netdev - Re: [PATCH net-next] tc: cls_bpf: make ingress and egress qdiscs consistent

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Date:	Sat, 04 Apr 2015 00:54:12 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Alexei Starovoitov <ast@...mgrid.com>,
	"David S. Miller" <davem@...emloft.net>
CC:	Jiri Pirko <jiri@...nulli.us>, Jamal Hadi Salim <jhs@...atatu.com>,
	linux-api@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] tc: cls_bpf: make ingress and egress qdiscs
 consistent

On 04/04/2015 12:17 AM, Alexei Starovoitov wrote:
...
> 1. there shouldn't be a choice at all for bpf. Because not pulling l2
> means it's bug.

Yep, correct. You would also loose context for a possible dissection,
at best you only have skb->protocol.

> 2. adding a flag means adding it to iproute2 with default off and making
> users forgetting it from time to time and have no way of knowing why
> their programs all of a sudden stopped working.
>
> classic falls under the same rules. It doesn't make sense at all to run
> a program on packet without L2 header. It's very odd both for classic
> and extended programs.

Yep.

> Two 'if' conditions in critical path is bogus argument, since these
> checks would be there in ingress as well. Same critical path.

Why bogus? There would be no such test on the normal egress path,
where this is irrelevant. I wasn't talking about ingress here.

I see the point regarding the user option. So, why not adding a flag
to tcf_proto_ops a la `.flags = CLS_REQUIRES_L2` that gets propagated
to tcf_proto, and only ingress_enqueue() would need to test if the
classifier imposes that requirement, so it can push/pull.
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