[ovs-dev] [PATCH ovn v2 2/3] actions: Add new OVN logical fields 'ip.src' and ip.dst'.

Mark Michelson mmichels at redhat.com
Thu Oct 15 20:37:41 UTC 2020


On 10/14/20 8:38 AM, Numan Siddique wrote:
> On Wed, Oct 14, 2020 at 5:51 PM Dumitru Ceara <dceara at redhat.com> wrote:
>>
>> On 10/14/20 2:13 PM, Numan Siddique wrote:
>>> On Wed, Oct 14, 2020 at 5:34 PM Dumitru Ceara <dceara at redhat.com> wrote:
>>>>
>>>> On 10/14/20 1:54 PM, Numan Siddique wrote:
>>>>> On Wed, Oct 14, 2020 at 4:40 PM Dumitru Ceara <dceara at redhat.com> wrote:
>>>>>>
>>>>>> On 10/14/20 12:50 PM, Numan Siddique wrote:
>>>>>>> On Wed, Oct 14, 2020 at 3:50 PM Dumitru Ceara <dceara at redhat.com> wrote:
>>>>>>>>
>>>>>>>> On 10/14/20 11:15 AM, numans at ovn.org wrote:
>>>>>>>>> From: Numan Siddique <numans at ovn.org>
>>>>>>>>>
>>>>>>>>> Thee new fields are version independent and these can be used in any
>>>>>>>>
>>>>>>>> Hi Numan,
>>>>>>>>
>>>>>>>> Nit: s/Thee/These
>>>>>>>>
>>>>>>>>> OVN action. Right now the usage of these fields are restricted to
>>>>>>>>> exchanging the IP source and destination fields.
>>>>>>>>>
>>>>>>>>> Eg. reject {... ip.src <-> ip.dst ... };
>>>>>>>>>
>>>>>>>>> "ip.src <-> ip.dst" translates to controller action with "pause" flag set.
>>>>>>>>> When pinctrl thread receives the packet in, it checks the IP version of the
>>>>>>>>> packet and either does - "ip4.src <-> ip4.dst" or "ip6.src <-> ip6.dst" and
>>>>>>>>> resumes the packet to continue with the pipeline.
>>>>>>>>>
>>>>>>>>> Upcoming patch will make use of these fields.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Numan Siddique <numans at ovn.org>
>>>>>>>>> ---
>>>>>>>>>   controller/pinctrl.c         |  49 +++++++++++++++
>>>>>>>>>   include/ovn/actions.h        |   4 ++
>>>>>>>>>   include/ovn/logical-fields.h |  18 ++++++
>>>>>>>>>   lib/actions.c                | 118 +++++++++++++++++++++++++++++++++++
>>>>>>>>>   lib/logical-fields.c         |  10 +++
>>>>>>>>>   ovn-sb.xml                   |  37 +++++++++++
>>>>>>>>>   tests/ovn.at                 |  27 ++++++++
>>>>>>>>>   utilities/ovn-trace.c        |  28 +++++++++
>>>>>>>>>   8 files changed, 291 insertions(+)
>>>>>>>>>
>>>>>>>>> diff --git a/controller/pinctrl.c b/controller/pinctrl.c
>>>>>>>>> index 631d058458..bc16a82404 100644
>>>>>>>>> --- a/controller/pinctrl.c
>>>>>>>>> +++ b/controller/pinctrl.c
>>>>>>>>> @@ -233,6 +233,11 @@ static void pinctrl_handle_put_icmp_frag_mtu(struct rconn *swconn,
>>>>>>>>>                                                struct ofputil_packet_in *pin,
>>>>>>>>>                                                struct ofpbuf *userdata,
>>>>>>>>>                                                struct ofpbuf *continuation);
>>>>>>>>> +static void pinctrl_handle_swap_src_dst_ip(struct rconn *swconn,
>>>>>>>>> +                                           const struct flow *in_flow,
>>>>>>>>> +                                           struct dp_packet *pkt_in,
>>>>>>>>> +                                           struct ofputil_packet_in *pin,
>>>>>>>>> +                                           struct ofpbuf *continuation);
>>>>>>>>>   static void
>>>>>>>>>   pinctrl_handle_event(struct ofpbuf *userdata)
>>>>>>>>>       OVS_REQUIRES(pinctrl_mutex);
>>>>>>>>> @@ -2835,6 +2840,11 @@ process_packet_in(struct rconn *swconn, const struct ofp_header *msg)
>>>>>>>>>           ovs_mutex_unlock(&pinctrl_mutex);
>>>>>>>>>           break;
>>>>>>>>>
>>>>>>>>> +    case ACTION_OPCODE_SWAP_SRC_DST_IP:
>>>>>>>>> +        pinctrl_handle_swap_src_dst_ip(swconn, &headers, &packet, &pin,
>>>>>>>>> +                                       &continuation);
>>>>>>>>> +        break;
>>>>>>>>> +
>>>>>>>>>       default:
>>>>>>>>>           VLOG_WARN_RL(&rl, "unrecognized packet-in opcode %"PRIu32,
>>>>>>>>>                        ntohl(ah->opcode));
>>>>>>>>> @@ -6508,3 +6518,42 @@ pinctrl_handle_svc_check(struct rconn *swconn, const struct flow *ip_flow,
>>>>>>>>>           svc_mon->next_send_time = time_msec() + svc_mon->interval;
>>>>>>>>>       }
>>>>>>>>>   }
>>>>>>>>> +
>>>>>>>>> +static void
>>>>>>>>> +pinctrl_handle_swap_src_dst_ip(struct rconn *swconn,
>>>>>>>>> +                               const struct flow *in_flow,
>>>>>>>>> +                               struct dp_packet *pkt_in,
>>>>>>>>> +                               struct ofputil_packet_in *pin,
>>>>>>>>> +                               struct ofpbuf *continuation)
>>>>>>>>> +{
>>>>>>>>> +    enum ofp_version version = rconn_get_version(swconn);
>>>>>>>>> +    enum ofputil_protocol proto = ofputil_protocol_from_ofp_version(version);
>>>>>>>>> +    struct dp_packet *pkt_out;
>>>>>>>>> +
>>>>>>>>> +    pkt_out = dp_packet_clone(pkt_in);
>>>>>>>>> +    pkt_out->l2_5_ofs = pkt_in->l2_5_ofs;
>>>>>>>>> +    pkt_out->l2_pad_size = pkt_in->l2_pad_size;
>>>>>>>>> +    pkt_out->l3_ofs = pkt_in->l3_ofs;
>>>>>>>>> +    pkt_out->l4_ofs = pkt_in->l4_ofs;
>>>>>>>>> +
>>>>>>>>> +    if (get_dl_type(in_flow) == htons(ETH_TYPE_IP)) {
>>>>>>>>> +        /* IPv4 packet. Swap nw_src with nw_dst. */
>>>>>>>>> +        packet_set_ipv4(pkt_out, in_flow->nw_dst, in_flow->nw_src,
>>>>>>>>> +                        in_flow->nw_tos, in_flow->nw_ttl);
>>>>>>>>> +    } else {
>>>>>>>>> +        /* IPv6 packet. Swap ip6_src with ip6_dst.
>>>>>>>>> +         * We could also use packet_set_ipv6() here, but that would require
>>>>>>>>> +         * to extract the 'tc' and 'label' from in_nh->ip6_flow which seems
>>>>>>>>> +         * unnecessary. */
>>>>>>>>> +        struct ovs_16aligned_ip6_hdr *out_nh = dp_packet_l3(pkt_out);
>>>>>>>>> +        union ovs_16aligned_in6_addr tmp = out_nh->ip6_src;
>>>>>>>>> +        out_nh->ip6_src = out_nh->ip6_dst;
>>>>>>>>> +        out_nh->ip6_dst = tmp;
>>>>>>>>> +    }
>>>>>>>>> +
>>>>>>>>> +    pin->packet = dp_packet_data(pkt_out);
>>>>>>>>> +    pin->packet_len = dp_packet_size(pkt_out);
>>>>>>>>> +
>>>>>>>>> +    queue_msg(swconn, ofputil_encode_resume(pin, continuation, proto));
>>>>>>>>> +    dp_packet_delete(pkt_out);
>>>>>>>>> +}
>>>>>>>>> diff --git a/include/ovn/actions.h b/include/ovn/actions.h
>>>>>>>>> index b4e5acabb9..bf1fe848b7 100644
>>>>>>>>> --- a/include/ovn/actions.h
>>>>>>>>> +++ b/include/ovn/actions.h
>>>>>>>>> @@ -97,6 +97,7 @@ struct ovn_extend_table;
>>>>>>>>>       OVNACT(DHCP6_REPLY,       ovnact_null)            \
>>>>>>>>>       OVNACT(ICMP6_ERROR,       ovnact_nest)            \
>>>>>>>>>       OVNACT(REJECT,            ovnact_nest)            \
>>>>>>>>> +    OVNACT(OVNFIELD_EXCHANGE, ovnact_move)            \
>>>>>>>>>
>>>>>>>>>   /* enum ovnact_type, with a member OVNACT_<ENUM> for each action. */
>>>>>>>>>   enum OVS_PACKED_ENUM ovnact_type {
>>>>>>>>> @@ -612,6 +613,9 @@ enum action_opcode {
>>>>>>>>>        * The actions, in OpenFlow 1.3 format, follow the action_header.
>>>>>>>>>        */
>>>>>>>>>       ACTION_OPCODE_REJECT,
>>>>>>>>> +
>>>>>>>>> +    /* ip.src <-> ip.dst */
>>>>>>>>> +    ACTION_OPCODE_SWAP_SRC_DST_IP,
>>>>>>>>>   };
>>>>>>>>>
>>>>>>>>>   /* Header. */
>>>>>>>>> diff --git a/include/ovn/logical-fields.h b/include/ovn/logical-fields.h
>>>>>>>>> index ac6f2f909b..bb6daa50ca 100644
>>>>>>>>> --- a/include/ovn/logical-fields.h
>>>>>>>>> +++ b/include/ovn/logical-fields.h
>>>>>>>>> @@ -116,6 +116,24 @@ enum ovn_field_id {
>>>>>>>>>        */
>>>>>>>>>       OVN_ICMP6_FRAG_MTU,
>>>>>>>>>
>>>>>>>>> +    /*
>>>>>>>>> +     * Name: "ip.src"
>>>>>>>>> +     * Type: be128
>>>>>>>>> +     * Description: Sets the field MFF_IPV4_SRC if eth.type == 0x800 (IPv4)
>>>>>>>>> +     *              or sets the field MFF_IPV6_SRC if
>>>>>>>>> +     *              eth.type == 0x86dd (IPV6).
>>>>>>>>> +     */
>>>>>>>>> +    OVN_IP_SRC,
>>>>>>>>> +
>>>>>>>>> +    /*
>>>>>>>>> +     * Name: "ip.dst"
>>>>>>>>> +     * Type: be128
>>>>>>>>> +     * Description: Sets the field MFF_IPV4_DST if eth.type == 0x800 (IPv4)
>>>>>>>>> +     *              or sets the field MFF_IPV6_DST if
>>>>>>>>> +     *              eth.type == 0x86dd (IPV6).
>>>>>>>>> +     */
>>>>>>>>> +    OVN_IP_DST,
>>>>>>>>> +
>>>>>>>>>       OVN_FIELD_N_IDS
>>>>>>>>>   };
>>>>>>>>>
>>>>>>>>> diff --git a/lib/actions.c b/lib/actions.c
>>>>>>>>> index 1e1bdeff24..e9c77d2a0a 100644
>>>>>>>>> --- a/lib/actions.c
>>>>>>>>> +++ b/lib/actions.c
>>>>>>>>> @@ -371,12 +371,35 @@ ovnact_next_free(struct ovnact_next *a OVS_UNUSED)
>>>>>>>>>   {
>>>>>>>>>   }
>>>>>>>>>
>>>>>>>>> +static bool
>>>>>>>>> +check_ovnfield_load(struct action_context *ctx, const struct expr_field *field)
>>>>>>>>> +{
>>>>>>>>> +    switch (field->symbol->ovn_field->id) {
>>>>>>>>> +    case OVN_ICMP4_FRAG_MTU:
>>>>>>>>> +    case OVN_ICMP6_FRAG_MTU:
>>>>>>>>> +        return true;
>>>>>>>>> +
>>>>>>>>> +    case OVN_IP_SRC:
>>>>>>>>> +    case OVN_IP_DST:
>>>>>>>>> +        lexer_error(ctx->lexer, "Can't load a value to ovn field (%s).",
>>>>>>>>> +                    field->symbol->name);
>>>>>>>>> +        return false;
>>>>>>>>> +
>>>>>>>>> +    case OVN_FIELD_N_IDS:
>>>>>>>>> +    default:
>>>>>>>>> +        OVS_NOT_REACHED();
>>>>>>>>> +    }
>>>>>>>>> +}
>>>>>>>>> +
>>>>>>>>>   static void
>>>>>>>>>   parse_LOAD(struct action_context *ctx, const struct expr_field *lhs)
>>>>>>>>>   {
>>>>>>>>>       size_t ofs = ctx->ovnacts->size;
>>>>>>>>>       struct ovnact_load *load;
>>>>>>>>>       if (lhs->symbol->ovn_field) {
>>>>>>>>> +        if (!check_ovnfield_load(ctx, lhs)) {
>>>>>>>>> +            return;
>>>>>>>>> +        }
>>>>>>>>>           load = ovnact_put_OVNFIELD_LOAD(ctx->ovnacts);
>>>>>>>>>       } else {
>>>>>>>>>           load = ovnact_put_LOAD(ctx->ovnacts);
>>>>>>>>> @@ -474,6 +497,46 @@ format_EXCHANGE(const struct ovnact_move *move, struct ds *s)
>>>>>>>>>       format_assignment(move, "<->", s);
>>>>>>>>>   }
>>>>>>>>>
>>>>>>>>> +static void
>>>>>>>>> +parse_ovnfield_exchange(struct action_context *ctx,
>>>>>>>>> +                        const struct expr_field *lhs,
>>>>>>>>> +                        const struct expr_field *rhs)
>>>>>>>>> +{
>>>>>>>>> +    if (!lhs->symbol->ovn_field || !rhs->symbol->ovn_field) {
>>>>>>>>> +        lexer_error(ctx->lexer,
>>>>>>>>> +                    "Can't exchange ovn field with non ovn field (%s <-> %s).",
>>>>>>>>> +                    lhs->symbol->name, rhs->symbol->name);
>>>>>>>>> +        return;
>>>>>>>>> +    }
>>>>>>>>> +
>>>>>>>>> +    if (lhs->symbol->ovn_field->id != OVN_IP_SRC &&
>>>>>>>>> +            lhs->symbol->ovn_field->id != OVN_IP_DST) {
>>>>>>>>> +        lexer_error(ctx->lexer,
>>>>>>>>> +                    "Can't exchange ovn field (%s) with ovn field (%s).",
>>>>>>>>> +                    lhs->symbol->name, rhs->symbol->name);
>>>>>>>>> +        return;
>>>>>>>>> +    }
>>>>>>>>> +
>>>>>>>>> +    if (rhs->symbol->ovn_field->id != OVN_IP_SRC &&
>>>>>>>>> +            rhs->symbol->ovn_field->id != OVN_IP_DST) {
>>>>>>>>> +        lexer_error(ctx->lexer,
>>>>>>>>> +                    "Can't exchange ovn field (%s) with ovn field (%s).",
>>>>>>>>> +                    lhs->symbol->name, rhs->symbol->name);
>>>>>>>>> +        return;
>>>>>>>>> +    }
>>>>>>>>> +
>>>>>>>>> +    if (lhs->symbol->ovn_field->id == rhs->symbol->ovn_field->id) {
>>>>>>>>> +        lexer_error(ctx->lexer,
>>>>>>>>> +                    "Can't exchange ovn field (%s) with ovn field (%s).",
>>>>>>>>> +                    lhs->symbol->name, rhs->symbol->name);
>>>>>>>>> +        return;
>>>>>>>>> +    }
>>>>>>>>> +
>>>>>>>>> +    struct ovnact_move *move = ovnact_put_OVNFIELD_EXCHANGE(ctx->ovnacts);
>>>>>>>>> +    move->lhs = *lhs;
>>>>>>>>> +    move->rhs = *rhs;
>>>>>>>>> +}
>>>>>>>>> +
>>>>>>>>>   static void
>>>>>>>>>   parse_assignment_action(struct action_context *ctx, bool exchange,
>>>>>>>>>                           const struct expr_field *lhs)
>>>>>>>>> @@ -483,6 +546,11 @@ parse_assignment_action(struct action_context *ctx, bool exchange,
>>>>>>>>>           return;
>>>>>>>>>       }
>>>>>>>>>
>>>>>>>>> +    if (exchange && (lhs->symbol->ovn_field || rhs.symbol->ovn_field)) {
>>>>>>>>> +        parse_ovnfield_exchange(ctx, lhs, &rhs);
>>>>>>>>> +        return;
>>>>>>>>> +    }
>>>>>>>>> +
>>>>>>>>>       const struct expr_symbol *ls = lhs->symbol;
>>>>>>>>>       const struct expr_symbol *rs = rhs.symbol;
>>>>>>>>>       if ((ls->width != 0) != (rs->width != 0)) {
>>>>>>>>> @@ -3128,6 +3196,8 @@ format_OVNFIELD_LOAD(const struct ovnact_load *load , struct ds *s)
>>>>>>>>>                         ntohs(load->imm.value.be16_int));
>>>>>>>>>           break;
>>>>>>>>>
>>>>>>>>> +    case OVN_IP_SRC:
>>>>>>>>> +    case OVN_IP_DST:
>>>>>>>>>       case OVN_FIELD_N_IDS:
>>>>>>>>>       default:
>>>>>>>>>           OVS_NOT_REACHED();
>>>>>>>>> @@ -3157,6 +3227,9 @@ encode_OVNFIELD_LOAD(const struct ovnact_load *load,
>>>>>>>>>           encode_finish_controller_op(oc_offset, ofpacts);
>>>>>>>>>           break;
>>>>>>>>>       }
>>>>>>>>> +
>>>>>>>>> +    case OVN_IP_SRC:
>>>>>>>>> +    case OVN_IP_DST:
>>>>>>>>>       case OVN_FIELD_N_IDS:
>>>>>>>>>       default:
>>>>>>>>>           OVS_NOT_REACHED();
>>>>>>>>> @@ -3451,6 +3524,51 @@ ovnact_fwd_group_free(struct ovnact_fwd_group *fwd_group)
>>>>>>>>>       free(fwd_group->child_ports);
>>>>>>>>>   }
>>>>>>>>>
>>>>>>>>> +static void
>>>>>>>>> +format_OVNFIELD_EXCHANGE(const struct ovnact_move *move , struct ds *s)
>>>>>>>>> +{
>>>>>>>>> +    const struct ovn_field *lhs = ovn_field_from_name(move->lhs.symbol->name);
>>>>>>>>> +    const struct ovn_field *rhs = ovn_field_from_name(move->rhs.symbol->name);
>>>>>>>>> +    switch (lhs->id) {
>>>>>>>>> +    case OVN_IP_SRC:
>>>>>>>>> +    case OVN_IP_DST:
>>>>>>>>> +        break;
>>>>>>>>> +
>>>>>>>>> +    case OVN_ICMP4_FRAG_MTU:
>>>>>>>>> +    case OVN_ICMP6_FRAG_MTU:
>>>>>>>>> +    case OVN_FIELD_N_IDS:
>>>>>>>>> +    default:
>>>>>>>>> +        OVS_NOT_REACHED();
>>>>>>>>> +    }
>>>>>>>>
>>>>>>>> Nit: I would use the shorter:
>>>>>>>> ovs_asssert(lhs->id == OVN_IP_SRC || lhs->id == OVN_IP_DST);
>>>>>>>
>>>>>>> You mean to drop the switch right ? If so, Ack.
>>>>>>>
>>>>>>
>>>>>> Right, I meant ovs_assert instead of switch.
>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>>> +
>>>>>>>>> +    switch (rhs->id) {
>>>>>>>>> +    case OVN_IP_SRC:
>>>>>>>>> +    case OVN_IP_DST:
>>>>>>>>> +        break;
>>>>>>>>> +
>>>>>>>>> +    case OVN_ICMP4_FRAG_MTU:
>>>>>>>>> +    case OVN_ICMP6_FRAG_MTU:
>>>>>>>>> +    case OVN_FIELD_N_IDS:
>>>>>>>>> +    default:
>>>>>>>>> +        OVS_NOT_REACHED();
>>>>>>>>> +    }
>>>>>>>>
>>>>>>>> Nit: I would use the shorter:
>>>>>>>> ovs_asssert(rhs->id == OVN_IP_SRC || rhs->id == OVN_IP_DST);
>>>>>>>>
>>>>>>>>> +
>>>>>>>>> +    ds_put_format(s, "%s <-> %s;", lhs->name, rhs->name);
>>>>>>>>> +}
>>>>>>>>> +
>>>>>>>>> +static void
>>>>>>>>> +encode_OVNFIELD_EXCHANGE(const struct ovnact_move *move OVS_UNUSED,
>>>>>>>>> +                         const struct ovnact_encode_params *ep OVS_UNUSED,
>>>>>>>>> +                         struct ofpbuf *ofpacts OVS_UNUSED)
>>>>>>>>> +{
>>>>>>>>> +    /* Right now we only support exchanging the IPs in
>>>>>>>>> +     * OVN fields (ip.src <-> ip.dst). */
>>>>>>>>> +    size_t oc_offset =
>>>>>>>>> +        encode_start_controller_op(ACTION_OPCODE_SWAP_SRC_DST_IP,
>>>>>>>>> +                                   true, NX_CTLR_NO_METER, ofpacts);
>>>>>>>>> +    encode_finish_controller_op(oc_offset, ofpacts);
>>>>>>>>
>>>>>>>> I think this means that all packets matching a flow with action "reject { ...
>>>>>>>> ip.src <-> ip.dst ... }" will generate two packet-ins, right? One for the
>>>>>>>> reject action, one for the ovnfield-exchange action.
>>>>>>>>
>>>>>>>> Is that a concern wrt. performance?
>>>>>>>
>>>>>>> Yes. It would have 2 packet-ins. Just like how we handle - icmp4 {...
>>>>>>> icmp4.frag_mtu = 1500; ...};
>>>>>>>
>>>>>>> If performance is a concern, we could just drop ... ip.src <-> ip.dst
>>>>>>> in reject and let reject action
>>>>>>> swap the ip src with ip destination. I thought about that and my take
>>>>>>> is that since reject { } results in
>>>>>>> TCP RST or ICMP unreachable packet, it should be fine. I see these
>>>>>>> packets as more of control packets.
>>>>>>>
>>>>>>> I think it should be ok. Let me know what you think.
>>>>>>>
>>>>>>
>>>>>> I think I like the approach of "reject" action implicitly swapping IPs best.
>>>>>> In the end it's not like we could implement reject withough swapping IP dst
>>>>>> with IP src so why not do it as part of the reject action.
>>>>>>
>>>>>
>>>>> Agree. reject action is expected to be used to send the generated tcp
>>>>> rst/icmp unreachable
>>>>> packet back to the sender.
>>>>>
>>>>> I'm ok to change the reject action to just swap the IPs internally if
>>>>> everyone is fine.
>>>>>
>>>>> @Mark Michelson  @Han Zhou  Do you have any comments here ?
>>>>>
>>>>> Option 1 - reject { ...}    -> The reject action handling in pinctrl.c
>>>>> will swap the ip source and destination
>>>>>
>>>>> Option 2: reject {... ip.src <-> ip.dst ...} which is the proposed
>>>>> approach in this patch series. This results in
>>>>> 2 packet-ins.
>>>>>
>>>>> I personally prefer (2) since in OVN we normally tell what inner
>>>>> actions to apply for many OVN actions.
>>>>> But I have no strong preference and I'm fine changing to (1).
>>>>>
>>>>> If we chose option (1), we could add a comment inside the action like
>>>>> - reject { /* ip.src <-> ip.dst is done implicitly*/,  eth.src <->
>>>>> eth.dst; output ; }
>>>>>
>>>>
>>>> Then, why not swap ETH addresses implicitly too?
>>>
>>> As I mentioned above, I'd prefer if ovn-northd says what actions to
>>> apply for the reject
>>> packet. Just like for icmp4 or arp actions, ovn-northd says what
>>> actions to apply for the
>>> transformed packet from the source packet.
>>>
>>
>> I was thinking that if we go this way when we build the packet in
>> ovn-controller it might look weird to a reader of the pinctrl code to see
>> something like:
>>
>> /* We only swap IPs because ETH addresses are swapped in OVS. */
>> pinctrl_compose_ipv4(&packet, ip_flow->dl_src, ip_flow->dl_dst,
>>                       ip_flow->nw_dst, ip_flow->nw_src, ...)
> 
> Right. I agree. It makes sense to swap both eth and ip if we go this
> way. Sorry for the confusion.
> 
> Thanks
> Numan

I've been reading through this, thinking about it, and have changed my 
mind on the matter probably 3 or 4 times while trying to write a response.

In short, I think that the savings in flow creation introduced by this 
patch series are brilliant, but I'm hesitant about the second packet-in. 
I have a feeling this could be more costly than the frag_mtu examples 
that Numan pointed out earlier in the thread. I think that the savings 
in flow creation should make us consider forging new ground with regards 
to what happens implicitly during a controller action. I think we have 
the facilities to get the point across to users what is going on even if 
there are no explicit exchange actions in the generated logical flow or 
OF flow.

I thought through this to try to figure out if there's a different way 
forward that both allows us to reduce the number of flows and still be 
explicit with the actions being performed. Unfortunately, the only ways 
I could think of required either parsing ACL matches in ovn-northd or 
generating just as many flows as before.

In conclusion, I'm fine with the reject action implicitly swapping 
values, but it needs to be well documented.

> 
>>
>> Regards,
>> Dumitru
>>
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