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

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Message-ID: <133be773-6d51-1d19-e5a6-1938accb0592@gmail.com>
Date:   Mon, 3 Dec 2018 09:04:10 -0700
From:   David Ahern <dsahern@...il.com>
To:     Peter Oskolkov <posk@...gle.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

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.