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Date:   Thu, 19 Sep 2019 11:24:42 +0200
From:   Florian Westphal <fw@strlen.de>
To:     Pablo Neira Ayuso <pablo@netfilter.org>
Cc:     Florian Westphal <fw@strlen.de>, Laura Garcia <nevola@gmail.com>,
        netfilter-devel <netfilter-devel@vger.kernel.org>
Subject: Re: What is 'dynamic' set flag supposed to mean?
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Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> On Wed, Sep 18, 2019 at 04:42:35PM +0200, Florian Westphal wrote:
> > Laura Garcia <nevola@gmail.com> wrote:
> > > > Following example loads fine:
> > > > table ip NAT {
> > > >   set set1 {
> > > >     type ipv4_addr
> > > >     size 64
> > > >     flags dynamic,timeout
> > > >     timeout 1m
> > > >   }
> > > >
> > > >   chain PREROUTING {
> > > >      type nat hook prerouting priority -101; policy accept;
> > > >   }
> > > > }
> > > >
> > > > But adding/using this set doesn't work:
> > > > nft -- add rule NAT PREROUTING tcp dport 80 ip saddr @set1 counter
> > > > Error: Could not process rule: Operation not supported
> > > 
> > > If this set is only for matching, 'dynamic' is not required.
> > 
> > I know, and the example above works if the 'dynamic' flag is omitted.
> 
> Looks like a kernel bug, kernel is selecting the fixed size hash with
> the dynamic flag. That should not happen.

No, it selects the rhashtable one -- its the only one that sets
NFT_SET_EVAL.

> > > > The rule add is rejected from the lookup expression (nft_lookup_init)
> > > > which has:
> > > >
> > > > if (set->flags & NFT_SET_EVAL)
> > > >     return -EOPNOTSUPP;

... and thats the reason why it won't work.  "dynamic" flag disables
lookup expression for the given set.

I can't remove the if () because that would make it possible to lookup
for meter-type sets.