linux-kernel - Re: [PATCH net-next RFC] netfilter: flowtable: add CT metadata action for nft flowtables

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Message-ID: <aNR12z5OQzsC0yKl@calendula>
Date: Thu, 25 Sep 2025 00:51:07 +0200
From: Pablo Neira Ayuso <pablo@...filter.org>
To: Elad Yifee <eladwf@...il.com>
Cc: Jozsef Kadlecsik <kadlec@...filter.org>,
	Florian Westphal <fw@...len.de>, Phil Sutter <phil@....cc>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, netfilter-devel@...r.kernel.org,
	coreteam@...filter.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next RFC] netfilter: flowtable: add CT metadata
 action for nft flowtables

On Wed, Sep 17, 2025 at 08:33:49PM +0300, Elad Yifee wrote:
> On Wed, Sep 17, 2025 at 11:18 AM Pablo Neira Ayuso <pablo@...filter.org> wrote:
> > Just to make sure we are on the same page: Software plane has to match
> > the capabilities of the hardware offload plan, new features must work
> > first in the software plane, then extend the hardware offload plane to
> > support it.
> 
> Thanks - I see what you meant now.
> 
> This isn’t a new feature that needs to be implemented in software
> first. We’re not introducing new user semantics, matches, or actions
> in nft/TC. no datapath changes (including the flowtable software
> offload fast path). The change only surfaces existing CT state
> (mark/labels/dir) as FLOW_ACTION_CT_METADATA at the hardware offload
> boundary so drivers can use it for per-flow QoS, or simply ignore it.
>
> When a flow stays in software, behavior remains exactly as today,
> software QoS continues to use existing tools (nft/TC setting
> skb->priority/mark, qdiscs, etc.). There’s no SW-HW mismatch
> introduced here.

You have to show me there is no mismatch.

This is exposing the current ct mark/label to your hardware, the
flowtable infrastructure (the software representation) makes no use of
this information from the flowtable datapath, can you explain how you
plan to use this?

Thanks.