Re: [PATCH bpf-next v5 8/8] selftests/bpf: Test switching TCP Congestion Control algorithms.

[Martin KaFai Lau <martin.lau@linux.dev>]

On 3/7/23 4:50 PM, Kui-Feng Lee wrote:
> 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);

nit. Use tcp_ca_update__open_and_load().

> +	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

Not used.

> +
> +#define min(a, b) ((a) < (b) ? (a) : (b))

Not used.

> +
> +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,

nit. I think it is more future proof to use '.init' to bump the ca1_cnt and 
ca2_cnt. '.init' must be called. Just in case for some unlikely stack change 
that may not call cong_control and then need to adjust the test accordingly.

It also needs a few negative tests like creating a link with a map without 
BPF_F_LINK. delete_elem on BPF_F_LINK map. Replace a link with a different 
tcp-cc-name which is not supported now, ...etc.

> +	.ssthresh = (void *)ca_update_ssthresh,
> +	.undo_cwnd = (void *)ca_update_undo_cwnd,
> +	.name = "tcp_ca_update",
> +};