netdev - Re: [PATCH bpf-next 1/2] bpf: add BPF_LWT_ENCAP_IP option to bpf_lwt_push

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Date:   Mon, 3 Dec 2018 08:55:59 -0800
From:   Peter Oskolkov <posk@...gle.com>
To:     David Ahern <dsahern@...il.com>
Cc:     ast@...nel.org, daniel@...earbox.net, netdev@...r.kernel.org,
        posk.devel@...il.com
Subject: Re: [PATCH bpf-next 1/2] bpf: add BPF_LWT_ENCAP_IP option to bpf_lwt_push_encap

Our case is a bit different - it is more like using the SRH header in
IPv6 to route packets via a non-default intermediate hop. But I see
your point - I'll expand the patchset to cover IPv6 and the ingress
path.
On Mon, Dec 3, 2018 at 8:04 AM David Ahern <dsahern@...il.com> wrote:
>
> On 11/30/18 5:14 PM, Peter Oskolkov wrote:
> > On Fri, Nov 30, 2018 at 3:52 PM David Ahern <dsahern@...il.com> wrote:
> >>
> >> On 11/30/18 4:35 PM, Peter Oskolkov wrote:
> >>> Thanks, David! This is for egress only, so I'll add an appropriate
> >>> check. I'll also address your other comments/concerns in a v2 version
> >>> of this patchset.
> >>
> >> Why are you limiting this to egress only?
> >
> > I'm focusing on egress because this is a use case that we have and
> > understand well, and would like to have a solution for sooner rather
> > than later.
> >
> > Without understanding why anybody would want to do lwt-bpf encap on
> > ingress, I don't know, for example, what a good test would look like;
> > but I'd be happy to look into a specific ingress use case if you have
> > one.
> >
>
> We can not have proliferation of helpers for a lot of one off use cases.
> A little thought now makes this helper useful for more than just your 1
> use case. And, IPv6 parity should be a minimal requirement for helpers.
>
> Based on your route lookup I presume your use case is capturing certain
> local traffic, pushing a custom header and sending that packet else
> where. The same could be done on the ingress path.