[linux.git] / fs / fat / cache.c

/*
 *  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/slab.h>
#include <linux/buffer_head.h>
#include "fat.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 struct kmem_cache *fat_cache_cachep;

static void init_once(void *foo)
{
	struct fat_cache *cache = (struct fat_cache *)foo;

	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|SLAB_MEM_SPREAD,
				init_once);
	if (fat_cache_cachep == NULL)
		return -ENOMEM;
	return 0;
}

void fat_cache_destroy(void)
{
	kmem_cache_destroy(fat_cache_cachep);
}

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

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);
			if (!tmp) {
				spin_lock(&MSDOS_I(inode)->cache_lru_lock);
				MSDOS_I(inode)->nr_caches--;
				spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
				return;
			}

			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 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_entry fatent;
	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);
	}

	fatent_init(&fatent);
	while (*fclus < cluster) {
		/* prevent the infinite loop of cluster chain */
		if (*fclus > limit) {
			fat_fs_error_ratelimit(sb,
					"%s: detected the cluster chain loop"
					" (i_pos %lld)", __func__,
					MSDOS_I(inode)->i_pos);
			nr = -EIO;
			goto out;
		}

		nr = fat_ent_read(inode, &fatent, *dclus);
		if (nr < 0)
			goto out;
		else if (nr == FAT_ENT_FREE) {
			fat_fs_error_ratelimit(sb, "%s: invalid cluster chain"
					       " (i_pos %lld)", __func__,
					       MSDOS_I(inode)->i_pos);
			nr = -EIO;
			goto out;
		} else if (nr == FAT_ENT_EOF) {
			fat_cache_add(inode, &cid);
			goto out;
		}
		(*fclus)++;
		*dclus = nr;
		if (!cache_contiguous(&cid, *dclus))
			cache_init(&cid, *fclus, *dclus);
	}
	nr = 0;
	fat_cache_add(inode, &cid);
out:
	fatent_brelse(&fatent);
	return nr;
}

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_error(sb, "%s: request beyond EOF (i_pos %lld)",
			     __func__, MSDOS_I(inode)->i_pos);
		return -EIO;
	}
	return dclus;
}

int fat_bmap(struct inode *inode, sector_t sector, sector_t *phys,
	     unsigned long *mapped_blocks, int create)
{
	struct super_block *sb = inode->i_sb;
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	const unsigned long blocksize = sb->s_blocksize;
	const unsigned char blocksize_bits = sb->s_blocksize_bits;
	sector_t last_block;
	int cluster, offset;

	*phys = 0;
	*mapped_blocks = 0;
	if ((sbi->fat_bits != 32) && (inode->i_ino == MSDOS_ROOT_INO)) {
		if (sector < (sbi->dir_entries >> sbi->dir_per_block_bits)) {
			*phys = sector + sbi->dir_start;
			*mapped_blocks = 1;
		}
		return 0;
	}

	last_block = (i_size_read(inode) + (blocksize - 1)) >> blocksize_bits;
	if (sector >= last_block) {
		if (!create)
			return 0;

		/*
		 * ->mmu_private can access on only allocation path.
		 * (caller must hold ->i_mutex)
		 */
		last_block = (MSDOS_I(inode)->mmu_private + (blocksize - 1))
			>> 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;
		*mapped_blocks = sbi->sec_per_clus - offset;
		if (*mapped_blocks > last_block - sector)
			*mapped_blocks = last_block - sector;
	}
	return 0;
}
Commit	Line	Data
1da177e4 LT	1	/*
	2	* linux/fs/fat/cache.c
	3	*
	4	* Written 1992,1993 by Werner Almesberger
	5	*
	6	* Mar 1999. AV. Changed cache, so that it uses the starting cluster instead
	7	* of inode number.
	8	* May 1999. AV. Fixed the bogosity with FAT32 (read "FAT28"). Fscking lusers.
	9	*/
	10
	11	#include <linux/fs.h>
5a0e3ad6	12	#include <linux/slab.h>
1da177e4	13	#include <linux/buffer_head.h>
9e975dae	14	#include "fat.h"
1da177e4 LT	15
	16	/* this must be > 0. */
	17	#define FAT_MAX_CACHE 8
	18
	19	struct fat_cache {
	20	struct list_head cache_list;
	21	int nr_contig; /* number of contiguous clusters */
	22	int fcluster; /* cluster number in the file. */
	23	int dcluster; /* cluster number on disk. */
	24	};
	25
	26	struct fat_cache_id {
	27	unsigned int id;
	28	int nr_contig;
	29	int fcluster;
	30	int dcluster;
	31	};
	32
	33	static inline int fat_max_cache(struct inode *inode)
	34	{
	35	return FAT_MAX_CACHE;
	36	}
	37
e18b890b	38	static struct kmem_cache *fat_cache_cachep;
1da177e4	39
51cc5068	40	static void init_once(void *foo)
1da177e4 LT	41	{
	42	struct fat_cache cache = (struct fat_cache )foo;
	43
a35afb83	44	INIT_LIST_HEAD(&cache->cache_list);
1da177e4 LT	45	}
	46
	47	int __init fat_cache_init(void)
	48	{
	49	fat_cache_cachep = kmem_cache_create("fat_cache",
	50	sizeof(struct fat_cache),
4b6a9316	51	0, SLAB_RECLAIM_ACCOUNT\|SLAB_MEM_SPREAD,
20c2df83	52	init_once);
1da177e4 LT	53	if (fat_cache_cachep == NULL)
	54	return -ENOMEM;
	55	return 0;
	56	}
	57
ef6689ef	58	void fat_cache_destroy(void)
1da177e4	59	{
1a1d92c1	60	kmem_cache_destroy(fat_cache_cachep);
1da177e4 LT	61	}
	62
	63	static inline struct fat_cache fat_cache_alloc(struct inode inode)
	64	{
8f593427	65	return kmem_cache_alloc(fat_cache_cachep, GFP_NOFS);
1da177e4 LT	66	}
	67
	68	static inline void fat_cache_free(struct fat_cache *cache)
	69	{
	70	BUG_ON(!list_empty(&cache->cache_list));
	71	kmem_cache_free(fat_cache_cachep, cache);
	72	}
	73
	74	static inline void fat_cache_update_lru(struct inode *inode,
	75	struct fat_cache *cache)
	76	{
	77	if (MSDOS_I(inode)->cache_lru.next != &cache->cache_list)
	78	list_move(&cache->cache_list, &MSDOS_I(inode)->cache_lru);
	79	}
	80
	81	static int fat_cache_lookup(struct inode *inode, int fclus,
	82	struct fat_cache_id *cid,
	83	int cached_fclus, int cached_dclus)
	84	{
	85	static struct fat_cache nohit = { .fcluster = 0, };
	86
	87	struct fat_cache hit = &nohit, p;
	88	int offset = -1;
	89
	90	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
	91	list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
	92	/* Find the cache of "fclus" or nearest cache. */
	93	if (p->fcluster <= fclus && hit->fcluster < p->fcluster) {
	94	hit = p;
	95	if ((hit->fcluster + hit->nr_contig) < fclus) {
	96	offset = hit->nr_contig;
	97	} else {
	98	offset = fclus - hit->fcluster;
	99	break;
	100	}
	101	}
	102	}
	103	if (hit != &nohit) {
	104	fat_cache_update_lru(inode, hit);
	105
	106	cid->id = MSDOS_I(inode)->cache_valid_id;
	107	cid->nr_contig = hit->nr_contig;
	108	cid->fcluster = hit->fcluster;
	109	cid->dcluster = hit->dcluster;
	110	*cached_fclus = cid->fcluster + offset;
	111	*cached_dclus = cid->dcluster + offset;
	112	}
	113	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
	114
	115	return offset;
	116	}
	117
	118	static struct fat_cache fat_cache_merge(struct inode inode,
	119	struct fat_cache_id *new)
	120	{
	121	struct fat_cache *p;
	122
	123	list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
	124	/* Find the same part as "new" in cluster-chain. */
	125	if (p->fcluster == new->fcluster) {
	126	BUG_ON(p->dcluster != new->dcluster);
	127	if (new->nr_contig > p->nr_contig)
	128	p->nr_contig = new->nr_contig;
	129	return p;
130	}
131	}
132	return NULL;
133	}
134
135	static void fat_cache_add(struct inode inode, struct fat_cache_id new)
136	{
137	struct fat_cache cache, tmp;
138
139	if (new->fcluster == -1) /* dummy cache */
140	return;
141
142	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
143	if (new->id != FAT_CACHE_VALID &&
144	new->id != MSDOS_I(inode)->cache_valid_id)
145	goto out; /* this cache was invalidated */
146
147	cache = fat_cache_merge(inode, new);
148	if (cache == NULL) {
149	if (MSDOS_I(inode)->nr_caches < fat_max_cache(inode)) {
150	MSDOS_I(inode)->nr_caches++;
151	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
152
153	tmp = fat_cache_alloc(inode);
70030929 OH	154	if (!tmp) {
	155	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
	156	MSDOS_I(inode)->nr_caches--;
	157	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
	158	return;
	159	}
	160
1da177e4 LT	161	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
	162	cache = fat_cache_merge(inode, new);
	163	if (cache != NULL) {
	164	MSDOS_I(inode)->nr_caches--;
	165	fat_cache_free(tmp);
	166	goto out_update_lru;
	167	}
	168	cache = tmp;
	169	} else {
	170	struct list_head *p = MSDOS_I(inode)->cache_lru.prev;
	171	cache = list_entry(p, struct fat_cache, cache_list);
	172	}
	173	cache->fcluster = new->fcluster;
	174	cache->dcluster = new->dcluster;
	175	cache->nr_contig = new->nr_contig;
	176	}
	177	out_update_lru:
	178	fat_cache_update_lru(inode, cache);
	179	out:
	180	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
	181	}
	182
	183	/*
	184	* Cache invalidation occurs rarely, thus the LRU chain is not updated. It
	185	* fixes itself after a while.
	186	*/
	187	static void __fat_cache_inval_inode(struct inode *inode)
	188	{
	189	struct msdos_inode_info *i = MSDOS_I(inode);
	190	struct fat_cache *cache;
	191
	192	while (!list_empty(&i->cache_lru)) {
	193	cache = list_entry(i->cache_lru.next, struct fat_cache, cache_list);
	194	list_del_init(&cache->cache_list);
	195	i->nr_caches--;
	196	fat_cache_free(cache);
	197	}
	198	/* Update. The copy of caches before this id is discarded. */
	199	i->cache_valid_id++;
	200	if (i->cache_valid_id == FAT_CACHE_VALID)
	201	i->cache_valid_id++;
	202	}
	203
	204	void fat_cache_inval_inode(struct inode *inode)
	205	{
	206	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
	207	__fat_cache_inval_inode(inode);
	208	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
	209	}
	210
	211	static inline int cache_contiguous(struct fat_cache_id *cid, int dclus)
	212	{
	213	cid->nr_contig++;
	214	return ((cid->dcluster + cid->nr_contig) == dclus);
	215	}
	216
	217	static inline void cache_init(struct fat_cache_id *cid, int fclus, int dclus)
	218	{
	219	cid->id = FAT_CACHE_VALID;
	220	cid->fcluster = fclus;
	221	cid->dcluster = dclus;
	222	cid->nr_contig = 0;
	223	}
	224
225	int fat_get_cluster(struct inode inode, int cluster, int fclus, int *dclus)
226	{
227	struct super_block *sb = inode->i_sb;
228	const int limit = sb->s_maxbytes >> MSDOS_SB(sb)->cluster_bits;
229	struct fat_entry fatent;
230	struct fat_cache_id cid;
231	int nr;
232
233	BUG_ON(MSDOS_I(inode)->i_start == 0);
234
235	*fclus = 0;
236	*dclus = MSDOS_I(inode)->i_start;
237	if (cluster == 0)
238	return 0;
239
240	if (fat_cache_lookup(inode, cluster, &cid, fclus, dclus) < 0) {
241	/*
242	* dummy, always not contiguous
243	* This is reinitialized by cache_init(), later.
244	*/
245	cache_init(&cid, -1, -1);
246	}
247
248	fatent_init(&fatent);
249	while (*fclus < cluster) {
250	/* prevent the infinite loop of cluster chain */
251	if (*fclus > limit) {
aaa04b48 OH	252	fat_fs_error_ratelimit(sb,
	253	"%s: detected the cluster chain loop"
	254	" (i_pos %lld)", __func__,
	255	MSDOS_I(inode)->i_pos);
1da177e4 LT	256	nr = -EIO;
	257	goto out;
	258	}
	259
	260	nr = fat_ent_read(inode, &fatent, *dclus);
	261	if (nr < 0)
	262	goto out;
	263	else if (nr == FAT_ENT_FREE) {
aaa04b48 OH	264	fat_fs_error_ratelimit(sb, "%s: invalid cluster chain"
	265	" (i_pos %lld)", __func__,
	266	MSDOS_I(inode)->i_pos);
1da177e4 LT	267	nr = -EIO;
	268	goto out;
	269	} else if (nr == FAT_ENT_EOF) {
	270	fat_cache_add(inode, &cid);
	271	goto out;
	272	}
	273	(*fclus)++;
	274	*dclus = nr;
	275	if (!cache_contiguous(&cid, *dclus))
	276	cache_init(&cid, fclus, dclus);
	277	}
	278	nr = 0;
	279	fat_cache_add(inode, &cid);
	280	out:
	281	fatent_brelse(&fatent);
	282	return nr;
	283	}
	284
	285	static int fat_bmap_cluster(struct inode *inode, int cluster)
	286	{
	287	struct super_block *sb = inode->i_sb;
	288	int ret, fclus, dclus;
	289
	290	if (MSDOS_I(inode)->i_start == 0)
	291	return 0;
	292
	293	ret = fat_get_cluster(inode, cluster, &fclus, &dclus);
	294	if (ret < 0)
	295	return ret;
	296	else if (ret == FAT_ENT_EOF) {
85c78591	297	fat_fs_error(sb, "%s: request beyond EOF (i_pos %lld)",
8e24eea7	298	__func__, MSDOS_I(inode)->i_pos);
1da177e4 LT	299	return -EIO;
	300	}
	301	return dclus;
	302	}
	303
e5174baa	304	int fat_bmap(struct inode inode, sector_t sector, sector_t phys,
2bdf67eb	305	unsigned long *mapped_blocks, int create)
1da177e4 LT	306	{
	307	struct super_block *sb = inode->i_sb;
	308	struct msdos_sb_info *sbi = MSDOS_SB(sb);
2bdf67eb OH	309	const unsigned long blocksize = sb->s_blocksize;
2bdf67eb OH	310	const unsigned char blocksize_bits = sb->s_blocksize_bits;
1da177e4 LT	311	sector_t last_block;
	312	int cluster, offset;
	313
	314	*phys = 0;
e5174baa	315	*mapped_blocks = 0;
1da177e4	316	if ((sbi->fat_bits != 32) && (inode->i_ino == MSDOS_ROOT_INO)) {
e5174baa	317	if (sector < (sbi->dir_entries >> sbi->dir_per_block_bits)) {
1da177e4	318	*phys = sector + sbi->dir_start;
e5174baa OH	319	*mapped_blocks = 1;
e5174baa OH	320	}
1da177e4 LT	321	return 0;
1da177e4 LT	322	}
2bdf67eb OH	323
	324	last_block = (i_size_read(inode) + (blocksize - 1)) >> blocksize_bits;
	325	if (sector >= last_block) {
	326	if (!create)
	327	return 0;
	328
	329	/*
	330	* ->mmu_private can access on only allocation path.
	331	* (caller must hold ->i_mutex)
	332	*/
	333	last_block = (MSDOS_I(inode)->mmu_private + (blocksize - 1))
	334	>> blocksize_bits;
	335	if (sector >= last_block)
	336	return 0;
	337	}
1da177e4 LT	338
	339	cluster = sector >> (sbi->cluster_bits - sb->s_blocksize_bits);
	340	offset = sector & (sbi->sec_per_clus - 1);
	341	cluster = fat_bmap_cluster(inode, cluster);
	342	if (cluster < 0)
	343	return cluster;
e5174baa	344	else if (cluster) {
1da177e4	345	*phys = fat_clus_to_blknr(sbi, cluster) + offset;
e5174baa OH	346	*mapped_blocks = sbi->sec_per_clus - offset;
	347	if (*mapped_blocks > last_block - sector)
	348	*mapped_blocks = last_block - sector;
	349	}
1da177e4 LT	350	return 0;
1da177e4 LT	351	}