Basic implementation of TCP over XDP for Knot server

including connection handling for kxdpgun in TCP mode.

The implementation is not perfect!! But the interface with other Knot parts is stable.

src/libknot/xdp/tcp.c

@@ -170,7 +170,15 @@ dynarray_define(tcp_relay, knot_tcp_relay_t, DYNARRAY_VISIBILITY_PUBLIC)
 
 static bool check_seq_ack(const knot_xdp_msg_t *msg, const knot_tcp_conn_t *conn)
 {
-	return (conn != NULL && conn->seqno == msg->seqno && conn->ackno == msg->ackno);
+	if (conn == NULL || conn->seqno != msg->seqno) {
+		return false;
+	}
+
+	if (conn->acked <= conn->ackno) { // ackno does not wrap around uint32
+		return (msg->ackno >= conn->acked && msg->ackno <= conn->ackno);
+	} else { // this is more tricky
+		return (msg->ackno >= conn->acked || msg->ackno <= conn->ackno);
+	}
 }
 
 _public_
@@ -217,6 +225,9 @@ int knot_xdp_tcp_relay(knot_xdp_socket_t *socket, knot_xdp_msg_t msgs[], uint32_
 			memcpy((*conn)->last_eth_rem, msg->eth_from, sizeof((*conn)->last_eth_rem));
 			memcpy((*conn)->last_eth_loc, msg->eth_to, sizeof((*conn)->last_eth_loc));
 			(*conn)->last_active = get_timestamp();
+			if (msg->flags & KNOT_XDP_MSG_ACK) {
+				(*conn)->acked = msg->ackno;
+			}
 		}
 
 		knot_tcp_relay_t relay = { .msg = msg, .conn = *conn };
@@ -234,7 +245,8 @@ int knot_xdp_tcp_relay(knot_xdp_socket_t *socket, knot_xdp_msg_t msgs[], uint32_
 				relay.conn->state = XDP_TCP_ESTABLISHING;
 				relay.conn->seqno++;
 				if (!synack) {
-					relay.conn->ackno = acks[n_acks - 1].seqno + 1;
+					relay.conn->acked = acks[n_acks - 1].seqno;
+					relay.conn->ackno = relay.conn->acked + 1;
 				}
 			} else {
 				resp_ack(msg, KNOT_XDP_MSG_RST); // TODO consider resetting the OLD conn and accepting new one