netdev - Re: [PATCH nf-next] netfilter: nf

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Date:   Wed, 31 Aug 2022 10:26:08 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Florian Westphal <fw@...len.de>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        Toke Høiland-Jørgensen <toke@...nel.org>,
        netfilter-devel <netfilter-devel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>
Subject: Re: [PATCH nf-next] netfilter: nf_tables: add ebpf expression

On Wed, Aug 31, 2022 at 8:53 AM Florian Westphal <fw@...len.de> wrote:
>
> Alexei Starovoitov <alexei.starovoitov@...il.com> wrote:
> > > 1 and 2 have the upside that its easy to handle a 'file not found'
> > > error.
> >
> > I'm strongly against calling into bpf from the inner guts of nft.
> > Nack to all options discussed in this thread.
> > None of them make any sense.
>
> -v please.  I can just rework userspace to allow going via xt_bpf
> but its brain damaged.

Right. xt_bpf was a dead end from the start.
It's time to deprecate it and remove it.

> This helps gradually moving towards move epbf for those that
> still heavily rely on the classic forwarding path.

No one is using it.
If it was, we would have seen at least one bug report over
all these years. We've seen none.

tbh we had a fair share of wrong design decisions that look
very reasonable early on and turned out to be useless with
zero users.
BPF_PROG_TYPE_SCHED_ACT and BPF_PROG_TYPE_LWT*
are in this category.
All this code does is bit rot.
As a minimum we shouldn't step on the same rakes.
xt_ebpf would be the same dead code as xt_bpf.

> If you are open to BPF_PROG_TYPE_NETFILTER I can go that route
> as well, raw bpf program attachment via NF_HOOK and the bpf dispatcher,
> but it will take significantly longer to get there.
>
> It involves reviving
> https://lore.kernel.org/netfilter-devel/20211014121046.29329-1-fw@strlen.de/

I missed it earlier. What is the end goal ?
Optimize nft run-time with on the fly generation of bpf byte code ?