netdev - Re: [PATCH bpf-next V3 4/6] bpf: make it possible to identify BPF redirected SKBs

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Date:   Fri, 9 Oct 2020 11:33:33 -0700
From:   Maciej Żenczykowski <maze@...gle.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>,
        bpf <bpf@...r.kernel.org>, Linux NetDev <netdev@...r.kernel.org>,
        Daniel Borkmann <borkmann@...earbox.net>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Lorenz Bauer <lmb@...udflare.com>,
        Shaun Crampton <shaun@...era.io>,
        Lorenzo Bianconi <lorenzo@...nel.org>,
        Marek Majkowski <marek@...udflare.com>,
        John Fastabend <john.fastabend@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Eyal Birger <eyal.birger@...il.com>
Subject: Re: [PATCH bpf-next V3 4/6] bpf: make it possible to identify BPF
 redirected SKBs

> > This change makes it possible to identify SKBs that have been redirected
> > by TC-BPF (cls_act). This is needed for a number of cases.
> >
> > (1) For collaborating with driver ifb net_devices.
> > (2) For avoiding starting generic-XDP prog on TC ingress redirect.
> >
> > Signed-off-by: Jesper Dangaard Brouer <brouer@...hat.com>
>
> Not sure if anyone actually cares about ifb devices, but my worry is that the
> generic XDP vs tc interaction has been as-is for quite some time so this change
> in behavior could break in the wild.

I'm not at all sure of the interactions/implications here.
But I do have a request to enable ifb on Android for ingress rate
limiting and separately we're trying to make XDP work...
So we might at some point end up with cellular interfaces with xdp
ebpf (redirect for forwarding/nat/tethering) + ifb + tc ebpf (for
device local stuff).
But this is still all very vague and 'ideas only' level.
(and in general I think I'd like to get rid of the redirect in tc
ebpf, and leave only xlat64 translation for to-the-device traffic in
there, so maybe there's no problem anyway??)