fs/fat/cache.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  *  linux/fs/fat/cache.c
   4  *
   5  *  Written 1992,1993 by Werner Almesberger
   6  *
   7  *  Mar 1999. AV. Changed cache, so that it uses the starting cluster instead
   8  *      of inode number.
   9  *  May 1999. AV. Fixed the bogosity with FAT32 (read "FAT28"). Fscking lusers.
  10  */
  11
  12 #include <linux/slab.h>
  13 #include "fat.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)
  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_NOFS);
  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                         if (!tmp) {
 154                                 spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 155                                 MSDOS_I(inode)->nr_caches--;
 156                                 spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 157                                 return;
 158                         }
 159
 160                         spin_lock(&MSDOS_I(inode)->cache_lru_lock);
 161                         cache = fat_cache_merge(inode, new);
 162                         if (cache != NULL) {
 163                                 MSDOS_I(inode)->nr_caches--;
 164                                 fat_cache_free(tmp);
 165                                 goto out_update_lru;
 166                         }
 167                         cache = tmp;
 168                 } else {
 169                         struct list_head *p = MSDOS_I(inode)->cache_lru.prev;
 170                         cache = list_entry(p, struct fat_cache, cache_list);
 171                 }
 172                 cache->fcluster = new->fcluster;
 173                 cache->dcluster = new->dcluster;
 174                 cache->nr_contig = new->nr_contig;
 175         }
 176 out_update_lru:
 177         fat_cache_update_lru(inode, cache);
 178 out:
 179         spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
 180 }
 181
 182 /*
 183  * Cache invalidation occurs rarely, thus the LRU chain is not updated. It
 184  * fixes itself after a while.
 185  */
 186 static void __fat_cache_inval_inode(struct inode *inode)
 187 {
 188         struct msdos_inode_info *i = MSDOS_I(inode);
 189         struct fat_cache *cache;
 190
 191         while (!list_empty(&i->cache_lru)) {
 192                 cache = list_entry(i->cache_lru.next,
 193                                    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,
 265                                        "%s: invalid cluster chain (i_pos %lld)",
 266                                        __func__,
 267                                        MSDOS_I(inode)->i_pos);
 268                         nr = -EIO;
 269                         goto out;
 270                 } else if (nr == FAT_ENT_EOF) {
 271                         fat_cache_add(inode, &cid);
 272                         goto out;
 273                 }
 274                 (*fclus)++;
 275                 *dclus = nr;
 276                 if (!cache_contiguous(&cid, *dclus))
 277                         cache_init(&cid, *fclus, *dclus);
 278         }
 279         nr = 0;
 280         fat_cache_add(inode, &cid);
 281 out:
 282         fatent_brelse(&fatent);
 283         return nr;
 284 }
 285
 286 static int fat_bmap_cluster(struct inode *inode, int cluster)
 287 {
 288         struct super_block *sb = inode->i_sb;
 289         int ret, fclus, dclus;
 290
 291         if (MSDOS_I(inode)->i_start == 0)
 292                 return 0;
 293
 294         ret = fat_get_cluster(inode, cluster, &fclus, &dclus);
 295         if (ret < 0)
 296                 return ret;
 297         else if (ret == FAT_ENT_EOF) {
 298                 fat_fs_error(sb, "%s: request beyond EOF (i_pos %lld)",
 299                              __func__, MSDOS_I(inode)->i_pos);
 300                 return -EIO;
 301         }
 302         return dclus;
 303 }
 304
 305 int fat_get_mapped_cluster(struct inode *inode, sector_t sector,
 306                            sector_t last_block,
 307                            unsigned long *mapped_blocks, sector_t *bmap)
 308 {
 309         struct super_block *sb = inode->i_sb;
 310         struct msdos_sb_info *sbi = MSDOS_SB(sb);
 311         int cluster, offset;
 312
 313         cluster = sector >> (sbi->cluster_bits - sb->s_blocksize_bits);
 314         offset  = sector & (sbi->sec_per_clus - 1);
 315         cluster = fat_bmap_cluster(inode, cluster);
 316         if (cluster < 0)
 317                 return cluster;
 318         else if (cluster) {
 319                 *bmap = fat_clus_to_blknr(sbi, cluster) + offset;
 320                 *mapped_blocks = sbi->sec_per_clus - offset;
 321                 if (*mapped_blocks > last_block - sector)
 322                         *mapped_blocks = last_block - sector;
 323         }
 324
 325         return 0;
 326 }
 327
 328 static int is_exceed_eof(struct inode *inode, sector_t sector,
 329                          sector_t *last_block, int create)
 330 {
 331         struct super_block *sb = inode->i_sb;
 332         const unsigned long blocksize = sb->s_blocksize;
 333         const unsigned char blocksize_bits = sb->s_blocksize_bits;
 334
 335         *last_block = (i_size_read(inode) + (blocksize - 1)) >> blocksize_bits;
 336         if (sector >= *last_block) {
 337                 if (!create)
 338                         return 1;
 339
 340                 /*
 341                  * ->mmu_private can access on only allocation path.
 342                  * (caller must hold ->i_mutex)
 343                  */
 344                 *last_block = (MSDOS_I(inode)->mmu_private + (blocksize - 1))
 345                         >> blocksize_bits;
 346                 if (sector >= *last_block)
 347                         return 1;
 348         }
 349
 350         return 0;
 351 }
 352
 353 int fat_bmap(struct inode *inode, sector_t sector, sector_t *phys,
 354              unsigned long *mapped_blocks, int create, bool from_bmap)
 355 {
 356         struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
 357         sector_t last_block;
 358
 359         *phys = 0;
 360         *mapped_blocks = 0;
 361         if ((sbi->fat_bits != 32) && (inode->i_ino == MSDOS_ROOT_INO)) {
 362                 if (sector < (sbi->dir_entries >> sbi->dir_per_block_bits)) {
 363                         *phys = sector + sbi->dir_start;
 364                         *mapped_blocks = 1;
 365                 }
 366                 return 0;
 367         }
 368
 369         if (!from_bmap) {
 370                 if (is_exceed_eof(inode, sector, &last_block, create))
 371                         return 0;
 372         } else {
 373                 last_block = inode->i_blocks >>
 374                                 (inode->i_sb->s_blocksize_bits - 9);
 375                 if (sector >= last_block)
 376                         return 0;
 377         }
 378
 379         return fat_get_mapped_cluster(inode, sector, last_block, mapped_blocks,
 380                                       phys);
 381 }