops = sbi->fatent_ops;
  	int err, offset;
  	sector_t blocknr;
  
  	if (entry < FAT_START_ENT || sbi->max_cluster <= entry) {
  		fatent_brelse(fatent);
  		fat_fs_error(sb, "invalid access to FAT (entry 0x%08x)", entry);
  		return -EIO;
  	}
  
  	fatent_set_entry(fatent, entry);
  	ops->ent_blocknr(sb, entry, &offset, &blocknr);
  
  	if (!fat_ent_update_ptr(sb, fatent, offset, blocknr)) {
  		fatent_brelse(fatent);
  		err = ops->ent_bread(sb, fatent, offset, blocknr);
  		if (err)
  			return err;
  	}
  	return ops->ent_get(fatent);
  }
  
  /* FIXME: We can write the blocks as more big chunk. */
  static int fat_mirror_bhs(struct super_block *sb, struct buffer_head **bhs,
  			  int nr_bhs)
  {
  	struct msdos_sb_info *sbi = MSDOS_SB(sb);
  	struct buffer_head *c_bh;
  	int err, n, copy;
  
  	err = 0;
  	for (copy = 1; copy < sbi->fats; copy++) {
  		sector_t backup_fat = sbi->fat_length * copy;
  
  		for (n = 0; n < nr_bhs; n++) {
  			c_bh = sb_getblk(sb, backup_fat + bhs[n]->b_blocknr);
  			if (!c_bh) {
  				err = -ENOMEM;
  				goto error;
  			}
  			memcpy(c_bh->b_data, bhs[n]->b_data, sb->s_blocksize);
  			set_buffer_uptodate(c_bh);
  			mark_buffer_dirty_inode(c_bh, sbi->fat_inode);
  			if (sb->s_flags & MS_SYNCHRONOUS)
  				err = sync_dirty_buffer(c_bh);
  			brelse(c_bh);
  			if (err)
  				goto error;
  		}
  	}
  error:
  	return err;
  }
  
  int fat_ent_write(struct inode *inode, struct fat_entry *fatent,
  		  int new, int wait)
  {
  	struct super_block *sb = inode->i_sb;
  	struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
  	int err;
  
  	ops->ent_put(fatent, new);
  	if (wait) {
  		err = fat_sync_bhs(fatent->bhs, fatent->nr_bhs);
  		if (err)
  			return err;
  	}
  	return fat_mirror_bhs(sb, fatent->bhs, fatent->nr_bhs);
  }
  
  static inline int fat_ent_next(struct msdos_sb_info *sbi,
  			       struct fat_entry *fatent)
  {
  	if (sbi->fatent_ops->ent_next(fatent)) {
  		if (fatent->entry < sbi->max_cluster)
  			return 1;
  	}
  	return 0;
  }
  
  static inline int fat_ent_read_block(struct super_block *sb,
  				     struct fat_entry *fatent)
  {
  	struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
  	sector_t blocknr;
  	int offset;
  
  	fatent_brelse(fatent);
  	ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
  	return ops->ent_bread(sb, fatent, offset, blocknr);
  }
  
  static void fat_collect_bhs(struct buffer_head **bhs, int *nr_bhs,
  			    struct fat_entry *fatent)
  {
  	int n, i;
  
  	for (n = 0; n < fatent->nr_bhs; n++) {
  		for (i = 0; i < *nr_bhs; i++) {
  			if (fatent->bhs[n] == bhs[i])
  				break;
  		}
  		if (i == *nr_bhs) {
  			get_bh(fatent->bhs[n]);
  			bhs[i] = fatent->bhs[n];
  			(*nr_bhs)++;
  		}
  	}
  }
  
  int fat_alloc_clusters(struct inode *inode, int *cluster, int nr_cluster)
  {
  	struct super_block *sb = inode->i_sb;
  	struct msdos_sb_info *sbi = MSDOS_SB(sb);
  	struct fatent_operations *ops = sbi->fatent_ops;
  	struct fat_entry fatent, prev_ent;
  	struct buffer_head *bhs[MAX_BUF_PER_PAGE];
  	int i, count, err, nr_bhs, idx_clus;
  
  	BUG_ON(nr_cluster > (MAX_BUF_PER_PAGE / 2));	/* fixed limit */
  
  	lock_fat(sbi);
  	if (sbi->free_clusters != -1 && sbi->free_clus_valid &&
  	    sbi->free_clusters < nr_cluster) {
  		unlock_fat(sbi);
  		return -ENOSPC;
  	}
  
  	err = nr_bhs = idx_clus = 0;
  	count = FAT_START_ENT;
  	fatent_init(&prev_ent);
  	fatent_init(&fatent);
  	fatent_set_entry(&fatent, sbi->prev_free + 1);
  	while (count < sbi->max_cluster) {
  		if (fatent.entry >= sbi->max_cluster)
  			fatent.entry = FAT_START_ENT;
  		fatent_set_entry(&fatent, fatent.entry);
  		err = fat_ent_read_block(sb, &fatent);
  		if (err)
  			goto out;
  
  		/* Find the free entries in a block */
  		do {
  			if (ops->ent_get(&fatent) == FAT_ENT_FREE) {
  				int entry = fatent.entry;
  
  				/* make the cluster chain */
  				ops->ent_put(&fatent, FAT_ENT_EOF);
  				if (prev_ent.nr_bhs)
  					ops->ent_put(&prev_ent, entry);
  
  				fat_collect_bhs(bhs, &nr_bhs, &fatent);
  
  				sbi->prev_free = entry;
  				if (sbi->free_clusters != -1)
  					sbi->free_clusters--;
  
  				cluster[idx_clus] = entry;
  				idx_clus++;
  				if (idx_clus == nr_cluster)
  					goto out;
  
  				/*
  				 * fat_collect_bhs() gets ref-count of bhs,
  				 * so we can still use the prev_ent.
  				 */
  				prev_ent = fatent;
  			}
  			count++;
  			if (count == sbi->max_cluster)
  				break;
  		} while (fat_ent_next(sbi, &fatent));
  	}
  
  	/* Couldn't allocate the free entries */
  	sbi->free_clusters = 0;
  	sbi->free_clus_valid = 1;
  	err = -ENOSPC;
  
  out:
  	unlock_fat(sbi);
  	mark_fsinfo_dirty(sb);
  	fatent_brelse(&fatent);
  	if (!err) {
  		if (inode_needs_sync(inode))
  			err = fat_sync_bhs(bhs, nr_bhs);
  		if (!err)
  			err = fat_mirror_bhs(sb, bhs, nr_bhs);
  	}
  	for (i = 0; i < nr_bhs; i++)
  		brelse(bhs[i]);
  
  	if (err && idx_clus)
  		fat_free_clusters(inode, cluster[0]);
  
  	return err;
  }
  
  int fat_free_clusters(struct inode *inode, int cluster)
  {
  	struct super_block *sb = inode->i_sb;
  	struct msdos_sb_info *sbi = MSDOS_SB(sb);
  	struct fatent_operations *ops = sbi->fatent_ops;
  	struct fat_entry fatent;
  	struct buffer_head *bhs[MAX_BUF_PER_PAGE];
  	int i, err, nr_bhs;
  	int first_cl = cluster, dirty_fsinfo = 0;
  
  	nr_bhs = 0;
  	fatent_init(&fatent);
  	lock_fat(sbi);
  	do {
  		cluster = fat_ent_read(inode, &fatent, cluster);
  		if (cluster < 0) {
  			err = cluster;
  			goto error;
  		} else if (cluster == FAT_ENT_FREE) {
  			fat_fs_error(sb, "%s: deleting FAT entry beyond EOF",
  				     __func__);
  			err = -EIO;
  			goto error;
  		}
  
  		if (sbi->options.discard) {
  			/*
  			 * Issue discard for the sectors we no longer
  			 * care about, batching contiguous clusters
  			 * into one request
  			 */
  			if (cluster != fatent.entry + 1) {
  				int nr_clus = fatent.entry - first_cl + 1;
  
  				sb_issue_discard(sb,
  					fat_clus_to_blknr(sbi, first_cl),
  					nr_clus * sbi->sec_per_clus,
  					GFP_NOFS, 0);
  
  				first_cl = cluster;
  			}
  		}
  
  		ops->ent_put(&fatent, FAT_ENT_FREE);
  		if (sbi->free_clusters != -1) {
  			sbi->free_clusters++;
  			dirty_fsinfo = 1;
  		}
  
  		if (nr_bhs + fatent.nr_bhs > MAX_BUF_PER_PAGE) {
  			if (sb->s_flags & MS_SYNCHRONOUS) {
  				err = fat_sync_bhs(bhs, nr_bhs);
  				if (err)
  					goto error;
  			}
  			err = fat_mirror_bhs(sb, bhs, nr_bhs);
  			if (err)
  				goto error;
  			for (i = 0; i < nr_bhs; i++)
  				brelse(bhs[i]);
  			nr_bhs = 0;
  		}
  		fat_collect_bhs(bhs, &nr_bhs, &fatent);
  	} while (cluster != FAT_ENT_EOF);
  
  	if (sb->s_flags & MS_SYNCHRONOUS) {
  		err = fat_sync_bhs(bhs, nr_bhs);
  		if (err)
  			goto error;
  	}
  	err = fat_mirror_bhs(sb, bhs, nr_bhs);
  error:
  	fatent_brelse(&fatent);
  	for (i = 0; i < nr_bhs; i++)
  		brelse(bhs[i]);
  	unlock_fat(sbi);
  	if (dirty_fsinfo)
  		mark_fsinfo_dirty(sb);
  
  	return err;
  }
  EXPORT_SYMBOL_GPL(fat_free_clusters);
  
  /* 128kb is the whole sectors for FAT12 and FAT16 */
  #define FAT_READA_SIZE		(128 * 1024)
  
  static void fat_ent_reada(struct super_block *sb, struct fat_entry *fatent,
  			  unsigned long reada_blocks)
  {
  	struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
  	sector_t blocknr;
  	int i, offset;
  
  	ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
  
  	for (i = 0; i < reada_blocks; i++)
  		sb_breadahead(sb, blocknr + i);
  }
  
  int fat_count_free_clusters(struct super_block *sb)
  {
  	struct msdos_sb_info *sbi = MSDOS_SB(sb);
  	struct fatent_operations *ops = sbi->fatent_ops;
  	struct fat_entry fatent;
  	unsigned long reada_blocks, reada_mask, cur_block;
  	int err = 0, free;
  
  	lock_fat(sbi);
  	if (sbi->free_clusters != -1 && sbi->free_clus_valid)
  		goto out;
  
  	reada_blocks = FAT_READA_SIZE >> sb->s_blocksize_bits;
  	reada_mask = reada_blocks - 1;
  	cur_block = 0;
  
  	free = 0;
  	fatent_init(&fatent);
  	fatent_set_entry(&fatent, FAT_START_ENT);
  	while (fatent.entry < sbi->max_cluster) {
  		/* readahead of fat blocks */
  		if ((cur_block & reada_mask) == 0) {
  			unsigned long rest = sbi->fat_length - cur_block;
  			fat_ent_reada(sb, &fatent, min(reada_blocks, rest));
  		}
  		cur_block++;
  
  		err = fat_ent_read_block(sb, &fatent);
  		if (err)
  			goto out;
  
  		do {
  			if (ops->ent_get(&fatent) == FAT_ENT_FREE)
  				free++;
  		} while (fat_ent_next(sbi, &fatent));
  	}
  	sbi->free_clusters = free;
  	sbi->free_clus_valid = 1;
  	mark_fsinfo_dirty(sb);
  	fatent_brelse(&fatent);
  out:
  	unlock_fat(sbi);
  	return err;
  }