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Date:   Thu, 27 Apr 2023 13:01:55 +0200
From:   Pablo Neira Ayuso <pablo@netfilter.org>
To:     Phil Sutter <phil@nwl.cc>, Florian Westphal <fw@strlen.de>,
        netfilter-devel@vger.kernel.org
Subject: Re: [nf-next PATCH v2] netfilter: nf_tables: Introduce
 NFTA_RULE_ACTUAL_EXPR
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On Thu, Apr 27, 2023 at 12:57:30PM +0200, Phil Sutter wrote:
> Hi Pablo,
> 
> On Wed, Apr 26, 2023 at 09:58:44PM +0200, Pablo Neira Ayuso wrote:
> [...]
> > My proposal:
> 
> Thanks for returning to this. Your approach requires to define a minimum
> version from which on forward-compat is guaranteed. I was trying to
> avoid this requirement though so things would work for "unknown user
> space".

You also require a kernel that supports your approach.

> Currently, the only offending extension is ebt_among since it doesn't
> exist (and never did) in non-native form. If I implement among extension
> parsing (even in non-functional form), my original approach would work.
> This also means having a minimum version for full compat, but it affects
> ebtables (actually, use of ebt_among) only.

Yes, but this is fully user data, kernel really does not need to do
anything with this alternative representation, which is what I do not
like from you proposal.

I really think userdata is the place to deal with this.