code: func ifaceAddIPv4Addr(iface *net.Interface, ip net.IP, mask net.IPMask) error {
  	if ip.To4() == nil {
  		return fmt.Errorf("IP %v is not a valid IPv4 address", ip)
  	}
  	brd := make(net.IP, net.IPv4len)
  	copy(brd, ip.To4())
  	for i := 0; i < net.IPv4len; i++ {
  		brd[i] |= ^mask[i]
  	}
  	prefixLen, _ := mask.Size()
  	return ipRunIface(iface, "addr add %s/%d brd %s dev %s", ip, prefixLen, brd, iface.Name)
  }
docs: // ifaceAddIPv4Addr adds the given IPv4 address to the network interface.