netdev - Re: [PATCH bpf-next 0/3] bpf: add MPTCP subflow support

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Date:   Mon, 24 Aug 2020 15:01:00 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Nicolas Rybowski <nicolas.rybowski@...sares.net>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andriin@...com>,
        Daniel Borkmann <daniel@...earbox.net>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Martin KaFai Lau <kafai@...com>,
        Mat Martineau <mathew.j.martineau@...ux.intel.com>,
        Matthieu Baerts <matthieu.baerts@...sares.net>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        mptcp@...ts.01.org, netdev@...r.kernel.org
Subject: Re: [PATCH bpf-next 0/3] bpf: add MPTCP subflow support

On Fri, Aug 21, 2020 at 05:15:38PM +0200, Nicolas Rybowski wrote:
> Previously it was not possible to make a distinction between plain TCP
> sockets and MPTCP subflow sockets on the BPF_PROG_TYPE_SOCK_OPS hook.
> 
> This patch series now enables a fine control of subflow sockets. In its
> current state, it allows to put different sockopt on each subflow from a
> same MPTCP connection (socket mark, TCP congestion algorithm, ...) using
> BPF programs.
> 
> It should also be the basis of exposing MPTCP-specific fields through BPF.

Looks fine, but I'd like to see the full picture a bit better.
What's the point of just 'token' ? What can be done with it?
What are you thinking to add later?
Also selftest for new feature is mandatory.