nilfs2: embed a back pointer to super block instance in nilfs object

Insert a back pointer to super block instance in nilfs object so that
functions of nilfs2 easily refer to the super block instance.  This
simplifies replacement of printk() in the successive change.

Link: http://lkml.kernel.org/r/1464875891-5443-4-git-send-email-konishi.ryusuke@lab.ntt.co.jp
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index e9fd241..7021151 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -56,12 +56,12 @@
 
 /**
  * alloc_nilfs - allocate a nilfs object
- * @bdev: block device to which the_nilfs is related
+ * @sb: super block instance
  *
  * Return Value: On success, pointer to the_nilfs is returned.
  * On error, NULL is returned.
  */
-struct the_nilfs *alloc_nilfs(struct block_device *bdev)
+struct the_nilfs *alloc_nilfs(struct super_block *sb)
 {
 	struct the_nilfs *nilfs;
 
@@ -69,7 +69,8 @@
 	if (!nilfs)
 		return NULL;
 
-	nilfs->ns_bdev = bdev;
+	nilfs->ns_sb = sb;
+	nilfs->ns_bdev = sb->s_bdev;
 	atomic_set(&nilfs->ns_ndirtyblks, 0);
 	init_rwsem(&nilfs->ns_sem);
 	mutex_init(&nilfs->ns_snapshot_mount_mutex);