selftests/bpf: Add bpf_stale test

This patch adds the bpf_stale scheduler test: test_stale(). Use sysctl to
set net.mptcp.scheduler to use this sched. Add two veth net devices to
simulate the multiple addresses case. Use 'ip mptcp endpoint' command to
add the new endpoint ADDR_2 to PM netlink. Send data and check bytes_sent
of 'ss' output after it to make sure the data has been only sent on ADDR_1
since ADDR_2 is set as stale.

Signed-off-by: Geliang Tang <geliang.tang@suse.com>

tools/testing/selftests/bpf/prog_tests/mptcp.c

@@ -15,6 +15,7 @@
 #include "mptcp_bpf_rr.skel.h"
 #include "mptcp_bpf_red.skel.h"
 #include "mptcp_bpf_burst.skel.h"
+#include "mptcp_bpf_stale.skel.h"
 
 #define NS_TEST "mptcp_ns"
 
@@ -651,6 +652,41 @@ static void test_burst(void)
 	mptcp_bpf_burst__destroy(burst_skel);
 }
 
+static void test_stale(void)
+{
+	struct mptcp_bpf_stale *stale_skel;
+	int server_fd, client_fd;
+	struct nstoken *nstoken;
+	struct bpf_link *link;
+
+	stale_skel = mptcp_bpf_stale__open_and_load();
+	if (!ASSERT_OK_PTR(stale_skel, "bpf_stale__open_and_load"))
+		return;
+
+	link = bpf_map__attach_struct_ops(stale_skel->maps.stale);
+	if (!ASSERT_OK_PTR(link, "bpf_map__attach_struct_ops")) {
+		mptcp_bpf_stale__destroy(stale_skel);
+		return;
+	}
+
+	nstoken = sched_init("subflow", "bpf_stale");
+	if (!ASSERT_OK_PTR(nstoken, "sched_init:bpf_stale"))
+		goto fail;
+	server_fd = start_mptcp_server(AF_INET, ADDR_1, PORT_1, 0);
+	client_fd = connect_to_fd(server_fd, 0);
+
+	send_data(server_fd, client_fd, "bpf_stale");
+	ASSERT_OK(has_bytes_sent(ADDR_1), "has_bytes_sent addr_1");
+	ASSERT_GT(has_bytes_sent(ADDR_2), 0, "has_bytes_sent addr_2");
+
+	close(client_fd);
+	close(server_fd);
+fail:
+	cleanup_netns(nstoken);
+	bpf_link__destroy(link);
+	mptcp_bpf_stale__destroy(stale_skel);
+}
+
 void test_mptcp(void)
 {
 	if (test__start_subtest("base"))
@@ -669,4 +705,6 @@ void test_mptcp(void)
 		test_red();
 	if (test__start_subtest("burst"))
 		test_burst();
+	if (test__start_subtest("stale"))
+		test_stale();
 }