WordPress Gallery Post type & meta box

define('MY_POST_TYPE', 'gallery');
define('MY_POST_SLUG', 'gallery');

add_action( 'init', 'my_register_post_type' );
function my_register_post_type () {
    $args = array (
        'label' => 'Gallery',
        'supports' => array( 'title', 'excerpt','thumbnail' ),
        'register_meta_box_cb' => 'my_meta_box_cb',
        'show_ui' => true,
        'query_var' => true
    );
    register_post_type( MY_POST_TYPE , $args );
}

function my_meta_box_cb () {
    add_meta_box( MY_POST_TYPE . '_details' , 'Media Library', 'my_meta_box_details', MY_POST_TYPE, 'normal', 'high' );
}

function my_meta_box_details () {
    global $post;
  $post_ID = $post->ID;
    printf( "<iframe frameborder='0' src=' %s ' style='width: 100%; height: 400px;'> </iframe>", get_upload_iframe_src('media') );
}