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(struct kmem_cache *cachep, 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_KERNEL);
  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                         spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 154                         cache = fat_cache_merge(inode, new);
 155                         if (cache != NULL) {
 156                                 MSDOS_I(inode)->nr_caches--;
 157                                 fat_cache_free(tmp);
 158                                 goto out_update_lru;
 159                         }
 160                         cache = tmp;
 161                 } else {
 162                         struct list_head *p = MSDOS_I(inode)->cache_lru.prev;
 163                         cache = list_entry(p, struct fat_cache, cache_list);
 164                 }
 165                 cache->fcluster = new->fcluster;
 166                 cache->dcluster = new->dcluster;
 167                 cache->nr_contig = new->nr_contig;
 168         }
 169 out_update_lru:
 170         fat_cache_update_lru(inode, cache);
 171 out:
 172         spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 173 }
 174
 175 /*
 176  * Cache invalidation occurs rarely, thus the LRU chain is not updated. It
 177  * fixes itself after a while.
 178  */
 179 static void __fat_cache_inval_inode(struct inode *inode)
 180 {
 181         struct msdos_inode_info *i = MSDOS_I(inode);
 182         struct fat_cache *cache;
 183
 184         while (!list_empty(&i->cache_lru)) {
 185                 cache = list_entry(i->cache_lru.next, struct fat_cache, cache_list);
 186                 list_del_init(&cache->cache_list);
 187                 i->nr_caches--;
 188                 fat_cache_free(cache);
 189         }
 190         /* Update. The copy of caches before this id is discarded. */
 191         i->cache_valid_id++;
 192         if (i->cache_valid_id == FAT_CACHE_VALID)
 193                 i->cache_valid_id++;
 194 }
 195
 196 void fat_cache_inval_inode(struct inode *inode)
 197 {
 198         spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 199         __fat_cache_inval_inode(inode);
 200         spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 201 }
 202
 203 static inline int cache_contiguous(struct fat_cache_id *cid, int dclus)
 204 {
 205         cid->nr_contig++;
 206         return ((cid->dcluster + cid->nr_contig) == dclus);
 207 }
 208
 209 static inline void cache_init(struct fat_cache_id *cid, int fclus, int dclus)
 210 {
 211         cid->id = FAT_CACHE_VALID;
 212         cid->fcluster = fclus;
 213         cid->dcluster = dclus;
 214         cid->nr_contig = 0;
 215 }
 216
 217 int fat_get_cluster(struct inode *inode, int cluster, int *fclus, int *dclus)
 218 {
 219         struct super_block *sb = inode->i_sb;
 220         const int limit = sb->s_maxbytes >> MSDOS_SB(sb)->cluster_bits;
 221         struct fat_entry fatent;
 222         struct fat_cache_id cid;
 223         int nr;
 224
 225         BUG_ON(MSDOS_I(inode)->i_start == 0);
 226
 227         *fclus = 0;
 228         *dclus = MSDOS_I(inode)->i_start;
 229         if (cluster == 0)
 230                 return 0;
 231
 232         if (fat_cache_lookup(inode, cluster, &cid, fclus, dclus) < 0) {
 233                 /*
 234                  * dummy, always not contiguous
 235                  * This is reinitialized by cache_init(), later.
 236                  */
 237                 cache_init(&cid, -1, -1);
 238         }
 239
 240         fatent_init(&fatent);
 241         while (*fclus < cluster) {
 242                 /* prevent the infinite loop of cluster chain */
 243                 if (*fclus > limit) {
 244                         fat_fs_panic(sb, "%s: detected the cluster chain loop"
 245                                      " (i_pos %lld)", __FUNCTION__,
 246                                      MSDOS_I(inode)->i_pos);
 247                         nr = -EIO;
 248                         goto out;
 249                 }
 250
 251                 nr = fat_ent_read(inode, &fatent, *dclus);
 252                 if (nr < 0)
 253                         goto out;
 254                 else if (nr == FAT_ENT_FREE) {
 255                         fat_fs_panic(sb, "%s: invalid cluster chain"
 256                                      " (i_pos %lld)", __FUNCTION__,
 257                                      MSDOS_I(inode)->i_pos);
 258                         nr = -EIO;
 259                         goto out;
 260                 } else if (nr == FAT_ENT_EOF) {
 261                         fat_cache_add(inode, &cid);
 262                         goto out;
 263                 }
 264                 (*fclus)++;
 265                 *dclus = nr;
 266                 if (!cache_contiguous(&cid, *dclus))
 267                         cache_init(&cid, *fclus, *dclus);
 268         }
 269         nr = 0;
 270         fat_cache_add(inode, &cid);
 271 out:
 272         fatent_brelse(&fatent);
 273         return nr;
 274 }
 275
 276 static int fat_bmap_cluster(struct inode *inode, int cluster)
 277 {
 278         struct super_block *sb = inode->i_sb;
 279         int ret, fclus, dclus;
 280
 281         if (MSDOS_I(inode)->i_start == 0)
 282                 return 0;
 283
 284         ret = fat_get_cluster(inode, cluster, &fclus, &dclus);
 285         if (ret < 0)
 286                 return ret;
 287         else if (ret == FAT_ENT_EOF) {
 288                 fat_fs_panic(sb, "%s: request beyond EOF (i_pos %lld)",
 289                              __FUNCTION__, MSDOS_I(inode)->i_pos);
 290                 return -EIO;
 291         }
 292         return dclus;
 293 }
 294
 295 int fat_bmap(struct inode *inode, sector_t sector, sector_t *phys,
 296              unsigned long *mapped_blocks)
 297 {
 298         struct super_block *sb = inode->i_sb;
 299         struct msdos_sb_info *sbi = MSDOS_SB(sb);
 300         sector_t last_block;
 301         int cluster, offset;
 302
 303         *phys = 0;
 304         *mapped_blocks = 0;
 305         if ((sbi->fat_bits != 32) && (inode->i_ino == MSDOS_ROOT_INO)) {
 306                 if (sector < (sbi->dir_entries >> sbi->dir_per_block_bits)) {
 307                         *phys = sector + sbi->dir_start;
 308                         *mapped_blocks = 1;
 309                 }
 310                 return 0;
 311         }
 312         last_block = (MSDOS_I(inode)->mmu_private + (sb->s_blocksize - 1))
 313                 >> sb->s_blocksize_bits;
 314         if (sector >= last_block)
 315                 return 0;
 316
 317         cluster = sector >> (sbi->cluster_bits - sb->s_blocksize_bits);
 318         offset  = sector & (sbi->sec_per_clus - 1);
 319         cluster = fat_bmap_cluster(inode, cluster);
 320         if (cluster < 0)
 321                 return cluster;
 322         else if (cluster) {
 323                 *phys = fat_clus_to_blknr(sbi, cluster) + offset;
 324                 *mapped_blocks = sbi->sec_per_clus - offset;
 325                 if (*mapped_blocks > last_block - sector)
 326                         *mapped_blocks = last_block - sector;
 327         }
 328         return 0;
 329 }