netdev - Re: [PATCH net-next,RFC 0/9] net: sched: prepare to reuse per-block callbacks from netfilter

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Date:   Fri, 26 Apr 2019 21:22:47 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     Jakub Kicinski <jakub.kicinski@...ronome.com>
Cc:     Jiri Pirko <jiri@...nulli.us>, netfilter-devel@...r.kernel.org,
        davem@...emloft.net, netdev@...r.kernel.org, jiri@...lanox.com,
        john.hurley@...ronome.com, ogerlitz@...lanox.com
Subject: Re: [PATCH net-next,RFC 0/9] net: sched: prepare to reuse per-block
 callbacks from netfilter

On Fri, Apr 26, 2019 at 09:14:40PM +0200, Pablo Neira Ayuso wrote:
> On Fri, Apr 26, 2019 at 11:55:12AM -0700, Jakub Kicinski wrote:
> > On Fri, 26 Apr 2019 20:41:45 +0200, Pablo Neira Ayuso wrote:
> > > If netfilter supports for chain definitions like this:
> > > 
> > >         table x {
> > >                 chain y {
> > >                         type filter hook ingress devices = { eth0, eth1 } priority 0;
> > >                 }
> > >         }
> > > 
> > > Then the chain 'y' implicitly becomes the block for the 'eth0' and
> > > 'eth1' devices.
> > 
> > Can there be more chains for those devices?  Or those will only run y
> > from netfilter perspective?
> 
> In software, the existing control plane allows you to register as
> many chains as you want, that would allow to include 'eth0' and 'eth1'.

I mean, you could add 'eth0' and 'eth1' to several chains, yes.

> However, But I don't have a usecase for this: One single chain should
> be enough given that the ingress hook is only used for filtering. We
> are inheriting this semantics from iptables, where multiple tables at
> different priorities (which specifies the order) make sense, such as
> 'raw', 'mangle' and so on. At ingress, these don't make sense and a
> single chain with priority 0 should be enough.

.. but it doesn't make much sense as I explained.

> In case of hardware offload, I think we should just allow one single
> chain at ingress with 'eth0' and 'eth1', just like tc does. Just
> return EOPNOTSUPP.