tcp, tcp_splice: Helpers for getting sockets from the pools

We maintain pools of ready-to-connect sockets in both the original and
(for pasta) guest namespace to reduce latency when starting new TCP
connections.  If we exhaust those pools we have to take a higher
latency path to get a new socket.

Currently we open-code that fallback in the places we need it.  To improve
clarity encapsulate that into helper functions.  While we're at it, give
those helpers clearer error reporting.

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

tcp.c

@@ -1792,7 +1792,7 @@ int tcp_conn_pool_sock(int pool[])
  *
  * Return: socket number on success, negative code if socket creation failed
  */
-int tcp_conn_new_sock(const struct ctx *c, sa_family_t af)
+static int tcp_conn_new_sock(const struct ctx *c, sa_family_t af)
 {
 	int s;
 
@@ -1811,6 +1811,32 @@ int tcp_conn_new_sock(const struct ctx *c, sa_family_t af)
 	return s;
 }
 
+/**
+ * tcp_conn_sock() - Obtain a connectable socket in the host/init namespace
+ * @c:		Execution context
+ * @af:		Address family (AF_INET or AF_INET6)
+ *
+ * Return: Socket fd on success, -errno on failure
+ */
+int tcp_conn_sock(const struct ctx *c, sa_family_t af)
+{
+	int *pool = af == AF_INET6 ? init_sock_pool6 : init_sock_pool4;
+	int s;
+
+	if ((s = tcp_conn_pool_sock(pool)) >= 0)
+		return s;
+
+	/* If the pool is empty we just open a new one without refilling the
+	 * pool to keep latency down.
+	 */
+	if ((s = tcp_conn_new_sock(c, af)) >= 0)
+		return s;
+
+	err("TCP: Unable to open socket for new connection: %s",
+	    strerror(-s));
+	return -1;
+}
+
 /**
  * tcp_conn_tap_mss() - Get MSS value advertised by tap/guest
  * @conn:	Connection pointer
@@ -1909,7 +1935,6 @@ static void tcp_conn_from_tap(struct ctx *c, sa_family_t af,
 			      const struct tcphdr *th, const char *opts,
 			      size_t optlen, const struct timespec *now)
 {
-	int *pool = af == AF_INET6 ? init_sock_pool6 : init_sock_pool4;
 	struct sockaddr_in addr4 = {
 		.sin_family = AF_INET,
 		.sin_port = th->dest,
@@ -1931,8 +1956,7 @@ static void tcp_conn_from_tap(struct ctx *c, sa_family_t af,
 	if (!(flow = flow_alloc()))
 		return;
 
-	if ((s = tcp_conn_pool_sock(pool)) < 0)
+	if ((s = tcp_conn_sock(c, af)) < 0)
-		if ((s = tcp_conn_new_sock(c, af)) < 0)
 		goto cancel;
 
 	if (!c->no_map_gw) {

tcp_conn.h

@@ -159,7 +159,7 @@ bool tcp_flow_defer(union flow *flow);
 bool tcp_splice_flow_defer(union flow *flow);
 void tcp_splice_timer(const struct ctx *c, union flow *flow);
 int tcp_conn_pool_sock(int pool[]);
-int tcp_conn_new_sock(const struct ctx *c, sa_family_t af);
+int tcp_conn_sock(const struct ctx *c, sa_family_t af);
 int tcp_sock_refill_pool(const struct ctx *c, int pool[], sa_family_t af);
 void tcp_splice_refill(const struct ctx *c);
 

tcp_splice.c

@@ -376,6 +376,34 @@ static int tcp_splice_connect(const struct ctx *c, struct tcp_splice_conn *conn,
 	return 0;
 }
 
+/**
+ * tcp_conn_sock_ns() - Obtain a connectable socket in the namespace
+ * @c:		Execution context
+ * @af:		Address family (AF_INET or AF_INET6)
+ *
+ * Return: Socket fd in the namespace on success, -errno on failure
+ */
+static int tcp_conn_sock_ns(const struct ctx *c, sa_family_t af)
+{
+	int *p = af == AF_INET6 ? ns_sock_pool6 : ns_sock_pool4;
+	int s;
+
+	if ((s = tcp_conn_pool_sock(p)) >= 0)
+		return s;
+
+	/* If the pool is empty we have to incur the latency of entering the ns.
+	 * Therefore, we might as well refill the whole pool while we're at it.
+	 * This differs from tcp_conn_sock().
+	 */
+	NS_CALL(tcp_sock_refill_ns, c);
+
+	if ((s = tcp_conn_pool_sock(p)) >= 0)
+		return s;
+
+	err("TCP: No available ns sockets for new connection");
+	return -1;
+}
+
 /**
  * tcp_splice_new() - Handle new spliced connection
  * @c:		Execution context
@@ -388,38 +416,19 @@ static int tcp_splice_connect(const struct ctx *c, struct tcp_splice_conn *conn,
 static int tcp_splice_new(const struct ctx *c, struct tcp_splice_conn *conn,
 			  in_port_t port, uint8_t pif)
 {
+	sa_family_t af = CONN_V6(conn) ? AF_INET6 : AF_INET;
 	int s = -1;
 
-	/* If the pool is empty we take slightly different approaches
-	 * for init or ns sockets.  For init sockets we just open a
-	 * new one without refilling the pool to keep latency down.
-	 * For ns sockets, we're going to incur the latency of
-	 * entering the ns anyway, so we might as well refill the
-	 * pool.
-	 */
 	if (pif == PIF_SPLICE) {
-		int *p = CONN_V6(conn) ? init_sock_pool6 : init_sock_pool4;
+		s = tcp_conn_sock(c, af);
-		sa_family_t af = CONN_V6(conn) ? AF_INET6 : AF_INET;
-
-		s = tcp_conn_pool_sock(p);
-		if (s < 0)
-			s = tcp_conn_new_sock(c, af);
 	} else {
-		int *p = CONN_V6(conn) ? ns_sock_pool6 : ns_sock_pool4;
-
 		ASSERT(pif == PIF_HOST);
 
-		/* If pool is empty, refill it first */
+		s = tcp_conn_sock_ns(c, af);
-		if (p[TCP_SOCK_POOL_SIZE-1] < 0)
-			NS_CALL(tcp_sock_refill_ns, c);
-
-		s = tcp_conn_pool_sock(p);
 	}
 
-	if (s < 0) {
+	if (s < 0)
-		warn("Couldn't open connectable socket for splice (%d)", s);
 		return s;
-	}
 
 	return tcp_splice_connect(c, conn, s, port);
 }