ovl_new_inode
inode = ovl_new_inode(dentry->d_sb, mode, 0);
inode = ovl_new_inode(dentry->d_sb, mode, rdev);
struct inode *ovl_new_inode(struct super_block *sb, umode_t mode, dev_t rdev);
root = d_make_root(ovl_new_inode(sb, S_IFDIR, 0));