netdev - Re: [PATCH nf-next v5 0/6] Netfilter egress hook

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Message-ID: <20210930090652.4f91be57@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Thu, 30 Sep 2021 09:06:52 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        netfilter-devel@...r.kernel.org, davem@...emloft.net,
        netdev@...r.kernel.org, lukas@...ner.de, kadlec@...filter.org,
        fw@...len.de, ast@...nel.org, edumazet@...gle.com, tgraf@...g.ch,
        nevola@...il.com, john.fastabend@...il.com, willemb@...gle.com
Subject: Re: [PATCH nf-next v5 0/6] Netfilter egress hook

On Thu, 30 Sep 2021 17:13:37 +0200 Pablo Neira Ayuso wrote:
> On Thu, Sep 30, 2021 at 07:28:35AM -0700, Jakub Kicinski wrote:
> > The lifetime of this information is constrained, can't it be a percpu
> > flag, like xmit_more?  
> 
> It's just one single bit in this case after all.

??

> > > Probably the sysctl for this new egress hook is the way to go as you
> > > suggest.  
> > 
> > Knobs is making users pay, let's do our best to avoid that.  
> 
> Could you elaborate?

My reading of Daniel's objections was that the layering is incorrect
because tc is not exclusively "under" nf. That problem is not solved 
by adding a knob. The only thing the knob achieves is let someone
deploying tc/bpf based solution protect themselves from accidental
nf deployment.

That's just background / level set. IDK what requires explanation 
in my statement itself. I thought "admin knobs are bad" is as
universally agreed on as, say, "testing is good".