[PATCH] tcp: Buffer sizes are *not* inherited on accept()/accept4()

[Stefano Brivio <sbrivio@redhat.com>]

...so it's pointless to set SO_RCVBUF and SO_SNDBUF on listening
sockets.

Call tcp_sock_set_bufsize() after accept4(), for inbound sockets.

As we didn't have large buffer sizes set for inbound sockets for
a long time (they are set explicitly only if the maximum size is
big enough, more than than the ~200 KiB default), I ran some more
throughput tests for this one, and I see slightly better numbers
(say, 17 gbps instead of 15 gbps guest to host without vhost-user).

Fixes: 904b86ade7db ("tcp: Rework window handling, timers, add SO_RCVLOWAT and pools for sockets/pipes")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
 tcp.c | 11 ++++-------
 1 file changed, 4 insertions(+), 7 deletions(-)

diff --git a/tcp.c b/tcp.c
index 3b3193a..a012b81 100644
--- a/tcp.c
+++ b/tcp.c
@@ -2057,6 +2057,8 @@ void tcp_listen_handler(const struct ctx *c, union epoll_ref ref,
 	if (s < 0)
 		goto cancel;
 
+	tcp_sock_set_bufsize(c, s);
+
 	/* FIXME: When listening port has a specific bound address, record that
 	 * as our address
 	 */
@@ -2260,7 +2262,6 @@ static int tcp_sock_init_one(const struct ctx *c, const union inany_addr *addr,
 	if (s < 0)
 		return s;
 
-	tcp_sock_set_bufsize(c, s);
 	return s;
 }
 
@@ -2317,9 +2318,7 @@ static void tcp_ns_sock_init4(const struct ctx *c, in_port_t port)
 
 	s = pif_sock_l4(c, EPOLL_TYPE_TCP_LISTEN, PIF_SPLICE, &inany_loopback4,
 			NULL, port, tref.u32);
-	if (s >= 0)
-		tcp_sock_set_bufsize(c, s);
-	else
+	if (s < 0)
 		s = -1;
 
 	if (c->tcp.fwd_out.mode == FWD_AUTO)
@@ -2343,9 +2342,7 @@ static void tcp_ns_sock_init6(const struct ctx *c, in_port_t port)
 
 	s = pif_sock_l4(c, EPOLL_TYPE_TCP_LISTEN, PIF_SPLICE, &inany_loopback6,
 			NULL, port, tref.u32);
-	if (s >= 0)
-		tcp_sock_set_bufsize(c, s);
-	else
+	if (s < 0)
 		s = -1;
 
 	if (c->tcp.fwd_out.mode == FWD_AUTO)
-- 
@@ -2057,6 +2057,8 @@ void tcp_listen_handler(const struct ctx *c, union epoll_ref ref,
 	if (s < 0)
 		goto cancel;
 
+	tcp_sock_set_bufsize(c, s);
+
 	/* FIXME: When listening port has a specific bound address, record that
 	 * as our address
 	 */
@@ -2260,7 +2262,6 @@ static int tcp_sock_init_one(const struct ctx *c, const union inany_addr *addr,
 	if (s < 0)
 		return s;
 
-	tcp_sock_set_bufsize(c, s);
 	return s;
 }
 
@@ -2317,9 +2318,7 @@ static void tcp_ns_sock_init4(const struct ctx *c, in_port_t port)
 
 	s = pif_sock_l4(c, EPOLL_TYPE_TCP_LISTEN, PIF_SPLICE, &inany_loopback4,
 			NULL, port, tref.u32);
-	if (s >= 0)
-		tcp_sock_set_bufsize(c, s);
-	else
+	if (s < 0)
 		s = -1;
 
 	if (c->tcp.fwd_out.mode == FWD_AUTO)
@@ -2343,9 +2342,7 @@ static void tcp_ns_sock_init6(const struct ctx *c, in_port_t port)
 
 	s = pif_sock_l4(c, EPOLL_TYPE_TCP_LISTEN, PIF_SPLICE, &inany_loopback6,
 			NULL, port, tref.u32);
-	if (s >= 0)
-		tcp_sock_set_bufsize(c, s);
-	else
+	if (s < 0)
 		s = -1;
 
 	if (c->tcp.fwd_out.mode == FWD_AUTO)
-- 
2.43.0