udp: Simplify updates to UDP flow timestamp

Since UDP has no built in knowledge of connections, the only way we
know when we're done with a UDP flow is a timeout with no activity.
To keep track of this struct udp_flow includes a timestamp to record
the last time we saw traffic on the flow.

For data from listening sockets and from tap, this is done implicitly via
udp_flow_from_{sock,tap}() but for reply sockets it's done explicitly.
However, that logic is duplicated between the vhost-user and "buf" paths.
Make it common in udp_reply_sock_handler() instead.

Technically this is a behavioural change: previously if we got an EPOLLIN
event, but there wasn't actually any data we wouldn't update the timestamp,
now we will.  This should be harmless: if there's an EPOLLIN we expect
there to be data, and even if there isn't the worst we can do is mildly
delay the cleanup of a stale flow.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

udp.c

@@ -758,27 +758,21 @@ void udp_listen_sock_handler(const struct ctx *c,
  * @c:		Execution context
  * @s:		Socket to read data from
  * @tosidx:	Flow & side to forward data from @s to
- * @now:	Current timestamp
  *
  * Return: true on success, false if can't forward from socket to flow's pif
  *
  * #syscalls recvmmsg
  */
 static bool udp_buf_reply_sock_data(const struct ctx *c,
-				    int s, flow_sidx_t tosidx,
-				    const struct timespec *now)
+				    int s, flow_sidx_t tosidx)
 {
 	const struct flowside *toside = flowside_at_sidx(tosidx);
-	struct udp_flow *uflow = udp_at_sidx(tosidx);
 	uint8_t topif = pif_at_sidx(tosidx);
 	int n, i;
 
 	if ((n = udp_sock_recv(c, s, udp_mh_recv)) <= 0)
 		return true;
 
-	flow_trace(uflow, "Received %d datagrams on reply socket", n);
-	uflow->ts = now->tv_sec;
-
 	for (i = 0; i < n; i++) {
 		if (pif_is_socket(topif))
 			udp_splice_prepare(udp_mh_recv, i);
@@ -825,10 +819,13 @@ void udp_reply_sock_handler(const struct ctx *c, union epoll_ref ref,
 		int s = ref.fd;
 		bool ret;
 
+		flow_trace(uflow, "Received data on reply socket");
+		uflow->ts = now->tv_sec;
+
 		if (c->mode == MODE_VU)
-			ret = udp_vu_reply_sock_data(c, s, tosidx, now);
+			ret = udp_vu_reply_sock_data(c, s, tosidx);
 		else
-			ret = udp_buf_reply_sock_data(c, s, tosidx, now);
+			ret = udp_buf_reply_sock_data(c, s, tosidx);
 
 		if (!ret) {
 			flow_err(uflow, "Unable to forward UDP");

udp_vu.c

@@ -275,22 +275,17 @@ void udp_vu_listen_sock_data(const struct ctx *c, union epoll_ref ref,
  * @c:		Execution context
  * @s:		Socket to read data from
  * @tosidx:	Flow & side to forward data from @s to
- * @now:	Current timestamp
  *
  * Return: true on success, false if can't forward from socket to flow's pif
  */
-bool udp_vu_reply_sock_data(const struct ctx *c, int s, flow_sidx_t tosidx,
-			    const struct timespec *now)
+bool udp_vu_reply_sock_data(const struct ctx *c, int s, flow_sidx_t tosidx)
 {
 	const struct flowside *toside = flowside_at_sidx(tosidx);
 	bool v6 = !(inany_v4(&toside->eaddr) && inany_v4(&toside->oaddr));
-	struct udp_flow *uflow = udp_at_sidx(tosidx);
 	struct vu_dev *vdev = c->vdev;
 	struct vu_virtq *vq = &vdev->vq[VHOST_USER_RX_QUEUE];
 	int i;
 
-	ASSERT(uflow);
-
 	if (pif_at_sidx(tosidx) != PIF_TAP)
 		return false;
 
@@ -301,8 +296,6 @@ bool udp_vu_reply_sock_data(const struct ctx *c, int s, flow_sidx_t tosidx,
 		iov_used = udp_vu_sock_recv(c, s, v6, &dlen);
 		if (iov_used <= 0)
 			break;
-		flow_trace(uflow, "Received 1 datagram on reply socket");
-		uflow->ts = now->tv_sec;
 
 		udp_vu_prepare(c, toside, dlen);
 		if (*c->pcap) {

udp_vu.h

@@ -8,7 +8,6 @@
 
 void udp_vu_listen_sock_data(const struct ctx *c, union epoll_ref ref,
 			     const struct timespec *now);
-bool udp_vu_reply_sock_data(const struct ctx *c, int s, flow_sidx_t tosidx,
-			    const struct timespec *now);
+bool udp_vu_reply_sock_data(const struct ctx *c, int s, flow_sidx_t tosidx);
 
 #endif /* UDP_VU_H */