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 kmem_cache_t *fat_cache_cachep;
  38
  39 static void init_once(void *foo, kmem_cache_t *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,
  53                                 init_once, NULL);
  54         if (fat_cache_cachep == NULL)
  55                 return -ENOMEM;
  56         return 0;
  57 }
  58
  59 void __exit fat_cache_destroy(void)
  60 {
  61         if (kmem_cache_destroy(fat_cache_cachep))
  62                 printk(KERN_INFO "fat_cache: not all structures were freed\n");
  63 }
  64
  65 static inline struct fat_cache *fat_cache_alloc(struct inode *inode)
  66 {
  67         return kmem_cache_alloc(fat_cache_cachep, SLAB_KERNEL);
  68 }
  69
  70 static inline void fat_cache_free(struct fat_cache *cache)
  71 {
  72         BUG_ON(!list_empty(&cache->cache_list));
  73         kmem_cache_free(fat_cache_cachep, cache);
  74 }
  75
  76 static inline void fat_cache_update_lru(struct inode *inode,
  77                                         struct fat_cache *cache)
  78 {
  79         if (MSDOS_I(inode)->cache_lru.next != &cache->cache_list)
  80                 list_move(&cache->cache_list, &MSDOS_I(inode)->cache_lru);
  81 }
  82
  83 static int fat_cache_lookup(struct inode *inode, int fclus,
  84                             struct fat_cache_id *cid,
  85                             int *cached_fclus, int *cached_dclus)
  86 {
  87         static struct fat_cache nohit = { .fcluster = 0, };
  88
  89         struct fat_cache *hit = &nohit, *p;
  90         int offset = -1;
  91
  92         spin_lock(&MSDOS_I(inode)->cache_lru_lock);
  93         list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
  94                 /* Find the cache of "fclus" or nearest cache. */
  95                 if (p->fcluster <= fclus && hit->fcluster < p->fcluster) {
  96                         hit = p;
  97                         if ((hit->fcluster + hit->nr_contig) < fclus) {
  98                                 offset = hit->nr_contig;
  99                         } else {
 100                                 offset = fclus - hit->fcluster;
 101                                 break;
 102                         }
 103                 }
 104         }
 105         if (hit != &nohit) {
 106                 fat_cache_update_lru(inode, hit);
 107
 108                 cid->id = MSDOS_I(inode)->cache_valid_id;
 109                 cid->nr_contig = hit->nr_contig;
 110                 cid->fcluster = hit->fcluster;
 111                 cid->dcluster = hit->dcluster;
 112                 *cached_fclus = cid->fcluster + offset;
 113                 *cached_dclus = cid->dcluster + offset;
 114         }
 115         spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 116
 117         return offset;
 118 }
 119
 120 static struct fat_cache *fat_cache_merge(struct inode *inode,
 121                                          struct fat_cache_id *new)
 122 {
 123         struct fat_cache *p;
 124
 125         list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
 126                 /* Find the same part as "new" in cluster-chain. */
 127                 if (p->fcluster == new->fcluster) {
 128                         BUG_ON(p->dcluster != new->dcluster);
 129                         if (new->nr_contig > p->nr_contig)
 130                                 p->nr_contig = new->nr_contig;
 131                         return p;
 132                 }
 133         }
 134         return NULL;
 135 }
 136
 137 static void fat_cache_add(struct inode *inode, struct fat_cache_id *new)
 138 {
 139         struct fat_cache *cache, *tmp;
 140
 141         if (new->fcluster == -1) /* dummy cache */
 142                 return;
 143
 144         spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 145         if (new->id != FAT_CACHE_VALID &&
 146             new->id != MSDOS_I(inode)->cache_valid_id)
 147                 goto out;       /* this cache was invalidated */
 148
 149         cache = fat_cache_merge(inode, new);
 150         if (cache == NULL) {
 151                 if (MSDOS_I(inode)->nr_caches < fat_max_cache(inode)) {
 152                         MSDOS_I(inode)->nr_caches++;
 153                         spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 154
 155                         tmp = fat_cache_alloc(inode);
 156                         spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 157                         cache = fat_cache_merge(inode, new);
 158                         if (cache != NULL) {
 159                                 MSDOS_I(inode)->nr_caches--;
 160                                 fat_cache_free(tmp);
 161                                 goto out_update_lru;
 162                         }
 163                         cache = tmp;
 164                 } else {
 165                         struct list_head *p = MSDOS_I(inode)->cache_lru.prev;
 166                         cache = list_entry(p, struct fat_cache, cache_list);
 167                 }
 168                 cache->fcluster = new->fcluster;
 169                 cache->dcluster = new->dcluster;
 170                 cache->nr_contig = new->nr_contig;
 171         }
 172 out_update_lru:
 173         fat_cache_update_lru(inode, cache);
 174 out:
 175         spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 176 }
 177
 178 /*
 179  * Cache invalidation occurs rarely, thus the LRU chain is not updated. It
 180  * fixes itself after a while.
 181  */
 182 static void __fat_cache_inval_inode(struct inode *inode)
 183 {
 184         struct msdos_inode_info *i = MSDOS_I(inode);
 185         struct fat_cache *cache;
 186
 187         while (!list_empty(&i->cache_lru)) {
 188                 cache = list_entry(i->cache_lru.next, struct fat_cache, cache_list);
 189                 list_del_init(&cache->cache_list);
 190                 i->nr_caches--;
 191                 fat_cache_free(cache);
 192         }
 193         /* Update. The copy of caches before this id is discarded. */
 194         i->cache_valid_id++;
 195         if (i->cache_valid_id == FAT_CACHE_VALID)
 196                 i->cache_valid_id++;
 197 }
 198
 199 void fat_cache_inval_inode(struct inode *inode)
 200 {
 201         spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 202         __fat_cache_inval_inode(inode);
 203         spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 204 }
 205
 206 static inline int cache_contiguous(struct fat_cache_id *cid, int dclus)
 207 {
 208         cid->nr_contig++;
 209         return ((cid->dcluster + cid->nr_contig) == dclus);
 210 }
 211
 212 static inline void cache_init(struct fat_cache_id *cid, int fclus, int dclus)
 213 {
 214         cid->id = FAT_CACHE_VALID;
 215         cid->fcluster = fclus;
 216         cid->dcluster = dclus;
 217         cid->nr_contig = 0;
 218 }
 219
 220 int fat_get_cluster(struct inode *inode, int cluster, int *fclus, int *dclus)
 221 {
 222         struct super_block *sb = inode->i_sb;
 223         const int limit = sb->s_maxbytes >> MSDOS_SB(sb)->cluster_bits;
 224         struct fat_entry fatent;
 225         struct fat_cache_id cid;
 226         int nr;
 227
 228         BUG_ON(MSDOS_I(inode)->i_start == 0);
 229
 230         *fclus = 0;
 231         *dclus = MSDOS_I(inode)->i_start;
 232         if (cluster == 0)
 233                 return 0;
 234
 235         if (fat_cache_lookup(inode, cluster, &cid, fclus, dclus) < 0) {
 236                 /*
 237                  * dummy, always not contiguous
 238                  * This is reinitialized by cache_init(), later.
 239                  */
 240                 cache_init(&cid, -1, -1);
 241         }
 242
 243         fatent_init(&fatent);
 244         while (*fclus < cluster) {
 245                 /* prevent the infinite loop of cluster chain */
 246                 if (*fclus > limit) {
 247                         fat_fs_panic(sb, "%s: detected the cluster chain loop"
 248                                      " (i_pos %lld)", __FUNCTION__,
 249                                      MSDOS_I(inode)->i_pos);
 250                         nr = -EIO;
 251                         goto out;
 252                 }
 253
 254                 nr = fat_ent_read(inode, &fatent, *dclus);
 255                 if (nr < 0)
 256                         goto out;
 257                 else if (nr == FAT_ENT_FREE) {
 258                         fat_fs_panic(sb, "%s: invalid cluster chain"
 259                                      " (i_pos %lld)", __FUNCTION__,
 260                                      MSDOS_I(inode)->i_pos);
 261                         nr = -EIO;
 262                         goto out;
 263                 } else if (nr == FAT_ENT_EOF) {
 264                         fat_cache_add(inode, &cid);
 265                         goto out;
 266                 }
 267                 (*fclus)++;
 268                 *dclus = nr;
 269                 if (!cache_contiguous(&cid, *dclus))
 270                         cache_init(&cid, *fclus, *dclus);
 271         }
 272         nr = 0;
 273         fat_cache_add(inode, &cid);
 274 out:
 275         fatent_brelse(&fatent);
 276         return nr;
 277 }
 278
 279 static int fat_bmap_cluster(struct inode *inode, int cluster)
 280 {
 281         struct super_block *sb = inode->i_sb;
 282         int ret, fclus, dclus;
 283
 284         if (MSDOS_I(inode)->i_start == 0)
 285                 return 0;
 286
 287         ret = fat_get_cluster(inode, cluster, &fclus, &dclus);
 288         if (ret < 0)
 289                 return ret;
 290         else if (ret == FAT_ENT_EOF) {
 291                 fat_fs_panic(sb, "%s: request beyond EOF (i_pos %lld)",
 292                              __FUNCTION__, MSDOS_I(inode)->i_pos);
 293                 return -EIO;
 294         }
 295         return dclus;
 296 }
 297
 298 int fat_bmap(struct inode *inode, sector_t sector, sector_t *phys)
 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         if ((sbi->fat_bits != 32) && (inode->i_ino == MSDOS_ROOT_INO)) {
 307                 if (sector < (sbi->dir_entries >> sbi->dir_per_block_bits))
 308                         *phys = sector + sbi->dir_start;
 309                 return 0;
 310         }
 311         last_block = (MSDOS_I(inode)->mmu_private + (sb->s_blocksize - 1))
 312                 >> sb->s_blocksize_bits;
 313         if (sector >= last_block)
 314                 return 0;
 315
 316         cluster = sector >> (sbi->cluster_bits - sb->s_blocksize_bits);
 317         offset  = sector & (sbi->sec_per_clus - 1);
 318         cluster = fat_bmap_cluster(inode, cluster);
 319         if (cluster < 0)
 320                 return cluster;
 321         else if (cluster)
 322                 *phys = fat_clus_to_blknr(sbi, cluster) + offset;
 323         return 0;
 324 }