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/msdos_fs.h>
  13 #include <linux/buffer_head.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, struct kmem_cache *cachep, unsigned long flags)
  40 {
  41         struct fat_cache *cache = (struct fat_cache *)foo;
  42
  43         if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
  44             SLAB_CTOR_CONSTRUCTOR)
  45                 INIT_LIST_HEAD(&cache->cache_list);
  46 }
  47
  48 int __init fat_cache_init(void)
  49 {
  50         fat_cache_cachep = kmem_cache_create("fat_cache",
  51                                 sizeof(struct fat_cache),
  52                                 0, SLAB_RECLAIM_ACCOUNT|SLAB_MEM_SPREAD,
  53                                 init_once, NULL);
  54         if (fat_cache_cachep == NULL)
  55                 return -ENOMEM;
  56         return 0;
  57 }
  58
  59 void fat_cache_destroy(void)
  60 {
  61         kmem_cache_destroy(fat_cache_cachep);
  62 }
  63
  64 static inline struct fat_cache *fat_cache_alloc(struct inode *inode)
  65 {
  66         return kmem_cache_alloc(fat_cache_cachep, GFP_KERNEL);
  67 }
  68
  69 static inline void fat_cache_free(struct fat_cache *cache)
  70 {
  71         BUG_ON(!list_empty(&cache->cache_list));
  72         kmem_cache_free(fat_cache_cachep, cache);
  73 }
  74
  75 static inline void fat_cache_update_lru(struct inode *inode,
  76                                         struct fat_cache *cache)
  77 {
  78         if (MSDOS_I(inode)->cache_lru.next != &cache->cache_list)
  79                 list_move(&cache->cache_list, &MSDOS_I(inode)->cache_lru);
  80 }
  81
  82 static int fat_cache_lookup(struct inode *inode, int fclus,
  83                             struct fat_cache_id *cid,
  84                             int *cached_fclus, int *cached_dclus)
  85 {
  86         static struct fat_cache nohit = { .fcluster = 0, };
  87
  88         struct fat_cache *hit = &nohit, *p;
  89         int offset = -1;
  90
  91         spin_lock(&MSDOS_I(inode)->cache_lru_lock);
  92         list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
  93                 /* Find the cache of "fclus" or nearest cache. */
  94                 if (p->fcluster <= fclus && hit->fcluster < p->fcluster) {
  95                         hit = p;
  96                         if ((hit->fcluster + hit->nr_contig) < fclus) {
  97                                 offset = hit->nr_contig;
  98                         } else {
  99                                 offset = fclus - hit->fcluster;
 100                                 break;
 101                         }
 102                 }
 103         }
 104         if (hit != &nohit) {
 105                 fat_cache_update_lru(inode, hit);
 106
 107                 cid->id = MSDOS_I(inode)->cache_valid_id;
 108                 cid->nr_contig = hit->nr_contig;
 109                 cid->fcluster = hit->fcluster;
 110                 cid->dcluster = hit->dcluster;
 111                 *cached_fclus = cid->fcluster + offset;
 112                 *cached_dclus = cid->dcluster + offset;
 113         }
 114         spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 115
 116         return offset;
 117 }
 118
 119 static struct fat_cache *fat_cache_merge(struct inode *inode,
 120                                          struct fat_cache_id *new)
 121 {
 122         struct fat_cache *p;
 123
 124         list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
 125                 /* Find the same part as "new" in cluster-chain. */
 126                 if (p->fcluster == new->fcluster) {
 127                         BUG_ON(p->dcluster != new->dcluster);
 128                         if (new->nr_contig > p->nr_contig)
 129                                 p->nr_contig = new->nr_contig;
 130                         return p;
 131                 }
 132         }
 133         return NULL;
 134 }
 135
 136 static void fat_cache_add(struct inode *inode, struct fat_cache_id *new)
 137 {
 138         struct fat_cache *cache, *tmp;
 139
 140         if (new->fcluster == -1) /* dummy cache */
 141                 return;
 142
 143         spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 144         if (new->id != FAT_CACHE_VALID &&
 145             new->id != MSDOS_I(inode)->cache_valid_id)
 146                 goto out;       /* this cache was invalidated */
 147
 148         cache = fat_cache_merge(inode, new);
 149         if (cache == NULL) {
 150                 if (MSDOS_I(inode)->nr_caches < fat_max_cache(inode)) {
 151                         MSDOS_I(inode)->nr_caches++;
 152                         spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 153
 154                         tmp = fat_cache_alloc(inode);
 155                         spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 156                         cache = fat_cache_merge(inode, new);
 157                         if (cache != NULL) {
 158                                 MSDOS_I(inode)->nr_caches--;
 159                                 fat_cache_free(tmp);
 160                                 goto out_update_lru;
 161                         }
 162                         cache = tmp;
 163                 } else {
 164                         struct list_head *p = MSDOS_I(inode)->cache_lru.prev;
 165                         cache = list_entry(p, struct fat_cache, cache_list);
 166                 }
 167                 cache->fcluster = new->fcluster;
 168                 cache->dcluster = new->dcluster;
 169                 cache->nr_contig = new->nr_contig;
 170         }
 171 out_update_lru:
 172         fat_cache_update_lru(inode, cache);
 173 out:
 174         spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 175 }
 176
 177 /*
 178  * Cache invalidation occurs rarely, thus the LRU chain is not updated. It
 179  * fixes itself after a while.
 180  */
 181 static void __fat_cache_inval_inode(struct inode *inode)
 182 {
 183         struct msdos_inode_info *i = MSDOS_I(inode);
 184         struct fat_cache *cache;
 185
 186         while (!list_empty(&i->cache_lru)) {
 187                 cache = list_entry(i->cache_lru.next, struct fat_cache, cache_list);
 188                 list_del_init(&cache->cache_list);
 189                 i->nr_caches--;
 190                 fat_cache_free(cache);
 191         }
 192         /* Update. The copy of caches before this id is discarded. */
 193         i->cache_valid_id++;
 194         if (i->cache_valid_id == FAT_CACHE_VALID)
 195                 i->cache_valid_id++;
 196 }
 197
 198 void fat_cache_inval_inode(struct inode *inode)
 199 {
 200         spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 201         __fat_cache_inval_inode(inode);
 202         spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 203 }
 204
 205 static inline int cache_contiguous(struct fat_cache_id *cid, int dclus)
 206 {
 207         cid->nr_contig++;
 208         return ((cid->dcluster + cid->nr_contig) == dclus);
 209 }
 210
 211 static inline void cache_init(struct fat_cache_id *cid, int fclus, int dclus)
 212 {
 213         cid->id = FAT_CACHE_VALID;
 214         cid->fcluster = fclus;
 215         cid->dcluster = dclus;
 216         cid->nr_contig = 0;
 217 }
 218
 219 int fat_get_cluster(struct inode *inode, int cluster, int *fclus, int *dclus)
 220 {
 221         struct super_block *sb = inode->i_sb;
 222         const int limit = sb->s_maxbytes >> MSDOS_SB(sb)->cluster_bits;
 223         struct fat_entry fatent;
 224         struct fat_cache_id cid;
 225         int nr;
 226
 227         BUG_ON(MSDOS_I(inode)->i_start == 0);
 228
 229         *fclus = 0;
 230         *dclus = MSDOS_I(inode)->i_start;
 231         if (cluster == 0)
 232                 return 0;
 233
 234         if (fat_cache_lookup(inode, cluster, &cid, fclus, dclus) < 0) {
 235                 /*
 236                  * dummy, always not contiguous
 237                  * This is reinitialized by cache_init(), later.
 238                  */
 239                 cache_init(&cid, -1, -1);
 240         }
 241
 242         fatent_init(&fatent);
 243         while (*fclus < cluster) {
 244                 /* prevent the infinite loop of cluster chain */
 245                 if (*fclus > limit) {
 246                         fat_fs_panic(sb, "%s: detected the cluster chain loop"
 247                                      " (i_pos %lld)", __FUNCTION__,
 248                                      MSDOS_I(inode)->i_pos);
 249                         nr = -EIO;
 250                         goto out;
 251                 }
 252
 253                 nr = fat_ent_read(inode, &fatent, *dclus);
 254                 if (nr < 0)
 255                         goto out;
 256                 else if (nr == FAT_ENT_FREE) {
 257                         fat_fs_panic(sb, "%s: invalid cluster chain"
 258                                      " (i_pos %lld)", __FUNCTION__,
 259                                      MSDOS_I(inode)->i_pos);
 260                         nr = -EIO;
 261                         goto out;
 262                 } else if (nr == FAT_ENT_EOF) {
 263                         fat_cache_add(inode, &cid);
 264                         goto out;
 265                 }
 266                 (*fclus)++;
 267                 *dclus = nr;
 268                 if (!cache_contiguous(&cid, *dclus))
 269                         cache_init(&cid, *fclus, *dclus);
 270         }
 271         nr = 0;
 272         fat_cache_add(inode, &cid);
 273 out:
 274         fatent_brelse(&fatent);
 275         return nr;
 276 }
 277
 278 static int fat_bmap_cluster(struct inode *inode, int cluster)
 279 {
 280         struct super_block *sb = inode->i_sb;
 281         int ret, fclus, dclus;
 282
 283         if (MSDOS_I(inode)->i_start == 0)
 284                 return 0;
 285
 286         ret = fat_get_cluster(inode, cluster, &fclus, &dclus);
 287         if (ret < 0)
 288                 return ret;
 289         else if (ret == FAT_ENT_EOF) {
 290                 fat_fs_panic(sb, "%s: request beyond EOF (i_pos %lld)",
 291                              __FUNCTION__, MSDOS_I(inode)->i_pos);
 292                 return -EIO;
 293         }
 294         return dclus;
 295 }
 296
 297 int fat_bmap(struct inode *inode, sector_t sector, sector_t *phys,
 298              unsigned long *mapped_blocks)
 299 {
 300         struct super_block *sb = inode->i_sb;
 301         struct msdos_sb_info *sbi = MSDOS_SB(sb);
 302         sector_t last_block;
 303         int cluster, offset;
 304
 305         *phys = 0;
 306         *mapped_blocks = 0;
 307         if ((sbi->fat_bits != 32) && (inode->i_ino == MSDOS_ROOT_INO)) {
 308                 if (sector < (sbi->dir_entries >> sbi->dir_per_block_bits)) {
 309                         *phys = sector + sbi->dir_start;
 310                         *mapped_blocks = 1;
 311                 }
 312                 return 0;
 313         }
 314         last_block = (MSDOS_I(inode)->mmu_private + (sb->s_blocksize - 1))
 315                 >> sb->s_blocksize_bits;
 316         if (sector >= last_block)
 317                 return 0;
 318
 319         cluster = sector >> (sbi->cluster_bits - sb->s_blocksize_bits);
 320         offset  = sector & (sbi->sec_per_clus - 1);
 321         cluster = fat_bmap_cluster(inode, cluster);
 322         if (cluster < 0)
 323                 return cluster;
 324         else if (cluster) {
 325                 *phys = fat_clus_to_blknr(sbi, cluster) + offset;
 326                 *mapped_blocks = sbi->sec_per_clus - offset;
 327                 if (*mapped_blocks > last_block - sector)
 328                         *mapped_blocks = last_block - sector;
 329         }
 330         return 0;
 331 }