direct-io: Prevent NULL pointer access in submit_page_section

[mirror_ubuntu-artful-kernel.git] / fs / fat / namei_vfat.c

/*
 *  linux/fs/vfat/namei.c
 *
 *  Written 1992,1993 by Werner Almesberger
 *
 *  Windows95/Windows NT compatible extended MSDOS filesystem
 *    by Gordon Chaffee Copyright (C) 1995.  Send bug reports for the
 *    VFAT filesystem to <chaffee@cs.berkeley.edu>.  Specify
 *    what file operation caused you trouble and if you can duplicate
 *    the problem, send a script that demonstrates it.
 *
 *  Short name translation 1999, 2001 by Wolfram Pienkoss <wp@bszh.de>
 *
 *  Support Multibyte characters and cleanup by
 *                              OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
 */

#include <linux/module.h>
#include <linux/ctype.h>
#include <linux/slab.h>
#include <linux/namei.h>
#include "fat.h"

static inline unsigned long vfat_d_version(struct dentry *dentry)
{
        return (unsigned long) dentry->d_fsdata;
}

static inline void vfat_d_version_set(struct dentry *dentry,
                                      unsigned long version)
{
        dentry->d_fsdata = (void *) version;
}

/*
 * If new entry was created in the parent, it could create the 8.3
 * alias (the shortname of logname).  So, the parent may have the
 * negative-dentry which matches the created 8.3 alias.
 *
 * If it happened, the negative dentry isn't actually negative
 * anymore.  So, drop it.
 */
static int vfat_revalidate_shortname(struct dentry *dentry)
{
        int ret = 1;
        spin_lock(&dentry->d_lock);
        if (vfat_d_version(dentry) != d_inode(dentry->d_parent)->i_version)
                ret = 0;
        spin_unlock(&dentry->d_lock);
        return ret;
}

static int vfat_revalidate(struct dentry *dentry, unsigned int flags)
{
        if (flags & LOOKUP_RCU)
                return -ECHILD;

        /* This is not negative dentry. Always valid. */
        if (d_really_is_positive(dentry))
                return 1;
        return vfat_revalidate_shortname(dentry);
}

static int vfat_revalidate_ci(struct dentry *dentry, unsigned int flags)
{
        if (flags & LOOKUP_RCU)
                return -ECHILD;

        /*
         * This is not negative dentry. Always valid.
         *
         * Note, rename() to existing directory entry will have ->d_inode,
         * and will use existing name which isn't specified name by user.
         *
         * We may be able to drop this positive dentry here. But dropping
         * positive dentry isn't good idea. So it's unsupported like
         * rename("filename", "FILENAME") for now.
         */
        if (d_really_is_positive(dentry))
                return 1;

        /*
         * This may be nfsd (or something), anyway, we can't see the
         * intent of this. So, since this can be for creation, drop it.
         */
        if (!flags)
                return 0;

        /*
         * Drop the negative dentry, in order to make sure to use the
         * case sensitive name which is specified by user if this is
         * for creation.
         */
        if (flags & (LOOKUP_CREATE | LOOKUP_RENAME_TARGET))
                return 0;

        return vfat_revalidate_shortname(dentry);
}

/* returns the length of a struct qstr, ignoring trailing dots */
static unsigned int __vfat_striptail_len(unsigned int len, const char *name)
{
        while (len && name[len - 1] == '.')
                len--;
        return len;
}

static unsigned int vfat_striptail_len(const struct qstr *qstr)
{
        return __vfat_striptail_len(qstr->len, qstr->name);
}

/*
 * Compute the hash for the vfat name corresponding to the dentry.
 * Note: if the name is invalid, we leave the hash code unchanged so
 * that the existing dentry can be used. The vfat fs routines will
 * return ENOENT or EINVAL as appropriate.
 */
static int vfat_hash(const struct dentry *dentry, struct qstr *qstr)
{
        qstr->hash = full_name_hash(dentry, qstr->name, vfat_striptail_len(qstr));
        return 0;
}

/*
 * Compute the hash for the vfat name corresponding to the dentry.
 * Note: if the name is invalid, we leave the hash code unchanged so
 * that the existing dentry can be used. The vfat fs routines will
 * return ENOENT or EINVAL as appropriate.
 */
static int vfat_hashi(const struct dentry *dentry, struct qstr *qstr)
{
        struct nls_table *t = MSDOS_SB(dentry->d_sb)->nls_io;
        const unsigned char *name;
        unsigned int len;
        unsigned long hash;

        name = qstr->name;
        len = vfat_striptail_len(qstr);

        hash = init_name_hash(dentry);
        while (len--)
                hash = partial_name_hash(nls_tolower(t, *name++), hash);
        qstr->hash = end_name_hash(hash);

        return 0;
}

/*
 * Case insensitive compare of two vfat names.
 */
static int vfat_cmpi(const struct dentry *dentry,
                unsigned int len, const char *str, const struct qstr *name)
{
        struct nls_table *t = MSDOS_SB(dentry->d_sb)->nls_io;
        unsigned int alen, blen;

        /* A filename cannot end in '.' or we treat it like it has none */
        alen = vfat_striptail_len(name);
        blen = __vfat_striptail_len(len, str);
        if (alen == blen) {
                if (nls_strnicmp(t, name->name, str, alen) == 0)
                        return 0;
        }
        return 1;
}

/*
 * Case sensitive compare of two vfat names.
 */
static int vfat_cmp(const struct dentry *dentry,
                unsigned int len, const char *str, const struct qstr *name)
{
        unsigned int alen, blen;

        /* A filename cannot end in '.' or we treat it like it has none */
        alen = vfat_striptail_len(name);
        blen = __vfat_striptail_len(len, str);
        if (alen == blen) {
                if (strncmp(name->name, str, alen) == 0)
                        return 0;
        }
        return 1;
}

static const struct dentry_operations vfat_ci_dentry_ops = {
        .d_revalidate   = vfat_revalidate_ci,
        .d_hash         = vfat_hashi,
        .d_compare      = vfat_cmpi,
};

static const struct dentry_operations vfat_dentry_ops = {
        .d_revalidate   = vfat_revalidate,
        .d_hash         = vfat_hash,
        .d_compare      = vfat_cmp,
};

/* Characters that are undesirable in an MS-DOS file name */

static inline wchar_t vfat_bad_char(wchar_t w)
{
        return (w < 0x0020)
            || (w == '*') || (w == '?') || (w == '<') || (w == '>')
            || (w == '|') || (w == '"') || (w == ':') || (w == '/')
            || (w == '\\');
}

static inline wchar_t vfat_replace_char(wchar_t w)
{
        return (w == '[') || (w == ']') || (w == ';') || (w == ',')
            || (w == '+') || (w == '=');
}

static wchar_t vfat_skip_char(wchar_t w)
{
        return (w == '.') || (w == ' ');
}

static inline int vfat_is_used_badchars(const wchar_t *s, int len)
{
        int i;

        for (i = 0; i < len; i++)
                if (vfat_bad_char(s[i]))
                        return -EINVAL;

        if (s[i - 1] == ' ') /* last character cannot be space */
                return -EINVAL;

        return 0;
}

static int vfat_find_form(struct inode *dir, unsigned char *name)
{
        struct fat_slot_info sinfo;
        int err = fat_scan(dir, name, &sinfo);
        if (err)
                return -ENOENT;
        brelse(sinfo.bh);
        return 0;
}

/*
 * 1) Valid characters for the 8.3 format alias are any combination of
 * letters, uppercase alphabets, digits, any of the
 * following special characters:
 *     $ % ' ` - @ { } ~ ! # ( ) & _ ^
 * In this case Longfilename is not stored in disk.
 *
 * WinNT's Extension:
 * File name and extension name is contain uppercase/lowercase
 * only. And it is expressed by CASE_LOWER_BASE and CASE_LOWER_EXT.
 *
 * 2) File name is 8.3 format, but it contain the uppercase and
 * lowercase char, muliti bytes char, etc. In this case numtail is not
 * added, but Longfilename is stored.
 *
 * 3) When the one except for the above, or the following special
 * character are contained:
 *        .   [ ] ; , + =
 * numtail is added, and Longfilename must be stored in disk .
 */
struct shortname_info {
        unsigned char lower:1,
                      upper:1,
                      valid:1;
};
#define INIT_SHORTNAME_INFO(x)  do {            \
        (x)->lower = 1;                         \
        (x)->upper = 1;                         \
        (x)->valid = 1;                         \
} while (0)

static inline int to_shortname_char(struct nls_table *nls,
                                    unsigned char *buf, int buf_size,
                                    wchar_t *src, struct shortname_info *info)
{
        int len;

        if (vfat_skip_char(*src)) {
                info->valid = 0;
                return 0;
        }
        if (vfat_replace_char(*src)) {
                info->valid = 0;
                buf[0] = '_';
                return 1;
        }

        len = nls->uni2char(*src, buf, buf_size);
        if (len <= 0) {
                info->valid = 0;
                buf[0] = '_';
                len = 1;
        } else if (len == 1) {
                unsigned char prev = buf[0];

                if (buf[0] >= 0x7F) {
                        info->lower = 0;
                        info->upper = 0;
                }

                buf[0] = nls_toupper(nls, buf[0]);
                if (isalpha(buf[0])) {
                        if (buf[0] == prev)
                                info->lower = 0;
                        else
                                info->upper = 0;
                }
        } else {
                info->lower = 0;
                info->upper = 0;
        }

        return len;
}

/*
 * Given a valid longname, create a unique shortname.  Make sure the
 * shortname does not exist
 * Returns negative number on error, 0 for a normal
 * return, and 1 for valid shortname
 */
static int vfat_create_shortname(struct inode *dir, struct nls_table *nls,
                                 wchar_t *uname, int ulen,
                                 unsigned char *name_res, unsigned char *lcase)
{
        struct fat_mount_options *opts = &MSDOS_SB(dir->i_sb)->options;
        wchar_t *ip, *ext_start, *end, *name_start;
        unsigned char base[9], ext[4], buf[5], *p;
        unsigned char charbuf[NLS_MAX_CHARSET_SIZE];
        int chl, chi;
        int sz = 0, extlen, baselen, i, numtail_baselen, numtail2_baselen;
        int is_shortname;
        struct shortname_info base_info, ext_info;

        is_shortname = 1;
        INIT_SHORTNAME_INFO(&base_info);
        INIT_SHORTNAME_INFO(&ext_info);

        /* Now, we need to create a shortname from the long name */
        ext_start = end = &uname[ulen];
        while (--ext_start >= uname) {
                if (*ext_start == 0x002E) {     /* is `.' */
                        if (ext_start == end - 1) {
                                sz = ulen;
                                ext_start = NULL;
                        }
                        break;
                }
        }

        if (ext_start == uname - 1) {
                sz = ulen;
                ext_start = NULL;
        } else if (ext_start) {
                /*
                 * Names which start with a dot could be just
                 * an extension eg. "...test".  In this case Win95
                 * uses the extension as the name and sets no extension.
                 */
                name_start = &uname[0];
                while (name_start < ext_start) {
                        if (!vfat_skip_char(*name_start))
                                break;
                        name_start++;
                }
                if (name_start != ext_start) {
                        sz = ext_start - uname;
                        ext_start++;
                } else {
                        sz = ulen;
                        ext_start = NULL;
                }
        }

        numtail_baselen = 6;
        numtail2_baselen = 2;
        for (baselen = i = 0, p = base, ip = uname; i < sz; i++, ip++) {
                chl = to_shortname_char(nls, charbuf, sizeof(charbuf),
                                        ip, &base_info);
                if (chl == 0)
                        continue;

                if (baselen < 2 && (baselen + chl) > 2)
                        numtail2_baselen = baselen;
                if (baselen < 6 && (baselen + chl) > 6)
                        numtail_baselen = baselen;
                for (chi = 0; chi < chl; chi++) {
                        *p++ = charbuf[chi];
                        baselen++;
                        if (baselen >= 8)
                                break;
                }
                if (baselen >= 8) {
                        if ((chi < chl - 1) || (ip + 1) - uname < sz)
                                is_shortname = 0;
                        break;
                }
        }
        if (baselen == 0) {
                return -EINVAL;
        }

        extlen = 0;
        if (ext_start) {
                for (p = ext, ip = ext_start; extlen < 3 && ip < end; ip++) {
                        chl = to_shortname_char(nls, charbuf, sizeof(charbuf),
                                                ip, &ext_info);
                        if (chl == 0)
                                continue;

                        if ((extlen + chl) > 3) {
                                is_shortname = 0;
                                break;
                        }
                        for (chi = 0; chi < chl; chi++) {
                                *p++ = charbuf[chi];
                                extlen++;
                        }
                        if (extlen >= 3) {
                                if (ip + 1 != end)
                                        is_shortname = 0;
                                break;
                        }
                }
        }
        ext[extlen] = '\0';
        base[baselen] = '\0';

        /* Yes, it can happen. ".\xe5" would do it. */
        if (base[0] == DELETED_FLAG)
                base[0] = 0x05;

        /* OK, at this point we know that base is not longer than 8 symbols,
         * ext is not longer than 3, base is nonempty, both don't contain
         * any bad symbols (lowercase transformed to uppercase).
         */

        memset(name_res, ' ', MSDOS_NAME);
        memcpy(name_res, base, baselen);
        memcpy(name_res + 8, ext, extlen);
        *lcase = 0;
        if (is_shortname && base_info.valid && ext_info.valid) {
                if (vfat_find_form(dir, name_res) == 0)
                        return -EEXIST;

                if (opts->shortname & VFAT_SFN_CREATE_WIN95) {
                        return (base_info.upper && ext_info.upper);
                } else if (opts->shortname & VFAT_SFN_CREATE_WINNT) {
                        if ((base_info.upper || base_info.lower) &&
                            (ext_info.upper || ext_info.lower)) {
                                if (!base_info.upper && base_info.lower)
                                        *lcase |= CASE_LOWER_BASE;
                                if (!ext_info.upper && ext_info.lower)
                                        *lcase |= CASE_LOWER_EXT;
                                return 1;
                        }
                        return 0;
                } else {
                        BUG();
                }
        }

        if (opts->numtail == 0)
                if (vfat_find_form(dir, name_res) < 0)
                        return 0;

        /*
         * Try to find a unique extension.  This used to
         * iterate through all possibilities sequentially,
         * but that gave extremely bad performance.  Windows
         * only tries a few cases before using random
         * values for part of the base.
         */

        if (baselen > 6) {
                baselen = numtail_baselen;
                name_res[7] = ' ';
        }
        name_res[baselen] = '~';
        for (i = 1; i < 10; i++) {
                name_res[baselen + 1] = i + '0';
                if (vfat_find_form(dir, name_res) < 0)
                        return 0;
        }

        i = jiffies;
        sz = (jiffies >> 16) & 0x7;
        if (baselen > 2) {
                baselen = numtail2_baselen;
                name_res[7] = ' ';
        }
        name_res[baselen + 4] = '~';
        name_res[baselen + 5] = '1' + sz;
        while (1) {
                snprintf(buf, sizeof(buf), "%04X", i & 0xffff);
                memcpy(&name_res[baselen], buf, 4);
                if (vfat_find_form(dir, name_res) < 0)
                        break;
                i -= 11;
        }
        return 0;
}

/* Translate a string, including coded sequences into Unicode */
static int
xlate_to_uni(const unsigned char *name, int len, unsigned char *outname,
             int *longlen, int *outlen, int escape, int utf8,
             struct nls_table *nls)
{
        const unsigned char *ip;
        unsigned char nc;
        unsigned char *op;
        unsigned int ec;
        int i, k, fill;
        int charlen;

        if (utf8) {
                *outlen = utf8s_to_utf16s(name, len, UTF16_HOST_ENDIAN,
                                (wchar_t *) outname, FAT_LFN_LEN + 2);
                if (*outlen < 0)
                        return *outlen;
                else if (*outlen > FAT_LFN_LEN)
                        return -ENAMETOOLONG;

                op = &outname[*outlen * sizeof(wchar_t)];
        } else {
                for (i = 0, ip = name, op = outname, *outlen = 0;
                         i < len && *outlen < FAT_LFN_LEN;
                         *outlen += 1) {
                        if (escape && (*ip == ':')) {
                                if (i > len - 5)
                                        return -EINVAL;
                                ec = 0;
                                for (k = 1; k < 5; k++) {
                                        nc = ip[k];
                                        ec <<= 4;
                                        if (nc >= '0' && nc <= '9') {
                                                ec |= nc - '0';
                                                continue;
                                        }
                                        if (nc >= 'a' && nc <= 'f') {
                                                ec |= nc - ('a' - 10);
                                                continue;
                                        }
                                        if (nc >= 'A' && nc <= 'F') {
                                                ec |= nc - ('A' - 10);
                                                continue;
                                        }
                                        return -EINVAL;
                                }
                                *op++ = ec & 0xFF;
                                *op++ = ec >> 8;
                                ip += 5;
                                i += 5;
                        } else {
                                charlen = nls->char2uni(ip, len - i,
                                                                        (wchar_t *)op);
                                if (charlen < 0)
                                        return -EINVAL;
                                ip += charlen;
                                i += charlen;
                                op += 2;
                        }
                }
                if (i < len)
                        return -ENAMETOOLONG;
        }

        *longlen = *outlen;
        if (*outlen % 13) {
                *op++ = 0;
                *op++ = 0;
                *outlen += 1;
                if (*outlen % 13) {
                        fill = 13 - (*outlen % 13);
                        for (i = 0; i < fill; i++) {
                                *op++ = 0xff;
                                *op++ = 0xff;
                        }
                        *outlen += fill;
                }
        }

        return 0;
}

static int vfat_build_slots(struct inode *dir, const unsigned char *name,
                            int len, int is_dir, int cluster,
                            struct timespec *ts,
                            struct msdos_dir_slot *slots, int *nr_slots)
{
        struct msdos_sb_info *sbi = MSDOS_SB(dir->i_sb);
        struct fat_mount_options *opts = &sbi->options;
        struct msdos_dir_slot *ps;
        struct msdos_dir_entry *de;
        unsigned char cksum, lcase;
        unsigned char msdos_name[MSDOS_NAME];
        wchar_t *uname;
        __le16 time, date;
        u8 time_cs;
        int err, ulen, usize, i;
        loff_t offset;

        *nr_slots = 0;

        uname = __getname();
        if (!uname)
                return -ENOMEM;

        err = xlate_to_uni(name, len, (unsigned char *)uname, &ulen, &usize,
                           opts->unicode_xlate, opts->utf8, sbi->nls_io);
        if (err)
                goto out_free;

        err = vfat_is_used_badchars(uname, ulen);
        if (err)
                goto out_free;

        err = vfat_create_shortname(dir, sbi->nls_disk, uname, ulen,
                                    msdos_name, &lcase);
        if (err < 0)
                goto out_free;
        else if (err == 1) {
                de = (struct msdos_dir_entry *)slots;
                err = 0;
                goto shortname;
        }

        /* build the entry of long file name */
        cksum = fat_checksum(msdos_name);

        *nr_slots = usize / 13;
        for (ps = slots, i = *nr_slots; i > 0; i--, ps++) {
                ps->id = i;
                ps->attr = ATTR_EXT;
                ps->reserved = 0;
                ps->alias_checksum = cksum;
                ps->start = 0;
                offset = (i - 1) * 13;
                fatwchar_to16(ps->name0_4, uname + offset, 5);
                fatwchar_to16(ps->name5_10, uname + offset + 5, 6);
                fatwchar_to16(ps->name11_12, uname + offset + 11, 2);
        }
        slots[0].id |= 0x40;
        de = (struct msdos_dir_entry *)ps;

shortname:
        /* build the entry of 8.3 alias name */
        (*nr_slots)++;
        memcpy(de->name, msdos_name, MSDOS_NAME);
        de->attr = is_dir ? ATTR_DIR : ATTR_ARCH;
        de->lcase = lcase;
        fat_time_unix2fat(sbi, ts, &time, &date, &time_cs);
        de->time = de->ctime = time;
        de->date = de->cdate = de->adate = date;
        de->ctime_cs = time_cs;
        fat_set_start(de, cluster);
        de->size = 0;
out_free:
        __putname(uname);
        return err;
}

static int vfat_add_entry(struct inode *dir, const struct qstr *qname,
                          int is_dir, int cluster, struct timespec *ts,
                          struct fat_slot_info *sinfo)
{
        struct msdos_dir_slot *slots;
        unsigned int len;
        int err, nr_slots;

        len = vfat_striptail_len(qname);
        if (len == 0)
                return -ENOENT;

        slots = kmalloc(sizeof(*slots) * MSDOS_SLOTS, GFP_NOFS);
        if (slots == NULL)
                return -ENOMEM;

        err = vfat_build_slots(dir, qname->name, len, is_dir, cluster, ts,
                               slots, &nr_slots);
        if (err)
                goto cleanup;

        err = fat_add_entries(dir, slots, nr_slots, sinfo);
        if (err)
                goto cleanup;

        /* update timestamp */
        dir->i_ctime = dir->i_mtime = dir->i_atime = *ts;
        if (IS_DIRSYNC(dir))
                (void)fat_sync_inode(dir);
        else
                mark_inode_dirty(dir);
cleanup:
        kfree(slots);
        return err;
}

static int vfat_find(struct inode *dir, const struct qstr *qname,
                     struct fat_slot_info *sinfo)
{
        unsigned int len = vfat_striptail_len(qname);
        if (len == 0)
                return -ENOENT;
        return fat_search_long(dir, qname->name, len, sinfo);
}

/*
 * (nfsd's) anonymous disconnected dentry?
 * NOTE: !IS_ROOT() is not anonymous (I.e. d_splice_alias() did the job).
 */
static int vfat_d_anon_disconn(struct dentry *dentry)
{
        return IS_ROOT(dentry) && (dentry->d_flags & DCACHE_DISCONNECTED);
}

static struct dentry *vfat_lookup(struct inode *dir, struct dentry *dentry,
                                  unsigned int flags)
{
        struct super_block *sb = dir->i_sb;
        struct fat_slot_info sinfo;
        struct inode *inode;
        struct dentry *alias;
        int err;

        mutex_lock(&MSDOS_SB(sb)->s_lock);

        err = vfat_find(dir, &dentry->d_name, &sinfo);
        if (err) {
                if (err == -ENOENT) {
                        inode = NULL;
                        goto out;
                }
                goto error;
        }

        inode = fat_build_inode(sb, sinfo.de, sinfo.i_pos);
        brelse(sinfo.bh);
        if (IS_ERR(inode)) {
                err = PTR_ERR(inode);
                goto error;
        }

        alias = d_find_alias(inode);
        /*
         * Checking "alias->d_parent == dentry->d_parent" to make sure
         * FS is not corrupted (especially double linked dir).
         */
        if (alias && alias->d_parent == dentry->d_parent &&
            !vfat_d_anon_disconn(alias)) {
                /*
                 * This inode has non anonymous-DCACHE_DISCONNECTED
                 * dentry. This means, the user did ->lookup() by an
                 * another name (longname vs 8.3 alias of it) in past.
                 *
                 * Switch to new one for reason of locality if possible.
                 */
                BUG_ON(d_unhashed(alias));
                if (!S_ISDIR(inode->i_mode))
                        d_move(alias, dentry);
                iput(inode);
                mutex_unlock(&MSDOS_SB(sb)->s_lock);
                return alias;
        } else
                dput(alias);

out:
        mutex_unlock(&MSDOS_SB(sb)->s_lock);
        if (!inode)
                vfat_d_version_set(dentry, dir->i_version);
        return d_splice_alias(inode, dentry);
error:
        mutex_unlock(&MSDOS_SB(sb)->s_lock);
        return ERR_PTR(err);
}

static int vfat_create(struct inode *dir, struct dentry *dentry, umode_t mode,
                       bool excl)
{
        struct super_block *sb = dir->i_sb;
        struct inode *inode;
        struct fat_slot_info sinfo;
        struct timespec ts;
        int err;

        mutex_lock(&MSDOS_SB(sb)->s_lock);

        ts = current_time(dir);
        err = vfat_add_entry(dir, &dentry->d_name, 0, 0, &ts, &sinfo);
        if (err)
                goto out;
        dir->i_version++;

        inode = fat_build_inode(sb, sinfo.de, sinfo.i_pos);
        brelse(sinfo.bh);
        if (IS_ERR(inode)) {
                err = PTR_ERR(inode);
                goto out;
        }
        inode->i_version++;
        inode->i_mtime = inode->i_atime = inode->i_ctime = ts;
        /* timestamp is already written, so mark_inode_dirty() is unneeded. */

        d_instantiate(dentry, inode);
out:
        mutex_unlock(&MSDOS_SB(sb)->s_lock);
        return err;
}

static int vfat_rmdir(struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);
        struct super_block *sb = dir->i_sb;
        struct fat_slot_info sinfo;
        int err;

        mutex_lock(&MSDOS_SB(sb)->s_lock);

        err = fat_dir_empty(inode);
        if (err)
                goto out;
        err = vfat_find(dir, &dentry->d_name, &sinfo);
        if (err)
                goto out;

        err = fat_remove_entries(dir, &sinfo);  /* and releases bh */
        if (err)
                goto out;
        drop_nlink(dir);

        clear_nlink(inode);
        inode->i_mtime = inode->i_atime = current_time(inode);
        fat_detach(inode);
        vfat_d_version_set(dentry, dir->i_version);
out:
        mutex_unlock(&MSDOS_SB(sb)->s_lock);

        return err;
}

static int vfat_unlink(struct inode *dir, struct dentry *dentry)
{
        struct inode *inode = d_inode(dentry);
        struct super_block *sb = dir->i_sb;
        struct fat_slot_info sinfo;
        int err;

        mutex_lock(&MSDOS_SB(sb)->s_lock);

        err = vfat_find(dir, &dentry->d_name, &sinfo);
        if (err)
                goto out;

        err = fat_remove_entries(dir, &sinfo);  /* and releases bh */
        if (err)
                goto out;
        clear_nlink(inode);
        inode->i_mtime = inode->i_atime = current_time(inode);
        fat_detach(inode);
        vfat_d_version_set(dentry, dir->i_version);
out:
        mutex_unlock(&MSDOS_SB(sb)->s_lock);

        return err;
}

static int vfat_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
{
        struct super_block *sb = dir->i_sb;
        struct inode *inode;
        struct fat_slot_info sinfo;
        struct timespec ts;
        int err, cluster;

        mutex_lock(&MSDOS_SB(sb)->s_lock);

        ts = current_time(dir);
        cluster = fat_alloc_new_dir(dir, &ts);
        if (cluster < 0) {
                err = cluster;
                goto out;
        }
        err = vfat_add_entry(dir, &dentry->d_name, 1, cluster, &ts, &sinfo);
        if (err)
                goto out_free;
        dir->i_version++;
        inc_nlink(dir);

        inode = fat_build_inode(sb, sinfo.de, sinfo.i_pos);
        brelse(sinfo.bh);
        if (IS_ERR(inode)) {
                err = PTR_ERR(inode);
                /* the directory was completed, just return a error */
                goto out;
        }
        inode->i_version++;
        set_nlink(inode, 2);
        inode->i_mtime = inode->i_atime = inode->i_ctime = ts;
        /* timestamp is already written, so mark_inode_dirty() is unneeded. */

        d_instantiate(dentry, inode);

        mutex_unlock(&MSDOS_SB(sb)->s_lock);
        return 0;

out_free:
        fat_free_clusters(dir, cluster);
out:
        mutex_unlock(&MSDOS_SB(sb)->s_lock);
        return err;
}

static int vfat_rename(struct inode *old_dir, struct dentry *old_dentry,
                       struct inode *new_dir, struct dentry *new_dentry,
                       unsigned int flags)
{
        struct buffer_head *dotdot_bh;
        struct msdos_dir_entry *dotdot_de;
        struct inode *old_inode, *new_inode;
        struct fat_slot_info old_sinfo, sinfo;
        struct timespec ts;
        loff_t new_i_pos;
        int err, is_dir, update_dotdot, corrupt = 0;
        struct super_block *sb = old_dir->i_sb;

        if (flags & ~RENAME_NOREPLACE)
                return -EINVAL;

        old_sinfo.bh = sinfo.bh = dotdot_bh = NULL;
        old_inode = d_inode(old_dentry);
        new_inode = d_inode(new_dentry);
        mutex_lock(&MSDOS_SB(sb)->s_lock);
        err = vfat_find(old_dir, &old_dentry->d_name, &old_sinfo);
        if (err)
                goto out;

        is_dir = S_ISDIR(old_inode->i_mode);
        update_dotdot = (is_dir && old_dir != new_dir);
        if (update_dotdot) {
                if (fat_get_dotdot_entry(old_inode, &dotdot_bh, &dotdot_de)) {
                        err = -EIO;
                        goto out;
                }
        }

        ts = current_time(old_dir);
        if (new_inode) {
                if (is_dir) {
                        err = fat_dir_empty(new_inode);
                        if (err)
                                goto out;
                }
                new_i_pos = MSDOS_I(new_inode)->i_pos;
                fat_detach(new_inode);
        } else {
                err = vfat_add_entry(new_dir, &new_dentry->d_name, is_dir, 0,
                                     &ts, &sinfo);
                if (err)
                        goto out;
                new_i_pos = sinfo.i_pos;
        }
        new_dir->i_version++;

        fat_detach(old_inode);
        fat_attach(old_inode, new_i_pos);
        if (IS_DIRSYNC(new_dir)) {
                err = fat_sync_inode(old_inode);
                if (err)
                        goto error_inode;
        } else
                mark_inode_dirty(old_inode);

        if (update_dotdot) {
                fat_set_start(dotdot_de, MSDOS_I(new_dir)->i_logstart);
                mark_buffer_dirty_inode(dotdot_bh, old_inode);
                if (IS_DIRSYNC(new_dir)) {
                        err = sync_dirty_buffer(dotdot_bh);
                        if (err)
                                goto error_dotdot;
                }
                drop_nlink(old_dir);
                if (!new_inode)
                        inc_nlink(new_dir);
        }

        err = fat_remove_entries(old_dir, &old_sinfo);  /* and releases bh */
        old_sinfo.bh = NULL;
        if (err)
                goto error_dotdot;
        old_dir->i_version++;
        old_dir->i_ctime = old_dir->i_mtime = ts;
        if (IS_DIRSYNC(old_dir))
                (void)fat_sync_inode(old_dir);
        else
                mark_inode_dirty(old_dir);

        if (new_inode) {
                drop_nlink(new_inode);
                if (is_dir)
                        drop_nlink(new_inode);
                new_inode->i_ctime = ts;
        }
out:
        brelse(sinfo.bh);
        brelse(dotdot_bh);
        brelse(old_sinfo.bh);
        mutex_unlock(&MSDOS_SB(sb)->s_lock);

        return err;

error_dotdot:
        /* data cluster is shared, serious corruption */
        corrupt = 1;

        if (update_dotdot) {
                fat_set_start(dotdot_de, MSDOS_I(old_dir)->i_logstart);
                mark_buffer_dirty_inode(dotdot_bh, old_inode);
                corrupt |= sync_dirty_buffer(dotdot_bh);
        }
error_inode:
        fat_detach(old_inode);
        fat_attach(old_inode, old_sinfo.i_pos);
        if (new_inode) {
                fat_attach(new_inode, new_i_pos);
                if (corrupt)
                        corrupt |= fat_sync_inode(new_inode);
        } else {
                /*
                 * If new entry was not sharing the data cluster, it
                 * shouldn't be serious corruption.
                 */
                int err2 = fat_remove_entries(new_dir, &sinfo);
                if (corrupt)
                        corrupt |= err2;
                sinfo.bh = NULL;
        }
        if (corrupt < 0) {
                fat_fs_error(new_dir->i_sb,
                             "%s: Filesystem corrupted (i_pos %lld)",
                             __func__, sinfo.i_pos);
        }
        goto out;
}

static const struct inode_operations vfat_dir_inode_operations = {
        .create         = vfat_create,
        .lookup         = vfat_lookup,
        .unlink         = vfat_unlink,
        .mkdir          = vfat_mkdir,
        .rmdir          = vfat_rmdir,
        .rename         = vfat_rename,
        .setattr        = fat_setattr,
        .getattr        = fat_getattr,
};

static void setup(struct super_block *sb)
{
        MSDOS_SB(sb)->dir_ops = &vfat_dir_inode_operations;
        if (MSDOS_SB(sb)->options.name_check != 's')
                sb->s_d_op = &vfat_ci_dentry_ops;
        else
                sb->s_d_op = &vfat_dentry_ops;
}

static int vfat_fill_super(struct super_block *sb, void *data, int silent)
{
        return fat_fill_super(sb, data, silent, 1, setup);
}

static struct dentry *vfat_mount(struct file_system_type *fs_type,
                       int flags, const char *dev_name,
                       void *data)
{
        return mount_bdev(fs_type, flags, dev_name, data, vfat_fill_super);
}

static struct file_system_type vfat_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "vfat",
        .mount          = vfat_mount,
        .kill_sb        = kill_block_super,
        .fs_flags       = FS_REQUIRES_DEV,
};
MODULE_ALIAS_FS("vfat");

static int __init init_vfat_fs(void)
{
        return register_filesystem(&vfat_fs_type);
}

static void __exit exit_vfat_fs(void)
{
        unregister_filesystem(&vfat_fs_type);
}

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("VFAT filesystem support");
MODULE_AUTHOR("Gordon Chaffee");

module_init(init_vfat_fs)
module_exit(exit_vfat_fs)