[PATCH bpf-next v3 8/8] selftests/bpf: Test switching TCP Congestion Control algorithms.

[Kui-Feng Lee <kuifeng@meta.com>]

Create a pair of sockets that utilize the congestion control algorithm
under a particular name. Then switch up this congestion control
algorithm to another implementation and check whether newly created
connections using the same cc name now run the new implementation.

Signed-off-by: Kui-Feng Lee <kuifeng@meta.com>
---
 .../selftests/bpf/prog_tests/bpf_tcp_ca.c     | 38 ++++++++++++
 .../selftests/bpf/progs/tcp_ca_update.c       | 62 +++++++++++++++++++
 2 files changed, 100 insertions(+)
 create mode 100644 tools/testing/selftests/bpf/progs/tcp_ca_update.c

diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
index e980188d4124..caaa9175ee36 100644
--- a/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_tcp_ca.c
@@ -8,6 +8,7 @@
 #include "bpf_dctcp.skel.h"
 #include "bpf_cubic.skel.h"
 #include "bpf_tcp_nogpl.skel.h"
+#include "tcp_ca_update.skel.h"
 #include "bpf_dctcp_release.skel.h"
 #include "tcp_ca_write_sk_pacing.skel.h"
 #include "tcp_ca_incompl_cong_ops.skel.h"
@@ -381,6 +382,41 @@ static void test_unsupp_cong_op(void)
 	libbpf_set_print(old_print_fn);
 }
 
+static void test_update_ca(void)
+{
+	struct tcp_ca_update *skel;
+	struct bpf_link *link;
+	int saved_ca1_cnt;
+	int err;
+
+	skel = tcp_ca_update__open();
+	if (!ASSERT_OK_PTR(skel, "open"))
+		return;
+
+	err = tcp_ca_update__load(skel);
+	if (!ASSERT_OK(err, "load")) {
+		tcp_ca_update__destroy(skel);
+		return;
+	}
+
+	link = bpf_map__attach_struct_ops(skel->maps.ca_update_1);
+	ASSERT_OK_PTR(link, "attach_struct_ops");
+
+	do_test("tcp_ca_update", NULL);
+	saved_ca1_cnt = skel->bss->ca1_cnt;
+	ASSERT_GT(saved_ca1_cnt, 0, "ca1_ca1_cnt");
+
+	err = bpf_link__update_map(link, skel->maps.ca_update_2);
+	ASSERT_OK(err, "update_struct_ops");
+
+	do_test("tcp_ca_update", NULL);
+	ASSERT_EQ(skel->bss->ca1_cnt, saved_ca1_cnt, "ca2_ca1_cnt");
+	ASSERT_GT(skel->bss->ca2_cnt, 0, "ca2_ca2_cnt");
+
+	bpf_link__destroy(link);
+	tcp_ca_update__destroy(skel);
+}
+
 void test_bpf_tcp_ca(void)
 {
 	if (test__start_subtest("dctcp"))
@@ -399,4 +435,6 @@ void test_bpf_tcp_ca(void)
 		test_incompl_cong_ops();
 	if (test__start_subtest("unsupp_cong_op"))
 		test_unsupp_cong_op();
+	if (test__start_subtest("update_ca"))
+		test_update_ca();
 }
diff --git a/tools/testing/selftests/bpf/progs/tcp_ca_update.c b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
new file mode 100644
index 000000000000..36a04be95df5
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/tcp_ca_update.c
@@ -0,0 +1,62 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+char _license[] SEC("license") = "GPL";
+
+int ca1_cnt = 0;
+int ca2_cnt = 0;
+
+#define USEC_PER_SEC 1000000UL
+
+#define min(a, b) ((a) < (b) ? (a) : (b))
+
+static inline struct tcp_sock *tcp_sk(const struct sock *sk)
+{
+	return (struct tcp_sock *)sk;
+}
+
+SEC("struct_ops/ca_update_1_cong_control")
+void BPF_PROG(ca_update_1_cong_control, struct sock *sk,
+	      const struct rate_sample *rs)
+{
+	ca1_cnt++;
+}
+
+SEC("struct_ops/ca_update_2_cong_control")
+void BPF_PROG(ca_update_2_cong_control, struct sock *sk,
+	      const struct rate_sample *rs)
+{
+	ca2_cnt++;
+}
+
+SEC("struct_ops/ca_update_ssthresh")
+__u32 BPF_PROG(ca_update_ssthresh, struct sock *sk)
+{
+	return tcp_sk(sk)->snd_ssthresh;
+}
+
+SEC("struct_ops/ca_update_undo_cwnd")
+__u32 BPF_PROG(ca_update_undo_cwnd, struct sock *sk)
+{
+	return tcp_sk(sk)->snd_cwnd;
+}
+
+SEC(".struct_ops.link")
+struct tcp_congestion_ops ca_update_1 = {
+	.cong_control = (void *)ca_update_1_cong_control,
+	.ssthresh = (void *)ca_update_ssthresh,
+	.undo_cwnd = (void *)ca_update_undo_cwnd,
+	.name = "tcp_ca_update",
+};
+
+SEC(".struct_ops.link")
+struct tcp_congestion_ops ca_update_2 = {
+	.cong_control = (void *)ca_update_2_cong_control,
+	.ssthresh = (void *)ca_update_ssthresh,
+	.undo_cwnd = (void *)ca_update_undo_cwnd,
+	.name = "tcp_ca_update",
+};
-- 
2.30.2