netdev - Re: [PATCH net-next] net: bpf: add hook for close of tcp timewait sock

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Message-ID: <CAADnVQLY2i+2YTj+Oi7+70e98sRC-t6rr536sc=3WYghpki+ug@mail.gmail.com>
Date:   Wed, 29 Dec 2021 08:46:01 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     menglong8.dong@...il.com
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>,
        Menglong Dong <imagedong@...cent.com>
Subject: Re: [PATCH net-next] net: bpf: add hook for close of tcp timewait sock

On Wed, Dec 29, 2021 at 3:33 AM <menglong8.dong@...il.com> wrote:
>
> From: Menglong Dong <imagedong@...cent.com>
>
> The cgroup eBPF attach type 'CGROUP_SOCK_OPS' is able to monitor the
> state change of a tcp connect with 'BPF_SOCK_OPS_STATE_CB' ops.
>
> However, it can't trace the whole state change of a tcp connect. While
> a connect becomes 'TCP_TIME_WAIT' state, this sock will be release and
> a tw sock will be created. While tcp sock release, 'TCP_CLOSE' state
> change will be passed to eBPF program. Howeven, the real state of this
> connect is 'TCP_TIME_WAIT'.
>
> To make eBPF get the real state change of a tcp connect, add
> 'CGROUP_TWSK_CLOSE' cgroup attach type, which will be called when
> tw sock release and tcp connect become CLOSE.

The use case is not explained.
Why bpf tracing cannot be used to achieve the same?

Also there are no selftests.