netdev - Re: [PATCH net-next 4/4] net/sched: act_mirred: Implement ingress actions

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Date:   Sun, 25 Sep 2016 20:33:51 +0200
From:   Florian Westphal <fw@...len.de>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Jamal Hadi Salim <jhs@...atatu.com>,
        Shmulik Ladkani <shmulik.ladkani@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        WANG Cong <xiyou.wangcong@...il.com>,
        Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
        Florian Westphal <fw@...len.de>
Subject: Re: [PATCH net-next 4/4] net/sched: act_mirred: Implement ingress
 actions

Daniel Borkmann <daniel@...earbox.net> wrote:
> On 09/25/2016 03:05 PM, Jamal Hadi Salim wrote:
> >MAX_RED_LOOP (stands for "Maximum Redirect loop") still exists in
> >current code. The idea above was that we would increment the rttl
> >counter  once and if we saw it again upto MAX_RED_LOOP we would assume
> >a loop and drop the packet (at the time i didnt think it was wise to
> >let the actions be in charge of setting the RTTL; it had to be central
> >core code - but it may not be neccessary)
> >
> >Florian, when we discussed I said it was fine to reclaim those 3 bits
> >on tc verdict for RTTL at the time because i had taken out the
> >feature and never added it back. Your comment at the time was we can
> >add it back when someone shows up with the feature.
> >Shmulik is looking to add it.
> 
> Why not just reuse xmit_recursion, which is what we did in tc cls_bpf
> programs f.e. see __bpf_tx_skb()? Would be a pity to waste 3 bits on
> this in the skb.

+1, don't (yet) understand why a per-skb counter is required for this.