netdev - Re: [PATCH bpf-next v7 1/3] bpf: Add "live packet" mode for XDP in bpf_prog

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Date:   Wed, 12 Jan 2022 17:37:54 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        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>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH bpf-next v7 1/3] bpf: Add "live packet" mode for XDP in bpf_prog_run()

On Sun, Jan 9, 2022 at 4:30 AM Toke Høiland-Jørgensen <toke@...hat.com> wrote:
>
> I left that out on purpose: I feel it's exposing an internal
> implementation detail as UAPI (as you said). And I'm not convinced it
> really needed (or helpful) - see below.

It's irrelevant whether it's documented or not.
Once this implementation detail is being relied upon
by user space it becomes an undocumented uapi that we cannot change.

> I'll try implementing a TCP stream mode in xdp_trafficgen just to make
> sure I'm not missing something. But I believe that sending out a stream
> of packets that looks like a coherent TCP stream should be simple
> enough, at least. Dealing with the full handshake + CWND control loop
> will be harder, though, and right now I think it'll require multiple
> trips back to userspace.

The patch set looks very close to being able to do such TCP streaming.
Let's make sure nothing is missing from API before we land it.