netdev - Re: [PATCH bpf-next 01/10] bpf: Add initial fd-based API to attach tc BPF programs

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Date:   Thu, 6 Oct 2022 16:29:20 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>, bpf <bpf@...r.kernel.org>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        John Fastabend <john.fastabend@...il.com>,
        Joanne Koong <joannelkoong@...il.com>,
        Kumar Kartikeya Dwivedi <memxor@...il.com>,
        Toke Høiland-Jørgensen <toke@...hat.com>,
        Joe Stringer <joe@...ium.io>,
        Network Development <netdev@...r.kernel.org>
Subject: Re: [PATCH bpf-next 01/10] bpf: Add initial fd-based API to attach tc
 BPF programs

On Thu, Oct 6, 2022 at 7:41 AM Jamal Hadi Salim <jhs@...atatu.com> wrote:
>
> On Thu, Oct 6, 2022 at 1:01 AM Alexei Starovoitov
> <alexei.starovoitov@...il.com> wrote:
> >
> > On Wed, Oct 05, 2022 at 01:11:34AM +0200, Daniel Borkmann wrote:
>
> >
> > I cannot help but feel that prio logic copy-paste from old tc, netfilter and friends
> > is done because "that's how things were done in the past".
> > imo it was a well intentioned mistake and all networking things (tc, netfilter, etc)
> > copy-pasted that cumbersome and hard to use concept.
> > Let's throw away that baggage?
> > In good set of cases the bpf prog inserter cares whether the prog is first or not.
> > Since the first prog returning anything but TC_NEXT will be final.
> > I think prog insertion flags: 'I want to run first' vs 'I don't care about order'
> > is good enough in practice. Any complex scheme should probably be programmable
> > as any policy should. For example in Meta we have 'xdp chainer' logic that is similar
> > to libxdp chaining, but we added a feature that allows a prog to jump over another
> > prog and continue the chain. Priority concept cannot express that.
> > Since we'd have to add some "policy program" anyway for use cases like this
> > let's keep things as simple as possible?
> > Then maybe we can adopt this "as-simple-as-possible" to XDP hooks ?
> > And allow bpf progs chaining in the kernel with "run_me_first" vs "run_me_anywhere"
> > in both tcx and xdp ?
>
> You just described the features already offered by tc opcodes + priority.

Ohh, right. All possible mechanisms were available in TC 20 years ago.
Moving on.