netdev - Re: [PATCH bpf-next] bpf: add bpf_ct_lookup

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Date:   Mon, 20 Jan 2020 22:11:31 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Matt Cover <werekraken@...il.com>,
        John Fastabend <john.fastabend@...il.com>
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        "David S. Miller" <davem@...emloft.net>,
        Shuah Khan <shuah@...nel.org>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Jakub Sitnicki <jakub@...udflare.com>,
        Quentin Monnet <quentin.monnet@...ronome.com>,
        Matthew Cover <matthew.cover@...ckpath.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Andrey Ignatov <rdna@...com>,
        Lorenz Bauer <lmb@...udflare.com>,
        Jiong Wang <jiong.wang@...ronome.com>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Subject: Re: [PATCH bpf-next] bpf: add bpf_ct_lookup_{tcp,udp}() helpers

On 1/20/20 9:10 PM, Matt Cover wrote:
> On Mon, Jan 20, 2020 at 11:11 AM Matt Cover <werekraken@...il.com> wrote:
>> On Sat, Jan 18, 2020 at 8:05 PM John Fastabend <john.fastabend@...il.com> wrote:
>>> Matthew Cover wrote:
>>>> Allow looking up an nf_conn. This allows eBPF programs to leverage
>>>> nf_conntrack state for similar purposes to socket state use cases,
>>>> as provided by the socket lookup helpers. This is particularly
>>>> useful when nf_conntrack state is locally available, but socket
>>>> state is not.
>>>>
>>>> Signed-off-by: Matthew Cover <matthew.cover@...ckpath.com>
>>>> ---
>>>
>>> Couple coding comments below. Also looks like a couple build errors
>>> so fix those up. I'm still thinking over this though.
>>
>> Thank you for taking the time to look this over. I will be looking
>> into the build issues.
> 
> Looks like I missed static inline on a couple functions when
> nf_conntrack isn't builtin. I'll include the fix in v2.

One of the big issues I'd see with this integration is that literally no-one
will be able to use it unless they manually recompile their distro kernel with
ct as builtin instead of module .. Have you considered writing a tcp/udp ct in
plain bpf? Perhaps would make sense to have some sort of tools/lib/bpf/util/
with bpf prog library code that can be included.