fat: Update free_clusters even if it is untrusted

[linux-2.6/openmoko-kernel/knife-kernel.git] / fs / fat / inode.c

/*
 *  linux/fs/fat/inode.c
 *
 *  Written 1992,1993 by Werner Almesberger
 *  VFAT extensions by Gordon Chaffee, merged with msdos fs by Henrik Storner
 *  Rewritten for the constant inumbers support by Al Viro
 *
 *  Fixes:
 *
 *      Max Cohan: Fixed invalid FSINFO offset when info_sector is 0
 */

#include <linux/module.h>
#include <linux/init.h>
#include <linux/time.h>
#include <linux/slab.h>
#include <linux/smp_lock.h>
#include <linux/seq_file.h>
#include <linux/msdos_fs.h>
#include <linux/pagemap.h>
#include <linux/mpage.h>
#include <linux/buffer_head.h>
#include <linux/exportfs.h>
#include <linux/mount.h>
#include <linux/vfs.h>
#include <linux/parser.h>
#include <linux/uio.h>
#include <linux/writeback.h>
#include <linux/log2.h>
#include <asm/unaligned.h>

#ifndef CONFIG_FAT_DEFAULT_IOCHARSET
/* if user don't select VFAT, this is undefined. */
#define CONFIG_FAT_DEFAULT_IOCHARSET    ""
#endif

static int fat_default_codepage = CONFIG_FAT_DEFAULT_CODEPAGE;
static char fat_default_iocharset[] = CONFIG_FAT_DEFAULT_IOCHARSET;


static int fat_add_cluster(struct inode *inode)
{
        int err, cluster;

        err = fat_alloc_clusters(inode, &cluster, 1);
        if (err)
                return err;
        /* FIXME: this cluster should be added after data of this
         * cluster is writed */
        err = fat_chain_add(inode, cluster, 1);
        if (err)
                fat_free_clusters(inode, cluster);
        return err;
}

static inline int __fat_get_block(struct inode *inode, sector_t iblock,
                                  unsigned long *max_blocks,
                                  struct buffer_head *bh_result, int create)
{
        struct super_block *sb = inode->i_sb;
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        unsigned long mapped_blocks;
        sector_t phys;
        int err, offset;

        err = fat_bmap(inode, iblock, &phys, &mapped_blocks);
        if (err)
                return err;
        if (phys) {
                map_bh(bh_result, sb, phys);
                *max_blocks = min(mapped_blocks, *max_blocks);
                return 0;
        }
        if (!create)
                return 0;

        if (iblock != MSDOS_I(inode)->mmu_private >> sb->s_blocksize_bits) {
                fat_fs_panic(sb, "corrupted file size (i_pos %lld, %lld)",
                        MSDOS_I(inode)->i_pos, MSDOS_I(inode)->mmu_private);
                return -EIO;
        }

        offset = (unsigned long)iblock & (sbi->sec_per_clus - 1);
        if (!offset) {
                /* TODO: multiple cluster allocation would be desirable. */
                err = fat_add_cluster(inode);
                if (err)
                        return err;
        }
        /* available blocks on this cluster */
        mapped_blocks = sbi->sec_per_clus - offset;

        *max_blocks = min(mapped_blocks, *max_blocks);
        MSDOS_I(inode)->mmu_private += *max_blocks << sb->s_blocksize_bits;

        err = fat_bmap(inode, iblock, &phys, &mapped_blocks);
        if (err)
                return err;

        BUG_ON(!phys);
        BUG_ON(*max_blocks != mapped_blocks);
        set_buffer_new(bh_result);
        map_bh(bh_result, sb, phys);

        return 0;
}

static int fat_get_block(struct inode *inode, sector_t iblock,
                         struct buffer_head *bh_result, int create)
{
        struct super_block *sb = inode->i_sb;
        unsigned long max_blocks = bh_result->b_size >> inode->i_blkbits;
        int err;

        err = __fat_get_block(inode, iblock, &max_blocks, bh_result, create);
        if (err)
                return err;
        bh_result->b_size = max_blocks << sb->s_blocksize_bits;
        return 0;
}

static int fat_writepage(struct page *page, struct writeback_control *wbc)
{
        return block_write_full_page(page, fat_get_block, wbc);
}

static int fat_writepages(struct address_space *mapping,
                          struct writeback_control *wbc)
{
        return mpage_writepages(mapping, wbc, fat_get_block);
}

static int fat_readpage(struct file *file, struct page *page)
{
        return mpage_readpage(page, fat_get_block);
}

static int fat_readpages(struct file *file, struct address_space *mapping,
                         struct list_head *pages, unsigned nr_pages)
{
        return mpage_readpages(mapping, pages, nr_pages, fat_get_block);
}

static int fat_write_begin(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned flags,
                        struct page **pagep, void **fsdata)
{
        *pagep = NULL;
        return cont_write_begin(file, mapping, pos, len, flags, pagep, fsdata,
                                fat_get_block,
                                &MSDOS_I(mapping->host)->mmu_private);
}

static int fat_write_end(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned copied,
                        struct page *pagep, void *fsdata)
{
        struct inode *inode = mapping->host;
        int err;
        err = generic_write_end(file, mapping, pos, len, copied, pagep, fsdata);
        if (!(err < 0) && !(MSDOS_I(inode)->i_attrs & ATTR_ARCH)) {
                inode->i_mtime = inode->i_ctime = CURRENT_TIME_SEC;
                MSDOS_I(inode)->i_attrs |= ATTR_ARCH;
                mark_inode_dirty(inode);
        }
        return err;
}

static ssize_t fat_direct_IO(int rw, struct kiocb *iocb,
                             const struct iovec *iov,
                             loff_t offset, unsigned long nr_segs)
{
        struct file *file = iocb->ki_filp;
        struct inode *inode = file->f_mapping->host;

        if (rw == WRITE) {
                /*
                 * FIXME: blockdev_direct_IO() doesn't use ->prepare_write(),
                 * so we need to update the ->mmu_private to block boundary.
                 *
                 * But we must fill the remaining area or hole by nul for
                 * updating ->mmu_private.
                 *
                 * Return 0, and fallback to normal buffered write.
                 */
                loff_t size = offset + iov_length(iov, nr_segs);
                if (MSDOS_I(inode)->mmu_private < size)
                        return 0;
        }

        /*
         * FAT need to use the DIO_LOCKING for avoiding the race
         * condition of fat_get_block() and ->truncate().
         */
        return blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov,
                                  offset, nr_segs, fat_get_block, NULL);
}

static sector_t _fat_bmap(struct address_space *mapping, sector_t block)
{
        return generic_block_bmap(mapping, block, fat_get_block);
}

static const struct address_space_operations fat_aops = {
        .readpage       = fat_readpage,
        .readpages      = fat_readpages,
        .writepage      = fat_writepage,
        .writepages     = fat_writepages,
        .sync_page      = block_sync_page,
        .write_begin    = fat_write_begin,
        .write_end      = fat_write_end,
        .direct_IO      = fat_direct_IO,
        .bmap           = _fat_bmap
};

/*
 * New FAT inode stuff. We do the following:
 *      a) i_ino is constant and has nothing with on-disk location.
 *      b) FAT manages its own cache of directory entries.
 *      c) *This* cache is indexed by on-disk location.
 *      d) inode has an associated directory entry, all right, but
 *              it may be unhashed.
 *      e) currently entries are stored within struct inode. That should
 *              change.
 *      f) we deal with races in the following way:
 *              1. readdir() and lookup() do FAT-dir-cache lookup.
 *              2. rename() unhashes the F-d-c entry and rehashes it in
 *                      a new place.
 *              3. unlink() and rmdir() unhash F-d-c entry.
 *              4. fat_write_inode() checks whether the thing is unhashed.
 *                      If it is we silently return. If it isn't we do bread(),
 *                      check if the location is still valid and retry if it
 *                      isn't. Otherwise we do changes.
 *              5. Spinlock is used to protect hash/unhash/location check/lookup
 *              6. fat_clear_inode() unhashes the F-d-c entry.
 *              7. lookup() and readdir() do igrab() if they find a F-d-c entry
 *                      and consider negative result as cache miss.
 */

static void fat_hash_init(struct super_block *sb)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        int i;

        spin_lock_init(&sbi->inode_hash_lock);
        for (i = 0; i < FAT_HASH_SIZE; i++)
                INIT_HLIST_HEAD(&sbi->inode_hashtable[i]);
}

static inline unsigned long fat_hash(struct super_block *sb, loff_t i_pos)
{
        unsigned long tmp = (unsigned long)i_pos | (unsigned long) sb;
        tmp = tmp + (tmp >> FAT_HASH_BITS) + (tmp >> FAT_HASH_BITS * 2);
        return tmp & FAT_HASH_MASK;
}

void fat_attach(struct inode *inode, loff_t i_pos)
{
        struct super_block *sb = inode->i_sb;
        struct msdos_sb_info *sbi = MSDOS_SB(sb);

        spin_lock(&sbi->inode_hash_lock);
        MSDOS_I(inode)->i_pos = i_pos;
        hlist_add_head(&MSDOS_I(inode)->i_fat_hash,
                        sbi->inode_hashtable + fat_hash(sb, i_pos));
        spin_unlock(&sbi->inode_hash_lock);
}

EXPORT_SYMBOL_GPL(fat_attach);

void fat_detach(struct inode *inode)
{
        struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
        spin_lock(&sbi->inode_hash_lock);
        MSDOS_I(inode)->i_pos = 0;
        hlist_del_init(&MSDOS_I(inode)->i_fat_hash);
        spin_unlock(&sbi->inode_hash_lock);
}

EXPORT_SYMBOL_GPL(fat_detach);

struct inode *fat_iget(struct super_block *sb, loff_t i_pos)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        struct hlist_head *head = sbi->inode_hashtable + fat_hash(sb, i_pos);
        struct hlist_node *_p;
        struct msdos_inode_info *i;
        struct inode *inode = NULL;

        spin_lock(&sbi->inode_hash_lock);
        hlist_for_each_entry(i, _p, head, i_fat_hash) {
                BUG_ON(i->vfs_inode.i_sb != sb);
                if (i->i_pos != i_pos)
                        continue;
                inode = igrab(&i->vfs_inode);
                if (inode)
                        break;
        }
        spin_unlock(&sbi->inode_hash_lock);
        return inode;
}

static int is_exec(unsigned char *extension)
{
        unsigned char *exe_extensions = "EXECOMBAT", *walk;

        for (walk = exe_extensions; *walk; walk += 3)
                if (!strncmp(extension, walk, 3))
                        return 1;
        return 0;
}

static int fat_calc_dir_size(struct inode *inode)
{
        struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
        int ret, fclus, dclus;

        inode->i_size = 0;
        if (MSDOS_I(inode)->i_start == 0)
                return 0;

        ret = fat_get_cluster(inode, FAT_ENT_EOF, &fclus, &dclus);
        if (ret < 0)
                return ret;
        inode->i_size = (fclus + 1) << sbi->cluster_bits;

        return 0;
}

/* doesn't deal with root inode */
static int fat_fill_inode(struct inode *inode, struct msdos_dir_entry *de)
{
        struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
        int error;

        MSDOS_I(inode)->i_pos = 0;
        inode->i_uid = sbi->options.fs_uid;
        inode->i_gid = sbi->options.fs_gid;
        inode->i_version++;
        inode->i_generation = get_seconds();

        if ((de->attr & ATTR_DIR) && !IS_FREE(de->name)) {
                inode->i_generation &= ~1;
                inode->i_mode = MSDOS_MKMODE(de->attr,
                        S_IRWXUGO & ~sbi->options.fs_dmask) | S_IFDIR;
                inode->i_op = sbi->dir_ops;
                inode->i_fop = &fat_dir_operations;

                MSDOS_I(inode)->i_start = le16_to_cpu(de->start);
                if (sbi->fat_bits == 32)
                        MSDOS_I(inode)->i_start |= (le16_to_cpu(de->starthi) << 16);

                MSDOS_I(inode)->i_logstart = MSDOS_I(inode)->i_start;
                error = fat_calc_dir_size(inode);
                if (error < 0)
                        return error;
                MSDOS_I(inode)->mmu_private = inode->i_size;

                inode->i_nlink = fat_subdirs(inode);
        } else { /* not a directory */
                inode->i_generation |= 1;
                inode->i_mode = MSDOS_MKMODE(de->attr,
                    ((sbi->options.showexec && !is_exec(de->name + 8))
                        ? S_IRUGO|S_IWUGO : S_IRWXUGO)
                    & ~sbi->options.fs_fmask) | S_IFREG;
                MSDOS_I(inode)->i_start = le16_to_cpu(de->start);
                if (sbi->fat_bits == 32)
                        MSDOS_I(inode)->i_start |= (le16_to_cpu(de->starthi) << 16);

                MSDOS_I(inode)->i_logstart = MSDOS_I(inode)->i_start;
                inode->i_size = le32_to_cpu(de->size);
                inode->i_op = &fat_file_inode_operations;
                inode->i_fop = &fat_file_operations;
                inode->i_mapping->a_ops = &fat_aops;
                MSDOS_I(inode)->mmu_private = inode->i_size;
        }
        if (de->attr & ATTR_SYS) {
                if (sbi->options.sys_immutable)
                        inode->i_flags |= S_IMMUTABLE;
        }
        MSDOS_I(inode)->i_attrs = de->attr & ATTR_UNUSED;
        inode->i_blocks = ((inode->i_size + (sbi->cluster_size - 1))
                           & ~((loff_t)sbi->cluster_size - 1)) >> 9;
        inode->i_mtime.tv_sec =
                date_dos2unix(le16_to_cpu(de->time), le16_to_cpu(de->date));
        inode->i_mtime.tv_nsec = 0;
        if (sbi->options.isvfat) {
                int secs = de->ctime_cs / 100;
                int csecs = de->ctime_cs % 100;
                inode->i_ctime.tv_sec  =
                        date_dos2unix(le16_to_cpu(de->ctime),
                                      le16_to_cpu(de->cdate)) + secs;
                inode->i_ctime.tv_nsec = csecs * 10000000;
                inode->i_atime.tv_sec =
                        date_dos2unix(0, le16_to_cpu(de->adate));
                inode->i_atime.tv_nsec = 0;
        } else
                inode->i_ctime = inode->i_atime = inode->i_mtime;

        return 0;
}

struct inode *fat_build_inode(struct super_block *sb,
                        struct msdos_dir_entry *de, loff_t i_pos)
{
        struct inode *inode;
        int err;

        inode = fat_iget(sb, i_pos);
        if (inode)
                goto out;
        inode = new_inode(sb);
        if (!inode) {
                inode = ERR_PTR(-ENOMEM);
                goto out;
        }
        inode->i_ino = iunique(sb, MSDOS_ROOT_INO);
        inode->i_version = 1;
        err = fat_fill_inode(inode, de);
        if (err) {
                iput(inode);
                inode = ERR_PTR(err);
                goto out;
        }
        fat_attach(inode, i_pos);
        insert_inode_hash(inode);
out:
        return inode;
}

EXPORT_SYMBOL_GPL(fat_build_inode);

static void fat_delete_inode(struct inode *inode)
{
        truncate_inode_pages(&inode->i_data, 0);
        inode->i_size = 0;
        fat_truncate(inode);
        clear_inode(inode);
}

static void fat_clear_inode(struct inode *inode)
{
        struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);

        lock_kernel();
        spin_lock(&sbi->inode_hash_lock);
        fat_cache_inval_inode(inode);
        hlist_del_init(&MSDOS_I(inode)->i_fat_hash);
        spin_unlock(&sbi->inode_hash_lock);
        unlock_kernel();
}

static void fat_write_super(struct super_block *sb)
{
        sb->s_dirt = 0;

        if (!(sb->s_flags & MS_RDONLY))
                fat_clusters_flush(sb);
}

static void fat_put_super(struct super_block *sb)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);

        if (sbi->nls_disk) {
                unload_nls(sbi->nls_disk);
                sbi->nls_disk = NULL;
                sbi->options.codepage = fat_default_codepage;
        }
        if (sbi->nls_io) {
                unload_nls(sbi->nls_io);
                sbi->nls_io = NULL;
        }
        if (sbi->options.iocharset != fat_default_iocharset) {
                kfree(sbi->options.iocharset);
                sbi->options.iocharset = fat_default_iocharset;
        }

        sb->s_fs_info = NULL;
        kfree(sbi);
}

static struct kmem_cache *fat_inode_cachep;

static struct inode *fat_alloc_inode(struct super_block *sb)
{
        struct msdos_inode_info *ei;
        ei = kmem_cache_alloc(fat_inode_cachep, GFP_KERNEL);
        if (!ei)
                return NULL;
        return &ei->vfs_inode;
}

static void fat_destroy_inode(struct inode *inode)
{
        kmem_cache_free(fat_inode_cachep, MSDOS_I(inode));
}

static void init_once(struct kmem_cache *cachep, void *foo)
{
        struct msdos_inode_info *ei = (struct msdos_inode_info *)foo;

        spin_lock_init(&ei->cache_lru_lock);
        ei->nr_caches = 0;
        ei->cache_valid_id = FAT_CACHE_VALID + 1;
        INIT_LIST_HEAD(&ei->cache_lru);
        INIT_HLIST_NODE(&ei->i_fat_hash);
        inode_init_once(&ei->vfs_inode);
}

static int __init fat_init_inodecache(void)
{
        fat_inode_cachep = kmem_cache_create("fat_inode_cache",
                                             sizeof(struct msdos_inode_info),
                                             0, (SLAB_RECLAIM_ACCOUNT|
                                                SLAB_MEM_SPREAD),
                                             init_once);
        if (fat_inode_cachep == NULL)
                return -ENOMEM;
        return 0;
}

static void __exit fat_destroy_inodecache(void)
{
        kmem_cache_destroy(fat_inode_cachep);
}

static int fat_remount(struct super_block *sb, int *flags, char *data)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        *flags |= MS_NODIRATIME | (sbi->options.isvfat ? 0 : MS_NOATIME);
        return 0;
}

static int fat_statfs(struct dentry *dentry, struct kstatfs *buf)
{
        struct msdos_sb_info *sbi = MSDOS_SB(dentry->d_sb);

        /* If the count of free cluster is still unknown, counts it here. */
        if (sbi->free_clusters == -1 || !sbi->free_clus_valid) {
                int err = fat_count_free_clusters(dentry->d_sb);
                if (err)
                        return err;
        }

        buf->f_type = dentry->d_sb->s_magic;
        buf->f_bsize = sbi->cluster_size;
        buf->f_blocks = sbi->max_cluster - FAT_START_ENT;
        buf->f_bfree = sbi->free_clusters;
        buf->f_bavail = sbi->free_clusters;
        buf->f_namelen = sbi->options.isvfat ? 260 : 12;

        return 0;
}

static int fat_write_inode(struct inode *inode, int wait)
{
        struct super_block *sb = inode->i_sb;
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        struct buffer_head *bh;
        struct msdos_dir_entry *raw_entry;
        loff_t i_pos;
        int err = 0;

retry:
        i_pos = MSDOS_I(inode)->i_pos;
        if (inode->i_ino == MSDOS_ROOT_INO || !i_pos)
                return 0;

        lock_kernel();
        bh = sb_bread(sb, i_pos >> sbi->dir_per_block_bits);
        if (!bh) {
                printk(KERN_ERR "FAT: unable to read inode block "
                       "for updating (i_pos %lld)\n", i_pos);
                err = -EIO;
                goto out;
        }
        spin_lock(&sbi->inode_hash_lock);
        if (i_pos != MSDOS_I(inode)->i_pos) {
                spin_unlock(&sbi->inode_hash_lock);
                brelse(bh);
                unlock_kernel();
                goto retry;
        }

        raw_entry = &((struct msdos_dir_entry *) (bh->b_data))
            [i_pos & (sbi->dir_per_block - 1)];
        if (S_ISDIR(inode->i_mode))
                raw_entry->size = 0;
        else
                raw_entry->size = cpu_to_le32(inode->i_size);
        raw_entry->attr = fat_attr(inode);
        raw_entry->start = cpu_to_le16(MSDOS_I(inode)->i_logstart);
        raw_entry->starthi = cpu_to_le16(MSDOS_I(inode)->i_logstart >> 16);
        fat_date_unix2dos(inode->i_mtime.tv_sec, &raw_entry->time, &raw_entry->date);
        if (sbi->options.isvfat) {
                __le16 atime;
                fat_date_unix2dos(inode->i_ctime.tv_sec,&raw_entry->ctime,&raw_entry->cdate);
                fat_date_unix2dos(inode->i_atime.tv_sec,&atime,&raw_entry->adate);
                raw_entry->ctime_cs = (inode->i_ctime.tv_sec & 1) * 100 +
                        inode->i_ctime.tv_nsec / 10000000;
        }
        spin_unlock(&sbi->inode_hash_lock);
        mark_buffer_dirty(bh);
        if (wait)
                err = sync_dirty_buffer(bh);
        brelse(bh);
out:
        unlock_kernel();
        return err;
}

int fat_sync_inode(struct inode *inode)
{
        return fat_write_inode(inode, 1);
}

EXPORT_SYMBOL_GPL(fat_sync_inode);

static int fat_show_options(struct seq_file *m, struct vfsmount *mnt);
static const struct super_operations fat_sops = {
        .alloc_inode    = fat_alloc_inode,
        .destroy_inode  = fat_destroy_inode,
        .write_inode    = fat_write_inode,
        .delete_inode   = fat_delete_inode,
        .put_super      = fat_put_super,
        .write_super    = fat_write_super,
        .statfs         = fat_statfs,
        .clear_inode    = fat_clear_inode,
        .remount_fs     = fat_remount,

        .show_options   = fat_show_options,
};

/*
 * a FAT file handle with fhtype 3 is
 *  0/  i_ino - for fast, reliable lookup if still in the cache
 *  1/  i_generation - to see if i_ino is still valid
 *          bit 0 == 0 iff directory
 *  2/  i_pos(8-39) - if ino has changed, but still in cache
 *  3/  i_pos(4-7)|i_logstart - to semi-verify inode found at i_pos
 *  4/  i_pos(0-3)|parent->i_logstart - maybe used to hunt for the file on disc
 *
 * Hack for NFSv2: Maximum FAT entry number is 28bits and maximum
 * i_pos is 40bits (blocknr(32) + dir offset(8)), so two 4bits
 * of i_logstart is used to store the directory entry offset.
 */

static struct dentry *fat_fh_to_dentry(struct super_block *sb,
                struct fid *fid, int fh_len, int fh_type)
{
        struct inode *inode = NULL;
        struct dentry *result;
        u32 *fh = fid->raw;

        if (fh_len < 5 || fh_type != 3)
                return NULL;

        inode = ilookup(sb, fh[0]);
        if (!inode || inode->i_generation != fh[1]) {
                if (inode)
                        iput(inode);
                inode = NULL;
        }
        if (!inode) {
                loff_t i_pos;
                int i_logstart = fh[3] & 0x0fffffff;

                i_pos = (loff_t)fh[2] << 8;
                i_pos |= ((fh[3] >> 24) & 0xf0) | (fh[4] >> 28);

                /* try 2 - see if i_pos is in F-d-c
                 * require i_logstart to be the same
                 * Will fail if you truncate and then re-write
                 */

                inode = fat_iget(sb, i_pos);
                if (inode && MSDOS_I(inode)->i_logstart != i_logstart) {
                        iput(inode);
                        inode = NULL;
                }
        }
        if (!inode) {
                /* For now, do nothing
                 * What we could do is:
                 * follow the file starting at fh[4], and record
                 * the ".." entry, and the name of the fh[2] entry.
                 * The follow the ".." file finding the next step up.
                 * This way we build a path to the root of
                 * the tree. If this works, we lookup the path and so
                 * get this inode into the cache.
                 * Finally try the fat_iget lookup again
                 * If that fails, then weare totally out of luck
                 * But all that is for another day
                 */
        }
        if (!inode)
                return ERR_PTR(-ESTALE);


        /* now to find a dentry.
         * If possible, get a well-connected one
         */
        result = d_alloc_anon(inode);
        if (result == NULL) {
                iput(inode);
                return ERR_PTR(-ENOMEM);
        }
        result->d_op = sb->s_root->d_op;
        return result;
}

static int
fat_encode_fh(struct dentry *de, __u32 *fh, int *lenp, int connectable)
{
        int len = *lenp;
        struct inode *inode =  de->d_inode;
        u32 ipos_h, ipos_m, ipos_l;

        if (len < 5)
                return 255; /* no room */

        ipos_h = MSDOS_I(inode)->i_pos >> 8;
        ipos_m = (MSDOS_I(inode)->i_pos & 0xf0) << 24;
        ipos_l = (MSDOS_I(inode)->i_pos & 0x0f) << 28;
        *lenp = 5;
        fh[0] = inode->i_ino;
        fh[1] = inode->i_generation;
        fh[2] = ipos_h;
        fh[3] = ipos_m | MSDOS_I(inode)->i_logstart;
        spin_lock(&de->d_lock);
        fh[4] = ipos_l | MSDOS_I(de->d_parent->d_inode)->i_logstart;
        spin_unlock(&de->d_lock);
        return 3;
}

static struct dentry *fat_get_parent(struct dentry *child)
{
        struct buffer_head *bh;
        struct msdos_dir_entry *de;
        loff_t i_pos;
        struct dentry *parent;
        struct inode *inode;
        int err;

        lock_kernel();

        err = fat_get_dotdot_entry(child->d_inode, &bh, &de, &i_pos);
        if (err) {
                parent = ERR_PTR(err);
                goto out;
        }
        inode = fat_build_inode(child->d_sb, de, i_pos);
        brelse(bh);
        if (IS_ERR(inode)) {
                parent = ERR_CAST(inode);
                goto out;
        }
        parent = d_alloc_anon(inode);
        if (!parent) {
                iput(inode);
                parent = ERR_PTR(-ENOMEM);
        }
out:
        unlock_kernel();

        return parent;
}

static const struct export_operations fat_export_ops = {
        .encode_fh      = fat_encode_fh,
        .fh_to_dentry   = fat_fh_to_dentry,
        .get_parent     = fat_get_parent,
};

static int fat_show_options(struct seq_file *m, struct vfsmount *mnt)
{
        struct msdos_sb_info *sbi = MSDOS_SB(mnt->mnt_sb);
        struct fat_mount_options *opts = &sbi->options;
        int isvfat = opts->isvfat;

        if (opts->fs_uid != 0)
                seq_printf(m, ",uid=%u", opts->fs_uid);
        if (opts->fs_gid != 0)
                seq_printf(m, ",gid=%u", opts->fs_gid);
        seq_printf(m, ",fmask=%04o", opts->fs_fmask);
        seq_printf(m, ",dmask=%04o", opts->fs_dmask);
        if (opts->allow_utime)
                seq_printf(m, ",allow_utime=%04o", opts->allow_utime);
        if (sbi->nls_disk)
                seq_printf(m, ",codepage=%s", sbi->nls_disk->charset);
        if (isvfat) {
                if (sbi->nls_io)
                        seq_printf(m, ",iocharset=%s", sbi->nls_io->charset);

                switch (opts->shortname) {
                case VFAT_SFN_DISPLAY_WIN95 | VFAT_SFN_CREATE_WIN95:
                        seq_puts(m, ",shortname=win95");
                        break;
                case VFAT_SFN_DISPLAY_WINNT | VFAT_SFN_CREATE_WINNT:
                        seq_puts(m, ",shortname=winnt");
                        break;
                case VFAT_SFN_DISPLAY_WINNT | VFAT_SFN_CREATE_WIN95:
                        seq_puts(m, ",shortname=mixed");
                        break;
                case VFAT_SFN_DISPLAY_LOWER | VFAT_SFN_CREATE_WIN95:
                        /* seq_puts(m, ",shortname=lower"); */
                        break;
                default:
                        seq_puts(m, ",shortname=unknown");
                        break;
                }
        }
        if (opts->name_check != 'n')
                seq_printf(m, ",check=%c", opts->name_check);
        if (opts->usefree)
                seq_puts(m, ",usefree");
        if (opts->quiet)
                seq_puts(m, ",quiet");
        if (opts->showexec)
                seq_puts(m, ",showexec");
        if (opts->sys_immutable)
                seq_puts(m, ",sys_immutable");
        if (!isvfat) {
                if (opts->dotsOK)
                        seq_puts(m, ",dotsOK=yes");
                if (opts->nocase)
                        seq_puts(m, ",nocase");
        } else {
                if (opts->utf8)
                        seq_puts(m, ",utf8");
                if (opts->unicode_xlate)
                        seq_puts(m, ",uni_xlate");
                if (!opts->numtail)
                        seq_puts(m, ",nonumtail");
        }
        if (sbi->options.flush)
                seq_puts(m, ",flush");

        return 0;
}

enum {
        Opt_check_n, Opt_check_r, Opt_check_s, Opt_uid, Opt_gid,
        Opt_umask, Opt_dmask, Opt_fmask, Opt_allow_utime, Opt_codepage,
        Opt_usefree, Opt_nocase, Opt_quiet, Opt_showexec, Opt_debug,
        Opt_immutable, Opt_dots, Opt_nodots,
        Opt_charset, Opt_shortname_lower, Opt_shortname_win95,
        Opt_shortname_winnt, Opt_shortname_mixed, Opt_utf8_no, Opt_utf8_yes,
        Opt_uni_xl_no, Opt_uni_xl_yes, Opt_nonumtail_no, Opt_nonumtail_yes,
        Opt_obsolate, Opt_flush, Opt_err,
};

static match_table_t fat_tokens = {
        {Opt_check_r, "check=relaxed"},
        {Opt_check_s, "check=strict"},
        {Opt_check_n, "check=normal"},
        {Opt_check_r, "check=r"},
        {Opt_check_s, "check=s"},
        {Opt_check_n, "check=n"},
        {Opt_uid, "uid=%u"},
        {Opt_gid, "gid=%u"},
        {Opt_umask, "umask=%o"},
        {Opt_dmask, "dmask=%o"},
        {Opt_fmask, "fmask=%o"},
        {Opt_allow_utime, "allow_utime=%o"},
        {Opt_codepage, "codepage=%u"},
        {Opt_usefree, "usefree"},
        {Opt_nocase, "nocase"},
        {Opt_quiet, "quiet"},
        {Opt_showexec, "showexec"},
        {Opt_debug, "debug"},
        {Opt_immutable, "sys_immutable"},
        {Opt_obsolate, "conv=binary"},
        {Opt_obsolate, "conv=text"},
        {Opt_obsolate, "conv=auto"},
        {Opt_obsolate, "conv=b"},
        {Opt_obsolate, "conv=t"},
        {Opt_obsolate, "conv=a"},
        {Opt_obsolate, "fat=%u"},
        {Opt_obsolate, "blocksize=%u"},
        {Opt_obsolate, "cvf_format=%20s"},
        {Opt_obsolate, "cvf_options=%100s"},
        {Opt_obsolate, "posix"},
        {Opt_flush, "flush"},
        {Opt_err, NULL},
};
static match_table_t msdos_tokens = {
        {Opt_nodots, "nodots"},
        {Opt_nodots, "dotsOK=no"},
        {Opt_dots, "dots"},
        {Opt_dots, "dotsOK=yes"},
        {Opt_err, NULL}
};
static match_table_t vfat_tokens = {
        {Opt_charset, "iocharset=%s"},
        {Opt_shortname_lower, "shortname=lower"},
        {Opt_shortname_win95, "shortname=win95"},
        {Opt_shortname_winnt, "shortname=winnt"},
        {Opt_shortname_mixed, "shortname=mixed"},
        {Opt_utf8_no, "utf8=0"},                /* 0 or no or false */
        {Opt_utf8_no, "utf8=no"},
        {Opt_utf8_no, "utf8=false"},
        {Opt_utf8_yes, "utf8=1"},               /* empty or 1 or yes or true */
        {Opt_utf8_yes, "utf8=yes"},
        {Opt_utf8_yes, "utf8=true"},
        {Opt_utf8_yes, "utf8"},
        {Opt_uni_xl_no, "uni_xlate=0"},         /* 0 or no or false */
        {Opt_uni_xl_no, "uni_xlate=no"},
        {Opt_uni_xl_no, "uni_xlate=false"},
        {Opt_uni_xl_yes, "uni_xlate=1"},        /* empty or 1 or yes or true */
        {Opt_uni_xl_yes, "uni_xlate=yes"},
        {Opt_uni_xl_yes, "uni_xlate=true"},
        {Opt_uni_xl_yes, "uni_xlate"},
        {Opt_nonumtail_no, "nonumtail=0"},      /* 0 or no or false */
        {Opt_nonumtail_no, "nonumtail=no"},
        {Opt_nonumtail_no, "nonumtail=false"},
        {Opt_nonumtail_yes, "nonumtail=1"},     /* empty or 1 or yes or true */
        {Opt_nonumtail_yes, "nonumtail=yes"},
        {Opt_nonumtail_yes, "nonumtail=true"},
        {Opt_nonumtail_yes, "nonumtail"},
        {Opt_err, NULL}
};

static int parse_options(char *options, int is_vfat, int silent, int *debug,
                         struct fat_mount_options *opts)
{
        char *p;
        substring_t args[MAX_OPT_ARGS];
        int option;
        char *iocharset;

        opts->isvfat = is_vfat;

        opts->fs_uid = current->uid;
        opts->fs_gid = current->gid;
        opts->fs_fmask = opts->fs_dmask = current->fs->umask;
        opts->allow_utime = -1;
        opts->codepage = fat_default_codepage;
        opts->iocharset = fat_default_iocharset;
        if (is_vfat)
                opts->shortname = VFAT_SFN_DISPLAY_LOWER|VFAT_SFN_CREATE_WIN95;
        else
                opts->shortname = 0;
        opts->name_check = 'n';
        opts->quiet = opts->showexec = opts->sys_immutable = opts->dotsOK =  0;
        opts->utf8 = opts->unicode_xlate = 0;
        opts->numtail = 1;
        opts->usefree = opts->nocase = 0;
        *debug = 0;

        if (!options)
                return 0;

        while ((p = strsep(&options, ",")) != NULL) {
                int token;
                if (!*p)
                        continue;

                token = match_token(p, fat_tokens, args);
                if (token == Opt_err) {
                        if (is_vfat)
                                token = match_token(p, vfat_tokens, args);
                        else
                                token = match_token(p, msdos_tokens, args);
                }
                switch (token) {
                case Opt_check_s:
                        opts->name_check = 's';
                        break;
                case Opt_check_r:
                        opts->name_check = 'r';
                        break;
                case Opt_check_n:
                        opts->name_check = 'n';
                        break;
                case Opt_usefree:
                        opts->usefree = 1;
                        break;
                case Opt_nocase:
                        if (!is_vfat)
                                opts->nocase = 1;
                        else {
                                /* for backward compatibility */
                                opts->shortname = VFAT_SFN_DISPLAY_WIN95
                                        | VFAT_SFN_CREATE_WIN95;
                        }
                        break;
                case Opt_quiet:
                        opts->quiet = 1;
                        break;
                case Opt_showexec:
                        opts->showexec = 1;
                        break;
                case Opt_debug:
                        *debug = 1;
                        break;
                case Opt_immutable:
                        opts->sys_immutable = 1;
                        break;
                case Opt_uid:
                        if (match_int(&args[0], &option))
                                return 0;
                        opts->fs_uid = option;
                        break;
                case Opt_gid:
                        if (match_int(&args[0], &option))
                                return 0;
                        opts->fs_gid = option;
                        break;
                case Opt_umask:
                        if (match_octal(&args[0], &option))
                                return 0;
                        opts->fs_fmask = opts->fs_dmask = option;
                        break;
                case Opt_dmask:
                        if (match_octal(&args[0], &option))
                                return 0;
                        opts->fs_dmask = option;
                        break;
                case Opt_fmask:
                        if (match_octal(&args[0], &option))
                                return 0;
                        opts->fs_fmask = option;
                        break;
                case Opt_allow_utime:
                        if (match_octal(&args[0], &option))
                                return 0;
                        opts->allow_utime = option & (S_IWGRP | S_IWOTH);
                        break;
                case Opt_codepage:
                        if (match_int(&args[0], &option))
                                return 0;
                        opts->codepage = option;
                        break;
                case Opt_flush:
                        opts->flush = 1;
                        break;

                /* msdos specific */
                case Opt_dots:
                        opts->dotsOK = 1;
                        break;
                case Opt_nodots:
                        opts->dotsOK = 0;
                        break;

                /* vfat specific */
                case Opt_charset:
                        if (opts->iocharset != fat_default_iocharset)
                                kfree(opts->iocharset);
                        iocharset = match_strdup(&args[0]);
                        if (!iocharset)
                                return -ENOMEM;
                        opts->iocharset = iocharset;
                        break;
                case Opt_shortname_lower:
                        opts->shortname = VFAT_SFN_DISPLAY_LOWER
                                        | VFAT_SFN_CREATE_WIN95;
                        break;
                case Opt_shortname_win95:
                        opts->shortname = VFAT_SFN_DISPLAY_WIN95
                                        | VFAT_SFN_CREATE_WIN95;
                        break;
                case Opt_shortname_winnt:
                        opts->shortname = VFAT_SFN_DISPLAY_WINNT
                                        | VFAT_SFN_CREATE_WINNT;
                        break;
                case Opt_shortname_mixed:
                        opts->shortname = VFAT_SFN_DISPLAY_WINNT
                                        | VFAT_SFN_CREATE_WIN95;
                        break;
                case Opt_utf8_no:               /* 0 or no or false */
                        opts->utf8 = 0;
                        break;
                case Opt_utf8_yes:              /* empty or 1 or yes or true */
                        opts->utf8 = 1;
                        break;
                case Opt_uni_xl_no:             /* 0 or no or false */
                        opts->unicode_xlate = 0;
                        break;
                case Opt_uni_xl_yes:            /* empty or 1 or yes or true */
                        opts->unicode_xlate = 1;
                        break;
                case Opt_nonumtail_no:          /* 0 or no or false */
                        opts->numtail = 1;      /* negated option */
                        break;
                case Opt_nonumtail_yes:         /* empty or 1 or yes or true */
                        opts->numtail = 0;      /* negated option */
                        break;

                /* obsolete mount options */
                case Opt_obsolate:
                        printk(KERN_INFO "FAT: \"%s\" option is obsolete, "
                               "not supported now\n", p);
                        break;
                /* unknown option */
                default:
                        if (!silent) {
                                printk(KERN_ERR
                                       "FAT: Unrecognized mount option \"%s\" "
                                       "or missing value\n", p);
                        }
                        return -EINVAL;
                }
        }
        /* UTF-8 doesn't provide FAT semantics */
        if (!strcmp(opts->iocharset, "utf8")) {
                printk(KERN_ERR "FAT: utf8 is not a recommended IO charset"
                       " for FAT filesystems, filesystem will be case sensitive!\n");
        }

        /* If user doesn't specify allow_utime, it's initialized from dmask. */
        if (opts->allow_utime == (unsigned short)-1)
                opts->allow_utime = ~opts->fs_dmask & (S_IWGRP | S_IWOTH);
        if (opts->unicode_xlate)
                opts->utf8 = 0;

        return 0;
}

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

        MSDOS_I(inode)->i_pos = 0;
        inode->i_uid = sbi->options.fs_uid;
        inode->i_gid = sbi->options.fs_gid;
        inode->i_version++;
        inode->i_generation = 0;
        inode->i_mode = (S_IRWXUGO & ~sbi->options.fs_dmask) | S_IFDIR;
        inode->i_op = sbi->dir_ops;
        inode->i_fop = &fat_dir_operations;
        if (sbi->fat_bits == 32) {
                MSDOS_I(inode)->i_start = sbi->root_cluster;
                error = fat_calc_dir_size(inode);
                if (error < 0)
                        return error;
        } else {
                MSDOS_I(inode)->i_start = 0;
                inode->i_size = sbi->dir_entries * sizeof(struct msdos_dir_entry);
        }
        inode->i_blocks = ((inode->i_size + (sbi->cluster_size - 1))
                           & ~((loff_t)sbi->cluster_size - 1)) >> 9;
        MSDOS_I(inode)->i_logstart = 0;
        MSDOS_I(inode)->mmu_private = inode->i_size;

        MSDOS_I(inode)->i_attrs = ATTR_NONE;
        inode->i_mtime.tv_sec = inode->i_atime.tv_sec = inode->i_ctime.tv_sec = 0;
        inode->i_mtime.tv_nsec = inode->i_atime.tv_nsec = inode->i_ctime.tv_nsec = 0;
        inode->i_nlink = fat_subdirs(inode)+2;

        return 0;
}

/*
 * Read the super block of an MS-DOS FS.
 */
int fat_fill_super(struct super_block *sb, void *data, int silent,
                   const struct inode_operations *fs_dir_inode_ops, int isvfat)
{
        struct inode *root_inode = NULL;
        struct buffer_head *bh;
        struct fat_boot_sector *b;
        struct msdos_sb_info *sbi;
        u16 logical_sector_size;
        u32 total_sectors, total_clusters, fat_clusters, rootdir_sectors;
        int debug;
        unsigned int media;
        long error;
        char buf[50];

        sbi = kzalloc(sizeof(struct msdos_sb_info), GFP_KERNEL);
        if (!sbi)
                return -ENOMEM;
        sb->s_fs_info = sbi;

        sb->s_flags |= MS_NODIRATIME;
        sb->s_magic = MSDOS_SUPER_MAGIC;
        sb->s_op = &fat_sops;
        sb->s_export_op = &fat_export_ops;
        sbi->dir_ops = fs_dir_inode_ops;

        error = parse_options(data, isvfat, silent, &debug, &sbi->options);
        if (error)
                goto out_fail;

        error = -EIO;
        sb_min_blocksize(sb, 512);
        bh = sb_bread(sb, 0);
        if (bh == NULL) {
                printk(KERN_ERR "FAT: unable to read boot sector\n");
                goto out_fail;
        }

        b = (struct fat_boot_sector *) bh->b_data;
        if (!b->reserved) {
                if (!silent)
                        printk(KERN_ERR "FAT: bogus number of reserved sectors\n");
                brelse(bh);
                goto out_invalid;
        }
        if (!b->fats) {
                if (!silent)
                        printk(KERN_ERR "FAT: bogus number of FAT structure\n");
                brelse(bh);
                goto out_invalid;
        }

        /*
         * Earlier we checked here that b->secs_track and b->head are nonzero,
         * but it turns out valid FAT filesystems can have zero there.
         */

        media = b->media;
        if (!FAT_VALID_MEDIA(media)) {
                if (!silent)
                        printk(KERN_ERR "FAT: invalid media value (0x%02x)\n",
                               media);
                brelse(bh);
                goto out_invalid;
        }
        logical_sector_size =
                le16_to_cpu(get_unaligned((__le16 *)&b->sector_size));
        if (!is_power_of_2(logical_sector_size)
            || (logical_sector_size < 512)
            || (PAGE_CACHE_SIZE < logical_sector_size)) {
                if (!silent)
                        printk(KERN_ERR "FAT: bogus logical sector size %u\n",
                               logical_sector_size);
                brelse(bh);
                goto out_invalid;
        }
        sbi->sec_per_clus = b->sec_per_clus;
        if (!is_power_of_2(sbi->sec_per_clus)) {
                if (!silent)
                        printk(KERN_ERR "FAT: bogus sectors per cluster %u\n",
                               sbi->sec_per_clus);
                brelse(bh);
                goto out_invalid;
        }

        if (logical_sector_size < sb->s_blocksize) {
                printk(KERN_ERR "FAT: logical sector size too small for device"
                       " (logical sector size = %u)\n", logical_sector_size);
                brelse(bh);
                goto out_fail;
        }
        if (logical_sector_size > sb->s_blocksize) {
                brelse(bh);

                if (!sb_set_blocksize(sb, logical_sector_size)) {
                        printk(KERN_ERR "FAT: unable to set blocksize %u\n",
                               logical_sector_size);
                        goto out_fail;
                }
                bh = sb_bread(sb, 0);
                if (bh == NULL) {
                        printk(KERN_ERR "FAT: unable to read boot sector"
                               " (logical sector size = %lu)\n",
                               sb->s_blocksize);
                        goto out_fail;
                }
                b = (struct fat_boot_sector *) bh->b_data;
        }

        sbi->cluster_size = sb->s_blocksize * sbi->sec_per_clus;
        sbi->cluster_bits = ffs(sbi->cluster_size) - 1;
        sbi->fats = b->fats;
        sbi->fat_bits = 0;              /* Don't know yet */
        sbi->fat_start = le16_to_cpu(b->reserved);
        sbi->fat_length = le16_to_cpu(b->fat_length);
        sbi->root_cluster = 0;
        sbi->free_clusters = -1;        /* Don't know yet */
        sbi->free_clus_valid = 0;
        sbi->prev_free = FAT_START_ENT;

        if (!sbi->fat_length && b->fat32_length) {
                struct fat_boot_fsinfo *fsinfo;
                struct buffer_head *fsinfo_bh;

                /* Must be FAT32 */
                sbi->fat_bits = 32;
                sbi->fat_length = le32_to_cpu(b->fat32_length);
                sbi->root_cluster = le32_to_cpu(b->root_cluster);

                sb->s_maxbytes = 0xffffffff;

                /* MC - if info_sector is 0, don't multiply by 0 */
                sbi->fsinfo_sector = le16_to_cpu(b->info_sector);
                if (sbi->fsinfo_sector == 0)
                        sbi->fsinfo_sector = 1;

                fsinfo_bh = sb_bread(sb, sbi->fsinfo_sector);
                if (fsinfo_bh == NULL) {
                        printk(KERN_ERR "FAT: bread failed, FSINFO block"
                               " (sector = %lu)\n", sbi->fsinfo_sector);
                        brelse(bh);
                        goto out_fail;
                }

                fsinfo = (struct fat_boot_fsinfo *)fsinfo_bh->b_data;
                if (!IS_FSINFO(fsinfo)) {
                        printk(KERN_WARNING "FAT: Invalid FSINFO signature: "
                               "0x%08x, 0x%08x (sector = %lu)\n",
                               le32_to_cpu(fsinfo->signature1),
                               le32_to_cpu(fsinfo->signature2),
                               sbi->fsinfo_sector);
                } else {
                        if (sbi->options.usefree)
                                sbi->free_clus_valid = 1;
                        sbi->free_clusters = le32_to_cpu(fsinfo->free_clusters);
                        sbi->prev_free = le32_to_cpu(fsinfo->next_cluster);
                }

                brelse(fsinfo_bh);
        }

        sbi->dir_per_block = sb->s_blocksize / sizeof(struct msdos_dir_entry);
        sbi->dir_per_block_bits = ffs(sbi->dir_per_block) - 1;

        sbi->dir_start = sbi->fat_start + sbi->fats * sbi->fat_length;
        sbi->dir_entries =
                le16_to_cpu(get_unaligned((__le16 *)&b->dir_entries));
        if (sbi->dir_entries & (sbi->dir_per_block - 1)) {
                if (!silent)
                        printk(KERN_ERR "FAT: bogus directroy-entries per block"
                               " (%u)\n", sbi->dir_entries);
                brelse(bh);
                goto out_invalid;
        }

        rootdir_sectors = sbi->dir_entries
                * sizeof(struct msdos_dir_entry) / sb->s_blocksize;
        sbi->data_start = sbi->dir_start + rootdir_sectors;
        total_sectors = le16_to_cpu(get_unaligned((__le16 *)&b->sectors));
        if (total_sectors == 0)
                total_sectors = le32_to_cpu(b->total_sect);

        total_clusters = (total_sectors - sbi->data_start) / sbi->sec_per_clus;

        if (sbi->fat_bits != 32)
                sbi->fat_bits = (total_clusters > MAX_FAT12) ? 16 : 12;

        /* check that FAT table does not overflow */
        fat_clusters = sbi->fat_length * sb->s_blocksize * 8 / sbi->fat_bits;
        total_clusters = min(total_clusters, fat_clusters - FAT_START_ENT);
        if (total_clusters > MAX_FAT(sb)) {
                if (!silent)
                        printk(KERN_ERR "FAT: count of clusters too big (%u)\n",
                               total_clusters);
                brelse(bh);
                goto out_invalid;
        }

        sbi->max_cluster = total_clusters + FAT_START_ENT;
        /* check the free_clusters, it's not necessarily correct */
        if (sbi->free_clusters != -1 && sbi->free_clusters > total_clusters)
                sbi->free_clusters = -1;
        /* check the prev_free, it's not necessarily correct */
        sbi->prev_free %= sbi->max_cluster;
        if (sbi->prev_free < FAT_START_ENT)
                sbi->prev_free = FAT_START_ENT;

        brelse(bh);

        /* set up enough so that it can read an inode */
        fat_hash_init(sb);
        fat_ent_access_init(sb);

        /*
         * The low byte of FAT's first entry must have same value with
         * media-field.  But in real world, too many devices is
         * writing wrong value.  So, removed that validity check.
         *
         * if (FAT_FIRST_ENT(sb, media) != first)
         */

        error = -EINVAL;
        sprintf(buf, "cp%d", sbi->options.codepage);
        sbi->nls_disk = load_nls(buf);
        if (!sbi->nls_disk) {
                printk(KERN_ERR "FAT: codepage %s not found\n", buf);
                goto out_fail;
        }

        /* FIXME: utf8 is using iocharset for upper/lower conversion */
        if (sbi->options.isvfat) {
                sbi->nls_io = load_nls(sbi->options.iocharset);
                if (!sbi->nls_io) {
                        printk(KERN_ERR "FAT: IO charset %s not found\n",
                               sbi->options.iocharset);
                        goto out_fail;
                }
        }

        error = -ENOMEM;
        root_inode = new_inode(sb);
        if (!root_inode)
                goto out_fail;
        root_inode->i_ino = MSDOS_ROOT_INO;
        root_inode->i_version = 1;
        error = fat_read_root(root_inode);
        if (error < 0)
                goto out_fail;
        error = -ENOMEM;
        insert_inode_hash(root_inode);
        sb->s_root = d_alloc_root(root_inode);
        if (!sb->s_root) {
                printk(KERN_ERR "FAT: get root inode failed\n");
                goto out_fail;
        }

        return 0;

out_invalid:
        error = -EINVAL;
        if (!silent)
                printk(KERN_INFO "VFS: Can't find a valid FAT filesystem"
                       " on dev %s.\n", sb->s_id);

out_fail:
        if (root_inode)
                iput(root_inode);
        if (sbi->nls_io)
                unload_nls(sbi->nls_io);
        if (sbi->nls_disk)
                unload_nls(sbi->nls_disk);
        if (sbi->options.iocharset != fat_default_iocharset)
                kfree(sbi->options.iocharset);
        sb->s_fs_info = NULL;
        kfree(sbi);
        return error;
}

EXPORT_SYMBOL_GPL(fat_fill_super);

/*
 * helper function for fat_flush_inodes.  This writes both the inode
 * and the file data blocks, waiting for in flight data blocks before
 * the start of the call.  It does not wait for any io started
 * during the call
 */
static int writeback_inode(struct inode *inode)
{

        int ret;
        struct address_space *mapping = inode->i_mapping;
        struct writeback_control wbc = {
               .sync_mode = WB_SYNC_NONE,
              .nr_to_write = 0,
        };
        /* if we used WB_SYNC_ALL, sync_inode waits for the io for the
        * inode to finish.  So WB_SYNC_NONE is sent down to sync_inode
        * and filemap_fdatawrite is used for the data blocks
        */
        ret = sync_inode(inode, &wbc);
        if (!ret)
               ret = filemap_fdatawrite(mapping);
        return ret;
}

/*
 * write data and metadata corresponding to i1 and i2.  The io is
 * started but we do not wait for any of it to finish.
 *
 * filemap_flush is used for the block device, so if there is a dirty
 * page for a block already in flight, we will not wait and start the
 * io over again
 */
int fat_flush_inodes(struct super_block *sb, struct inode *i1, struct inode *i2)
{
        int ret = 0;
        if (!MSDOS_SB(sb)->options.flush)
                return 0;
        if (i1)
                ret = writeback_inode(i1);
        if (!ret && i2)
                ret = writeback_inode(i2);
        if (!ret) {
                struct address_space *mapping = sb->s_bdev->bd_inode->i_mapping;
                ret = filemap_flush(mapping);
        }
        return ret;
}
EXPORT_SYMBOL_GPL(fat_flush_inodes);

static int __init init_fat_fs(void)
{
        int err;

        err = fat_cache_init();
        if (err)
                return err;

        err = fat_init_inodecache();
        if (err)
                goto failed;

        return 0;

failed:
        fat_cache_destroy();
        return err;
}

static void __exit exit_fat_fs(void)
{
        fat_cache_destroy();
        fat_destroy_inodecache();
}

module_init(init_fat_fs)
module_exit(exit_fat_fs)

MODULE_LICENSE("GPL");