def METHOD_NAME(vm_name, disk_boot):
    """
    Update boot order of vm's 1st disk before test
    :param vm_name: vm name
    :param disk_boot: boot order of disk
    """
    vmxml = vm_xml.VMXML.new_from_dumpxml(vm_name)
    vm_os = vmxml.os
    vm_os.del_boots()
    vmxml.os = vm_os
    disk = vmxml.get_devices('disk')[0]
    target_dev = disk.target.get('dev', '')
    LOG.debug('Set boot order %s to device %s', disk_boot, target_dev)
    vmxml.set_boot_order_by_target_dev(target_dev, disk_boot)
    vmxml.sync()