From: Geliang Tang <tanggeliang@kylinos.cn>

This patch adds a subtest named test_bpf_iter to load and verify the newly
added mptcp_subflow type bpf_iter example in test_mptcp. Use the helper
endpoint_init() to add 3 new subflow endpoints. A new helper recv_byte()
is invoked to trigger the ftrace hook for mptcp_sched_get_send() after
wait_for_new_subflows(). Check if skel->bss->subflows equals 4 to verify
whether the "fentry" program loops fourth as expected.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
---
 .../testing/selftests/bpf/prog_tests/mptcp.c  | 78 +++++++++++++++++++
 1 file changed, 78 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/mptcp.c b/tools/testing/selftests/bpf/prog_tests/mptcp.c
index 64b5ce25e1a1..233da5317e47 100644
--- a/tools/testing/selftests/bpf/prog_tests/mptcp.c
+++ b/tools/testing/selftests/bpf/prog_tests/mptcp.c
@@ -11,6 +11,7 @@
 #include "mptcp_sock.skel.h"
 #include "mptcpify.skel.h"
 #include "mptcp_subflow.skel.h"
+#include "mptcp_bpf_iter.skel.h"
 #include "mptcp_bpf_first.skel.h"
 #include "mptcp_bpf_bkup.skel.h"
 #include "mptcp_bpf_rr.skel.h"
@@ -261,6 +262,19 @@ static void send_byte(int fd)
 	ASSERT_EQ(write(fd, &b, sizeof(b)), 1, "send single byte");
 }
 
+static int recv_byte(int fd)
+{
+	char buf[1];
+	ssize_t n;
+
+	n = recv(fd, buf, sizeof(buf), 0);
+	if (CHECK(n <= 0, "recv_byte", "recv")) {
+		log_err("failed/partial recv");
+		return -1;
+	}
+	return 0;
+}
+
 static int verify_mptcpify(int server_fd, int client_fd)
 {
 	struct __mptcp_info info;
@@ -501,6 +515,68 @@ static void test_subflow(void)
 	close(cgroup_fd);
 }
 
+static void run_bpf_iter(void)
+{
+	int server_fd, client_fd, accept_fd;
+
+	server_fd = start_mptcp_server(AF_INET, ADDR_1, PORT_1, 0);
+	if (!ASSERT_OK_FD(server_fd, "start_mptcp_server"))
+		return;
+
+	client_fd = connect_to_fd(server_fd, 0);
+	if (!ASSERT_OK_FD(client_fd, "connect_to_fd"))
+		goto close_server;
+
+	accept_fd = accept(server_fd, NULL, NULL);
+	if (!ASSERT_OK_FD(accept_fd, "accept"))
+		goto close_client;
+
+	send_byte(client_fd);
+	wait_for_new_subflows(client_fd);
+	recv_byte(accept_fd);
+	send_byte(client_fd);
+
+	close(accept_fd);
+close_client:
+	close(client_fd);
+close_server:
+	close(server_fd);
+}
+
+static void test_bpf_iter(void)
+{
+	struct mptcp_bpf_iter *skel;
+	struct nstoken *nstoken;
+	int subflows = 4;
+	int err;
+
+	skel = mptcp_bpf_iter__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open_load: mptcp_iter"))
+		return;
+
+	skel->bss->pid = getpid();
+
+	err = mptcp_bpf_iter__attach(skel);
+	if (!ASSERT_OK(err, "skel_attach: mptcp_iter"))
+		goto skel_destroy;
+
+	nstoken = create_netns();
+	if (!ASSERT_OK_PTR(nstoken, "create_netns: mptcp_iter"))
+		goto skel_destroy;
+
+	if (endpoint_init("subflow", subflows) < 0)
+		goto close_netns;
+
+	run_bpf_iter();
+
+	ASSERT_EQ(skel->bss->subflows, subflows, "subflows");
+
+close_netns:
+	cleanup_netns(nstoken);
+skel_destroy:
+	mptcp_bpf_iter__destroy(skel);
+}
+
 static struct nstoken *sched_init(char *flags, char *sched)
 {
 	struct nstoken *nstoken;
@@ -682,6 +758,8 @@ void test_mptcp(void)
 		test_mptcpify();
 	if (test__start_subtest("subflow"))
 		test_subflow();
+	if (test__start_subtest("bpf_iter"))
+		test_bpf_iter();
 	if (test__start_subtest("default"))
 		test_default();
 	if (test__start_subtest("first"))
-- 
2.43.0