/*
   *  linux/fs/fat/cache.c
   *
   *  Written 1992,1993 by Werner Almesberger
   *
   *  Mar 1999. AV. Changed cache, so that it uses the starting cluster instead
   *	of inode number.
   *  May 1999. AV. Fixed the bogosity with FAT32 (read "FAT28"). Fscking lusers.
   */
  
  #include <linux/fs.h>

  #include <linux/slab.h>

  #include <linux/buffer_head.h>

  #include "fat.h"

  
  /* 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 struct kmem_cache *fat_cache_cachep;

  static void init_once(void *foo)

  {
  	struct fat_cache *cache = (struct fat_cache *)foo;

  	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|SLAB_MEM_SPREAD,

  				init_once);

  	if (fat_cache_cachep == NULL)
  		return -ENOMEM;
  	return 0;
  }

  void fat_cache_destroy(void)

  {

  	kmem_cache_destroy(fat_cache_cachep);

  }
  
  static inline struct fat_cache *fat_cache_alloc(struct inode *inode)
  {

  	return kmem_cache_alloc(fat_cache_cachep, GFP_NOFS);

  }
  
  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);

  			if (!tmp) {
  				spin_lock(&MSDOS_I(inode)->cache_lru_lock);
  				MSDOS_I(inode)->nr_caches--;
  				spin_unlock(&MSDOS_I(inode)->cache_lru_lock);
  				return;
  			}

  			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 inline int cache_contiguous(struct fat_cache_id *cid, int dclus)
  {
  	cid->nr_contig++;
  	return ((cid->dcluster + cid->nr_contig) == dclus);
  }
  
  static inline void cache_init(struct fat_cache_id *cid, int fclus, int dclus)
  {
  	cid->id = FAT_CACHE_VALID;
  	cid->fcluster = fclus;
  	cid->dcluster = dclus;
  	cid->nr_contig = 0;
  }
  
  int fat_get_cluster(struct inode *inode, int cluster, int *fclus, int *dclus)
  {
  	struct super_block *sb = inode->i_sb;
  	const int limit = sb->s_maxbytes >> MSDOS_SB(sb)->cluster_bits;
  	struct fat_entry fatent;
  	struct fat_cache_id cid;
  	int nr;
  
  	BUG_ON(MSDOS_I(inode)->i_start == 0);
  
  	*fclus = 0;
  	*dclus = MSDOS_I(inode)->i_start;
  	if (cluster == 0)
  		return 0;
  
  	if (fat_cache_lookup(inode, cluster, &cid, fclus, dclus) < 0) {
  		/*
  		 * dummy, always not contiguous
  		 * This is reinitialized by cache_init(), later.
  		 */
  		cache_init(&cid, -1, -1);
  	}
  
  	fatent_init(&fatent);
  	while (*fclus < cluster) {
  		/* prevent the infinite loop of cluster chain */
  		if (*fclus > limit) {

  			fat_fs_error_ratelimit(sb,
  					"%s: detected the cluster chain loop"
  					" (i_pos %lld)", __func__,
  					MSDOS_I(inode)->i_pos);

  			nr = -EIO;
  			goto out;
  		}
  
  		nr = fat_ent_read(inode, &fatent, *dclus);
  		if (nr < 0)
  			goto out;
  		else if (nr == FAT_ENT_FREE) {

  			fat_fs_error_ratelimit(sb, "%s: invalid cluster chain"
  					       " (i_pos %lld)", __func__,
  					       MSDOS_I(inode)->i_pos);

  			nr = -EIO;
  			goto out;
  		} else if (nr == FAT_ENT_EOF) {
  			fat_cache_add(inode, &cid);
  			goto out;
  		}
  		(*fclus)++;
  		*dclus = nr;
  		if (!cache_contiguous(&cid, *dclus))
  			cache_init(&cid, *fclus, *dclus);
  	}
  	nr = 0;
  	fat_cache_add(inode, &cid);
  out:
  	fatent_brelse(&fatent);
  	return nr;
  }
  
  static int fat_bmap_cluster(struct inode *inode, int cluster)
  {
  	struct super_block *sb = inode->i_sb;
  	int ret, fclus, dclus;
  
  	if (MSDOS_I(inode)->i_start == 0)
  		return 0;
  
  	ret = fat_get_cluster(inode, cluster, &fclus, &dclus);
  	if (ret < 0)
  		return ret;
  	else if (ret == FAT_ENT_EOF) {

  		fat_fs_error(sb, "%s: request beyond EOF (i_pos %lld)",

  			     __func__, MSDOS_I(inode)->i_pos);

  		return -EIO;
  	}
  	return dclus;
  }

  int fat_bmap(struct inode *inode, sector_t sector, sector_t *phys,

  	     unsigned long *mapped_blocks, int create)

  {
  	struct super_block *sb = inode->i_sb;
  	struct msdos_sb_info *sbi = MSDOS_SB(sb);

  	const unsigned long blocksize = sb->s_blocksize;
  	const unsigned char blocksize_bits = sb->s_blocksize_bits;

  	sector_t last_block;
  	int cluster, offset;
  
  	*phys = 0;

  	*mapped_blocks = 0;

  	if ((sbi->fat_bits != 32) && (inode->i_ino == MSDOS_ROOT_INO)) {

  		if (sector < (sbi->dir_entries >> sbi->dir_per_block_bits)) {

  			*phys = sector + sbi->dir_start;

  			*mapped_blocks = 1;
  		}

  		return 0;
  	}

  
  	last_block = (i_size_read(inode) + (blocksize - 1)) >> blocksize_bits;
  	if (sector >= last_block) {
  		if (!create)
  			return 0;
  
  		/*
  		 * ->mmu_private can access on only allocation path.
  		 * (caller must hold ->i_mutex)
  		 */
  		last_block = (MSDOS_I(inode)->mmu_private + (blocksize - 1))
  			>> blocksize_bits;
  		if (sector >= last_block)
  			return 0;
  	}

  
  	cluster = sector >> (sbi->cluster_bits - sb->s_blocksize_bits);
  	offset  = sector & (sbi->sec_per_clus - 1);
  	cluster = fat_bmap_cluster(inode, cluster);
  	if (cluster < 0)
  		return cluster;

  	else if (cluster) {

  		*phys = fat_clus_to_blknr(sbi, cluster) + offset;

  		*mapped_blocks = sbi->sec_per_clus - offset;
  		if (*mapped_blocks > last_block - sector)
  			*mapped_blocks = last_block - sector;
  	}

  	return 0;
  }