nilfs2: move cleanup code of metadata file from inode routines

Refactor nilfs_clear_inode() and nilfs_i_callback() so that cleanup
code or resource deallocation related to metadata file will be moved
out to mdt.c.

Link: http://lkml.kernel.org/r/1461935747-10380-9-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/super.c b/fs/nilfs2/super.c
index 2ed3e40..2cb78b8 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -169,12 +169,10 @@
 static void nilfs_i_callback(struct rcu_head *head)
 {
 	struct inode *inode = container_of(head, struct inode, i_rcu);
-	struct nilfs_mdt_info *mdi = NILFS_MDT(inode);
 
-	if (mdi) {
-		kfree(mdi->mi_bgl); /* kfree(NULL) is safe */
-		kfree(mdi);
-	}
+	if (nilfs_is_metadata_file_inode(inode))
+		nilfs_mdt_destroy(inode);
+
 	kmem_cache_free(nilfs_inode_cachep, NILFS_I(inode));
 }