route_bench: Filter out all responses.

Install a socket filter to reduce the pure netlink overhead.

Unfortunately the libmnl library does not provide a way to
set socket options that are of level other than SOL_NETLINK.

So we hack it by knowing some things about libmnl internals.

Signed-off-by: David S. Miller <davem@davemloft.net>

route_bench.c

diff --git a/route_bench.c b/route_bench.c
index c75ea45..6c6b525 100644
--- a/route_bench.c
+++ b/route_bench.c
@@ -22,6 +22,17 @@
 #include <linux/if.h>
 #include <linux/if_link.h>
 #include <linux/rtnetlink.h>
+#include <linux/filter.h>
+
+/* XXX Ugly knowledge of internals, but there is currently no way
+ * XXX provided by the libmnl library to set socket options that are
+ * XXX of level other than SOL_NETLINK.   And we need to set one of
+ * XXX level SOL_SOCKET to install the socket filter.
+ */
+struct mnl_socket {
+	int 			fd;
+	struct sockaddr_nl	addr;
+};
 
 static int usage(void)
 {
@@ -139,8 +150,10 @@
 		    unsigned int mark, unsigned int iif)
 {
 	char send_buf[MNL_SOCKET_BUFFER_SIZE];
-	char recv_buf[MNL_SOCKET_BUFFER_SIZE];
 	unsigned int min, sec, frac, tmp;
+	struct sock_filter insns = { .code = BPF_RET | BPF_K,
+				     .k = 0 };
+	struct sock_fprog filter = { .len = 1, .filter = &insns, };
 	struct bench_state *s = &state;
 	struct timeval start_time;
 	struct timeval end_time;
@@ -148,7 +161,7 @@
 	struct nlmsghdr *nlh;
 	unsigned int portid;
 	struct rtmsg *rtm;
-	int i;
+	int i, err;
 
 	init_bench_state(s);
 
@@ -165,10 +178,15 @@
 
 	portid = mnl_socket_get_portid(nl);
 
+	err = setsockopt(nl->fd, SOL_SOCKET, SO_ATTACH_FILTER, &filter, sizeof(filter));
+	if (err) {
+		perror("setsockopt");
+		return -1;
+	}
+
 	gettimeofday(&start_time, NULL);
 	for (i = 0; i < count; i++) {
 		unsigned int seq;
-		int ret;
 
 		nlh = mnl_nlmsg_put_header(send_buf);
 		nlh->nlmsg_type = RTM_GETROUTE;
@@ -197,11 +215,10 @@
 			perror("mnl_socket_sendto");
 			return -1;
 		}
-		ret = mnl_socket_recvfrom(nl, recv_buf, sizeof(recv_buf));
-		if (ret < 0) {
-			perror("mnl_sock_recvfrom");
-			return -1;
-		}
+
+		/* No need to do a receive, as the socket filter rejects
+		 * all packets.
+		 */
 
 		advance_bench_state(s);
 	}