Subject: Re: [PATCH bpf v3 2/2] selftests/bpf: Test TCP_NODELAY in TCP hdr opt callbacks

From: Jiayuan Chen <[email-masked]>
Date: Fri, 17 Apr 2026 18:45:07 +0800

On 4/17/26 5:20 PM, KaFai Wan wrote:
> Add a sockops selftest for the TCP_NODELAY restriction in
> BPF_SOCK_OPS_HDR_OPT_LEN_CB and BPF_SOCK_OPS_WRITE_HDR_OPT_CB.
>
> With BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG enabled,
> bpf_setsockopt(TCP_NODELAY) returns -EOPNOTSUPP from
> BPF_SOCK_OPS_HDR_OPT_LEN_CB and BPF_SOCK_OPS_WRITE_HDR_OPT_CB, avoiding
> unbounded recursion and kernel stack overflow.
>
> Other cases continue to work as before, including
> BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB and user space
> setsockopt(TCP_NODELAY).
>
> Signed-off-by: KaFai Wan <[email-masked]>

Reviewed-by: Jiayuan Chen <[email-masked]>

A little nit below, no need to resend.

> ---
>   .../selftests/bpf/prog_tests/tcp_hdr_options.c    | 12 +++++++++++-
>   .../bpf/progs/test_misc_tcp_hdr_options.c         | 15 ++++++++++++++-
>   2 files changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c b/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
> index 56685fc03c7e..7b9dbbb84316 100644
> --- a/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
> +++ b/tools/testing/selftests/bpf/prog_tests/tcp_hdr_options.c
> @@ -461,7 +461,7 @@ static void misc(void)
>   	const unsigned int nr_data = 2;
>   	struct bpf_link *link;
>   	struct sk_fds sk_fds;
> -	int i, ret;
> +	int i, ret, true_val = 1;
>   

NIT: please follow the reverse xmas tree variable ordering

>   	lport_linum_map_fd = bpf_map__fd(misc_skel->maps.lport_linum_map);
>   
> @@ -477,6 +477,10 @@ static void misc(void)
>   		return;
>   	}
>   
> +	ret = setsockopt(sk_fds.active_fd, SOL_TCP, TCP_NODELAY, &true_val, sizeof(true_val));
> +	if (!ASSERT_OK(ret, "setsockopt(TCP_NODELAY)"))
> +		goto check_linum;
> +
>   	for (i = 0; i < nr_data; i++) {
>   		/* MSG_EOR to ensure skb will not be combined */
>   		ret = send(sk_fds.active_fd, send_msg, sizeof(send_msg),
> @@ -507,6 +511,12 @@ static void misc(void)
>   
>   	ASSERT_EQ(misc_skel->bss->nr_hwtstamp, 0, "nr_hwtstamp");
>   
> +	ASSERT_TRUE(misc_skel->data->nodelay_est_ok, "unexpected nodelay_est_ok");
> +
> +	ASSERT_TRUE(misc_skel->data->nodelay_hdr_len_err, "unexpected nodelay_hdr_len_err");
> +
> +	ASSERT_TRUE(misc_skel->data->nodelay_write_hdr_err, "unexpected nodelay_write_hdr_err");
> +

NIT: It's would be misleading if you run ./test_progs with "-v"
misc:PASS:unexpected nodelay_est_ok 0 nsec

"PASS:unexpected" ?

>   check_linum:
>   	ASSERT_FALSE(check_error_linum(&sk_fds), "check_error_linum");
>   	sk_fds_close(&sk_fds);
> diff --git a/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c b/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c
> index d487153a839d..a02e28d9db2e 100644
> --- a/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c
> +++ b/tools/testing/selftests/bpf/progs/test_misc_tcp_hdr_options.c
> @@ -29,6 +29,10 @@ unsigned int nr_syn = 0;
>   unsigned int nr_fin = 0;
>   unsigned int nr_hwtstamp = 0;
>   
> +bool nodelay_est_ok = true;
> +bool nodelay_hdr_len_err = true;
> +bool nodelay_write_hdr_err = true;

I prefer "nodelay_hdr_len_reject"