nilfs2: allow nilfs_dirty_inode to mark metadata file inodes dirty

This allows sop->dirty_inode callback function (nilfs_dirty_inode) to
handle metadata file inodes.
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>

fs/nilfs2/inode.c

@@ -808,6 +808,7 @@ int nilfs_mark_inode_dirty(struct inode *inode)
 void nilfs_dirty_inode(struct inode *inode)
 {
 	struct nilfs_transaction_info ti;
+	struct nilfs_mdt_info *mdi = NILFS_MDT(inode);
 
 	if (is_bad_inode(inode)) {
 		nilfs_warning(inode->i_sb, __func__,
@@ -815,6 +816,10 @@ void nilfs_dirty_inode(struct inode *inode)
 		dump_stack();
 		return;
 	}
+	if (mdi) {
+		nilfs_mdt_mark_dirty(inode);
+		return;
+	}
 	nilfs_transaction_begin(inode->i_sb, &ti, 0);
 	nilfs_mark_inode_dirty(inode);
 	nilfs_transaction_commit(inode->i_sb); /* never fails */