fatent.c

linux环境下基于FAT的文件系统的通用代码

	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_panic(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(c_bh);
			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_panic(sb, "%s: deleting FAT entry beyond EOF",
				     __func__);
			err = -EIO;
			goto error;
		}

		/* 
		 * 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;
}