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>

1 files changed, 29 insertions, 5 deletions

diff --git a/tcp.c b/tcp.c
index 044c57f..40a79b4 100644
--- a/tcp.c
+++ b/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;
 
@@ -1812,6 +1812,32 @@ int tcp_conn_new_sock(const struct ctx *c, sa_family_t af)
 }
 
 /**
+ * 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
  * @opts:	Pointer to start of TCP options
@@ -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,
@@ -1931,9 +1956,8 @@ 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_new_sock(c, af)) < 0)
-			goto cancel;
+	if ((s = tcp_conn_sock(c, af)) < 0)
+		goto cancel;
 
 	if (!c->no_map_gw) {
 		if (af == AF_INET && IN4_ARE_ADDR_EQUAL(daddr, &c->ip4.gw))