/*
 *  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);
                        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;
}