// SPDX-License-Identifier: GPL-2.0-only
/*
 *  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/pagemap.h>
#include <linux/mpage.h>
#include <linux/vfs.h>
#include <linux/seq_file.h>
#include <linux/parser.h>
#include <linux/uio.h>
#include <linux/blkdev.h>
#include <linux/backing-dev.h>
#include <asm/unaligned.h>
#include <linux/random.h>
#include <linux/iversion.h>
#include "fat.h"

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

#define KB_IN_SECTORS 2

/* DOS dates from 1980/1/1 through 2107/12/31 */
#define FAT_DATE_MIN (0<<9 | 1<<5 | 1)
#define FAT_DATE_MAX (127<<9 | 12<<5 | 31)
#define FAT_TIME_MAX (23<<11 | 59<<5 | 29)

/*
 * A deserialized copy of the on-disk structure laid out in struct
 * fat_boot_sector.
 */
struct fat_bios_param_block {
        u16     fat_sector_size;
        u8      fat_sec_per_clus;
        u16     fat_reserved;
        u8      fat_fats;
        u16     fat_dir_entries;
        u16     fat_sectors;
        u16     fat_fat_length;
        u32     fat_total_sect;

        u8      fat16_state;
        u32     fat16_vol_id;

        u32     fat32_length;
        u32     fat32_root_cluster;
        u16     fat32_info_sector;
        u8      fat32_state;
        u32     fat32_vol_id;
};

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

static struct fat_floppy_defaults {
        unsigned nr_sectors;
        unsigned sec_per_clus;
        unsigned dir_entries;
        unsigned media;
        unsigned fat_length;
} floppy_defaults[] = {
{
        .nr_sectors = 160 * KB_IN_SECTORS,
        .sec_per_clus = 1,
        .dir_entries = 64,
        .media = 0xFE,
        .fat_length = 1,
},
{
        .nr_sectors = 180 * KB_IN_SECTORS,
        .sec_per_clus = 1,
        .dir_entries = 64,
        .media = 0xFC,
        .fat_length = 2,
},
{
        .nr_sectors = 320 * KB_IN_SECTORS,
        .sec_per_clus = 2,
        .dir_entries = 112,
        .media = 0xFF,
        .fat_length = 1,
},
{
        .nr_sectors = 360 * KB_IN_SECTORS,
        .sec_per_clus = 2,
        .dir_entries = 112,
        .media = 0xFD,
        .fat_length = 2,
},
};

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, last_block;
        int err, offset;

        err = fat_bmap(inode, iblock, &phys, &mapped_blocks, create, false);
        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_error(sb, "corrupted file size (i_pos %lld, %lld)",
                        MSDOS_I(inode)->i_pos, MSDOS_I(inode)->mmu_private);
                return -EIO;
        }

        last_block = inode->i_blocks >> (sb->s_blocksize_bits - 9);
        offset = (unsigned long)iblock & (sbi->sec_per_clus - 1);
        /*
         * allocate a cluster according to the following.
         * 1) no more available blocks
         * 2) not part of fallocate region
         */
        if (!offset && !(iblock < last_block)) {
                /* 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, create, false);
        if (err)
                return err;
        if (!phys) {
                fat_fs_error(sb,
                             "invalid FAT chain (i_pos %lld, last_block %llu)",
                             MSDOS_I(inode)->i_pos,
                             (unsigned long long)last_block);
                return -EIO;
        }

        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 void fat_readahead(struct readahead_control *rac)
{
        mpage_readahead(rac, fat_get_block);
}

static void fat_write_failed(struct address_space *mapping, loff_t to)
{
        struct inode *inode = mapping->host;

        if (to > inode->i_size) {
                truncate_pagecache(inode, inode->i_size);
                fat_truncate_blocks(inode, inode->i_size);
        }
}

static int fat_write_begin(struct file *file, struct address_space *mapping,
                        loff_t pos, unsigned len, unsigned flags,
                        struct page **pagep, void **fsdata)
{
        int err;

        *pagep = NULL;
        err = cont_write_begin(file, mapping, pos, len, flags,
                                pagep, fsdata, fat_get_block,
                                &MSDOS_I(mapping->host)->mmu_private);
        if (err < 0)
                fat_write_failed(mapping, pos + len);
        return err;
}

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 < len)
                fat_write_failed(mapping, pos + len);
        if (!(err < 0) && !(MSDOS_I(inode)->i_attrs & ATTR_ARCH)) {
                fat_truncate_time(inode, NULL, S_CTIME|S_MTIME);
                MSDOS_I(inode)->i_attrs |= ATTR_ARCH;
                mark_inode_dirty(inode);
        }
        return err;
}

static ssize_t fat_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
{
        struct file *file = iocb->ki_filp;
        struct address_space *mapping = file->f_mapping;
        struct inode *inode = mapping->host;
        size_t count = iov_iter_count(iter);
        loff_t offset = iocb->ki_pos;
        ssize_t ret;

        if (iov_iter_rw(iter) == WRITE) {
                /*
                 * FIXME: blockdev_direct_IO() doesn't use ->write_begin(),
                 * 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 + count;
                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().
         */
        ret = blockdev_direct_IO(iocb, inode, iter, fat_get_block);
        if (ret < 0 && iov_iter_rw(iter) == WRITE)
                fat_write_failed(mapping, offset + count);

        return ret;
}

static int fat_get_block_bmap(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;
        sector_t bmap;
        unsigned long mapped_blocks;

        BUG_ON(create != 0);

        err = fat_bmap(inode, iblock, &bmap, &mapped_blocks, create, true);
        if (err)
                return err;

        if (bmap) {
                map_bh(bh_result, sb, bmap);
                max_blocks = min(mapped_blocks, max_blocks);
        }

        bh_result->b_size = max_blocks << sb->s_blocksize_bits;

        return 0;
}

static sector_t _fat_bmap(struct address_space *mapping, sector_t block)
{
        sector_t blocknr;

        /* fat_get_cluster() assumes the requested blocknr isn't truncated. */
        down_read(&MSDOS_I(mapping->host)->truncate_lock);
        blocknr = generic_block_bmap(mapping, block, fat_get_block_bmap);
        up_read(&MSDOS_I(mapping->host)->truncate_lock);

        return blocknr;
}

/*
 * fat_block_truncate_page() zeroes out a mapping from file offset `from'
 * up to the end of the block which corresponds to `from'.
 * This is required during truncate to physically zeroout the tail end
 * of that block so it doesn't yield old data if the file is later grown.
 * Also, avoid causing failure from fsx for cases of "data past EOF"
 */
int fat_block_truncate_page(struct inode *inode, loff_t from)
{
        return block_truncate_page(inode->i_mapping, from, fat_get_block);
}

static const struct address_space_operations fat_aops = {
        .readpage       = fat_readpage,
        .readahead      = fat_readahead,
        .writepage      = fat_writepage,
        .writepages     = fat_writepages,
        .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_evict_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(loff_t i_pos)
{
        return hash_32(i_pos, FAT_HASH_BITS);
}

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

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

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

        if (inode->i_ino != MSDOS_ROOT_INO) {
                struct hlist_head *head =   sbi->inode_hashtable
                                          + fat_hash(i_pos);

                spin_lock(&sbi->inode_hash_lock);
                MSDOS_I(inode)->i_pos = i_pos;
                hlist_add_head(&MSDOS_I(inode)->i_fat_hash, head);
                spin_unlock(&sbi->inode_hash_lock);
        }

        /* If NFS support is enabled, cache the mapping of start cluster
         * to directory inode. This is used during reconnection of
         * dentries to the filesystem root.
         */
        if (S_ISDIR(inode->i_mode) && sbi->options.nfs) {
                struct hlist_head *d_head = sbi->dir_hashtable;
                d_head += fat_dir_hash(MSDOS_I(inode)->i_logstart);

                spin_lock(&sbi->dir_hash_lock);
                hlist_add_head(&MSDOS_I(inode)->i_dir_hash, d_head);
                spin_unlock(&sbi->dir_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);

        if (S_ISDIR(inode->i_mode) && sbi->options.nfs) {
                spin_lock(&sbi->dir_hash_lock);
                hlist_del_init(&MSDOS_I(inode)->i_dir_hash);
                spin_unlock(&sbi->dir_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(i_pos);
        struct msdos_inode_info *i;
        struct inode *inode = NULL;

        spin_lock(&sbi->inode_hash_lock);
        hlist_for_each_entry(i, 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;
}

static int fat_validate_dir(struct inode *dir)
{
        struct super_block *sb = dir->i_sb;

        if (dir->i_nlink < 2) {
                /* Directory should have "."/".." entries at least. */
                fat_fs_error(sb, "corrupted directory (invalid entries)");
                return -EIO;
        }
        if (MSDOS_I(dir)->i_start == 0 ||
            MSDOS_I(dir)->i_start == MSDOS_SB(sb)->root_cluster) {
                /* Directory should point valid cluster. */
                fat_fs_error(sb, "corrupted directory (invalid i_start)");
                return -EIO;
        }
        return 0;
}

/* doesn't deal with root inode */
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_inc_iversion(inode);
        inode->i_generation = prandom_u32();

        if ((de->attr & ATTR_DIR) && !IS_FREE(de->name)) {
                inode->i_generation &= ~1;
                inode->i_mode = fat_make_mode(sbi, de->attr, S_IRWXUGO);
                inode->i_op = sbi->dir_ops;
                inode->i_fop = &fat_dir_operations;

                MSDOS_I(inode)->i_start = fat_get_start(sbi, de);
                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;

                set_nlink(inode, fat_subdirs(inode));

                error = fat_validate_dir(inode);
                if (error < 0)
                        return error;
        } else { /* not a directory */
                inode->i_generation |= 1;
                inode->i_mode = fat_make_mode(sbi, de->attr,
                        ((sbi->options.showexec && !is_exec(de->name + 8))
                         ? S_IRUGO|S_IWUGO : S_IRWXUGO));
                MSDOS_I(inode)->i_start = fat_get_start(sbi, de);

                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;
        }
        fat_save_attrs(inode, de->attr);

        inode->i_blocks = ((inode->i_size + (sbi->cluster_size - 1))
                           & ~((loff_t)sbi->cluster_size - 1)) >> 9;

        fat_time_fat2unix(sbi, &inode->i_mtime, de->time, de->date, 0);
        if (sbi->options.isvfat) {
                fat_time_fat2unix(sbi, &inode->i_ctime, de->ctime,
                                  de->cdate, de->ctime_cs);
                fat_time_fat2unix(sbi, &inode->i_atime, 0, de->adate, 0);
        } else
                fat_truncate_time(inode, &inode->i_mtime, S_ATIME|S_CTIME);

        return 0;
}

static inline void fat_lock_build_inode(struct msdos_sb_info *sbi)
{
        if (sbi->options.nfs == FAT_NFS_NOSTALE_RO)
                mutex_lock(&sbi->nfs_build_inode_lock);
}

static inline void fat_unlock_build_inode(struct msdos_sb_info *sbi)
{
        if (sbi->options.nfs == FAT_NFS_NOSTALE_RO)
                mutex_unlock(&sbi->nfs_build_inode_lock);
}

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

        fat_lock_build_inode(MSDOS_SB(sb));
        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_set_iversion(inode, 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:
        fat_unlock_build_inode(MSDOS_SB(sb));
        return inode;
}

EXPORT_SYMBOL_GPL(fat_build_inode);

static int __fat_write_inode(struct inode *inode, int wait);

static void fat_free_eofblocks(struct inode *inode)
{
        /* Release unwritten fallocated blocks on inode eviction. */
        if ((inode->i_blocks << 9) >
                        round_up(MSDOS_I(inode)->mmu_private,
                                MSDOS_SB(inode->i_sb)->cluster_size)) {
                int err;

                fat_truncate_blocks(inode, MSDOS_I(inode)->mmu_private);
                /* Fallocate results in updating the i_start/iogstart
                 * for the zero byte file. So, make it return to
                 * original state during evict and commit it to avoid
                 * any corruption on the next access to the cluster
                 * chain for the file.
                 */
                err = __fat_write_inode(inode, inode_needs_sync(inode));
                if (err) {
                        fat_msg(inode->i_sb, KERN_WARNING, "Failed to "
                                        "update on disk inode for unused "
                                        "fallocated blocks, inode could be "
                                        "corrupted. Please run fsck");
                }

        }
}

static void fat_evict_inode(struct inode *inode)
{
        truncate_inode_pages_final(&inode->i_data);
        if (!inode->i_nlink) {
                inode->i_size = 0;
                fat_truncate_blocks(inode, 0);
        } else
                fat_free_eofblocks(inode);

        invalidate_inode_buffers(inode);
        clear_inode(inode);
        fat_cache_inval_inode(inode);
        fat_detach(inode);
}

static void fat_set_state(struct super_block *sb,
                        unsigned int set, unsigned int force)
{
        struct buffer_head *bh;
        struct fat_boot_sector *b;
        struct msdos_sb_info *sbi = MSDOS_SB(sb);

        /* do not change any thing if mounted read only */
        if (sb_rdonly(sb) && !force)
                return;

        /* do not change state if fs was dirty */
        if (sbi->dirty) {
                /* warn only on set (mount). */
                if (set)
                        fat_msg(sb, KERN_WARNING, "Volume was not properly "
                                "unmounted. Some data may be corrupt. "
                                "Please run fsck.");
                return;
        }

        bh = sb_bread(sb, 0);
        if (bh == NULL) {
                fat_msg(sb, KERN_ERR, "unable to read boot sector "
                        "to mark fs as dirty");
                return;
        }

        b = (struct fat_boot_sector *) bh->b_data;

        if (is_fat32(sbi)) {
                if (set)
                        b->fat32.state |= FAT_STATE_DIRTY;
                else
                        b->fat32.state &= ~FAT_STATE_DIRTY;
        } else /* fat 16 and 12 */ {
                if (set)
                        b->fat16.state |= FAT_STATE_DIRTY;
                else
                        b->fat16.state &= ~FAT_STATE_DIRTY;
        }

        mark_buffer_dirty(bh);
        sync_dirty_buffer(bh);
        brelse(bh);
}

static void fat_reset_iocharset(struct fat_mount_options *opts)
{
        if (opts->iocharset != fat_default_iocharset) {
                /* Note: opts->iocharset can be NULL here */
                kfree(opts->iocharset);
                opts->iocharset = fat_default_iocharset;
        }
}

static void delayed_free(struct rcu_head *p)
{
        struct msdos_sb_info *sbi = container_of(p, struct msdos_sb_info, rcu);
        unload_nls(sbi->nls_disk);
        unload_nls(sbi->nls_io);
        fat_reset_iocharset(&sbi->options);
        kfree(sbi);
}

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

        fat_set_state(sb, 0, 0);

        iput(sbi->fsinfo_inode);
        iput(sbi->fat_inode);

        call_rcu(&sbi->rcu, delayed_free);
}

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_NOFS);
        if (!ei)
                return NULL;

        init_rwsem(&ei->truncate_lock);
        /* Zeroing to allow iput() even if partial initialized inode. */
        ei->mmu_private = 0;
        ei->i_start = 0;
        ei->i_logstart = 0;
        ei->i_attrs = 0;
        ei->i_pos = 0;

        return &ei->vfs_inode;
}

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

static void init_once(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);
        INIT_HLIST_NODE(&ei->i_dir_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|SLAB_ACCOUNT),
                                             init_once);
        if (fat_inode_cachep == NULL)
                return -ENOMEM;
        return 0;
}

static void __exit fat_destroy_inodecache(void)
{
        /*
         * Make sure all delayed rcu free inodes are flushed before we
         * destroy cache.
         */
        rcu_barrier();
        kmem_cache_destroy(fat_inode_cachep);
}

static int fat_remount(struct super_block *sb, int *flags, char *data)
{
        bool new_rdonly;
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        *flags |= SB_NODIRATIME | (sbi->options.isvfat ? 0 : SB_NOATIME);

        sync_filesystem(sb);

        /* make sure we update state on remount. */
        new_rdonly = *flags & SB_RDONLY;
        if (new_rdonly != sb_rdonly(sb)) {
                if (new_rdonly)
                        fat_set_state(sb, 0, 0);
                else
                        fat_set_state(sb, 1, 1);
        }
        return 0;
}

static int fat_statfs(struct dentry *dentry, struct kstatfs *buf)
{
        struct super_block *sb = dentry->d_sb;
        struct msdos_sb_info *sbi = MSDOS_SB(sb);
        u64 id = huge_encode_dev(sb->s_bdev->bd_dev);

        /* 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_fsid = u64_to_fsid(id);
        buf->f_namelen =
                (sbi->options.isvfat ? FAT_LFN_LEN : 12) * NLS_MAX_CHARSET_SIZE;

        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;
        sector_t blocknr;
        int err, offset;

        if (inode->i_ino == MSDOS_ROOT_INO)
                return 0;

retry:
        i_pos = fat_i_pos_read(sbi, inode);
        if (!i_pos)
                return 0;

        fat_get_blknr_offset(sbi, i_pos, &blocknr, &offset);
        bh = sb_bread(sb, blocknr);
        if (!bh) {
                fat_msg(sb, KERN_ERR, "unable to read inode block "
                       "for updating (i_pos %lld)", i_pos);
                return -EIO;
        }
        spin_lock(&sbi->inode_hash_lock);
        if (i_pos != MSDOS_I(inode)->i_pos) {
                spin_unlock(&sbi->inode_hash_lock);
                brelse(bh);
                goto retry;
        }

        raw_entry = &((struct msdos_dir_entry *) (bh->b_data))[offset];
        if (S_ISDIR(inode->i_mode))
                raw_entry->size = 0;
        else
                raw_entry->size = cpu_to_le32(inode->i_size);
        raw_entry->attr = fat_make_attrs(inode);
        fat_set_start(raw_entry, MSDOS_I(inode)->i_logstart);
        fat_time_unix2fat(sbi, &inode->i_mtime, &raw_entry->time,
                          &raw_entry->date, NULL);
        if (sbi->options.isvfat) {
                __le16 atime;
                fat_time_unix2fat(sbi, &inode->i_ctime, &raw_entry->ctime,
                                  &raw_entry->cdate, &raw_entry->ctime_cs);
                fat_time_unix2fat(sbi, &inode->i_atime, &atime,
                                  &raw_entry->adate, NULL);
        }
        spin_unlock(&sbi->inode_hash_lock);
        mark_buffer_dirty(bh);
        err = 0;
        if (wait)
                err = sync_dirty_buffer(bh);
        brelse(bh);
        return err;
}

static int fat_write_inode(struct inode *inode, struct writeback_control *wbc)
{
        int err;

        if (inode->i_ino == MSDOS_FSINFO_INO) {
                struct super_block *sb = inode->i_sb;

                mutex_lock(&MSDOS_SB(sb)->s_lock);
                err = fat_clusters_flush(sb);
                mutex_unlock(&MSDOS_SB(sb)->s_lock);
        } else
                err = __fat_write_inode(inode, wbc->sync_mode == WB_SYNC_ALL);

        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 dentry *root);
static const struct super_operations fat_sops = {
        .alloc_inode    = fat_alloc_inode,
        .free_inode     = fat_free_inode,
        .write_inode    = fat_write_inode,
        .evict_inode    = fat_evict_inode,
        .put_super      = fat_put_super,
        .statfs         = fat_statfs,
        .remount_fs     = fat_remount,

        .show_options   = fat_show_options,
};

static int fat_show_options(struct seq_file *m, struct dentry *root)
{
        struct msdos_sb_info *sbi = MSDOS_SB(root->d_sb);
        struct fat_mount_options *opts = &sbi->options;
        int isvfat = opts->isvfat;

        if (!uid_eq(opts->fs_uid, GLOBAL_ROOT_UID))
                seq_printf(m, ",uid=%u",
                                from_kuid_munged(&init_user_ns, opts->fs_uid));
        if (!gid_eq(opts->fs_gid, GLOBAL_ROOT_GID))
                seq_printf(m, ",gid=%u",
                                from_kgid_munged(&init_user_ns, 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)
                /* strip "cp" prefix from displayed option */
                seq_printf(m, ",codepage=%s", &sbi->nls_disk->charset[2]);
        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 (opts->rodir)
                        seq_puts(m, ",rodir");
        }
        if (opts->flush)
                seq_puts(m, ",flush");
        if (opts->tz_set) {
                if (opts->time_offset)
                        seq_printf(m, ",time_offset=%d", opts->time_offset);
                else
                        seq_puts(m, ",tz=UTC");
        }
        if (opts->errors == FAT_ERRORS_CONT)
                seq_puts(m, ",errors=continue");
        else if (opts->errors == FAT_ERRORS_PANIC)
                seq_puts(m, ",errors=panic");
        else
                seq_puts(m, ",errors=remount-ro");
        if (opts->nfs == FAT_NFS_NOSTALE_RO)
                seq_puts(m, ",nfs=nostale_ro");
        else if (opts->nfs)
                seq_puts(m, ",nfs=stale_rw");
        if (opts->discard)
                seq_puts(m, ",discard");
        if (opts->dos1xfloppy)
                seq_puts(m, ",dos1xfloppy");

        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_obsolete, Opt_flush, Opt_tz_utc, Opt_rodir, Opt_err_cont,
        Opt_err_panic, Opt_err_ro, Opt_discard, Opt_nfs, Opt_time_offset,
        Opt_nfs_stale_rw, Opt_nfs_nostale_ro, Opt_err, Opt_dos1xfloppy,
};

static const 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_flush, "flush"},
        {Opt_tz_utc, "tz=UTC"},
        {Opt_time_offset, "time_offset=%d"},
        {Opt_err_cont, "errors=continue"},
        {Opt_err_panic, "errors=panic"},
        {Opt_err_ro, "errors=remount-ro"},
        {Opt_discard, "discard"},
        {Opt_nfs_stale_rw, "nfs"},
        {Opt_nfs_stale_rw, "nfs=stale_rw"},
        {Opt_nfs_nostale_ro, "nfs=nostale_ro"},
        {Opt_dos1xfloppy, "dos1xfloppy"},
        {Opt_obsolete, "conv=binary"},
        {Opt_obsolete, "conv=text"},
        {Opt_obsolete, "conv=auto"},
        {Opt_obsolete, "conv=b"},
        {Opt_obsolete, "conv=t"},
        {Opt_obsolete, "conv=a"},
        {Opt_obsolete, "fat=%u"},
        {Opt_obsolete, "blocksize=%u"},
        {Opt_obsolete, "cvf_format=%20s"},
        {Opt_obsolete, "cvf_options=%100s"},
        {Opt_obsolete, "posix"},
        {Opt_err, NULL},
};
static const match_table_t msdos_tokens = {
        {Opt_nodots, "nodots"},
        {Opt_nodots, "dotsOK=no"},
        {Opt_dots, "dots"},
        {Opt_dots, "dotsOK=yes"},
        {Opt_err, NULL}
};
static const 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_rodir, "rodir"},
        {Opt_err, NULL}
};

static int parse_options(struct super_block *sb, 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_umask();
        opts->allow_utime = -1;
        opts->codepage = fat_default_codepage;
        fat_reset_iocharset(opts);
        if (is_vfat) {
                opts->shortname = VFAT_SFN_DISPLAY_WINNT|VFAT_SFN_CREATE_WIN95;
                opts->rodir = 0;
        } else {
                opts->shortname = 0;
                opts->rodir = 1;
        }
        opts->name_check = 'n';
        opts->quiet = opts->showexec = opts->sys_immutable = opts->dotsOK =  0;
        opts->unicode_xlate = 0;
        opts->numtail = 1;
        opts->usefree = opts->nocase = 0;
        opts->tz_set = 0;
        opts->nfs = 0;
        opts->errors = FAT_ERRORS_RO;
        *debug = 0;

        opts->utf8 = IS_ENABLED(CONFIG_FAT_DEFAULT_UTF8) && is_vfat;

        if (!options)
                goto out;

        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 -EINVAL;
                        opts->fs_uid = make_kuid(current_user_ns(), option);
                        if (!uid_valid(opts->fs_uid))
                                return -EINVAL;
                        break;
                case Opt_gid:
                        if (match_int(&args[0], &option))
                                return -EINVAL;
                        opts->fs_gid = make_kgid(current_user_ns(), option);
                        if (!gid_valid(opts->fs_gid))
                                return -EINVAL;
                        break;
                case Opt_umask:
                        if (match_octal(&args[0], &option))
                                return -EINVAL;
                        opts->fs_fmask = opts->fs_dmask = option;
                        break;
                case Opt_dmask:
                        if (match_octal(&args[0], &option))
                                return -EINVAL;
                        opts->fs_dmask = option;
                        break;
                case Opt_fmask:
                        if (match_octal(&args[0], &option))
                                return -EINVAL;
                        opts->fs_fmask = option;
                        break;
                case Opt_allow_utime:
                        if (match_octal(&args[0], &option))
                                return -EINVAL;
                        opts->allow_utime = option & (S_IWGRP | S_IWOTH);
                        break;
                case Opt_codepage:
                        if (match_int(&args[0], &option))
                                return -EINVAL;
                        opts->codepage = option;
                        break;
                case Opt_flush:
                        opts->flush = 1;
                        break;
                case Opt_time_offset:
                        if (match_int(&args[0], &option))
                                return -EINVAL;
                        /*
                         * GMT+-12 zones may have DST corrections so at least
                         * 13 hours difference is needed. Make the limit 24
                         * just in case someone invents something unusual.
                         */
                        if (option < -24 * 60 || option > 24 * 60)
                                return -EINVAL;
                        opts->tz_set = 1;
                        opts->time_offset = option;
                        break;
                case Opt_tz_utc:
                        opts->tz_set = 1;
                        opts->time_offset = 0;
                        break;
                case Opt_err_cont:
                        opts->errors = FAT_ERRORS_CONT;
                        break;
                case Opt_err_panic:
                        opts->errors = FAT_ERRORS_PANIC;
                        break;
                case Opt_err_ro:
                        opts->errors = FAT_ERRORS_RO;
                        break;
                case Opt_nfs_stale_rw:
                        opts->nfs = FAT_NFS_STALE_RW;
                        break;
                case Opt_nfs_nostale_ro:
                        opts->nfs = FAT_NFS_NOSTALE_RO;
                        break;
                case Opt_dos1xfloppy:
                        opts->dos1xfloppy = 1;
                        break;

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

                /* vfat specific */
                case Opt_charset:
                        fat_reset_iocharset(opts);
                        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;
                case Opt_rodir:
                        opts->rodir = 1;
                        break;
                case Opt_discard:
                        opts->discard = 1;
                        break;

                /* obsolete mount options */
                case Opt_obsolete:
                        fat_msg(sb, KERN_INFO, "\"%s\" option is obsolete, "
                               "not supported now", p);
                        break;
                /* unknown option */
                default:
                        if (!silent) {
                                fat_msg(sb, KERN_ERR,
                                       "Unrecognized mount option \"%s\" "
                                       "or missing value", p);
                        }
                        return -EINVAL;
                }
        }

out:
        /* UTF-8 doesn't provide FAT semantics */
        if (!strcmp(opts->iocharset, "utf8")) {
                fat_msg(sb, KERN_WARNING, "utf8 is not a recommended IO charset"
                       " for FAT filesystems, filesystem will be "
                       "case sensitive!");
        }

        /* 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;
        if (opts->nfs == FAT_NFS_NOSTALE_RO) {
                sb->s_flags |= SB_RDONLY;
                sb->s_export_op = &fat_export_ops_nostale;
        }

        return 0;
}

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

        MSDOS_I(inode)->i_pos = MSDOS_ROOT_INO;
        inode->i_uid = sbi->options.fs_uid;
        inode->i_gid = sbi->options.fs_gid;
        inode_inc_iversion(inode);
        inode->i_generation = 0;
        inode->i_mode = fat_make_mode(sbi, ATTR_DIR, S_IRWXUGO);
        inode->i_op = sbi->dir_ops;
        inode->i_fop = &fat_dir_operations;
        if (is_fat32(sbi)) {
                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;

        fat_save_attrs(inode, ATTR_DIR);
        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;
        set_nlink(inode, fat_subdirs(inode)+2);

        return 0;
}

static unsigned long calc_fat_clusters(struct super_block *sb)
{
        struct msdos_sb_info *sbi = MSDOS_SB(sb);

        /* Divide first to avoid overflow */
        if (!is_fat12(sbi)) {
                unsigned long ent_per_sec = sb->s_blocksize * 8 / sbi->fat_bits;
                return ent_per_sec * sbi->fat_length;
        }

        return sbi->fat_length * sb->s_blocksize * 8 / sbi->fat_bits;
}

static bool fat_bpb_is_zero(struct fat_boot_sector *b)
{
        if (get_unaligned_le16(&b->sector_size))
                return false;
        if (b->sec_per_clus)
                return false;
        if (b->reserved)
                return false;
        if (b->fats)
                return false;
        if (get_unaligned_le16(&b->dir_entries))
                return false;
        if (get_unaligned_le16(&b->sectors))
                return false;
        if (b->media)
                return false;
        if (b->fat_length)
                return false;
        if (b->secs_track)
                return false;
        if (b->heads)
                return false;
        return true;
}

static int fat_read_bpb(struct super_block *sb, struct fat_boot_sector *b,
        int silent, struct fat_bios_param_block *bpb)
{
        int error = -EINVAL;

        /* Read in BPB ... */
        memset(bpb, 0, sizeof(*bpb));
        bpb->fat_sector_size = get_unaligned_le16(&b->sector_size);
        bpb->fat_sec_per_clus = b->sec_per_clus;
        bpb->fat_reserved = le16_to_cpu(b->reserved);
        bpb->fat_fats = b->fats;
        bpb->fat_dir_entries = get_unaligned_le16(&b->dir_entries);
        bpb->fat_sectors = get_unaligned_le16(&b->sectors);
        bpb->fat_fat_length = le16_to_cpu(b->fat_length);
        bpb->fat_total_sect = le32_to_cpu(b->total_sect);

        bpb->fat16_state = b->fat16.state;
        bpb->fat16_vol_id = get_unaligned_le32(b->fat16.vol_id);

        bpb->fat32_length = le32_to_cpu(b->fat32.length);
        bpb->fat32_root_cluster = le32_to_cpu(b->fat32.root_cluster);
        bpb->fat32_info_sector = le16_to_cpu(b->fat32.info_sector);
        bpb->fat32_state = b->fat32.state;
        bpb->fat32_vol_id = get_unaligned_le32(b->fat32.vol_id);

        /* Validate this looks like a FAT filesystem BPB */
        if (!bpb->fat_reserved) {
                if (!silent)
                        fat_msg(sb, KERN_ERR,
                                "bogus number of reserved sectors");
                goto out;
        }
        if (!bpb->fat_fats) {
                if (!silent)
                        fat_msg(sb, KERN_ERR, "bogus number of FAT structure");
                goto out;
        }

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

        if (!fat_valid_media(b->media)) {
                if (!silent)
                        fat_msg(sb, KERN_ERR, "invalid media value (0x%02x)",
                                (unsigned)b->media);
                goto out;
        }

        if (!is_power_of_2(bpb->fat_sector_size)
            || (bpb->fat_sector_size < 512)
            || (bpb->fat_sector_size > 4096)) {
                if (!silent)
                        fat_msg(sb, KERN_ERR, "bogus logical sector size %u",
                               (unsigned)bpb->fat_sector_size);
                goto out;
        }

        if (!is_power_of_2(bpb->fat_sec_per_clus)) {
                if (!silent)
                        fat_msg(sb, KERN_ERR, "bogus sectors per cluster %u",
                                (unsigned)bpb->fat_sec_per_clus);
                goto out;
        }

        if (bpb->fat_fat_length == 0 && bpb->fat32_length == 0) {
                if (!silent)
                        fat_msg(sb, KERN_ERR, "bogus number of FAT sectors");
                goto out;
        }

        error = 0;

out:
        return error;
}

static int fat_read_static_bpb(struct super_block *sb,
        struct fat_boot_sector *b, int silent,
        struct fat_bios_param_block *bpb)
{
        static const char *notdos1x = "This doesn't look like a DOS 1.x volume";

        struct fat_floppy_defaults *fdefaults = NULL;
        int error = -EINVAL;
        sector_t bd_sects;
        unsigned i;

        bd_sects = i_size_read(sb->s_bdev->bd_inode) / SECTOR_SIZE;

        /* 16-bit DOS 1.x reliably wrote bootstrap short-jmp code */
        if (b->ignored[0] != 0xeb || b->ignored[2] != 0x90) {
                if (!silent)
                        fat_msg(sb, KERN_ERR,
                                "%s; no bootstrapping code", notdos1x);
                goto out;
        }

        /*
         * If any value in this region is non-zero, it isn't archaic
         * DOS.
         */
        if (!fat_bpb_is_zero(b)) {
                if (!silent)
                        fat_msg(sb, KERN_ERR,
                                "%s; DOS 2.x BPB is non-zero", notdos1x);
                goto out;
        }

        for (i = 0; i < ARRAY_SIZE(floppy_defaults); i++) {
                if (floppy_defaults[i].nr_sectors == bd_sects) {
                        fdefaults = &floppy_defaults[i];
                        break;
                }
        }

        if (fdefaults == NULL) {
                if (!silent)
                        fat_msg(sb, KERN_WARNING,
                                "This looks like a DOS 1.x volume, but isn't a recognized floppy size (%llu sectors)",
                                (u64)bd_sects);
                goto out;
        }

        if (!silent)
                fat_msg(sb, KERN_INFO,
                        "This looks like a DOS 1.x volume; assuming default BPB values");

        memset(bpb, 0, sizeof(*bpb));
        bpb->fat_sector_size = SECTOR_SIZE;
        bpb->fat_sec_per_clus = fdefaults->sec_per_clus;
        bpb->fat_reserved = 1;
        bpb->fat_fats = 2;
        bpb->fat_dir_entries = fdefaults->dir_entries;
        bpb->fat_sectors = fdefaults->nr_sectors;
        bpb->fat_fat_length = fdefaults->fat_length;

        error = 0;

out:
        return error;
}

/*
 * Read the super block of an MS-DOS FS.
 */
int fat_fill_super(struct super_block *sb, void *data, int silent, int isvfat,
                   void (*setup)(struct super_block *))
{
        struct inode *root_inode = NULL, *fat_inode = NULL;
        struct inode *fsinfo_inode = NULL;
        struct buffer_head *bh;
        struct fat_bios_param_block bpb;
        struct msdos_sb_info *sbi;
        u16 logical_sector_size;
        u32 total_sectors, total_clusters, fat_clusters, rootdir_sectors;
        int debug;
        long error;
        char buf[50];
        struct timespec64 ts;

        /*
         * GFP_KERNEL is ok here, because while we do hold the
         * superblock lock, memory pressure can't call back into
         * the filesystem, since we're only just about to mount
         * it and have no inodes etc active!
         */
        sbi = kzalloc(sizeof(struct msdos_sb_info), GFP_KERNEL);
        if (!sbi)
                return -ENOMEM;
        sb->s_fs_info = sbi;

        sb->s_flags |= SB_NODIRATIME;
        sb->s_magic = MSDOS_SUPER_MAGIC;
        sb->s_op = &fat_sops;
        sb->s_export_op = &fat_export_ops;
        /*
         * fat timestamps are complex and truncated by fat itself, so
         * we set 1 here to be fast
         */
        sb->s_time_gran = 1;
        mutex_init(&sbi->nfs_build_inode_lock);
        ratelimit_state_init(&sbi->ratelimit, DEFAULT_RATELIMIT_INTERVAL,
                             DEFAULT_RATELIMIT_BURST);

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

        setup(sb); /* flavour-specific stuff that needs options */

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

        error = fat_read_bpb(sb, (struct fat_boot_sector *)bh->b_data, silent,
                &bpb);
        if (error == -EINVAL && sbi->options.dos1xfloppy)
                error = fat_read_static_bpb(sb,
                        (struct fat_boot_sector *)bh->b_data, silent, &bpb);
        brelse(bh);

        if (error == -EINVAL)
                goto out_invalid;
        else if (error)
                goto out_fail;

        logical_sector_size = bpb.fat_sector_size;
        sbi->sec_per_clus = bpb.fat_sec_per_clus;

        error = -EIO;
        if (logical_sector_size < sb->s_blocksize) {
                fat_msg(sb, KERN_ERR, "logical sector size too small for device"
                       " (logical sector size = %u)", logical_sector_size);
                goto out_fail;
        }

        if (logical_sector_size > sb->s_blocksize) {
                struct buffer_head *bh_resize;

                if (!sb_set_blocksize(sb, logical_sector_size)) {
                        fat_msg(sb, KERN_ERR, "unable to set blocksize %u",
                               logical_sector_size);
                        goto out_fail;
                }

                /* Verify that the larger boot sector is fully readable */
                bh_resize = sb_bread(sb, 0);
                if (bh_resize == NULL) {
                        fat_msg(sb, KERN_ERR, "unable to read boot sector"
                               " (logical sector size = %lu)",
                               sb->s_blocksize);
                        goto out_fail;
                }
                brelse(bh_resize);
        }

        mutex_init(&sbi->s_lock);
        sbi->cluster_size = sb->s_blocksize * sbi->sec_per_clus;
        sbi->cluster_bits = ffs(sbi->cluster_size) - 1;
        sbi->fats = bpb.fat_fats;
        sbi->fat_bits = 0;              /* Don't know yet */
        sbi->fat_start = bpb.fat_reserved;
        sbi->fat_length = bpb.fat_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;
        sb->s_maxbytes = 0xffffffff;
        fat_time_fat2unix(sbi, &ts, 0, cpu_to_le16(FAT_DATE_MIN), 0);
        sb->s_time_min = ts.tv_sec;

        fat_time_fat2unix(sbi, &ts, cpu_to_le16(FAT_TIME_MAX),
                          cpu_to_le16(FAT_DATE_MAX), 0);
        sb->s_time_max = ts.tv_sec;

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

                /* Must be FAT32 */
                sbi->fat_bits = 32;
                sbi->fat_length = bpb.fat32_length;
                sbi->root_cluster = bpb.fat32_root_cluster;

                /* MC - if info_sector is 0, don't multiply by 0 */
                sbi->fsinfo_sector = bpb.fat32_info_sector;
                if (sbi->fsinfo_sector == 0)
                        sbi->fsinfo_sector = 1;

                fsinfo_bh = sb_bread(sb, sbi->fsinfo_sector);
                if (fsinfo_bh == NULL) {
                        fat_msg(sb, KERN_ERR, "bread failed, FSINFO block"
                               " (sector = %lu)", sbi->fsinfo_sector);
                        goto out_fail;
                }

                fsinfo = (struct fat_boot_fsinfo *)fsinfo_bh->b_data;
                if (!IS_FSINFO(fsinfo)) {
                        fat_msg(sb, KERN_WARNING, "Invalid FSINFO signature: "
                               "0x%08x, 0x%08x (sector = %lu)",
                               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);
        }

        /* interpret volume ID as a little endian 32 bit integer */
        if (is_fat32(sbi))
                sbi->vol_id = bpb.fat32_vol_id;
        else /* fat 16 or 12 */
                sbi->vol_id = bpb.fat16_vol_id;

        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 = bpb.fat_dir_entries;
        if (sbi->dir_entries & (sbi->dir_per_block - 1)) {
                if (!silent)
                        fat_msg(sb, KERN_ERR, "bogus number of directory entries"
                               " (%u)", sbi->dir_entries);
                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 = bpb.fat_sectors;
        if (total_sectors == 0)
                total_sectors = bpb.fat_total_sect;

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

        if (!is_fat32(sbi))
                sbi->fat_bits = (total_clusters > MAX_FAT12) ? 16 : 12;

        /* some OSes set FAT_STATE_DIRTY and clean it on unmount. */
        if (is_fat32(sbi))
                sbi->dirty = bpb.fat32_state & FAT_STATE_DIRTY;
        else /* fat 16 or 12 */
                sbi->dirty = bpb.fat16_state & FAT_STATE_DIRTY;

        /* check that FAT table does not overflow */
        fat_clusters = calc_fat_clusters(sb);
        total_clusters = min(total_clusters, fat_clusters - FAT_START_ENT);
        if (total_clusters > max_fat(sb)) {
                if (!silent)
                        fat_msg(sb, KERN_ERR, "count of clusters too big (%u)",
                               total_clusters);
                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;

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

        /*
         * The low byte of the first FAT entry must have the same value as
         * the media field of the boot sector. But in real world, too many
         * devices are writing wrong values. So, removed that validity check.
         *
         * The removed check compared the first FAT entry to a value dependent
         * on the media field like this:
         * == (0x0F00 | media), for FAT12
         * == (0XFF00 | media), for FAT16
         * == (0x0FFFFF | media), for FAT32
         */

        error = -EINVAL;
        sprintf(buf, "cp%d", sbi->options.codepage);
        sbi->nls_disk = load_nls(buf);
        if (!sbi->nls_disk) {
                fat_msg(sb, KERN_ERR, "codepage %s not found", 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) {
                        fat_msg(sb, KERN_ERR, "IO charset %s not found",
                               sbi->options.iocharset);
                        goto out_fail;
                }
        }

        error = -ENOMEM;
        fat_inode = new_inode(sb);
        if (!fat_inode)
                goto out_fail;
        sbi->fat_inode = fat_inode;

        fsinfo_inode = new_inode(sb);
        if (!fsinfo_inode)
                goto out_fail;
        fsinfo_inode->i_ino = MSDOS_FSINFO_INO;
        sbi->fsinfo_inode = fsinfo_inode;
        insert_inode_hash(fsinfo_inode);

        root_inode = new_inode(sb);
        if (!root_inode)
                goto out_fail;
        root_inode->i_ino = MSDOS_ROOT_INO;
        inode_set_iversion(root_inode, 1);
        error = fat_read_root(root_inode);
        if (error < 0) {
                iput(root_inode);
                goto out_fail;
        }
        error = -ENOMEM;
        insert_inode_hash(root_inode);
        fat_attach(root_inode, 0);
        sb->s_root = d_make_root(root_inode);
        if (!sb->s_root) {
                fat_msg(sb, KERN_ERR, "get root inode failed");
                goto out_fail;
        }

        if (sbi->options.discard) {
                struct request_queue *q = bdev_get_queue(sb->s_bdev);
                if (!blk_queue_discard(q))
                        fat_msg(sb, KERN_WARNING,
                                        "mounting with \"discard\" option, but "
                                        "the device does not support discard");
        }

        fat_set_state(sb, 1, 0);
        return 0;

out_invalid:
        error = -EINVAL;
        if (!silent)
                fat_msg(sb, KERN_INFO, "Can't find a valid FAT filesystem");

out_fail:
        if (fsinfo_inode)
                iput(fsinfo_inode);
        if (fat_inode)
                iput(fat_inode);
        unload_nls(sbi->nls_io);
        unload_nls(sbi->nls_disk);
        fat_reset_iocharset(&sbi->options);
        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;

        /* if we used wait=1, sync_inode_metadata waits for the io for the
        * inode to finish.  So wait=0 is sent down to sync_inode_metadata
        * and filemap_fdatawrite is used for the data blocks
        */
        ret = sync_inode_metadata(inode, 0);
        if (!ret)
                ret = filemap_fdatawrite(inode->i_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");