fs/fat/cache.c

   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>
  12 #include <linux/slab.h>
  13 #include <linux/buffer_head.h>
  14 #include "fat.h"
  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
  38 static struct kmem_cache *fat_cache_cachep;
  39
  40 static void init_once(void *foo)
  41 {
  42         struct fat_cache *cache = (struct fat_cache *)foo;
  43
  44         INIT_LIST_HEAD(&cache->cache_list);
  45 }
  46
  47 int __init fat_cache_init(void)
  48 {
  49         fat_cache_cachep = kmem_cache_create("fat_cache",
  50                                 sizeof(struct fat_cache),
  51                                 0, SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD,
  52                                 init_once);
  53         if (fat_cache_cachep == NULL)
  54                 return -ENOMEM;
  55         return 0;
  56 }
  57
  58 void fat_cache_destroy(void)
  59 {
  60         kmem_cache_destroy(fat_cache_cachep);
  61 }
  62
  63 static inline struct fat_cache *fat_cache_alloc(struct inode *inode)
  64 {
  65         return kmem_cache_alloc(fat_cache_cachep, GFP_NOFS);
  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);
 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
 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) {
 252                         fat_fs_error_ratelimit(sb,
 253                                         "%s: detected the cluster chain loop"
 254                                         " (i_pos %lld)", __func__,
 255                                         MSDOS_I(inode)->i_pos);
 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) {
 264                         fat_fs_error_ratelimit(sb, "%s: invalid cluster chain"
 265                                                " (i_pos %lld)", __func__,
 266                                                MSDOS_I(inode)->i_pos);
 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) {
 297                 fat_fs_error(sb, "%s: request beyond EOF (i_pos %lld)",
 298                              __func__, MSDOS_I(inode)->i_pos);
 299                 return -EIO;
 300         }
 301         return dclus;
 302 }
 303
 304 int fat_bmap(struct inode *inode, sector_t sector, sector_t *phys,
 305              unsigned long *mapped_blocks, int create)
 306 {
 307         struct super_block *sb = inode->i_sb;
 308         struct msdos_sb_info *sbi = MSDOS_SB(sb);
 309         const unsigned long blocksize = sb->s_blocksize;
 310         const unsigned char blocksize_bits = sb->s_blocksize_bits;
 311         sector_t last_block;
 312         int cluster, offset;
 313
 314         *phys = 0;
 315         *mapped_blocks = 0;
 316         if ((sbi->fat_bits != 32) && (inode->i_ino == MSDOS_ROOT_INO)) {
 317                 if (sector < (sbi->dir_entries >> sbi->dir_per_block_bits)) {
 318                         *phys = sector + sbi->dir_start;
 319                         *mapped_blocks = 1;
 320                 }
 321                 return 0;
 322         }
 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         }
 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;
 344         else if (cluster) {
 345                 *phys = fat_clus_to_blknr(sbi, cluster) + offset;
 346                 *mapped_blocks = sbi->sec_per_clus - offset;
 347                 if (*mapped_blocks > last_block - sector)
 348                         *mapped_blocks = last_block - sector;
 349         }
 350         return 0;
 351 }