1 files changed, 692 insertions, 0 deletions

diff --git a/kernel/fs/fat/fatent.c b/kernel/fs/fat/fatent.c
new file mode 100644
index 000000000..822655713
--- /dev/null
+++ b/kernel/fs/fat/fatent.c
@@ -0,0 +1,692 @@
+/*
+ * Copyright (C) 2004, OGAWA Hirofumi
+ * Released under GPL v2.
+ */
+
+#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:
+	fat_msg(sb, KERN_ERR, "FAT read failed (blocknr %llu)", (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]) {
+		fat_msg(sb, KERN_ERR, "FAT read failed (blocknr %llu)",
+		       (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)
+{
+	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 void mark_fsinfo_dirty(struct super_block *sb)
+{
+	struct msdos_sb_info *sbi = MSDOS_SB(sb);
+
+	if (sb->s_flags & MS_RDONLY || sbi->fat_bits != 32)
+		return;
+
+	__mark_inode_dirty(sbi->fsinfo_inode, I_DIRTY_SYNC);
+}
+
+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--;
+
+				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;
+	err = -ENOSPC;
+
+out:
+	unlock_fat(sbi);
+	mark_fsinfo_dirty(sb);
+	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, dirty_fsinfo = 0;
+
+	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,
+					GFP_NOFS, 0);
+
+				first_cl = cluster;
+			}
+		}
+
+		ops->ent_put(&fatent, FAT_ENT_FREE);
+		if (sbi->free_clusters != -1) {
+			sbi->free_clusters++;
+			dirty_fsinfo = 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);
+	if (dirty_fsinfo)
+		mark_fsinfo_dirty(sb);
+
+	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;
+	mark_fsinfo_dirty(sb);
+	fatent_brelse(&fatent);
+out:
+	unlock_fat(sbi);
+	return err;
+}