[RFC PATCH 6/7] exfat: introduce exfat_count_contig_clusters

[Chi Zhiling <chizhiling@163.com>]

From: Chi Zhiling <chizhiling@kylinos.cn>

This patch introduces exfat_count_contig_clusters to obtain batch entries,
which is an infrastructure used to support iomap.

Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
---
 fs/exfat/exfat_fs.h |  2 ++
 fs/exfat/fatent.c   | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/fs/exfat/exfat_fs.h b/fs/exfat/exfat_fs.h
index d52893276e9a..421dd7c61cca 100644
--- a/fs/exfat/exfat_fs.h
+++ b/fs/exfat/exfat_fs.h
@@ -449,6 +449,8 @@ int exfat_find_last_cluster(struct super_block *sb, struct exfat_chain *p_chain,
 		unsigned int *ret_clu);
 int exfat_count_num_clusters(struct super_block *sb,
 		struct exfat_chain *p_chain, unsigned int *ret_count);
+int exfat_count_contig_clusters(struct super_block *sb,
+		struct exfat_chain *p_chain, unsigned int *ret_count);
 
 /* balloc.c */
 int exfat_load_bitmap(struct super_block *sb);
diff --git a/fs/exfat/fatent.c b/fs/exfat/fatent.c
index d980d17176c2..9dcee9524155 100644
--- a/fs/exfat/fatent.c
+++ b/fs/exfat/fatent.c
@@ -524,3 +524,36 @@ int exfat_count_num_clusters(struct super_block *sb,
 
 	return 0;
 }
+
+int exfat_count_contig_clusters(struct super_block *sb,
+		struct exfat_chain *p_chain, unsigned int *ret_count)
+{
+	struct buffer_head *bh = NULL;
+	unsigned int clu, next_clu;
+	unsigned int count;
+
+	if (!p_chain->dir || p_chain->dir == EXFAT_EOF_CLUSTER) {
+		*ret_count = 0;
+		return 0;
+	}
+
+	if (p_chain->flags == ALLOC_NO_FAT_CHAIN) {
+		*ret_count = p_chain->size;
+		return 0;
+	}
+
+	clu = p_chain->dir;
+	for (count = 1; count < p_chain->size; count++) {
+		if (exfat_ent_get(sb, clu, &next_clu, &bh))
+			return -EIO;
+		if (++clu != next_clu)
+			break;
+	}
+
+	/* TODO: Update p_claim to help caller read ahead the next block */
+
+	brelse(bh);
+	*ret_count = count;
+
+	return 0;
+}
-- 
2.43.0