Re: [PATCH v2 1/1] dts: add send_packets to test suites and rework packet addressing

["Juraj Linkeš" <juraj.linkes@pantheon.tech>]

>>> +            if num_ip_layers > 0:
>>> +                ip_src_is_unset = "src" not in l3_to_use.fields
>>> +                ip_dst_is_unset = "dst" not in l3_to_use.fields
>>> +            else:
>>> +                ip_src_is_unset = None
>>> +                ip_dst_is_unset = None
>>>
>>> -            # The packet is routed from TG egress to TG ingress
>>> -            # update l3 addresses
>>> -            packet.payload.src = self._tg_ip_address_egress.ip.exploded
>>> -            packet.payload.dst = self._tg_ip_address_ingress.ip.exploded
>>> -        else:
>>> -            # The packet leaves TG towards SUT
>>>                # update l2 addresses
>>> -            packet.src = self._tg_port_egress.mac_address
>>> -            packet.dst = self._sut_port_ingress.mac_address
>>> +            # If `expected` is :data:`True`, the packet enters the TG from SUT, otherwise the
>>> +            # packet leaves the TG towards the SUT
>>> +            if pkt_src_is_unset:
>>> +                packet.src = (
>>> +                    self._sut_port_egress.mac_address
>>> +                    if expected
>>> +                    else self._tg_port_egress.mac_address
>>> +                )
>>> +            if pkt_dst_is_unset:
>>> +                packet.dst = (
>>> +                    self._tg_port_ingress.mac_address
>>> +                    if expected
>>> +                    else self._sut_port_ingress.mac_address
>>> +                )
>>>
>>> -            # The packet is routed from TG egress to TG ingress
>>>                # update l3 addresses
>>> -            packet.payload.src = self._tg_ip_address_egress.ip.exploded
>>> -            packet.payload.dst = self._tg_ip_address_ingress.ip.exploded
>>> +            # The packet is routed from TG egress to TG ingress regardless of whether it is
>>> +            # expected or not.
>>
>> Is this true? This might've been an error in the original
>> implementation. If it's expected (that is, the returning packet), it
>> should be routed from TG ingress to TG egress, no?
> 
> I guess I'm not completely sure. It would make sense that the L3
> addresses should be switched as well based on either expected or not,
> but currently it isn't modified, and os_udp still works which makes me
> think the addresses aren't switched by the kernel interfaces, which I
> believe is the only time these addresses are actually used (since we
> use sendp in scapy).
> 

Right, I went too deep in my thinking and confused myself :-). The path 
of the packet is:
TG egress -> SUT ingress -> SUT egress -> TG ingress

That is just one way path and I mixed the other direction into my 
thinking as well. With just one path, the MAC addresses are going to 
change, but not IP addresses.