Added the ability to match fields in ARP packets.

Specifically implemented the ability to match on
the lower 8 bits of the ARP opcode as nw_proto, and
the ARP source and dest protocol addresses as nw_src
and nw_dst respectively.

lib/flow.c

@@ -44,6 +44,16 @@
 #include "vlog.h"
 #define THIS_MODULE VLM_flow
 
+static struct arp_header *
+pull_arp(struct ofpbuf *packet)
+{
+    if (packet->size >= ARP_ETH_HEADER_LEN) {
+        struct arp_eth_header *arp = packet->data;
+        return ofpbuf_pull(packet, ARP_ETH_HEADER_LEN);
+    }
+    return NULL;
+}
+
 static struct ip_header *
 pull_ip(struct ofpbuf *packet)
 {
@@ -198,6 +208,13 @@ flow_extract(struct ofpbuf *packet, uint16_t in_port, struct flow *flow)
                     retval = 1;
                 }
             }
+        } else if (flow->dl_type == htons(ETH_TYPE_ARP)) {
+            const struct arp_eth_header *arp = pull_arp(&b);
+            if (arp) {
+                flow->nw_src = arp->ar_spa;
+                flow->nw_dst = arp->ar_tpa;
+                flow->nw_proto = ntohs(arp->ar_op) && 0xff;
+            }
         }
     }
     return retval;