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Subject: Re: [PATCH bpf-next] bpf: add bpf_ct_lookup_{tcp,udp}() helpers
To:     Matt Cover <werekraken@gmail.com>,
        John Fastabend <john.fastabend@gmail.com>
Cc:     Alexei Starovoitov <ast@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andriin@fb.com>,
        "David S. Miller" <davem@davemloft.net>,
        Shuah Khan <shuah@kernel.org>,
        Jakub Kicinski <jakub.kicinski@netronome.com>,
        Jesper Dangaard Brouer <hawk@kernel.org>,
        Jakub Sitnicki <jakub@cloudflare.com>,
        Quentin Monnet <quentin.monnet@netronome.com>,
        Matthew Cover <matthew.cover@stackpath.com>,
        Stanislav Fomichev <sdf@google.com>,
        Andrey Ignatov <rdna@fb.com>,
        Lorenz Bauer <lmb@cloudflare.com>,
        Jiong Wang <jiong.wang@netronome.com>, netdev@vger.kernel.org,
        bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-kselftest@vger.kernel.org
References: <20200118000128.15746-1-matthew.cover@stackpath.com>
 <5e23c773d7a67_13602b2359ea05b824@john-XPS-13-9370.notmuch>
 <CAGyo_hrUXWzui9FNiZpNGXjsphSreLEYYm4K7xkp+H+de=QKSA@mail.gmail.com>
 <CAGyo_hpcO-f9uxQFDfKZNz=1t6Yux+LzxN1qLHKf6PXMAtWQ-w@mail.gmail.com>
From:   Daniel Borkmann <daniel@iogearbox.net>
Message-ID: <360a11cd-2c41-159e-b92a-c7c1ec42767f@iogearbox.net>
Date:   Mon, 20 Jan 2020 22:11:31 +0100
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On 1/20/20 9:10 PM, Matt Cover wrote:
> On Mon, Jan 20, 2020 at 11:11 AM Matt Cover <werekraken@gmail.com> wrote:
>> On Sat, Jan 18, 2020 at 8:05 PM John Fastabend <john.fastabend@gmail.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@stackpath.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.