nilfs2: add bmap function to seek a valid key

Add a new bmap function, nilfs_bmap_seek_key(), which seeks a valid
entry and returns its key starting from a given key.  This function
can be used to skip hole blocks efficiently.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/nilfs2/bmap.h b/fs/nilfs2/bmap.h
index 9230d33..bfa817c 100644
--- a/fs/nilfs2/bmap.h
+++ b/fs/nilfs2/bmap.h
@@ -76,8 +76,10 @@
 			  union nilfs_binfo *);
 	int (*bop_mark)(struct nilfs_bmap *, __u64, int);
 
-	/* The following functions are internal use only. */
+	int (*bop_seek_key)(const struct nilfs_bmap *, __u64, __u64 *);
 	int (*bop_last_key)(const struct nilfs_bmap *, __u64 *);
+
+	/* The following functions are internal use only. */
 	int (*bop_check_insert)(const struct nilfs_bmap *, __u64);
 	int (*bop_check_delete)(struct nilfs_bmap *, __u64);
 	int (*bop_gather_data)(struct nilfs_bmap *, __u64 *, __u64 *, int);
@@ -155,6 +157,7 @@
 int nilfs_bmap_lookup_contig(struct nilfs_bmap *, __u64, __u64 *, unsigned);
 int nilfs_bmap_insert(struct nilfs_bmap *bmap, __u64 key, unsigned long rec);
 int nilfs_bmap_delete(struct nilfs_bmap *bmap, __u64 key);
+int nilfs_bmap_seek_key(struct nilfs_bmap *bmap, __u64 start, __u64 *keyp);
 int nilfs_bmap_last_key(struct nilfs_bmap *bmap, __u64 *keyp);
 int nilfs_bmap_truncate(struct nilfs_bmap *bmap, __u64 key);
 void nilfs_bmap_clear(struct nilfs_bmap *);