xref: /openbmc/linux/fs/fat/cache.c (revision b830f94f)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  *  linux/fs/fat/cache.c
4  *
5  *  Written 1992,1993 by Werner Almesberger
6  *
7  *  Mar 1999. AV. Changed cache, so that it uses the starting cluster instead
8  *	of inode number.
9  *  May 1999. AV. Fixed the bogosity with FAT32 (read "FAT28"). Fscking lusers.
10  */
11 
12 #include <linux/slab.h>
13 #include "fat.h"
14 
15 /* this must be > 0. */
16 #define FAT_MAX_CACHE	8
17 
18 struct fat_cache {
19 	struct list_head cache_list;
20 	int nr_contig;	/* number of contiguous clusters */
21 	int fcluster;	/* cluster number in the file. */
22 	int dcluster;	/* cluster number on disk. */
23 };
24 
25 struct fat_cache_id {
26 	unsigned int id;
27 	int nr_contig;
28 	int fcluster;
29 	int dcluster;
30 };
31 
32 static inline int fat_max_cache(struct inode *inode)
33 {
34 	return FAT_MAX_CACHE;
35 }
36 
37 static struct kmem_cache *fat_cache_cachep;
38 
39 static void init_once(void *foo)
40 {
41 	struct fat_cache *cache = (struct fat_cache *)foo;
42 
43 	INIT_LIST_HEAD(&cache->cache_list);
44 }
45 
46 int __init fat_cache_init(void)
47 {
48 	fat_cache_cachep = kmem_cache_create("fat_cache",
49 				sizeof(struct fat_cache),
50 				0, SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD,
51 				init_once);
52 	if (fat_cache_cachep == NULL)
53 		return -ENOMEM;
54 	return 0;
55 }
56 
57 void fat_cache_destroy(void)
58 {
59 	kmem_cache_destroy(fat_cache_cachep);
60 }
61 
62 static inline struct fat_cache *fat_cache_alloc(struct inode *inode)
63 {
64 	return kmem_cache_alloc(fat_cache_cachep, GFP_NOFS);
65 }
66 
67 static inline void fat_cache_free(struct fat_cache *cache)
68 {
69 	BUG_ON(!list_empty(&cache->cache_list));
70 	kmem_cache_free(fat_cache_cachep, cache);
71 }
72 
73 static inline void fat_cache_update_lru(struct inode *inode,
74 					struct fat_cache *cache)
75 {
76 	if (MSDOS_I(inode)->cache_lru.next != &cache->cache_list)
77 		list_move(&cache->cache_list, &MSDOS_I(inode)->cache_lru);
78 }
79 
80 static int fat_cache_lookup(struct inode *inode, int fclus,
81 			    struct fat_cache_id *cid,
82 			    int *cached_fclus, int *cached_dclus)
83 {
84 	static struct fat_cache nohit = { .fcluster = 0, };
85 
86 	struct fat_cache *hit = &nohit, *p;
87 	int offset = -1;
88 
89 	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
90 	list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
91 		/* Find the cache of "fclus" or nearest cache. */
92 		if (p->fcluster <= fclus && hit->fcluster < p->fcluster) {
93 			hit = p;
94 			if ((hit->fcluster + hit->nr_contig) < fclus) {
95 				offset = hit->nr_contig;
96 			} else {
97 				offset = fclus - hit->fcluster;
98 				break;
99 			}
100 		}
101 	}
102 	if (hit != &nohit) {
103 		fat_cache_update_lru(inode, hit);
104 
105 		cid->id = MSDOS_I(inode)->cache_valid_id;
106 		cid->nr_contig = hit->nr_contig;
107 		cid->fcluster = hit->fcluster;
108 		cid->dcluster = hit->dcluster;
109 		*cached_fclus = cid->fcluster + offset;
110 		*cached_dclus = cid->dcluster + offset;
111 	}
112 	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
113 
114 	return offset;
115 }
116 
117 static struct fat_cache *fat_cache_merge(struct inode *inode,
118 					 struct fat_cache_id *new)
119 {
120 	struct fat_cache *p;
121 
122 	list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
123 		/* Find the same part as "new" in cluster-chain. */
124 		if (p->fcluster == new->fcluster) {
125 			BUG_ON(p->dcluster != new->dcluster);
126 			if (new->nr_contig > p->nr_contig)
127 				p->nr_contig = new->nr_contig;
128 			return p;
129 		}
130 	}
131 	return NULL;
132 }
133 
134 static void fat_cache_add(struct inode *inode, struct fat_cache_id *new)
135 {
136 	struct fat_cache *cache, *tmp;
137 
138 	if (new->fcluster == -1) /* dummy cache */
139 		return;
140 
141 	spin_lock(&MSDOS_I(inode)->cache_lru_lock);
142 	if (new->id != FAT_CACHE_VALID &&
143 	    new->id != MSDOS_I(inode)->cache_valid_id)
144 		goto out;	/* this cache was invalidated */
145 
146 	cache = fat_cache_merge(inode, new);
147 	if (cache == NULL) {
148 		if (MSDOS_I(inode)->nr_caches < fat_max_cache(inode)) {
149 			MSDOS_I(inode)->nr_caches++;
150 			spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
151 
152 			tmp = fat_cache_alloc(inode);
153 			if (!tmp) {
154 				spin_lock(&MSDOS_I(inode)->cache_lru_lock);
155 				MSDOS_I(inode)->nr_caches--;
156 				spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
157 				return;
158 			}
159 
160 			spin_lock(&MSDOS_I(inode)->cache_lru_lock);
161 			cache = fat_cache_merge(inode, new);
162 			if (cache != NULL) {
163 				MSDOS_I(inode)->nr_caches--;
164 				fat_cache_free(tmp);
165 				goto out_update_lru;
166 			}
167 			cache = tmp;
168 		} else {
169 			struct list_head *p = MSDOS_I(inode)->cache_lru.prev;
170 			cache = list_entry(p, struct fat_cache, cache_list);
171 		}
172 		cache->fcluster = new->fcluster;
173 		cache->dcluster = new->dcluster;
174 		cache->nr_contig = new->nr_contig;
175 	}
176 out_update_lru:
177 	fat_cache_update_lru(inode, cache);
178 out:
179 	spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
180 }
181 
182 /*
183  * Cache invalidation occurs rarely, thus the LRU chain is not updated. It
184  * fixes itself after a while.
185  */
186 static void __fat_cache_inval_inode(struct inode *inode)
187 {
188 	struct msdos_inode_info *i = MSDOS_I(inode);
189 	struct fat_cache *cache;
190 
191 	while (!list_empty(&i->cache_lru)) {
192 		cache = list_entry(i->cache_lru.next,
193 				   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 	struct msdos_sb_info *sbi = MSDOS_SB(sb);
229 	const int limit = sb->s_maxbytes >> sbi->cluster_bits;
230 	struct fat_entry fatent;
231 	struct fat_cache_id cid;
232 	int nr;
233 
234 	BUG_ON(MSDOS_I(inode)->i_start == 0);
235 
236 	*fclus = 0;
237 	*dclus = MSDOS_I(inode)->i_start;
238 	if (!fat_valid_entry(sbi, *dclus)) {
239 		fat_fs_error_ratelimit(sb,
240 			"%s: invalid start cluster (i_pos %lld, start %08x)",
241 			__func__, MSDOS_I(inode)->i_pos, *dclus);
242 		return -EIO;
243 	}
244 	if (cluster == 0)
245 		return 0;
246 
247 	if (fat_cache_lookup(inode, cluster, &cid, fclus, dclus) < 0) {
248 		/*
249 		 * dummy, always not contiguous
250 		 * This is reinitialized by cache_init(), later.
251 		 */
252 		cache_init(&cid, -1, -1);
253 	}
254 
255 	fatent_init(&fatent);
256 	while (*fclus < cluster) {
257 		/* prevent the infinite loop of cluster chain */
258 		if (*fclus > limit) {
259 			fat_fs_error_ratelimit(sb,
260 				"%s: detected the cluster chain loop (i_pos %lld)",
261 				__func__, MSDOS_I(inode)->i_pos);
262 			nr = -EIO;
263 			goto out;
264 		}
265 
266 		nr = fat_ent_read(inode, &fatent, *dclus);
267 		if (nr < 0)
268 			goto out;
269 		else if (nr == FAT_ENT_FREE) {
270 			fat_fs_error_ratelimit(sb,
271 				"%s: invalid cluster chain (i_pos %lld)",
272 				__func__, MSDOS_I(inode)->i_pos);
273 			nr = -EIO;
274 			goto out;
275 		} else if (nr == FAT_ENT_EOF) {
276 			fat_cache_add(inode, &cid);
277 			goto out;
278 		}
279 		(*fclus)++;
280 		*dclus = nr;
281 		if (!cache_contiguous(&cid, *dclus))
282 			cache_init(&cid, *fclus, *dclus);
283 	}
284 	nr = 0;
285 	fat_cache_add(inode, &cid);
286 out:
287 	fatent_brelse(&fatent);
288 	return nr;
289 }
290 
291 static int fat_bmap_cluster(struct inode *inode, int cluster)
292 {
293 	struct super_block *sb = inode->i_sb;
294 	int ret, fclus, dclus;
295 
296 	if (MSDOS_I(inode)->i_start == 0)
297 		return 0;
298 
299 	ret = fat_get_cluster(inode, cluster, &fclus, &dclus);
300 	if (ret < 0)
301 		return ret;
302 	else if (ret == FAT_ENT_EOF) {
303 		fat_fs_error(sb, "%s: request beyond EOF (i_pos %lld)",
304 			     __func__, MSDOS_I(inode)->i_pos);
305 		return -EIO;
306 	}
307 	return dclus;
308 }
309 
310 int fat_get_mapped_cluster(struct inode *inode, sector_t sector,
311 			   sector_t last_block,
312 			   unsigned long *mapped_blocks, sector_t *bmap)
313 {
314 	struct super_block *sb = inode->i_sb;
315 	struct msdos_sb_info *sbi = MSDOS_SB(sb);
316 	int cluster, offset;
317 
318 	cluster = sector >> (sbi->cluster_bits - sb->s_blocksize_bits);
319 	offset  = sector & (sbi->sec_per_clus - 1);
320 	cluster = fat_bmap_cluster(inode, cluster);
321 	if (cluster < 0)
322 		return cluster;
323 	else if (cluster) {
324 		*bmap = fat_clus_to_blknr(sbi, cluster) + offset;
325 		*mapped_blocks = sbi->sec_per_clus - offset;
326 		if (*mapped_blocks > last_block - sector)
327 			*mapped_blocks = last_block - sector;
328 	}
329 
330 	return 0;
331 }
332 
333 static int is_exceed_eof(struct inode *inode, sector_t sector,
334 			 sector_t *last_block, int create)
335 {
336 	struct super_block *sb = inode->i_sb;
337 	const unsigned long blocksize = sb->s_blocksize;
338 	const unsigned char blocksize_bits = sb->s_blocksize_bits;
339 
340 	*last_block = (i_size_read(inode) + (blocksize - 1)) >> blocksize_bits;
341 	if (sector >= *last_block) {
342 		if (!create)
343 			return 1;
344 
345 		/*
346 		 * ->mmu_private can access on only allocation path.
347 		 * (caller must hold ->i_mutex)
348 		 */
349 		*last_block = (MSDOS_I(inode)->mmu_private + (blocksize - 1))
350 			>> blocksize_bits;
351 		if (sector >= *last_block)
352 			return 1;
353 	}
354 
355 	return 0;
356 }
357 
358 int fat_bmap(struct inode *inode, sector_t sector, sector_t *phys,
359 	     unsigned long *mapped_blocks, int create, bool from_bmap)
360 {
361 	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
362 	sector_t last_block;
363 
364 	*phys = 0;
365 	*mapped_blocks = 0;
366 	if (!is_fat32(sbi) && (inode->i_ino == MSDOS_ROOT_INO)) {
367 		if (sector < (sbi->dir_entries >> sbi->dir_per_block_bits)) {
368 			*phys = sector + sbi->dir_start;
369 			*mapped_blocks = 1;
370 		}
371 		return 0;
372 	}
373 
374 	if (!from_bmap) {
375 		if (is_exceed_eof(inode, sector, &last_block, create))
376 			return 0;
377 	} else {
378 		last_block = inode->i_blocks >>
379 				(inode->i_sb->s_blocksize_bits - 9);
380 		if (sector >= last_block)
381 			return 0;
382 	}
383 
384 	return fat_get_mapped_cluster(inode, sector, last_block, mapped_blocks,
385 				      phys);
386 }
387