cache.c

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/*
 *  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;
}