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

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Message-ID: <551F0A1B.3000100@iogearbox.net>
Date:	Fri, 03 Apr 2015 23:46:03 +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 04/03/2015 11:16 PM, Alexei Starovoitov wrote:
> BPF programs attached to ingress and egress qdiscs see inconsistent skb->data.
> For ingress L2 header is already pulled, whereas for egress it's present.
> That makes writing programs more difficult.
> Make them consistent by pushing L2 before running the programs and pulling
> it back afterwards.
> Similar approach is taken by skb_defer_rx_timestamp() which does push/pull
> before calling ptp_classify_raw()->BPF_PROG_RUN().
>
> Signed-off-by: Alexei Starovoitov <ast@...mgrid.com>

Thanks for looking into this. This ends up going via ingress_enqueue(),
right? Maybe it would be better to add a new netlink attribute for
ingress qdisc there that sets a flag in ingress_qdisc_data to pull the
header space before calling tc_classify() and restore it later on?
So, it would be configurable from tc. Would that work?
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