WP meta boxes

//DISPLAY META BOXES
add_action("admin_init", "admin_init");
function admin_init(){
	global $pagenow, $typenow;
    if (empty($typenow) && !empty($_GET['post'])) {
        $post = get_post($_GET['post']);
        $typenow = $post->post_type;
    }
 
 
	add_meta_box("function_name", "box title", "function_name", 'post_type', "normal", "high");
}
 
function function_name() {
	global $post; ?>
	<p>Label:</p><textarea cols="80" rows="3" name="meta_name"><? echo get_post_meta($post->ID, 'meta_name', true); ?></textarea>
	<?		
}
 
 
 
//SAVING META BOXES
add_action('save_post', 'save_details');
function save_details() {
  	global $post;
 
	if(isset($_POST['meta_name'])) {
		update_post_meta($post->ID, "meta_name", $_POST['meta_name']);
	}
}