aboutsummaryrefslogtreecommitdiffstats
path: root/fs/fat/cache.c
blob: 3a9ecac8d61f081e295655822d311dc27f51f02f (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
/*
 *  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 struct kmem_cache *fat_cache_cachep;

static void init_once(struct kmem_cache *cachep, 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);
			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_panic(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_panic(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_panic(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)
{
	struct super_block *sb = inode->i_sb;
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	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 = (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;
		*mapped_blocks = sbi->sec_per_clus - offset;
		if (*mapped_blocks > last_block - sector)
			*mapped_blocks = last_block - sector;
	}
	return 0;
}