+/* this must be > 0. */
+#define FAT_MAX_CACHE 8
+
+struct fat_cache {
+ struct list_head cache_list;
+ int nr_contig; /* number of contiguous clusters */
+ int fcluster; /* cluster number in the file. */
+ int dcluster; /* cluster number on disk. */
+};
+
+struct fat_cache_id {
+ unsigned int id;
+ int nr_contig;
+ int fcluster;
+ int dcluster;
+};
+
+static inline int fat_max_cache(struct inode *inode)
+{
+ return FAT_MAX_CACHE;
+}
+
+static kmem_cache_t *fat_cache_cachep;
+
+static void init_once(void *foo, kmem_cache_t *cachep, unsigned long flags)
+{
+ struct fat_cache *cache = (struct fat_cache *)foo;
+
+ if ((flags & (SLAB_CTOR_VERIFY|SLAB_CTOR_CONSTRUCTOR)) ==
+ SLAB_CTOR_CONSTRUCTOR)
+ INIT_LIST_HEAD(&cache->cache_list);
+}
+
+int __init fat_cache_init(void)
+{
+ fat_cache_cachep = kmem_cache_create("fat_cache",
+ sizeof(struct fat_cache),
+ 0, SLAB_RECLAIM_ACCOUNT,
+ init_once, NULL);
+ if (fat_cache_cachep == NULL)
+ return -ENOMEM;
+ return 0;
+}
+
+void __exit fat_cache_destroy(void)
+{
+ if (kmem_cache_destroy(fat_cache_cachep))
+ printk(KERN_INFO "fat_cache: not all structures were freed\n");
+}
+
+static inline struct fat_cache *fat_cache_alloc(struct inode *inode)
+{
+ return kmem_cache_alloc(fat_cache_cachep, SLAB_KERNEL);
+}
+
+static inline void fat_cache_free(struct fat_cache *cache)
+{
+ BUG_ON(!list_empty(&cache->cache_list));
+ kmem_cache_free(fat_cache_cachep, cache);
+}
+
+static inline void fat_cache_update_lru(struct inode *inode,
+ struct fat_cache *cache)
+{
+ if (MSDOS_I(inode)->cache_lru.next != &cache->cache_list)
+ list_move(&cache->cache_list, &MSDOS_I(inode)->cache_lru);
+}
+
+static int fat_cache_lookup(struct inode *inode, int fclus,
+ struct fat_cache_id *cid,
+ int *cached_fclus, int *cached_dclus)
+{
+ static struct fat_cache nohit = { .fcluster = 0, };
+
+ struct fat_cache *hit = &nohit, *p;
+ int offset = -1;
+
+ spin_lock(&MSDOS_I(inode)->cache_lru_lock);
+ list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
+ /* Find the cache of "fclus" or nearest cache. */
+ if (p->fcluster <= fclus && hit->fcluster < p->fcluster) {
+ hit = p;
+ if ((hit->fcluster + hit->nr_contig) < fclus) {
+ offset = hit->nr_contig;
+ } else {
+ offset = fclus - hit->fcluster;
+ break;
+ }
+ }
+ }
+ if (hit != &nohit) {
+ fat_cache_update_lru(inode, hit);
+
+ cid->id = MSDOS_I(inode)->cache_valid_id;
+ cid->nr_contig = hit->nr_contig;
+ cid->fcluster = hit->fcluster;
+ cid->dcluster = hit->dcluster;
+ *cached_fclus = cid->fcluster + offset;
+ *cached_dclus = cid->dcluster + offset;
+ }
+ spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
+
+ return offset;
+}
+
+static struct fat_cache *fat_cache_merge(struct inode *inode,
+ struct fat_cache_id *new)
+{
+ struct fat_cache *p;
+
+ list_for_each_entry(p, &MSDOS_I(inode)->cache_lru, cache_list) {
+ /* Find the same part as "new" in cluster-chain. */
+ if (p->fcluster == new->fcluster) {
+ BUG_ON(p->dcluster != new->dcluster);
+ if (new->nr_contig > p->nr_contig)
+ p->nr_contig = new->nr_contig;
+ return p;
+ }
+ }
+ return NULL;
+}
+
+static void fat_cache_add(struct inode *inode, struct fat_cache_id *new)
+{
+ struct fat_cache *cache, *tmp;
+
+ if (new->fcluster == -1) /* dummy cache */
+ return;
+
+ spin_lock(&MSDOS_I(inode)->cache_lru_lock);
+ if (new->id != FAT_CACHE_VALID &&
+ new->id != MSDOS_I(inode)->cache_valid_id)
+ goto out; /* this cache was invalidated */
+
+ cache = fat_cache_merge(inode, new);
+ if (cache == NULL) {
+ if (MSDOS_I(inode)->nr_caches < fat_max_cache(inode)) {
+ MSDOS_I(inode)->nr_caches++;
+ spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
+
+ tmp = fat_cache_alloc(inode);
+ spin_lock(&MSDOS_I(inode)->cache_lru_lock);
+ cache = fat_cache_merge(inode, new);
+ if (cache != NULL) {
+ MSDOS_I(inode)->nr_caches--;
+ fat_cache_free(tmp);
+ goto out_update_lru;
+ }
+ cache = tmp;
+ } else {
+ struct list_head *p = MSDOS_I(inode)->cache_lru.prev;
+ cache = list_entry(p, struct fat_cache, cache_list);
+ }
+ cache->fcluster = new->fcluster;
+ cache->dcluster = new->dcluster;
+ cache->nr_contig = new->nr_contig;
+ }
+out_update_lru:
+ fat_cache_update_lru(inode, cache);
+out:
+ spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
+}
+
+/*
+ * Cache invalidation occurs rarely, thus the LRU chain is not updated. It
+ * fixes itself after a while.
+ */
+static void __fat_cache_inval_inode(struct inode *inode)
+{
+ struct msdos_inode_info *i = MSDOS_I(inode);
+ struct fat_cache *cache;
+
+ while (!list_empty(&i->cache_lru)) {
+ cache = list_entry(i->cache_lru.next, struct fat_cache, cache_list);
+ list_del_init(&cache->cache_list);
+ i->nr_caches--;
+ fat_cache_free(cache);
+ }
+ /* Update. The copy of caches before this id is discarded. */
+ i->cache_valid_id++;
+ if (i->cache_valid_id == FAT_CACHE_VALID)
+ i->cache_valid_id++;
+}
+
+void fat_cache_inval_inode(struct inode *inode)
+{
+ spin_lock(&MSDOS_I(inode)->cache_lru_lock);
+ __fat_cache_inval_inode(inode);
+ spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
+}
+
+static int __fat_access(struct super_block *sb, int nr, int new_value)