ip: Fragmentation fixes

Type: fix

if the packet is about to be fragmented, then don't call any of the
actions that expect the rewrite to have been written.
1) don't double count packets thru the adjacency (original & fragments)
2) don't double decrement the TTL for fragments
3) return to ip4-midchain post ip-frag if that's where we started.
4) only run midchain/mcast fixups if not fragmenting (if no errors)

Change-Id: Ib2866787a42713ee5871b87b597d8f74b901044b
Signed-off-by: Neale Ranns <nranns@cisco.com>

test/test_ip4.py

@@ -21,6 +21,7 @@ from vpp_ip_route import VppIpRoute, VppRoutePath, VppIpMRoute, \
 from vpp_ip import VppIpAddress
 from vpp_sub_interface import VppSubInterface, VppDot1QSubint, VppDot1ADSubint
 from vpp_papi import VppEnum
+from vpp_neighbor import VppNeighbor
 
 NUM_PKTS = 67
 
@@ -1918,12 +1919,19 @@ class TestIPv4Frag(VppTestCase):
     def test_frag_large_packets(self):
         """ Fragmentation of large packets """
 
+        self.vapi.cli("adjacency counters enable")
+
         p = (Ether(dst=self.src_if.local_mac, src=self.src_if.remote_mac) /
              IP(src=self.src_if.remote_ip4, dst=self.dst_if.remote_ip4) /
              UDP(sport=1234, dport=5678) / Raw())
         self.extend_packet(p, 6000, "abcde")
         saved_payload = p[Raw].load
 
+        nbr = VppNeighbor(self,
+                          self.dst_if.sw_if_index,
+                          self.dst_if.remote_mac,
+                          self.dst_if.remote_ip4).add_vpp_config()
+
         # Force fragmentation by setting MTU of output interface
         # lower than packet size
         self.vapi.sw_interface_set_mtu(self.dst_if.sw_if_index,
@@ -1937,6 +1945,9 @@ class TestIPv4Frag(VppTestCase):
         # cannot be larger then VPP buffer size (which is 2048)
         packets = self.dst_if.get_capture(3)
 
+        # we should show 3 packets thru the neighbor
+        self.assertEqual(3, nbr.get_stats()['packets'])
+
         # Assume VPP sends the fragments in order
         payload = b''
         for p in packets: