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                         spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 155                         cache = fat_cache_merge(inode, new);
 156                         if (cache != NULL) {
 157                                 MSDOS_I(inode)->nr_caches--;
 158                                 fat_cache_free(tmp);
 159                                 goto out_update_lru;
 160                         }
 161                         cache = tmp;
 162                 } else {
 163                         struct list_head *p = MSDOS_I(inode)->cache_lru.prev;
 164                         cache = list_entry(p, struct fat_cache, cache_list);
 165                 }
 166                 cache->fcluster = new->fcluster;
 167                 cache->dcluster = new->dcluster;
 168                 cache->nr_contig = new->nr_contig;
 169         }
 170 out_update_lru:
 171         fat_cache_update_lru(inode, cache);
 172 out:
 173         spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 174 }
 175
 176 /*
 177  * Cache invalidation occurs rarely, thus the LRU chain is not updated. It
 178  * fixes itself after a while.
 179  */
 180 static void __fat_cache_inval_inode(struct inode *inode)
 181 {
 182         struct msdos_inode_info *i = MSDOS_I(inode);
 183         struct fat_cache *cache;
 184
 185         while (!list_empty(&i->cache_lru)) {
 186                 cache = list_entry(i->cache_lru.next, struct fat_cache, cache_list);
 187                 list_del_init(&cache->cache_list);
 188                 i->nr_caches--;
 189                 fat_cache_free(cache);
 190         }
 191         /* Update. The copy of caches before this id is discarded. */
 192         i->cache_valid_id++;
 193         if (i->cache_valid_id == FAT_CACHE_VALID)
 194                 i->cache_valid_id++;
 195 }
 196
 197 void fat_cache_inval_inode(struct inode *inode)
 198 {
 199         spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 200         __fat_cache_inval_inode(inode);
 201         spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 202 }
 203
 204 static inline int cache_contiguous(struct fat_cache_id *cid, int dclus)
 205 {
 206         cid->nr_contig++;
 207         return ((cid->dcluster + cid->nr_contig) == dclus);
 208 }
 209
 210 static inline void cache_init(struct fat_cache_id *cid, int fclus, int dclus)
 211 {
 212         cid->id = FAT_CACHE_VALID;
 213         cid->fcluster = fclus;
 214         cid->dcluster = dclus;
 215         cid->nr_contig = 0;
 216 }
 217
 218 int fat_get_cluster(struct inode *inode, int cluster, int *fclus, int *dclus)
 219 {
 220         struct super_block *sb = inode->i_sb;
 221         const int limit = sb->s_maxbytes >> MSDOS_SB(sb)->cluster_bits;
 222         struct fat_entry fatent;
 223         struct fat_cache_id cid;
 224         int nr;
 225
 226         BUG_ON(MSDOS_I(inode)->i_start == 0);
 227
 228         *fclus = 0;
 229         *dclus = MSDOS_I(inode)->i_start;
 230         if (cluster == 0)
 231                 return 0;
 232
 233         if (fat_cache_lookup(inode, cluster, &cid, fclus, dclus) < 0) {
 234                 /*
 235                  * dummy, always not contiguous
 236                  * This is reinitialized by cache_init(), later.
 237                  */
 238                 cache_init(&cid, -1, -1);
 239         }
 240
 241         fatent_init(&fatent);
 242         while (*fclus < cluster) {
 243                 /* prevent the infinite loop of cluster chain */
 244                 if (*fclus > limit) {
 245                         fat_fs_error(sb, "%s: detected the cluster chain loop"
 246                                      " (i_pos %lld)", __func__,
 247                                      MSDOS_I(inode)->i_pos);
 248                         nr = -EIO;
 249                         goto out;
 250                 }
 251
 252                 nr = fat_ent_read(inode, &fatent, *dclus);
 253                 if (nr < 0)
 254                         goto out;
 255                 else if (nr == FAT_ENT_FREE) {
 256                         fat_fs_error(sb, "%s: invalid cluster chain"
 257                                      " (i_pos %lld)", __func__,
 258                                      MSDOS_I(inode)->i_pos);
 259                         nr = -EIO;
 260                         goto out;
 261                 } else if (nr == FAT_ENT_EOF) {
 262                         fat_cache_add(inode, &cid);
 263                         goto out;
 264                 }
 265                 (*fclus)++;
 266                 *dclus = nr;
 267                 if (!cache_contiguous(&cid, *dclus))
 268                         cache_init(&cid, *fclus, *dclus);
 269         }
 270         nr = 0;
 271         fat_cache_add(inode, &cid);
 272 out:
 273         fatent_brelse(&fatent);
 274         return nr;
 275 }
 276
 277 static int fat_bmap_cluster(struct inode *inode, int cluster)
 278 {
 279         struct super_block *sb = inode->i_sb;
 280         int ret, fclus, dclus;
 281
 282         if (MSDOS_I(inode)->i_start == 0)
 283                 return 0;
 284
 285         ret = fat_get_cluster(inode, cluster, &fclus, &dclus);
 286         if (ret < 0)
 287                 return ret;
 288         else if (ret == FAT_ENT_EOF) {
 289                 fat_fs_error(sb, "%s: request beyond EOF (i_pos %lld)",
 290                              __func__, MSDOS_I(inode)->i_pos);
 291                 return -EIO;
 292         }
 293         return dclus;
 294 }
 295
 296 int fat_bmap(struct inode *inode, sector_t sector, sector_t *phys,
 297              unsigned long *mapped_blocks, int create)
 298 {
 299         struct super_block *sb = inode->i_sb;
 300         struct msdos_sb_info *sbi = MSDOS_SB(sb);
 301         const unsigned long blocksize = sb->s_blocksize;
 302         const unsigned char blocksize_bits = sb->s_blocksize_bits;
 303         sector_t last_block;
 304         int cluster, offset;
 305
 306         *phys = 0;
 307         *mapped_blocks = 0;
 308         if ((sbi->fat_bits != 32) && (inode->i_ino == MSDOS_ROOT_INO)) {
 309                 if (sector < (sbi->dir_entries >> sbi->dir_per_block_bits)) {
 310                         *phys = sector + sbi->dir_start;
 311                         *mapped_blocks = 1;
 312                 }
 313                 return 0;
 314         }
 315
 316         last_block = (i_size_read(inode) + (blocksize - 1)) >> blocksize_bits;
 317         if (sector >= last_block) {
 318                 if (!create)
 319                         return 0;
 320
 321                 /*
 322                  * ->mmu_private can access on only allocation path.
 323                  * (caller must hold ->i_mutex)
 324                  */
 325                 last_block = (MSDOS_I(inode)->mmu_private + (blocksize - 1))
 326                         >> blocksize_bits;
 327                 if (sector >= last_block)
 328                         return 0;
 329         }
 330
 331         cluster = sector >> (sbi->cluster_bits - sb->s_blocksize_bits);
 332         offset  = sector & (sbi->sec_per_clus - 1);
 333         cluster = fat_bmap_cluster(inode, cluster);
 334         if (cluster < 0)
 335                 return cluster;
 336         else if (cluster) {
 337                 *phys = fat_clus_to_blknr(sbi, cluster) + offset;
 338                 *mapped_blocks = sbi->sec_per_clus - offset;
 339                 if (*mapped_blocks > last_block - sector)
 340                         *mapped_blocks = last_block - sector;
 341         }
 342         return 0;
 343 }