net: flow_dissector: Parse PTP L2 packet header

Add support for parsing PTP L2 packet header. Such packet consists
of an L2 header (with ethertype of ETH_P_1588), PTP header, body
and an optional suffix.
Signed-off-by: Eran Ben Elisha <eranbe@nvidia.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/core/flow_dissector.c

@@ -23,6 +23,7 @@
 #include <linux/if_ether.h>
 #include <linux/mpls.h>
 #include <linux/tcp.h>
+#include <linux/ptp_classify.h>
 #include <net/flow_dissector.h>
 #include <scsi/fc/fc_fcoe.h>
 #include <uapi/linux/batadv_packet.h>
@@ -1251,6 +1252,21 @@ bool __skb_flow_dissect(const struct net *net,
 						  &proto, &nhoff, hlen, flags);
 		break;
 
+	case htons(ETH_P_1588): {
+		struct ptp_header *hdr, _hdr;
+
+		hdr = __skb_header_pointer(skb, nhoff, sizeof(_hdr), data,
+					   hlen, &_hdr);
+		if (!hdr) {
+			fdret = FLOW_DISSECT_RET_OUT_BAD;
+			break;
+		}
+
+		nhoff += ntohs(hdr->message_length);
+		fdret = FLOW_DISSECT_RET_OUT_GOOD;
+		break;
+	}
+
 	default:
 		fdret = FLOW_DISSECT_RET_OUT_BAD;
 		break;