fs/fat/cache.c - linux - Git at Google

 /*
  *  linux/fs/fat/cache.c
  *
  *  Written 1992,1993 by Werner Almesberger
  *
  *  Mar 1999. AV. Changed cache, so that it uses the starting cluster instead
  *	of inode number.
  *  May 1999. AV. Fixed the bogosity with FAT32 (read "FAT28"). Fscking lusers.
  */

 #include <linux/fs.h>
 #include <linux/msdos_fs.h>
 #include <linux/buffer_head.h>

 /* this must be > 0. */
 #define FAT_MAX_CACHE	8

 struct fat_cache {
 	struct list_head cache_list;
 	int nr_contig;	/* number of contiguous clusters */
 	int fcluster;	/* cluster number in the file. */
 	int dcluster;	/* cluster number on disk. */
 };

 struct fat_cache_id {
 	unsigned int id;
 	int nr_contig;
 	int fcluster;
 	int dcluster;
 };

 static inline int fat_max_cache(struct inode *inode)
 {
 	return FAT_MAX_CACHE;
 }

 static kmem_cache_t *fat_cache_cachep;

 static void init_once(void *foo, kmem_cache_t *cachep, unsigned long flags)
 {
 	struct fat_cache *cache = (struct fat_cache *)foo;

 	if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
 	    SLAB_CTOR_CONSTRUCTOR)
 		INIT_LIST_HEAD(&cache->cache_list);
 }

 int __init fat_cache_init(void)
 {
 	fat_cache_cachep = kmem_cache_create("fat_cache",
 				sizeof(struct fat_cache),
 				0, SLAB_RECLAIM_ACCOUNT,
 				init_once, NULL);
 	if (fat_cache_cachep == NULL)
 		return -ENOMEM;
 	return 0;
 }

 void __exit fat_cache_destroy(void)
 {
 	if (kmem_cache_destroy(fat_cache_cachep))
 		printk(KERN_INFO "fat_cache: not all structures were freed\n");
 }

 static inline struct fat_cache *fat_cache_alloc(struct inode *inode)
 {
 	return kmem_cache_alloc(fat_cache_cachep, SLAB_KERNEL);
 }

 static inline void fat_cache_free(struct fat_cache *cache)
 {
 	BUG_ON(!list_empty(&cache->cache_list));
 	kmem_cache_free(fat_cache_cachep, cache);
 }

 static inline void fat_cache_update_lru(struct inode *inode,
 					struct fat_cache *cache)
 {
 	if (MSDOS_I(inode)->cache_lru.next != &cache->cache_list)
 		list_move(&cache->cache_list, &MSDOS_I(inode)->cache_lru);
 }

 static int fat_cache_lookup(struct inode *inode, int fclus,
 			    struct fat_cache_id *cid,
 			    int *cached_fclus, int *cached_dclus)
 {
 	static struct fat_cache nohit = { .fcluster = 0, };

 	struct fat_cache *hit = &nohit, *p;
 	int offset = -1;

 	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 	list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
 		/* Find the cache of "fclus" or nearest cache. */
 		if (p->fcluster <= fclus && hit->fcluster < p->fcluster) {
 			hit = p;
 			if ((hit->fcluster + hit->nr_contig) < fclus) {
 				offset = hit->nr_contig;
 			} else {
 				offset = fclus - hit->fcluster;
 				break;
 			}
 		}
 	}
 	if (hit != &nohit) {
 		fat_cache_update_lru(inode, hit);

 		cid->id = MSDOS_I(inode)->cache_valid_id;
 		cid->nr_contig = hit->nr_contig;
 		cid->fcluster = hit->fcluster;
 		cid->dcluster = hit->dcluster;
 		*cached_fclus = cid->fcluster + offset;
 		*cached_dclus = cid->dcluster + offset;
 	}
 	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);

 	return offset;
 }

 static struct fat_cache *fat_cache_merge(struct inode *inode,
 					 struct fat_cache_id *new)
 {
 	struct fat_cache *p;

 	list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
 		/* Find the same part as "new" in cluster-chain. */
 		if (p->fcluster == new->fcluster) {
 			BUG_ON(p->dcluster != new->dcluster);
 			if (new->nr_contig > p->nr_contig)
 				p->nr_contig = new->nr_contig;
 			return p;
 		}
 	}
 	return NULL;
 }

 static void fat_cache_add(struct inode *inode, struct fat_cache_id *new)
 {
 	struct fat_cache *cache, *tmp;

 	if (new->fcluster == -1) /* dummy cache */
 		return;

 	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 	if (new->id != FAT_CACHE_VALID &&
 	    new->id != MSDOS_I(inode)->cache_valid_id)
 		goto out;	/* this cache was invalidated */

 	cache = fat_cache_merge(inode, new);
 	if (cache == NULL) {
 		if (MSDOS_I(inode)->nr_caches < fat_max_cache(inode)) {
 			MSDOS_I(inode)->nr_caches++;
 			spin_unlock(&MSDOS_I(inode)->cache_lru_lock);

 			tmp = fat_cache_alloc(inode);
 			spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 			cache = fat_cache_merge(inode, new);
 			if (cache != NULL) {
 				MSDOS_I(inode)->nr_caches--;
 				fat_cache_free(tmp);
 				goto out_update_lru;
 			}
 			cache = tmp;
 		} else {
 			struct list_head *p = MSDOS_I(inode)->cache_lru.prev;
 			cache = list_entry(p, struct fat_cache, cache_list);
 		}
 		cache->fcluster = new->fcluster;
 		cache->dcluster = new->dcluster;
 		cache->nr_contig = new->nr_contig;
 	}
 out_update_lru:
 	fat_cache_update_lru(inode, cache);
 out:
 	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 }

 /*
  * Cache invalidation occurs rarely, thus the LRU chain is not updated. It
  * fixes itself after a while.
  */
 static void __fat_cache_inval_inode(struct inode *inode)
 {
 	struct msdos_inode_info *i = MSDOS_I(inode);
 	struct fat_cache *cache;

 	while (!list_empty(&i->cache_lru)) {
 		cache = list_entry(i->cache_lru.next, struct fat_cache, cache_list);
 		list_del_init(&cache->cache_list);
 		i->nr_caches--;
 		fat_cache_free(cache);
 	}
 	/* Update. The copy of caches before this id is discarded. */
 	i->cache_valid_id++;
 	if (i->cache_valid_id == FAT_CACHE_VALID)
 		i->cache_valid_id++;
 }

 void fat_cache_inval_inode(struct inode *inode)
 {
 	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 	__fat_cache_inval_inode(inode);
 	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 }

 static int __fat_access(struct super_block *sb, int nr, int new_value)
 {
 	struct msdos_sb_info *sbi = MSDOS_SB(sb);
 	struct buffer_head *bh, *bh2, *c_bh, *c_bh2;
 	unsigned char *p_first, *p_last;
 	int copy, first, last, next, b;

 	if (sbi->fat_bits == 32) {
 		first = last = nr*4;
 	} else if (sbi->fat_bits == 16) {
 		first = last = nr*2;
 	} else {
 		first = nr*3/2;
 		last = first+1;
 	}
 	b = sbi->fat_start + (first >> sb->s_blocksize_bits);
 	if (!(bh = sb_bread(sb, b))) {
 		printk(KERN_ERR "FAT: bread(block %d) in"
 		       " fat_access failed\n", b);
 		return -EIO;
 	}
 	if ((first >> sb->s_blocksize_bits) == (last >> sb->s_blocksize_bits)) {
 		bh2 = bh;
 	} else {
 		if (!(bh2 = sb_bread(sb, b + 1))) {
 			brelse(bh);
 			printk(KERN_ERR "FAT: bread(block %d) in"
 			       " fat_access failed\n", b + 1);
 			return -EIO;
 		}
 	}
 	if (sbi->fat_bits == 32) {
 		p_first = p_last = NULL; /* GCC needs that stuff */
 		next = le32_to_cpu(((__le32 *) bh->b_data)[(first &
 		    (sb->s_blocksize - 1)) >> 2]);
 		/* Fscking Microsoft marketing department. Their "32" is 28. */
 		next &= 0x0fffffff;
 	} else if (sbi->fat_bits == 16) {
 		p_first = p_last = NULL; /* GCC needs that stuff */
 		next = le16_to_cpu(((__le16 *) bh->b_data)[(first &
 		    (sb->s_blocksize - 1)) >> 1]);
 	} else {
 		p_first = &((__u8 *)bh->b_data)[first & (sb->s_blocksize - 1)];
 		p_last = &((__u8 *)bh2->b_data)[(first + 1) & (sb->s_blocksize - 1)];
 		if (nr & 1)
 			next = ((*p_first >> 4) | (*p_last << 4)) & 0xfff;
 		else
 			next = (*p_first+(*p_last << 8)) & 0xfff;
 	}
 	if (new_value != -1) {
 		if (sbi->fat_bits == 32) {
 			((__le32 *)bh->b_data)[(first & (sb->s_blocksize - 1)) >> 2]
 				= cpu_to_le32(new_value);
 		} else if (sbi->fat_bits == 16) {
 			((__le16 *)bh->b_data)[(first & (sb->s_blocksize - 1)) >> 1]
 				= cpu_to_le16(new_value);
 		} else {
 			if (nr & 1) {
 				*p_first = (*p_first & 0xf) | (new_value << 4);
 				*p_last = new_value >> 4;
 			}
 			else {
 				*p_first = new_value & 0xff;
 				*p_last = (*p_last & 0xf0) | (new_value >> 8);
 			}
 			mark_buffer_dirty(bh2);
 		}
 		mark_buffer_dirty(bh);
 		for (copy = 1; copy < sbi->fats; copy++) {
 			b = sbi->fat_start + (first >> sb->s_blocksize_bits)
 				+ sbi->fat_length * copy;
 			if (!(c_bh = sb_bread(sb, b)))
 				break;
 			if (bh != bh2) {
 				if (!(c_bh2 = sb_bread(sb, b+1))) {
 					brelse(c_bh);
 					break;
 				}
 				memcpy(c_bh2->b_data, bh2->b_data, sb->s_blocksize);
 				mark_buffer_dirty(c_bh2);
 				brelse(c_bh2);
 			}
 			memcpy(c_bh->b_data, bh->b_data, sb->s_blocksize);
 			mark_buffer_dirty(c_bh);
 			brelse(c_bh);
 		}
 	}
 	brelse(bh);
 	if (bh != bh2)
 		brelse(bh2);
 	return next;
 }

 /*
  * Returns the this'th FAT entry, -1 if it is an end-of-file entry. If
  * new_value is != -1, that FAT entry is replaced by it.
  */
 int fat_access(struct super_block *sb, int nr, int new_value)
 {
 	int next;

 	next = -EIO;
 	if (nr < FAT_START_ENT || MSDOS_SB(sb)->max_cluster <= nr) {
 		fat_fs_panic(sb, "invalid access to FAT (entry 0x%08x)", nr);
 		goto out;
 	}
 	if (new_value == FAT_ENT_EOF)
 		new_value = EOF_FAT(sb);

 	next = __fat_access(sb, nr, new_value);
 	if (next < 0)
 		goto out;
 	if (next >= BAD_FAT(sb))
 		next = FAT_ENT_EOF;
 out:
 	return next;
 }

 static inline int cache_contiguous(struct fat_cache_id *cid, int dclus)
 {
 	cid->nr_contig++;
 	return ((cid->dcluster + cid->nr_contig) == dclus);
 }

 static inline void cache_init(struct fat_cache_id *cid, int fclus, int dclus)
 {
 	cid->id = FAT_CACHE_VALID;
 	cid->fcluster = fclus;
 	cid->dcluster = dclus;
 	cid->nr_contig = 0;
 }

 int fat_get_cluster(struct inode *inode, int cluster, int *fclus, int *dclus)
 {
 	struct super_block *sb = inode->i_sb;
 	const int limit = sb->s_maxbytes >> MSDOS_SB(sb)->cluster_bits;
 	struct fat_cache_id cid;
 	int nr;

 	BUG_ON(MSDOS_I(inode)->i_start == 0);

 	*fclus = 0;
 	*dclus = MSDOS_I(inode)->i_start;
 	if (cluster == 0)
 		return 0;

 	if (fat_cache_lookup(inode, cluster, &cid, fclus, dclus) < 0) {
 		/*
 		 * dummy, always not contiguous
 		 * This is reinitialized by cache_init(), later.
 		 */
 		cache_init(&cid, -1, -1);
 	}

 	while (*fclus < cluster) {
 		/* prevent the infinite loop of cluster chain */
 		if (*fclus > limit) {
 			fat_fs_panic(sb, "%s: detected the cluster chain loop"
 				     " (i_pos %lld)", __FUNCTION__,
 				     MSDOS_I(inode)->i_pos);
 			return -EIO;
 		}

 		nr = fat_access(sb, *dclus, -1);
 		if (nr < 0)
 			return nr;
 		else if (nr == FAT_ENT_FREE) {
 			fat_fs_panic(sb, "%s: invalid cluster chain"
 				     " (i_pos %lld)", __FUNCTION__,
 				     MSDOS_I(inode)->i_pos);
 			return -EIO;
 		} else if (nr == FAT_ENT_EOF) {
 			fat_cache_add(inode, &cid);
 			return FAT_ENT_EOF;
 		}
 		(*fclus)++;
 		*dclus = nr;
 		if (!cache_contiguous(&cid, *dclus))
 			cache_init(&cid, *fclus, *dclus);
 	}
 	fat_cache_add(inode, &cid);
 	return 0;
 }

 static int fat_bmap_cluster(struct inode *inode, int cluster)
 {
 	struct super_block *sb = inode->i_sb;
 	int ret, fclus, dclus;

 	if (MSDOS_I(inode)->i_start == 0)
 		return 0;

 	ret = fat_get_cluster(inode, cluster, &fclus, &dclus);
 	if (ret < 0)
 		return ret;
 	else if (ret == FAT_ENT_EOF) {
 		fat_fs_panic(sb, "%s: request beyond EOF (i_pos %lld)",
 			     __FUNCTION__, MSDOS_I(inode)->i_pos);
 		return -EIO;
 	}
 	return dclus;
 }

 int fat_bmap(struct inode *inode, sector_t sector, sector_t *phys)
 {
 	struct super_block *sb = inode->i_sb;
 	struct msdos_sb_info *sbi = MSDOS_SB(sb);
 	sector_t last_block;
 	int cluster, offset;

 	*phys = 0;
 	if ((sbi->fat_bits != 32) &&
 	    (inode->i_ino == MSDOS_ROOT_INO || (S_ISDIR(inode->i_mode) &&
 	     !MSDOS_I(inode)->i_start))) {
 		if (sector < (sbi->dir_entries >> sbi->dir_per_block_bits))
 			*phys = sector + sbi->dir_start;
 		return 0;
 	}
 	last_block = (MSDOS_I(inode)->mmu_private + (sb->s_blocksize - 1))
 		>> sb->s_blocksize_bits;
 	if (sector >= last_block)
 		return 0;

 	cluster = sector >> (sbi->cluster_bits - sb->s_blocksize_bits);
 	offset  = sector & (sbi->sec_per_clus - 1);
 	cluster = fat_bmap_cluster(inode, cluster);
 	if (cluster < 0)
 		return cluster;
 	else if (cluster)
 		*phys = fat_clus_to_blknr(sbi, cluster) + offset;
 	return 0;
 }
	/*
	* linux/fs/fat/cache.c
	*
	* Written 1992,1993 by Werner Almesberger
	*
	* Mar 1999. AV. Changed cache, so that it uses the starting cluster instead
	* of inode number.
	* May 1999. AV. Fixed the bogosity with FAT32 (read "FAT28"). Fscking lusers.
	*/

	#include <linux/fs.h>
	#include <linux/msdos_fs.h>
	#include <linux/buffer_head.h>

	/* this must be > 0. */
	#define FAT_MAX_CACHE 8

	struct fat_cache {
	struct list_head cache_list;
	int nr_contig; /* number of contiguous clusters */
	int fcluster; /* cluster number in the file. */
	int dcluster; /* cluster number on disk. */
	};

	struct fat_cache_id {
	unsigned int id;
	int nr_contig;
	int fcluster;
	int dcluster;
	};

	static inline int fat_max_cache(struct inode *inode)
	{
	return FAT_MAX_CACHE;
	}

	static kmem_cache_t *fat_cache_cachep;

	static void init_once(void foo, kmem_cache_t cachep, unsigned long flags)
	{
	struct fat_cache cache = (struct fat_cache )foo;

	if ((flags & (SLAB_CTOR_VERIFY\|SLAB_CTOR_CONSTRUCTOR)) ==
	SLAB_CTOR_CONSTRUCTOR)
	INIT_LIST_HEAD(&cache->cache_list);
	}

	int __init fat_cache_init(void)
	{
	fat_cache_cachep = kmem_cache_create("fat_cache",
	sizeof(struct fat_cache),
	0, SLAB_RECLAIM_ACCOUNT,
	init_once, NULL);
	if (fat_cache_cachep == NULL)
	return -ENOMEM;
	return 0;
	}

	void __exit fat_cache_destroy(void)
	{
	if (kmem_cache_destroy(fat_cache_cachep))
	printk(KERN_INFO "fat_cache: not all structures were freed\n");
	}

	static inline struct fat_cache fat_cache_alloc(struct inode inode)
	{
	return kmem_cache_alloc(fat_cache_cachep, SLAB_KERNEL);
	}

	static inline void fat_cache_free(struct fat_cache *cache)
	{
	BUG_ON(!list_empty(&cache->cache_list));
	kmem_cache_free(fat_cache_cachep, cache);
	}

	static inline void fat_cache_update_lru(struct inode *inode,
	struct fat_cache *cache)
	{
	if (MSDOS_I(inode)->cache_lru.next != &cache->cache_list)
	list_move(&cache->cache_list, &MSDOS_I(inode)->cache_lru);
	}

	static int fat_cache_lookup(struct inode *inode, int fclus,
	struct fat_cache_id *cid,
	int cached_fclus, int cached_dclus)
	{
	static struct fat_cache nohit = { .fcluster = 0, };

	struct fat_cache hit = &nohit, p;
	int offset = -1;

	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
	list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
	/* Find the cache of "fclus" or nearest cache. */
	if (p->fcluster <= fclus && hit->fcluster < p->fcluster) {
	hit = p;
	if ((hit->fcluster + hit->nr_contig) < fclus) {
	offset = hit->nr_contig;
	} else {
	offset = fclus - hit->fcluster;
	break;
	}
	}
	}
	if (hit != &nohit) {
	fat_cache_update_lru(inode, hit);

	cid->id = MSDOS_I(inode)->cache_valid_id;
	cid->nr_contig = hit->nr_contig;
	cid->fcluster = hit->fcluster;
	cid->dcluster = hit->dcluster;
	*cached_fclus = cid->fcluster + offset;
	*cached_dclus = cid->dcluster + offset;
	}
	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);

	return offset;
	}

	static struct fat_cache fat_cache_merge(struct inode inode,
	struct fat_cache_id *new)
	{
	struct fat_cache *p;

	list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
	/* Find the same part as "new" in cluster-chain. */
	if (p->fcluster == new->fcluster) {
	BUG_ON(p->dcluster != new->dcluster);
	if (new->nr_contig > p->nr_contig)
	p->nr_contig = new->nr_contig;
	return p;
	}
	}
	return NULL;
	}

	static void fat_cache_add(struct inode inode, struct fat_cache_id new)
	{
	struct fat_cache cache, tmp;

	if (new->fcluster == -1) /* dummy cache */
	return;

	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
	if (new->id != FAT_CACHE_VALID &&
	new->id != MSDOS_I(inode)->cache_valid_id)
	goto out; /* this cache was invalidated */

	cache = fat_cache_merge(inode, new);
	if (cache == NULL) {
	if (MSDOS_I(inode)->nr_caches < fat_max_cache(inode)) {
	MSDOS_I(inode)->nr_caches++;
	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);

	tmp = fat_cache_alloc(inode);
	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
	cache = fat_cache_merge(inode, new);
	if (cache != NULL) {
	MSDOS_I(inode)->nr_caches--;
	fat_cache_free(tmp);
	goto out_update_lru;
	}
	cache = tmp;
	} else {
	struct list_head *p = MSDOS_I(inode)->cache_lru.prev;
	cache = list_entry(p, struct fat_cache, cache_list);
	}
	cache->fcluster = new->fcluster;
	cache->dcluster = new->dcluster;
	cache->nr_contig = new->nr_contig;
	}
	out_update_lru:
	fat_cache_update_lru(inode, cache);
	out:
	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
	}

	/*
	* Cache invalidation occurs rarely, thus the LRU chain is not updated. It
	* fixes itself after a while.
	*/
	static void __fat_cache_inval_inode(struct inode *inode)
	{
	struct msdos_inode_info *i = MSDOS_I(inode);
	struct fat_cache *cache;

	while (!list_empty(&i->cache_lru)) {
	cache = list_entry(i->cache_lru.next, struct fat_cache, cache_list);
	list_del_init(&cache->cache_list);
	i->nr_caches--;
	fat_cache_free(cache);
	}
	/* Update. The copy of caches before this id is discarded. */
	i->cache_valid_id++;
	if (i->cache_valid_id == FAT_CACHE_VALID)
	i->cache_valid_id++;
	}

	void fat_cache_inval_inode(struct inode *inode)
	{
	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
	__fat_cache_inval_inode(inode);
	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
	}

	static int __fat_access(struct super_block *sb, int nr, int new_value)
	{
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	struct buffer_head bh, bh2, c_bh, c_bh2;
	unsigned char p_first, p_last;
	int copy, first, last, next, b;

	if (sbi->fat_bits == 32) {
	first = last = nr*4;
	} else if (sbi->fat_bits == 16) {
	first = last = nr*2;
	} else {
	first = nr*3/2;
	last = first+1;
	}
	b = sbi->fat_start + (first >> sb->s_blocksize_bits);
	if (!(bh = sb_bread(sb, b))) {
	printk(KERN_ERR "FAT: bread(block %d) in"
	" fat_access failed\n", b);
	return -EIO;
	}
	if ((first >> sb->s_blocksize_bits) == (last >> sb->s_blocksize_bits)) {
	bh2 = bh;
	} else {
	if (!(bh2 = sb_bread(sb, b + 1))) {
	brelse(bh);
	printk(KERN_ERR "FAT: bread(block %d) in"
	" fat_access failed\n", b + 1);
	return -EIO;
	}
	}
	if (sbi->fat_bits == 32) {
	p_first = p_last = NULL; /* GCC needs that stuff */
	next = le32_to_cpu(((__le32 *) bh->b_data)[(first &
	(sb->s_blocksize - 1)) >> 2]);
	/* Fscking Microsoft marketing department. Their "32" is 28. */
	next &= 0x0fffffff;
	} else if (sbi->fat_bits == 16) {
	p_first = p_last = NULL; /* GCC needs that stuff */
	next = le16_to_cpu(((__le16 *) bh->b_data)[(first &
	(sb->s_blocksize - 1)) >> 1]);
	} else {
	p_first = &((__u8 *)bh->b_data)[first & (sb->s_blocksize - 1)];
	p_last = &((__u8 *)bh2->b_data)[(first + 1) & (sb->s_blocksize - 1)];
	if (nr & 1)
	next = ((p_first >> 4) \| (p_last << 4)) & 0xfff;
	else
	next = (p_first+(p_last << 8)) & 0xfff;
	}
	if (new_value != -1) {
	if (sbi->fat_bits == 32) {
	((__le32 *)bh->b_data)[(first & (sb->s_blocksize - 1)) >> 2]
	= cpu_to_le32(new_value);
	} else if (sbi->fat_bits == 16) {
	((__le16 *)bh->b_data)[(first & (sb->s_blocksize - 1)) >> 1]
	= cpu_to_le16(new_value);
	} else {
	if (nr & 1) {
	p_first = (p_first & 0xf) \| (new_value << 4);
	*p_last = new_value >> 4;
	}
	else {
	*p_first = new_value & 0xff;
	p_last = (p_last & 0xf0) \| (new_value >> 8);
	}
	mark_buffer_dirty(bh2);
	}
	mark_buffer_dirty(bh);
	for (copy = 1; copy < sbi->fats; copy++) {
	b = sbi->fat_start + (first >> sb->s_blocksize_bits)
	+ sbi->fat_length * copy;
	if (!(c_bh = sb_bread(sb, b)))
	break;
	if (bh != bh2) {
	if (!(c_bh2 = sb_bread(sb, b+1))) {
	brelse(c_bh);
	break;
	}
	memcpy(c_bh2->b_data, bh2->b_data, sb->s_blocksize);
	mark_buffer_dirty(c_bh2);
	brelse(c_bh2);
	}
	memcpy(c_bh->b_data, bh->b_data, sb->s_blocksize);
	mark_buffer_dirty(c_bh);
	brelse(c_bh);
	}
	}
	brelse(bh);
	if (bh != bh2)
	brelse(bh2);
	return next;
	}

	/*
	* Returns the this'th FAT entry, -1 if it is an end-of-file entry. If
	* new_value is != -1, that FAT entry is replaced by it.
	*/
	int fat_access(struct super_block *sb, int nr, int new_value)
	{
	int next;

	next = -EIO;
	if (nr < FAT_START_ENT \|\| MSDOS_SB(sb)->max_cluster <= nr) {
	fat_fs_panic(sb, "invalid access to FAT (entry 0x%08x)", nr);
	goto out;
	}
	if (new_value == FAT_ENT_EOF)
	new_value = EOF_FAT(sb);

	next = __fat_access(sb, nr, new_value);
	if (next < 0)
	goto out;
	if (next >= BAD_FAT(sb))
	next = FAT_ENT_EOF;
	out:
	return next;
	}

	static inline int cache_contiguous(struct fat_cache_id *cid, int dclus)
	{
	cid->nr_contig++;
	return ((cid->dcluster + cid->nr_contig) == dclus);
	}

	static inline void cache_init(struct fat_cache_id *cid, int fclus, int dclus)
	{
	cid->id = FAT_CACHE_VALID;
	cid->fcluster = fclus;
	cid->dcluster = dclus;
	cid->nr_contig = 0;
	}

	int fat_get_cluster(struct inode inode, int cluster, int fclus, int *dclus)
	{
	struct super_block *sb = inode->i_sb;
	const int limit = sb->s_maxbytes >> MSDOS_SB(sb)->cluster_bits;
	struct fat_cache_id cid;
	int nr;

	BUG_ON(MSDOS_I(inode)->i_start == 0);

	*fclus = 0;
	*dclus = MSDOS_I(inode)->i_start;
	if (cluster == 0)
	return 0;

	if (fat_cache_lookup(inode, cluster, &cid, fclus, dclus) < 0) {
	/*
	* dummy, always not contiguous
	* This is reinitialized by cache_init(), later.
	*/
	cache_init(&cid, -1, -1);
	}

	while (*fclus < cluster) {
	/* prevent the infinite loop of cluster chain */
	if (*fclus > limit) {
	fat_fs_panic(sb, "%s: detected the cluster chain loop"
	" (i_pos %lld)", __FUNCTION__,
	MSDOS_I(inode)->i_pos);
	return -EIO;
	}

	nr = fat_access(sb, *dclus, -1);
	if (nr < 0)
	return nr;
	else if (nr == FAT_ENT_FREE) {
	fat_fs_panic(sb, "%s: invalid cluster chain"
	" (i_pos %lld)", __FUNCTION__,
	MSDOS_I(inode)->i_pos);
	return -EIO;
	} else if (nr == FAT_ENT_EOF) {
	fat_cache_add(inode, &cid);
	return FAT_ENT_EOF;
	}
	(*fclus)++;
	*dclus = nr;
	if (!cache_contiguous(&cid, *dclus))
	cache_init(&cid, fclus, dclus);
	}
	fat_cache_add(inode, &cid);
	return 0;
	}

	static int fat_bmap_cluster(struct inode *inode, int cluster)
	{
	struct super_block *sb = inode->i_sb;
	int ret, fclus, dclus;

	if (MSDOS_I(inode)->i_start == 0)
	return 0;

	ret = fat_get_cluster(inode, cluster, &fclus, &dclus);
	if (ret < 0)
	return ret;
	else if (ret == FAT_ENT_EOF) {
	fat_fs_panic(sb, "%s: request beyond EOF (i_pos %lld)",
	__FUNCTION__, MSDOS_I(inode)->i_pos);
	return -EIO;
	}
	return dclus;
	}

	int fat_bmap(struct inode inode, sector_t sector, sector_t phys)
	{
	struct super_block *sb = inode->i_sb;
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	sector_t last_block;
	int cluster, offset;

	*phys = 0;
	if ((sbi->fat_bits != 32) &&
	(inode->i_ino == MSDOS_ROOT_INO \|\| (S_ISDIR(inode->i_mode) &&
	!MSDOS_I(inode)->i_start))) {
	if (sector < (sbi->dir_entries >> sbi->dir_per_block_bits))
	*phys = sector + sbi->dir_start;
	return 0;
	}
	last_block = (MSDOS_I(inode)->mmu_private + (sb->s_blocksize - 1))
	>> sb->s_blocksize_bits;
	if (sector >= last_block)
	return 0;

	cluster = sector >> (sbi->cluster_bits - sb->s_blocksize_bits);
	offset = sector & (sbi->sec_per_clus - 1);
	cluster = fat_bmap_cluster(inode, cluster);
	if (cluster < 0)
	return cluster;
	else if (cluster)
	*phys = fat_clus_to_blknr(sbi, cluster) + offset;
	return 0;
	}