[linux.git] / fs / fat / fatent.c

/*
 * Copyright (C) 2004, OGAWA Hirofumi
 * Released under GPL v2.
 */

#include <linux/module.h>
#include <linux/fs.h>
#include <linux/msdos_fs.h>
#include <linux/blkdev.h>
#include "fat.h"

struct fatent_operations {
	void (*ent_blocknr)(struct super_block *, int, int *, sector_t *);
	void (*ent_set_ptr)(struct fat_entry *, int);
	int (*ent_bread)(struct super_block *, struct fat_entry *,
			 int, sector_t);
	int (*ent_get)(struct fat_entry *);
	void (*ent_put)(struct fat_entry *, int);
	int (*ent_next)(struct fat_entry *);
};

static DEFINE_SPINLOCK(fat12_entry_lock);

static void fat12_ent_blocknr(struct super_block *sb, int entry,
			      int *offset, sector_t *blocknr)
{
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	int bytes = entry + (entry >> 1);
	WARN_ON(entry < FAT_START_ENT || sbi->max_cluster <= entry);
	*offset = bytes & (sb->s_blocksize - 1);
	*blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
}

static void fat_ent_blocknr(struct super_block *sb, int entry,
			    int *offset, sector_t *blocknr)
{
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	int bytes = (entry << sbi->fatent_shift);
	WARN_ON(entry < FAT_START_ENT || sbi->max_cluster <= entry);
	*offset = bytes & (sb->s_blocksize - 1);
	*blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
}

static void fat12_ent_set_ptr(struct fat_entry *fatent, int offset)
{
	struct buffer_head **bhs = fatent->bhs;
	if (fatent->nr_bhs == 1) {
		WARN_ON(offset >= (bhs[0]->b_size - 1));
		fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
		fatent->u.ent12_p[1] = bhs[0]->b_data + (offset + 1);
	} else {
		WARN_ON(offset != (bhs[0]->b_size - 1));
		fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
		fatent->u.ent12_p[1] = bhs[1]->b_data;
	}
}

static void fat16_ent_set_ptr(struct fat_entry *fatent, int offset)
{
	WARN_ON(offset & (2 - 1));
	fatent->u.ent16_p = (__le16 *)(fatent->bhs[0]->b_data + offset);
}

static void fat32_ent_set_ptr(struct fat_entry *fatent, int offset)
{
	WARN_ON(offset & (4 - 1));
	fatent->u.ent32_p = (__le32 *)(fatent->bhs[0]->b_data + offset);
}

static int fat12_ent_bread(struct super_block *sb, struct fat_entry *fatent,
			   int offset, sector_t blocknr)
{
	struct buffer_head **bhs = fatent->bhs;

	WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
	fatent->fat_inode = MSDOS_SB(sb)->fat_inode;

	bhs[0] = sb_bread(sb, blocknr);
	if (!bhs[0])
		goto err;

	if ((offset + 1) < sb->s_blocksize)
		fatent->nr_bhs = 1;
	else {
		/* This entry is block boundary, it needs the next block */
		blocknr++;
		bhs[1] = sb_bread(sb, blocknr);
		if (!bhs[1])
			goto err_brelse;
		fatent->nr_bhs = 2;
	}
	fat12_ent_set_ptr(fatent, offset);
	return 0;

err_brelse:
	brelse(bhs[0]);
err:
	printk(KERN_ERR "FAT: FAT read failed (blocknr %llu)\n", (llu)blocknr);
	return -EIO;
}

static int fat_ent_bread(struct super_block *sb, struct fat_entry *fatent,
			 int offset, sector_t blocknr)
{
	struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;

	WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
	fatent->fat_inode = MSDOS_SB(sb)->fat_inode;
	fatent->bhs[0] = sb_bread(sb, blocknr);
	if (!fatent->bhs[0]) {
		printk(KERN_ERR "FAT: FAT read failed (blocknr %llu)\n",
		       (llu)blocknr);
		return -EIO;
	}
	fatent->nr_bhs = 1;
	ops->ent_set_ptr(fatent, offset);
	return 0;
}

static int fat12_ent_get(struct fat_entry *fatent)
{
	u8 **ent12_p = fatent->u.ent12_p;
	int next;

	spin_lock(&fat12_entry_lock);
	if (fatent->entry & 1)
		next = (*ent12_p[0] >> 4) | (*ent12_p[1] << 4);
	else
		next = (*ent12_p[1] << 8) | *ent12_p[0];
	spin_unlock(&fat12_entry_lock);

	next &= 0x0fff;
	if (next >= BAD_FAT12)
		next = FAT_ENT_EOF;
	return next;
}

static int fat16_ent_get(struct fat_entry *fatent)
{
	int next = le16_to_cpu(*fatent->u.ent16_p);
	WARN_ON((unsigned long)fatent->u.ent16_p & (2 - 1));
	if (next >= BAD_FAT16)
		next = FAT_ENT_EOF;
	return next;
}

static int fat32_ent_get(struct fat_entry *fatent)
{
	int next = le32_to_cpu(*fatent->u.ent32_p) & 0x0fffffff;
	WARN_ON((unsigned long)fatent->u.ent32_p & (4 - 1));
	if (next >= BAD_FAT32)
		next = FAT_ENT_EOF;
	return next;
}

static void fat12_ent_put(struct fat_entry *fatent, int new)
{
	u8 **ent12_p = fatent->u.ent12_p;

	if (new == FAT_ENT_EOF)
		new = EOF_FAT12;

	spin_lock(&fat12_entry_lock);
	if (fatent->entry & 1) {
		*ent12_p[0] = (new << 4) | (*ent12_p[0] & 0x0f);
		*ent12_p[1] = new >> 4;
	} else {
		*ent12_p[0] = new & 0xff;
		*ent12_p[1] = (*ent12_p[1] & 0xf0) | (new >> 8);
	}
	spin_unlock(&fat12_entry_lock);

	mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
	if (fatent->nr_bhs == 2)
		mark_buffer_dirty_inode(fatent->bhs[1], fatent->fat_inode);
}

static void fat16_ent_put(struct fat_entry *fatent, int new)
{
	if (new == FAT_ENT_EOF)
		new = EOF_FAT16;

	*fatent->u.ent16_p = cpu_to_le16(new);
	mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
}

static void fat32_ent_put(struct fat_entry *fatent, int new)
{
	if (new == FAT_ENT_EOF)
		new = EOF_FAT32;

	WARN_ON(new & 0xf0000000);
	new |= le32_to_cpu(*fatent->u.ent32_p) & ~0x0fffffff;
	*fatent->u.ent32_p = cpu_to_le32(new);
	mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
}

static int fat12_ent_next(struct fat_entry *fatent)
{
	u8 **ent12_p = fatent->u.ent12_p;
	struct buffer_head **bhs = fatent->bhs;
	u8 *nextp = ent12_p[1] + 1 + (fatent->entry & 1);

	fatent->entry++;
	if (fatent->nr_bhs == 1) {
		WARN_ON(ent12_p[0] > (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 2)));
		WARN_ON(ent12_p[1] > (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1)));
		if (nextp < (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1))) {
			ent12_p[0] = nextp - 1;
			ent12_p[1] = nextp;
			return 1;
		}
	} else {
		WARN_ON(ent12_p[0] != (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1)));
		WARN_ON(ent12_p[1] != (u8 *)bhs[1]->b_data);
		ent12_p[0] = nextp - 1;
		ent12_p[1] = nextp;
		brelse(bhs[0]);
		bhs[0] = bhs[1];
		fatent->nr_bhs = 1;
		return 1;
	}
	ent12_p[0] = NULL;
	ent12_p[1] = NULL;
	return 0;
}

static int fat16_ent_next(struct fat_entry *fatent)
{
	const struct buffer_head *bh = fatent->bhs[0];
	fatent->entry++;
	if (fatent->u.ent16_p < (__le16 *)(bh->b_data + (bh->b_size - 2))) {
		fatent->u.ent16_p++;
		return 1;
	}
	fatent->u.ent16_p = NULL;
	return 0;
}

static int fat32_ent_next(struct fat_entry *fatent)
{
	const struct buffer_head *bh = fatent->bhs[0];
	fatent->entry++;
	if (fatent->u.ent32_p < (__le32 *)(bh->b_data + (bh->b_size - 4))) {
		fatent->u.ent32_p++;
		return 1;
	}
	fatent->u.ent32_p = NULL;
	return 0;
}

static struct fatent_operations fat12_ops = {
	.ent_blocknr	= fat12_ent_blocknr,
	.ent_set_ptr	= fat12_ent_set_ptr,
	.ent_bread	= fat12_ent_bread,
	.ent_get	= fat12_ent_get,
	.ent_put	= fat12_ent_put,
	.ent_next	= fat12_ent_next,
};

static struct fatent_operations fat16_ops = {
	.ent_blocknr	= fat_ent_blocknr,
	.ent_set_ptr	= fat16_ent_set_ptr,
	.ent_bread	= fat_ent_bread,
	.ent_get	= fat16_ent_get,
	.ent_put	= fat16_ent_put,
	.ent_next	= fat16_ent_next,
};

static struct fatent_operations fat32_ops = {
	.ent_blocknr	= fat_ent_blocknr,
	.ent_set_ptr	= fat32_ent_set_ptr,
	.ent_bread	= fat_ent_bread,
	.ent_get	= fat32_ent_get,
	.ent_put	= fat32_ent_put,
	.ent_next	= fat32_ent_next,
};

static inline void lock_fat(struct msdos_sb_info *sbi)
{
	mutex_lock(&sbi->fat_lock);
}

static inline void unlock_fat(struct msdos_sb_info *sbi)
{
	mutex_unlock(&sbi->fat_lock);
}

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

	mutex_init(&sbi->fat_lock);

	switch (sbi->fat_bits) {
	case 32:
		sbi->fatent_shift = 2;
		sbi->fatent_ops = &fat32_ops;
		break;
	case 16:
		sbi->fatent_shift = 1;
		sbi->fatent_ops = &fat16_ops;
		break;
	case 12:
		sbi->fatent_shift = -1;
		sbi->fatent_ops = &fat12_ops;
		break;
	}
}

static inline int fat_ent_update_ptr(struct super_block *sb,
				     struct fat_entry *fatent,
				     int offset, sector_t blocknr)
{
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	struct fatent_operations *ops = sbi->fatent_ops;
	struct buffer_head **bhs = fatent->bhs;

	/* Is this fatent's blocks including this entry? */
	if (!fatent->nr_bhs || bhs[0]->b_blocknr != blocknr)
		return 0;
	if (sbi->fat_bits == 12) {
		if ((offset + 1) < sb->s_blocksize) {
			/* This entry is on bhs[0]. */
			if (fatent->nr_bhs == 2) {
				brelse(bhs[1]);
				fatent->nr_bhs = 1;
			}
		} else {
			/* This entry needs the next block. */
			if (fatent->nr_bhs != 2)
				return 0;
			if (bhs[1]->b_blocknr != (blocknr + 1))
				return 0;
		}
	}
	ops->ent_set_ptr(fatent, offset);
	return 1;
}

int fat_ent_read(struct inode *inode, struct fat_entry *fatent, int entry)
{
	struct super_block *sb = inode->i_sb;
	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
	struct fatent_operations *ops = sbi->fatent_ops;
	int err, offset;
	sector_t blocknr;

	if (entry < FAT_START_ENT || sbi->max_cluster <= entry) {
		fatent_brelse(fatent);
		fat_fs_error(sb, "invalid access to FAT (entry 0x%08x)", entry);
		return -EIO;
	}

	fatent_set_entry(fatent, entry);
	ops->ent_blocknr(sb, entry, &offset, &blocknr);

	if (!fat_ent_update_ptr(sb, fatent, offset, blocknr)) {
		fatent_brelse(fatent);
		err = ops->ent_bread(sb, fatent, offset, blocknr);
		if (err)
			return err;
	}
	return ops->ent_get(fatent);
}

/* FIXME: We can write the blocks as more big chunk. */
static int fat_mirror_bhs(struct super_block *sb, struct buffer_head **bhs,
			  int nr_bhs)
{
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	struct buffer_head *c_bh;
	int err, n, copy;

	err = 0;
	for (copy = 1; copy < sbi->fats; copy++) {
		sector_t backup_fat = sbi->fat_length * copy;

		for (n = 0; n < nr_bhs; n++) {
			c_bh = sb_getblk(sb, backup_fat + bhs[n]->b_blocknr);
			if (!c_bh) {
				err = -ENOMEM;
				goto error;
			}
			memcpy(c_bh->b_data, bhs[n]->b_data, sb->s_blocksize);
			set_buffer_uptodate(c_bh);
			mark_buffer_dirty_inode(c_bh, sbi->fat_inode);
			if (sb->s_flags & MS_SYNCHRONOUS)
				err = sync_dirty_buffer(c_bh);
			brelse(c_bh);
			if (err)
				goto error;
		}
	}
error:
	return err;
}

int fat_ent_write(struct inode *inode, struct fat_entry *fatent,
		  int new, int wait)
{
	struct super_block *sb = inode->i_sb;
	struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
	int err;

	ops->ent_put(fatent, new);
	if (wait) {
		err = fat_sync_bhs(fatent->bhs, fatent->nr_bhs);
		if (err)
			return err;
	}
	return fat_mirror_bhs(sb, fatent->bhs, fatent->nr_bhs);
}

static inline int fat_ent_next(struct msdos_sb_info *sbi,
			       struct fat_entry *fatent)
{
	if (sbi->fatent_ops->ent_next(fatent)) {
		if (fatent->entry < sbi->max_cluster)
			return 1;
	}
	return 0;
}

static inline int fat_ent_read_block(struct super_block *sb,
				     struct fat_entry *fatent)
{
	struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
	sector_t blocknr;
	int offset;

	fatent_brelse(fatent);
	ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
	return ops->ent_bread(sb, fatent, offset, blocknr);
}

static void fat_collect_bhs(struct buffer_head **bhs, int *nr_bhs,
			    struct fat_entry *fatent)
{
	int n, i;

	for (n = 0; n < fatent->nr_bhs; n++) {
		for (i = 0; i < *nr_bhs; i++) {
			if (fatent->bhs[n] == bhs[i])
				break;
		}
		if (i == *nr_bhs) {
			get_bh(fatent->bhs[n]);
			bhs[i] = fatent->bhs[n];
			(*nr_bhs)++;
		}
	}
}

int fat_alloc_clusters(struct inode *inode, int *cluster, int nr_cluster)
{
	struct super_block *sb = inode->i_sb;
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	struct fatent_operations *ops = sbi->fatent_ops;
	struct fat_entry fatent, prev_ent;
	struct buffer_head *bhs[MAX_BUF_PER_PAGE];
	int i, count, err, nr_bhs, idx_clus;

	BUG_ON(nr_cluster > (MAX_BUF_PER_PAGE / 2));	/* fixed limit */

	lock_fat(sbi);
	if (sbi->free_clusters != -1 && sbi->free_clus_valid &&
	    sbi->free_clusters < nr_cluster) {
		unlock_fat(sbi);
		return -ENOSPC;
	}

	err = nr_bhs = idx_clus = 0;
	count = FAT_START_ENT;
	fatent_init(&prev_ent);
	fatent_init(&fatent);
	fatent_set_entry(&fatent, sbi->prev_free + 1);
	while (count < sbi->max_cluster) {
		if (fatent.entry >= sbi->max_cluster)
			fatent.entry = FAT_START_ENT;
		fatent_set_entry(&fatent, fatent.entry);
		err = fat_ent_read_block(sb, &fatent);
		if (err)
			goto out;

		/* Find the free entries in a block */
		do {
			if (ops->ent_get(&fatent) == FAT_ENT_FREE) {
				int entry = fatent.entry;

				/* make the cluster chain */
				ops->ent_put(&fatent, FAT_ENT_EOF);
				if (prev_ent.nr_bhs)
					ops->ent_put(&prev_ent, entry);

				fat_collect_bhs(bhs, &nr_bhs, &fatent);

				sbi->prev_free = entry;
				if (sbi->free_clusters != -1)
					sbi->free_clusters--;
				sb->s_dirt = 1;

				cluster[idx_clus] = entry;
				idx_clus++;
				if (idx_clus == nr_cluster)
					goto out;

				/*
				 * fat_collect_bhs() gets ref-count of bhs,
				 * so we can still use the prev_ent.
				 */
				prev_ent = fatent;
			}
			count++;
			if (count == sbi->max_cluster)
				break;
		} while (fat_ent_next(sbi, &fatent));
	}

	/* Couldn't allocate the free entries */
	sbi->free_clusters = 0;
	sbi->free_clus_valid = 1;
	sb->s_dirt = 1;
	err = -ENOSPC;

out:
	unlock_fat(sbi);
	fatent_brelse(&fatent);
	if (!err) {
		if (inode_needs_sync(inode))
			err = fat_sync_bhs(bhs, nr_bhs);
		if (!err)
			err = fat_mirror_bhs(sb, bhs, nr_bhs);
	}
	for (i = 0; i < nr_bhs; i++)
		brelse(bhs[i]);

	if (err && idx_clus)
		fat_free_clusters(inode, cluster[0]);

	return err;
}

int fat_free_clusters(struct inode *inode, int cluster)
{
	struct super_block *sb = inode->i_sb;
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	struct fatent_operations *ops = sbi->fatent_ops;
	struct fat_entry fatent;
	struct buffer_head *bhs[MAX_BUF_PER_PAGE];
	int i, err, nr_bhs;
	int first_cl = cluster;

	nr_bhs = 0;
	fatent_init(&fatent);
	lock_fat(sbi);
	do {
		cluster = fat_ent_read(inode, &fatent, cluster);
		if (cluster < 0) {
			err = cluster;
			goto error;
		} else if (cluster == FAT_ENT_FREE) {
			fat_fs_error(sb, "%s: deleting FAT entry beyond EOF",
				     __func__);
			err = -EIO;
			goto error;
		}

		if (sbi->options.discard) {
			/*
			 * Issue discard for the sectors we no longer
			 * care about, batching contiguous clusters
			 * into one request
			 */
			if (cluster != fatent.entry + 1) {
				int nr_clus = fatent.entry - first_cl + 1;

				sb_issue_discard(sb,
					fat_clus_to_blknr(sbi, first_cl),
					nr_clus * sbi->sec_per_clus);

				first_cl = cluster;
			}
		}

		ops->ent_put(&fatent, FAT_ENT_FREE);
		if (sbi->free_clusters != -1) {
			sbi->free_clusters++;
			sb->s_dirt = 1;
		}

		if (nr_bhs + fatent.nr_bhs > MAX_BUF_PER_PAGE) {
			if (sb->s_flags & MS_SYNCHRONOUS) {
				err = fat_sync_bhs(bhs, nr_bhs);
				if (err)
					goto error;
			}
			err = fat_mirror_bhs(sb, bhs, nr_bhs);
			if (err)
				goto error;
			for (i = 0; i < nr_bhs; i++)
				brelse(bhs[i]);
			nr_bhs = 0;
		}
		fat_collect_bhs(bhs, &nr_bhs, &fatent);
	} while (cluster != FAT_ENT_EOF);

	if (sb->s_flags & MS_SYNCHRONOUS) {
		err = fat_sync_bhs(bhs, nr_bhs);
		if (err)
			goto error;
	}
	err = fat_mirror_bhs(sb, bhs, nr_bhs);
error:
	fatent_brelse(&fatent);
	for (i = 0; i < nr_bhs; i++)
		brelse(bhs[i]);
	unlock_fat(sbi);

	return err;
}

EXPORT_SYMBOL_GPL(fat_free_clusters);

/* 128kb is the whole sectors for FAT12 and FAT16 */
#define FAT_READA_SIZE		(128 * 1024)

static void fat_ent_reada(struct super_block *sb, struct fat_entry *fatent,
			  unsigned long reada_blocks)
{
	struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
	sector_t blocknr;
	int i, offset;

	ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);

	for (i = 0; i < reada_blocks; i++)
		sb_breadahead(sb, blocknr + i);
}

int fat_count_free_clusters(struct super_block *sb)
{
	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	struct fatent_operations *ops = sbi->fatent_ops;
	struct fat_entry fatent;
	unsigned long reada_blocks, reada_mask, cur_block;
	int err = 0, free;

	lock_fat(sbi);
	if (sbi->free_clusters != -1 && sbi->free_clus_valid)
		goto out;

	reada_blocks = FAT_READA_SIZE >> sb->s_blocksize_bits;
	reada_mask = reada_blocks - 1;
	cur_block = 0;

	free = 0;
	fatent_init(&fatent);
	fatent_set_entry(&fatent, FAT_START_ENT);
	while (fatent.entry < sbi->max_cluster) {
		/* readahead of fat blocks */
		if ((cur_block & reada_mask) == 0) {
			unsigned long rest = sbi->fat_length - cur_block;
			fat_ent_reada(sb, &fatent, min(reada_blocks, rest));
		}
		cur_block++;

		err = fat_ent_read_block(sb, &fatent);
		if (err)
			goto out;

		do {
			if (ops->ent_get(&fatent) == FAT_ENT_FREE)
				free++;
		} while (fat_ent_next(sbi, &fatent));
	}
	sbi->free_clusters = free;
	sbi->free_clus_valid = 1;
	sb->s_dirt = 1;
	fatent_brelse(&fatent);
out:
	unlock_fat(sbi);
	return err;
}
Commit	Line	Data
1da177e4 LT	1	/*
	2	* Copyright (C) 2004, OGAWA Hirofumi
	3	* Released under GPL v2.
	4	*/
	5
	6	#include <linux/module.h>
	7	#include <linux/fs.h>
	8	#include <linux/msdos_fs.h>
8c540a96	9	#include <linux/blkdev.h>
9e975dae	10	#include "fat.h"
1da177e4 LT	11
	12	struct fatent_operations {
	13	void (ent_blocknr)(struct super_block , int, int , sector_t );
	14	void (ent_set_ptr)(struct fat_entry , int);
	15	int (ent_bread)(struct super_block , struct fat_entry *,
	16	int, sector_t);
	17	int (ent_get)(struct fat_entry );
	18	void (ent_put)(struct fat_entry , int);
	19	int (ent_next)(struct fat_entry );
	20	};
	21
98283bb4 OH	22	static DEFINE_SPINLOCK(fat12_entry_lock);
98283bb4 OH	23
1da177e4 LT	24	static void fat12_ent_blocknr(struct super_block *sb, int entry,
	25	int offset, sector_t blocknr)
	26	{
	27	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	28	int bytes = entry + (entry >> 1);
	29	WARN_ON(entry < FAT_START_ENT \|\| sbi->max_cluster <= entry);
	30	*offset = bytes & (sb->s_blocksize - 1);
	31	*blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
	32	}
	33
	34	static void fat_ent_blocknr(struct super_block *sb, int entry,
	35	int offset, sector_t blocknr)
	36	{
	37	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	38	int bytes = (entry << sbi->fatent_shift);
	39	WARN_ON(entry < FAT_START_ENT \|\| sbi->max_cluster <= entry);
	40	*offset = bytes & (sb->s_blocksize - 1);
	41	*blocknr = sbi->fat_start + (bytes >> sb->s_blocksize_bits);
	42	}
	43
	44	static void fat12_ent_set_ptr(struct fat_entry *fatent, int offset)
	45	{
	46	struct buffer_head **bhs = fatent->bhs;
	47	if (fatent->nr_bhs == 1) {
	48	WARN_ON(offset >= (bhs[0]->b_size - 1));
	49	fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
	50	fatent->u.ent12_p[1] = bhs[0]->b_data + (offset + 1);
	51	} else {
	52	WARN_ON(offset != (bhs[0]->b_size - 1));
	53	fatent->u.ent12_p[0] = bhs[0]->b_data + offset;
	54	fatent->u.ent12_p[1] = bhs[1]->b_data;
	55	}
	56	}
	57
	58	static void fat16_ent_set_ptr(struct fat_entry *fatent, int offset)
	59	{
	60	WARN_ON(offset & (2 - 1));
	61	fatent->u.ent16_p = (__le16 *)(fatent->bhs[0]->b_data + offset);
	62	}
	63
	64	static void fat32_ent_set_ptr(struct fat_entry *fatent, int offset)
	65	{
	66	WARN_ON(offset & (4 - 1));
	67	fatent->u.ent32_p = (__le32 *)(fatent->bhs[0]->b_data + offset);
	68	}
	69
	70	static int fat12_ent_bread(struct super_block sb, struct fat_entry fatent,
	71	int offset, sector_t blocknr)
	72	{
	73	struct buffer_head **bhs = fatent->bhs;
	74
	75	WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
b522412a AV	76	fatent->fat_inode = MSDOS_SB(sb)->fat_inode;
b522412a AV	77
1da177e4 LT	78	bhs[0] = sb_bread(sb, blocknr);
	79	if (!bhs[0])
	80	goto err;
	81
	82	if ((offset + 1) < sb->s_blocksize)
	83	fatent->nr_bhs = 1;
	84	else {
	85	/* This entry is block boundary, it needs the next block */
	86	blocknr++;
	87	bhs[1] = sb_bread(sb, blocknr);
	88	if (!bhs[1])
	89	goto err_brelse;
	90	fatent->nr_bhs = 2;
	91	}
	92	fat12_ent_set_ptr(fatent, offset);
	93	return 0;
	94
	95	err_brelse:
	96	brelse(bhs[0]);
	97	err:
c3302931	98	printk(KERN_ERR "FAT: FAT read failed (blocknr %llu)\n", (llu)blocknr);
1da177e4 LT	99	return -EIO;
	100	}
	101
	102	static int fat_ent_bread(struct super_block sb, struct fat_entry fatent,
	103	int offset, sector_t blocknr)
	104	{
	105	struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
	106
	107	WARN_ON(blocknr < MSDOS_SB(sb)->fat_start);
b522412a	108	fatent->fat_inode = MSDOS_SB(sb)->fat_inode;
1da177e4 LT	109	fatent->bhs[0] = sb_bread(sb, blocknr);
	110	if (!fatent->bhs[0]) {
	111	printk(KERN_ERR "FAT: FAT read failed (blocknr %llu)\n",
c3302931	112	(llu)blocknr);
1da177e4 LT	113	return -EIO;
	114	}
	115	fatent->nr_bhs = 1;
	116	ops->ent_set_ptr(fatent, offset);
	117	return 0;
	118	}
	119
	120	static int fat12_ent_get(struct fat_entry *fatent)
	121	{
	122	u8 **ent12_p = fatent->u.ent12_p;
	123	int next;
	124
98283bb4	125	spin_lock(&fat12_entry_lock);
1da177e4 LT	126	if (fatent->entry & 1)
	127	next = (ent12_p[0] >> 4) \| (ent12_p[1] << 4);
	128	else
	129	next = (ent12_p[1] << 8) \| ent12_p[0];
98283bb4 OH	130	spin_unlock(&fat12_entry_lock);
98283bb4 OH	131
1da177e4 LT	132	next &= 0x0fff;
	133	if (next >= BAD_FAT12)
	134	next = FAT_ENT_EOF;
	135	return next;
	136	}
	137
	138	static int fat16_ent_get(struct fat_entry *fatent)
	139	{
	140	int next = le16_to_cpu(*fatent->u.ent16_p);
	141	WARN_ON((unsigned long)fatent->u.ent16_p & (2 - 1));
	142	if (next >= BAD_FAT16)
	143	next = FAT_ENT_EOF;
	144	return next;
	145	}
	146
	147	static int fat32_ent_get(struct fat_entry *fatent)
	148	{
	149	int next = le32_to_cpu(*fatent->u.ent32_p) & 0x0fffffff;
	150	WARN_ON((unsigned long)fatent->u.ent32_p & (4 - 1));
	151	if (next >= BAD_FAT32)
	152	next = FAT_ENT_EOF;
	153	return next;
	154	}
	155
	156	static void fat12_ent_put(struct fat_entry *fatent, int new)
	157	{
	158	u8 **ent12_p = fatent->u.ent12_p;
	159
	160	if (new == FAT_ENT_EOF)
	161	new = EOF_FAT12;
	162
98283bb4	163	spin_lock(&fat12_entry_lock);
1da177e4 LT	164	if (fatent->entry & 1) {
	165	ent12_p[0] = (new << 4) \| (ent12_p[0] & 0x0f);
	166	*ent12_p[1] = new >> 4;
	167	} else {
	168	*ent12_p[0] = new & 0xff;
	169	ent12_p[1] = (ent12_p[1] & 0xf0) \| (new >> 8);
	170	}
98283bb4	171	spin_unlock(&fat12_entry_lock);
1da177e4	172
b522412a	173	mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
1da177e4	174	if (fatent->nr_bhs == 2)
b522412a	175	mark_buffer_dirty_inode(fatent->bhs[1], fatent->fat_inode);
1da177e4 LT	176	}
	177
	178	static void fat16_ent_put(struct fat_entry *fatent, int new)
	179	{
	180	if (new == FAT_ENT_EOF)
	181	new = EOF_FAT16;
	182
	183	*fatent->u.ent16_p = cpu_to_le16(new);
b522412a	184	mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
1da177e4 LT	185	}
	186
	187	static void fat32_ent_put(struct fat_entry *fatent, int new)
	188	{
	189	if (new == FAT_ENT_EOF)
	190	new = EOF_FAT32;
	191
	192	WARN_ON(new & 0xf0000000);
	193	new \|= le32_to_cpu(*fatent->u.ent32_p) & ~0x0fffffff;
	194	*fatent->u.ent32_p = cpu_to_le32(new);
b522412a	195	mark_buffer_dirty_inode(fatent->bhs[0], fatent->fat_inode);
1da177e4 LT	196	}
	197
	198	static int fat12_ent_next(struct fat_entry *fatent)
	199	{
	200	u8 **ent12_p = fatent->u.ent12_p;
	201	struct buffer_head **bhs = fatent->bhs;
	202	u8 *nextp = ent12_p[1] + 1 + (fatent->entry & 1);
	203
	204	fatent->entry++;
	205	if (fatent->nr_bhs == 1) {
	206	WARN_ON(ent12_p[0] > (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 2)));
	207	WARN_ON(ent12_p[1] > (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1)));
	208	if (nextp < (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1))) {
	209	ent12_p[0] = nextp - 1;
	210	ent12_p[1] = nextp;
	211	return 1;
	212	}
	213	} else {
	214	WARN_ON(ent12_p[0] != (u8 *)(bhs[0]->b_data + (bhs[0]->b_size - 1)));
	215	WARN_ON(ent12_p[1] != (u8 *)bhs[1]->b_data);
	216	ent12_p[0] = nextp - 1;
	217	ent12_p[1] = nextp;
	218	brelse(bhs[0]);
	219	bhs[0] = bhs[1];
	220	fatent->nr_bhs = 1;
	221	return 1;
	222	}
	223	ent12_p[0] = NULL;
	224	ent12_p[1] = NULL;
	225	return 0;
	226	}
	227
	228	static int fat16_ent_next(struct fat_entry *fatent)
	229	{
	230	const struct buffer_head *bh = fatent->bhs[0];
	231	fatent->entry++;
	232	if (fatent->u.ent16_p < (__le16 *)(bh->b_data + (bh->b_size - 2))) {
	233	fatent->u.ent16_p++;
	234	return 1;
	235	}
	236	fatent->u.ent16_p = NULL;
	237	return 0;
	238	}
	239
	240	static int fat32_ent_next(struct fat_entry *fatent)
	241	{
	242	const struct buffer_head *bh = fatent->bhs[0];
	243	fatent->entry++;
	244	if (fatent->u.ent32_p < (__le32 *)(bh->b_data + (bh->b_size - 4))) {
	245	fatent->u.ent32_p++;
	246	return 1;
	247	}
	248	fatent->u.ent32_p = NULL;
	249	return 0;
	250	}
	251
	252	static struct fatent_operations fat12_ops = {
	253	.ent_blocknr = fat12_ent_blocknr,
	254	.ent_set_ptr = fat12_ent_set_ptr,
	255	.ent_bread = fat12_ent_bread,
	256	.ent_get = fat12_ent_get,
	257	.ent_put = fat12_ent_put,
	258	.ent_next = fat12_ent_next,
	259	};
260
261	static struct fatent_operations fat16_ops = {
262	.ent_blocknr = fat_ent_blocknr,
263	.ent_set_ptr = fat16_ent_set_ptr,
264	.ent_bread = fat_ent_bread,
265	.ent_get = fat16_ent_get,
266	.ent_put = fat16_ent_put,
267	.ent_next = fat16_ent_next,
268	};
269
270	static struct fatent_operations fat32_ops = {
271	.ent_blocknr = fat_ent_blocknr,
272	.ent_set_ptr = fat32_ent_set_ptr,
273	.ent_bread = fat_ent_bread,
274	.ent_get = fat32_ent_get,
275	.ent_put = fat32_ent_put,
276	.ent_next = fat32_ent_next,
277	};
278
279	static inline void lock_fat(struct msdos_sb_info *sbi)
280	{
6b9438e1	281	mutex_lock(&sbi->fat_lock);
1da177e4 LT	282	}
	283
	284	static inline void unlock_fat(struct msdos_sb_info *sbi)
	285	{
6b9438e1	286	mutex_unlock(&sbi->fat_lock);
1da177e4 LT	287	}
	288
	289	void fat_ent_access_init(struct super_block *sb)
	290	{
	291	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	292
6b9438e1	293	mutex_init(&sbi->fat_lock);
1da177e4 LT	294
	295	switch (sbi->fat_bits) {
	296	case 32:
	297	sbi->fatent_shift = 2;
	298	sbi->fatent_ops = &fat32_ops;
	299	break;
	300	case 16:
	301	sbi->fatent_shift = 1;
	302	sbi->fatent_ops = &fat16_ops;
	303	break;
	304	case 12:
	305	sbi->fatent_shift = -1;
	306	sbi->fatent_ops = &fat12_ops;
	307	break;
	308	}
	309	}
	310
	311	static inline int fat_ent_update_ptr(struct super_block *sb,
	312	struct fat_entry *fatent,
	313	int offset, sector_t blocknr)
	314	{
	315	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	316	struct fatent_operations *ops = sbi->fatent_ops;
	317	struct buffer_head **bhs = fatent->bhs;
	318
	319	/* Is this fatent's blocks including this entry? */
	320	if (!fatent->nr_bhs \|\| bhs[0]->b_blocknr != blocknr)
	321	return 0;
5e35dd46 OH	322	if (sbi->fat_bits == 12) {
	323	if ((offset + 1) < sb->s_blocksize) {
	324	/* This entry is on bhs[0]. */
	325	if (fatent->nr_bhs == 2) {
	326	brelse(bhs[1]);
	327	fatent->nr_bhs = 1;
	328	}
	329	} else {
	330	/* This entry needs the next block. */
	331	if (fatent->nr_bhs != 2)
	332	return 0;
	333	if (bhs[1]->b_blocknr != (blocknr + 1))
	334	return 0;
	335	}
1da177e4 LT	336	}
	337	ops->ent_set_ptr(fatent, offset);
	338	return 1;
	339	}
	340
	341	int fat_ent_read(struct inode inode, struct fat_entry fatent, int entry)
	342	{
	343	struct super_block *sb = inode->i_sb;
	344	struct msdos_sb_info *sbi = MSDOS_SB(inode->i_sb);
	345	struct fatent_operations *ops = sbi->fatent_ops;
	346	int err, offset;
	347	sector_t blocknr;
	348
	349	if (entry < FAT_START_ENT \|\| sbi->max_cluster <= entry) {
	350	fatent_brelse(fatent);
85c78591	351	fat_fs_error(sb, "invalid access to FAT (entry 0x%08x)", entry);
1da177e4 LT	352	return -EIO;
	353	}
	354
	355	fatent_set_entry(fatent, entry);
	356	ops->ent_blocknr(sb, entry, &offset, &blocknr);
	357
	358	if (!fat_ent_update_ptr(sb, fatent, offset, blocknr)) {
	359	fatent_brelse(fatent);
	360	err = ops->ent_bread(sb, fatent, offset, blocknr);
	361	if (err)
	362	return err;
	363	}
	364	return ops->ent_get(fatent);
	365	}
	366
	367	/* FIXME: We can write the blocks as more big chunk. */
	368	static int fat_mirror_bhs(struct super_block sb, struct buffer_head *bhs,
	369	int nr_bhs)
	370	{
	371	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	372	struct buffer_head *c_bh;
	373	int err, n, copy;
	374
	375	err = 0;
	376	for (copy = 1; copy < sbi->fats; copy++) {
	377	sector_t backup_fat = sbi->fat_length * copy;
	378
	379	for (n = 0; n < nr_bhs; n++) {
	380	c_bh = sb_getblk(sb, backup_fat + bhs[n]->b_blocknr);
	381	if (!c_bh) {
	382	err = -ENOMEM;
	383	goto error;
	384	}
	385	memcpy(c_bh->b_data, bhs[n]->b_data, sb->s_blocksize);
	386	set_buffer_uptodate(c_bh);
b522412a	387	mark_buffer_dirty_inode(c_bh, sbi->fat_inode);
1da177e4 LT	388	if (sb->s_flags & MS_SYNCHRONOUS)
	389	err = sync_dirty_buffer(c_bh);
	390	brelse(c_bh);
	391	if (err)
	392	goto error;
	393	}
	394	}
	395	error:
	396	return err;
	397	}
	398
	399	int fat_ent_write(struct inode inode, struct fat_entry fatent,
	400	int new, int wait)
	401	{
	402	struct super_block *sb = inode->i_sb;
	403	struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
	404	int err;
	405
	406	ops->ent_put(fatent, new);
	407	if (wait) {
	408	err = fat_sync_bhs(fatent->bhs, fatent->nr_bhs);
	409	if (err)
	410	return err;
	411	}
	412	return fat_mirror_bhs(sb, fatent->bhs, fatent->nr_bhs);
	413	}
	414
	415	static inline int fat_ent_next(struct msdos_sb_info *sbi,
	416	struct fat_entry *fatent)
	417	{
	418	if (sbi->fatent_ops->ent_next(fatent)) {
	419	if (fatent->entry < sbi->max_cluster)
	420	return 1;
	421	}
	422	return 0;
	423	}
	424
	425	static inline int fat_ent_read_block(struct super_block *sb,
	426	struct fat_entry *fatent)
	427	{
	428	struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
	429	sector_t blocknr;
	430	int offset;
	431
	432	fatent_brelse(fatent);
	433	ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
	434	return ops->ent_bread(sb, fatent, offset, blocknr);
	435	}
	436
	437	static void fat_collect_bhs(struct buffer_head *bhs, int nr_bhs,
	438	struct fat_entry *fatent)
	439	{
	440	int n, i;
	441
	442	for (n = 0; n < fatent->nr_bhs; n++) {
	443	for (i = 0; i < *nr_bhs; i++) {
	444	if (fatent->bhs[n] == bhs[i])
	445	break;
	446	}
	447	if (i == *nr_bhs) {
	448	get_bh(fatent->bhs[n]);
	449	bhs[i] = fatent->bhs[n];
	450	(*nr_bhs)++;
	451	}
452	}
453	}
454
455	int fat_alloc_clusters(struct inode inode, int cluster, int nr_cluster)
456	{
457	struct super_block *sb = inode->i_sb;
458	struct msdos_sb_info *sbi = MSDOS_SB(sb);
459	struct fatent_operations *ops = sbi->fatent_ops;
460	struct fat_entry fatent, prev_ent;
461	struct buffer_head *bhs[MAX_BUF_PER_PAGE];
462	int i, count, err, nr_bhs, idx_clus;
463
464	BUG_ON(nr_cluster > (MAX_BUF_PER_PAGE / 2)); /* fixed limit */
465
466	lock_fat(sbi);
606e423e OH	467	if (sbi->free_clusters != -1 && sbi->free_clus_valid &&
606e423e OH	468	sbi->free_clusters < nr_cluster) {
1da177e4 LT	469	unlock_fat(sbi);
	470	return -ENOSPC;
	471	}
	472
	473	err = nr_bhs = idx_clus = 0;
	474	count = FAT_START_ENT;
	475	fatent_init(&prev_ent);
	476	fatent_init(&fatent);
	477	fatent_set_entry(&fatent, sbi->prev_free + 1);
	478	while (count < sbi->max_cluster) {
	479	if (fatent.entry >= sbi->max_cluster)
	480	fatent.entry = FAT_START_ENT;
	481	fatent_set_entry(&fatent, fatent.entry);
	482	err = fat_ent_read_block(sb, &fatent);
	483	if (err)
	484	goto out;
	485
	486	/* Find the free entries in a block */
	487	do {
	488	if (ops->ent_get(&fatent) == FAT_ENT_FREE) {
	489	int entry = fatent.entry;
	490
	491	/* make the cluster chain */
	492	ops->ent_put(&fatent, FAT_ENT_EOF);
	493	if (prev_ent.nr_bhs)
	494	ops->ent_put(&prev_ent, entry);
	495
	496	fat_collect_bhs(bhs, &nr_bhs, &fatent);
	497
	498	sbi->prev_free = entry;
	499	if (sbi->free_clusters != -1)
	500	sbi->free_clusters--;
a6bf6b21	501	sb->s_dirt = 1;
1da177e4 LT	502
	503	cluster[idx_clus] = entry;
	504	idx_clus++;
	505	if (idx_clus == nr_cluster)
	506	goto out;
	507
	508	/*
	509	* fat_collect_bhs() gets ref-count of bhs,
	510	* so we can still use the prev_ent.
	511	*/
	512	prev_ent = fatent;
	513	}
	514	count++;
	515	if (count == sbi->max_cluster)
	516	break;
	517	} while (fat_ent_next(sbi, &fatent));
	518	}
	519
	520	/* Couldn't allocate the free entries */
	521	sbi->free_clusters = 0;
606e423e	522	sbi->free_clus_valid = 1;
a6bf6b21	523	sb->s_dirt = 1;
1da177e4 LT	524	err = -ENOSPC;
	525
	526	out:
	527	unlock_fat(sbi);
	528	fatent_brelse(&fatent);
	529	if (!err) {
	530	if (inode_needs_sync(inode))
	531	err = fat_sync_bhs(bhs, nr_bhs);
	532	if (!err)
	533	err = fat_mirror_bhs(sb, bhs, nr_bhs);
	534	}
	535	for (i = 0; i < nr_bhs; i++)
	536	brelse(bhs[i]);
1da177e4 LT	537
	538	if (err && idx_clus)
	539	fat_free_clusters(inode, cluster[0]);
	540
	541	return err;
	542	}
	543
	544	int fat_free_clusters(struct inode *inode, int cluster)
	545	{
	546	struct super_block *sb = inode->i_sb;
	547	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	548	struct fatent_operations *ops = sbi->fatent_ops;
	549	struct fat_entry fatent;
	550	struct buffer_head *bhs[MAX_BUF_PER_PAGE];
	551	int i, err, nr_bhs;
8c540a96	552	int first_cl = cluster;
1da177e4 LT	553
	554	nr_bhs = 0;
	555	fatent_init(&fatent);
	556	lock_fat(sbi);
	557	do {
	558	cluster = fat_ent_read(inode, &fatent, cluster);
	559	if (cluster < 0) {
	560	err = cluster;
	561	goto error;
	562	} else if (cluster == FAT_ENT_FREE) {
85c78591	563	fat_fs_error(sb, "%s: deleting FAT entry beyond EOF",
8e24eea7	564	__func__);
1da177e4 LT	565	err = -EIO;
	566	goto error;
	567	}
	568
681142f9 CH	569	if (sbi->options.discard) {
	570	/*
	571	* Issue discard for the sectors we no longer
	572	* care about, batching contiguous clusters
	573	* into one request
	574	*/
	575	if (cluster != fatent.entry + 1) {
	576	int nr_clus = fatent.entry - first_cl + 1;
	577
	578	sb_issue_discard(sb,
	579	fat_clus_to_blknr(sbi, first_cl),
	580	nr_clus * sbi->sec_per_clus);
	581
	582	first_cl = cluster;
	583	}
8c540a96 DW	584	}
8c540a96 DW	585
1da177e4	586	ops->ent_put(&fatent, FAT_ENT_FREE);
a6bf6b21	587	if (sbi->free_clusters != -1) {
1da177e4	588	sbi->free_clusters++;
a6bf6b21 OH	589	sb->s_dirt = 1;
a6bf6b21 OH	590	}
1da177e4 LT	591
	592	if (nr_bhs + fatent.nr_bhs > MAX_BUF_PER_PAGE) {
	593	if (sb->s_flags & MS_SYNCHRONOUS) {
	594	err = fat_sync_bhs(bhs, nr_bhs);
	595	if (err)
	596	goto error;
	597	}
	598	err = fat_mirror_bhs(sb, bhs, nr_bhs);
	599	if (err)
	600	goto error;
	601	for (i = 0; i < nr_bhs; i++)
	602	brelse(bhs[i]);
	603	nr_bhs = 0;
	604	}
	605	fat_collect_bhs(bhs, &nr_bhs, &fatent);
	606	} while (cluster != FAT_ENT_EOF);
	607
	608	if (sb->s_flags & MS_SYNCHRONOUS) {
	609	err = fat_sync_bhs(bhs, nr_bhs);
	610	if (err)
	611	goto error;
	612	}
	613	err = fat_mirror_bhs(sb, bhs, nr_bhs);
	614	error:
	615	fatent_brelse(&fatent);
	616	for (i = 0; i < nr_bhs; i++)
	617	brelse(bhs[i]);
	618	unlock_fat(sbi);
	619
1da177e4 LT	620	return err;
	621	}
	622
7c709d00	623	EXPORT_SYMBOL_GPL(fat_free_clusters);
1da177e4	624
9f966be8 OH	625	/* 128kb is the whole sectors for FAT12 and FAT16 */
	626	#define FAT_READA_SIZE (128 * 1024)
	627
	628	static void fat_ent_reada(struct super_block sb, struct fat_entry fatent,
	629	unsigned long reada_blocks)
	630	{
	631	struct fatent_operations *ops = MSDOS_SB(sb)->fatent_ops;
	632	sector_t blocknr;
	633	int i, offset;
	634
	635	ops->ent_blocknr(sb, fatent->entry, &offset, &blocknr);
	636
	637	for (i = 0; i < reada_blocks; i++)
	638	sb_breadahead(sb, blocknr + i);
	639	}
	640
1da177e4 LT	641	int fat_count_free_clusters(struct super_block *sb)
	642	{
	643	struct msdos_sb_info *sbi = MSDOS_SB(sb);
	644	struct fatent_operations *ops = sbi->fatent_ops;
	645	struct fat_entry fatent;
9f966be8	646	unsigned long reada_blocks, reada_mask, cur_block;
1da177e4 LT	647	int err = 0, free;
	648
	649	lock_fat(sbi);
606e423e	650	if (sbi->free_clusters != -1 && sbi->free_clus_valid)
1da177e4 LT	651	goto out;
1da177e4 LT	652
9f966be8 OH	653	reada_blocks = FAT_READA_SIZE >> sb->s_blocksize_bits;
	654	reada_mask = reada_blocks - 1;
	655	cur_block = 0;
	656
1da177e4 LT	657	free = 0;
	658	fatent_init(&fatent);
	659	fatent_set_entry(&fatent, FAT_START_ENT);
	660	while (fatent.entry < sbi->max_cluster) {
9f966be8 OH	661	/* readahead of fat blocks */
	662	if ((cur_block & reada_mask) == 0) {
	663	unsigned long rest = sbi->fat_length - cur_block;
	664	fat_ent_reada(sb, &fatent, min(reada_blocks, rest));
	665	}
	666	cur_block++;
	667
1da177e4 LT	668	err = fat_ent_read_block(sb, &fatent);
	669	if (err)
	670	goto out;
	671
	672	do {
	673	if (ops->ent_get(&fatent) == FAT_ENT_FREE)
	674	free++;
	675	} while (fat_ent_next(sbi, &fatent));
	676	}
	677	sbi->free_clusters = free;
606e423e	678	sbi->free_clus_valid = 1;
a6bf6b21	679	sb->s_dirt = 1;
1da177e4 LT	680	fatent_brelse(&fatent);
	681	out:
	682	unlock_fat(sbi);
	683	return err;
	684	}