diff --git a/fs/block_dev.c b/fs/block_dev.c
index b07f1da..4b322a5 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -493,7 +493,7 @@
 	.kill_sb	= kill_anon_super,
 };
 
-struct super_block *blockdev_superblock __read_mostly;
+static struct super_block *blockdev_superblock __read_mostly;
 
 void __init bdev_cache_init(void)
 {
@@ -639,6 +639,11 @@
 	return bdev;
 }
 
+static inline int sb_is_blkdev_sb(struct super_block *sb)
+{
+	return sb == blockdev_superblock;
+}
+
 /* Call when you free inode */
 
 void bd_forget(struct inode *inode)