common: add: a PACKET_TOO_BIG packet drop reason

WHATSNEW

@@ -402,6 +402,12 @@ Notable backward incompatible changes are the following:
 
    A TCP algorithm implemented outside INET needs a simple module type that extends TcpAlgorithm, and Define_Module() in place of Register_Class(); without the type, the connection stops with an error. Its initialize() is now initializeAlgorithm(), and the cancelEvent() helper of TcpAlgorithmBase is now cancelTimer(). See the migration guide.
 
+50. A packet drop reason for datagrams that are too big
+
+   PacketDropReason gains PACKET_TOO_BIG, for a datagram that is larger than the MTU of the next link and may not be fragmented, with the result filter packetDropReasonIsPacketTooBig. Ipv4 reports it for a datagram with the Don't Fragment flag set, and Mpls for a labeled datagram with that flag; both reported OTHER_PACKET_DROP before. Ipv4 records the new statistic packetDropPacketTooBig.
+
+   Ipv4's packetDropUndefined no longer counts these drops, so its results change in simulations where routers drop such datagrams, for example examples/inet/tcp_pmtud and examples/quic/dplpmtud. A PacketDropVisualizer label that shows the reason now shows 16 or PACKET_TOO_BIG instead of -1 or OTHER_PACKET_DROP.
+
 Notable backward compatible changes are the following:
 
 1. IEEE 802.11 per-station rate statistics

src/inet/common/ResultFilters.cc

@@ -1128,6 +1128,7 @@ Register_PacketDropReason_ResultFilter("packetDropReasonIsCongestion", Congestio
 Register_PacketDropReason_ResultFilter("packetDropReasonIsNoProtocolFound", NoProtocolFoundPacketDropReasonFilter, NO_PROTOCOL_FOUND);
 Register_PacketDropReason_ResultFilter("packetDropReasonIsNoPortFound", NoPortFoundPacketDropReasonFilter, NO_PORT_FOUND);
 Register_PacketDropReason_ResultFilter("packetDropReasonIsDuplicateDetected", DuplicateDetectedPacketDropReasonFilter, DUPLICATE_DETECTED);
+Register_PacketDropReason_ResultFilter("packetDropReasonIsPacketTooBig", PacketTooBigPacketDropReasonFilter, PACKET_TOO_BIG);
 Register_PacketDropReason_ResultFilter("packetDropReasonIsOther", OtherPacketDropReasonFilter, OTHER_PACKET_DROP);
 
 Register_ResultFilter("minimumSnir", MinimumSnirFromSnirIndFilter);

src/inet/common/Simsignals.msg

@@ -26,6 +26,7 @@ enum PacketDropReason
     NO_PROTOCOL_FOUND         = 13;
     NO_PORT_FOUND             = 14;
     DUPLICATE_DETECTED        = 15;
+    PACKET_TOO_BIG            = 16;
     OTHER_PACKET_DROP         = -1;
 }
 

src/inet/networklayer/ipv4/Ipv4.cc

@@ -980,6 +980,7 @@ void Ipv4::fragmentAndSend(Packet *packet)
     // if "don't fragment" bit is set, throw datagram away and send ICMP error message
     if (ipv4Header->getDontFragment()) {
         PacketDropDetails details;
+        details.setReason(PACKET_TOO_BIG);
         emit(packetDroppedSignal, packet, &details);
         EV_WARN << "datagram larger than MTU and don't fragment bit set, sending ICMP_DESTINATION_UNREACHABLE\n";
         icmp->sendPtbMessage(packet, mtu);

src/inet/networklayer/ipv4/Ipv4.ned

@@ -120,6 +120,7 @@ simple Ipv4 extends SimpleModule like IIpv4
         @statistic[packetDropLifetimeExpired](title="packet drop: lifetime expired"; source=packetDropReasonIsLifetimeExpired(packetDropped); record=count,sum(packetBytes),vector(packetBytes); interpolationmode=none);
         @statistic[packetDropNoInterfaceFound](title="packet drop: no interface found"; source=packetDropReasonIsNoInterfaceFound(packetDropped); record=count,sum(packetBytes),vector(packetBytes); interpolationmode=none);
         @statistic[packetDropNoRouteFound](title="packet drop: no route found"; source=packetDropReasonIsNoRouteFound(packetDropped); record=count,sum(packetBytes),vector(packetBytes); interpolationmode=none);
+        @statistic[packetDropPacketTooBig](title="packet drop: packet too big"; source=packetDropReasonIsPacketTooBig(packetDropped); record=count,sum(packetBytes),vector(packetBytes); interpolationmode=none);
         @statistic[packetDropUndefined](title="packet drop: undefined"; source=packetDropReasonIsUndefined(packetDropped); record=count,sum(packetBytes),vector(packetBytes); interpolationmode=none);
     gates:
         input transportIn @labels(Ipv4ControlInfo/down,TcpHeader,UdpHeader,SctpHeader);

src/inet/networklayer/mpls/Mpls.cc

@@ -409,7 +409,7 @@ void Mpls::processTooBigDatagram(Packet *packet, const NetworkInterface *network
         // Destination Unreachable message whose Next-Hop MTU leaves room for the label stack
         EV_WARN << "discarding a too-big datagram with the DF bit, sending ICMP_DESTINATION_UNREACHABLE" << endl;
         PacketDropDetails details;
-        details.setReason(OTHER_PACKET_DROP);
+        details.setReason(PACKET_TOO_BIG);
         emit(packetDroppedSignal, packet, &details);
         if (icmp != nullptr)
             icmp->sendPtbMessage(packet, maxDatagramLength);

tests/module/IPv4_dont_fragment_drop_reason.test

@@ -0,0 +1,66 @@
+%description:
+Tests that IPv4 reports a datagram that is larger than the MTU of the next link
+and has the Don't Fragment (DF) flag set with the packet drop reason
+PACKET_TOO_BIG, so that the packetDropPacketTooBig statistic of Ipv4 counts it
+and packetDropUndefined does not.
+
+hostA sends three UDP datagrams with a 1000-byte payload and DF set to hostB. The router's
+link toward hostB has an MTU of 576 bytes, so the router drops all three and
+sends ICMP Destination Unreachable (Fragmentation Needed) to hostA.
+
+%#--------------------------------------------------------------------------------------------------------------
+%file: test.ned
+import inet.networklayer.configurator.ipv4.Ipv4NetworkConfigurator;
+import inet.node.inet.Router;
+import inet.node.inet.StandardHost;
+import ned.DatarateChannel;
+
+network DontFragmentNetwork
+{
+    types:
+        channel ethline extends DatarateChannel
+        {
+            delay = 0.1us;
+            datarate = 100Mbps;
+        }
+    submodules:
+        configurator: Ipv4NetworkConfigurator;
+        hostA: StandardHost;
+        router: Router;
+        hostB: StandardHost;
+    connections:
+        hostA.ethg++ <--> ethline <--> router.ethg++;
+        router.ethg++ <--> ethline <--> hostB.ethg++;
+}
+%#--------------------------------------------------------------------------------------------------------------
+%inifile: omnetpp.ini
+[General]
+ned-path = ../../../../src
+network = DontFragmentNetwork
+sim-time-limit = 5s
+record-vector-results = false
+cmdenv-express-mode = true
+
+**.router.eth[1].mac.mtu = 576B
+
+**.hostA.numApps = 1
+**.hostA.app[0].typename = "UdpBasicApp"
+**.hostA.app[0].destAddresses = "hostB"
+**.hostA.app[0].destPort = 1000
+**.hostA.app[0].messageLength = 1000B
+**.hostA.app[0].dontFragment = true
+**.hostA.app[0].startTime = 1s
+**.hostA.app[0].sendInterval = 1s
+**.hostA.app[0].stopTime = 3.5s
+%#--------------------------------------------------------------------------------------------------------------
+%postrun-command: gawk '$1 == "scalar" && $2 == "DontFragmentNetwork.router.ipv4.ip" && ($3 == "packetDropPacketTooBig:count" || $3 == "packetDropUndefined:count") { print $3, $4 }' results/*.sca > drops.out
+%contains: drops.out
+packetDropPacketTooBig:count 3
+%#--------------------------------------------------------------------------------------------------------------
+%contains: drops.out
+packetDropUndefined:count 0
+%#--------------------------------------------------------------------------------------------------------------
+%postrun-command: grep "undisposed object:" test.out > test_undisposed.out || true
+%not-contains: test_undisposed.out
+undisposed object: (
+%#--------------------------------------------------------------------------------------------------------------