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

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Date:   Fri, 2 Sep 2022 10:06:28 -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 Thu, Sep 1, 2022 at 3:14 AM Florian Westphal <fw@...len.de> wrote:
>
> Daniel Borkmann <daniel@...earbox.net> wrote:
> > On 8/31/22 7:26 PM, Alexei Starovoitov wrote:
> > > On Wed, Aug 31, 2022 at 8:53 AM Florian Westphal <fw@...len.de> wrote:
> > > As a minimum we shouldn't step on the same rakes.
> > > xt_ebpf would be the same dead code as xt_bpf.
> >
> > +1, and on top, the user experience will just be horrible. :(
>
> Compared to what?
>
> > > > 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 ?
> >
> > Or rather to provide a pendant to nft given existence of xt_bpf, and the
> > latter will be removed at some point? (If so, can't we just deprecate the
> > old xt_bpf?)
>
> See my reply to Alexey, immediate goal was to get rid of the indirect
> calls by providing a tailored/jitted equivalent of nf_hook_slow().
>
> The next step could be to allow implementation of netfilter hooks
> (i.e., kernel modules that call nf_register_net_hook()) in bpf
> but AFAIU it requires addition of BPF_PROG_TYPE_NETFILTER etc.

We were adding new prog and maps types in the past.
Now new features are being added differently.
All of the networking either works with sk_buff-s or xdp frames.
We try hard not to add any new uapi helpers.
Everything is moving to kfuncs.
Other sub-systems should be able to use bpf without touching
the bpf core. See hid-bpf as an example.
It needs several verifier improvements, but doesn't need
new prog types, helpers, etc.

> After that, yes, one could think about how to jit nft_do_chain() and
> all the rest of the nft machinery.

Sounds like a ton of work. All that just to accelerate nft a bit?
I think there are more impactful projects to work on.
For example, accelerating classic iptables with bpf would immediately
help a bunch of users.