netdev - Re: [PATCH v5 bpf-next 09/12] bpf: tcp: Allow bpf prog to write and parse TCP header option

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Date:   Wed, 30 Sep 2020 08:23:47 -0700
From:   sdf@...gle.com
To:     Martin KaFai Lau <kafai@...com>
Cc:     bpf@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Eric Dumazet <edumazet@...gle.com>, kernel-team@...com,
        Lawrence Brakmo <brakmo@...com>,
        Neal Cardwell <ncardwell@...gle.com>, netdev@...r.kernel.org,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH v5 bpf-next 09/12] bpf: tcp: Allow bpf prog to write and
 parse TCP header option

On 08/20, Martin KaFai Lau wrote:
> [..]
> +static inline void bpf_skops_init_child(const struct sock *sk,
> +					struct sock *child)
> +{
> +	tcp_sk(child)->bpf_sock_ops_cb_flags =
> +		tcp_sk(sk)->bpf_sock_ops_cb_flags &
> +		(BPF_SOCK_OPS_PARSE_ALL_HDR_OPT_CB_FLAG |
> +		 BPF_SOCK_OPS_PARSE_UNKNOWN_HDR_OPT_CB_FLAG |
> +		 BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG);
> +}
It looks like it breaks test_tcpbpf_user test in an interesting way, can
you verify on your side?

Awhile ago, I've added retries to this test to make it less flaky.
The test is waiting for 3 BPF_TCP_CLOSE events and now it
only gets 2 BPF_TCP_CLOSE events.

IIUC, we used to copy/inherit parent bpf_sock_ops_cb_flags and now
we are doing only a small subset (bpf tcp header) with the code above.

I'm still trying to understand whether that's working as intended
and we need to fix the test or it's a user-visible breakage.
Thoughts?