Re: [nft PATCH v2 0/4] xt: Implement dump and restore support

[Florian Westphal <fw@strlen.de>]

Phil Sutter <phil@nwl.cc> wrote:
> On Fri, Nov 18, 2022 at 11:11:42AM +0100, Pablo Neira Ayuso wrote:
> > Merging threads.
> > 
> > On Fri, Nov 18, 2022 at 10:55:04AM +0100, Phil Sutter wrote:
> > [...]
> > > > I think this more or less a summary of what we discussed in the NFWS.
> > >
> > > Pablo, I think you're mixing up two things here:
> > >
> > > This "support dump and load of compat expression" feature is to sanitize
> > > the current situation with up to date iptables and nftables.
> > 
> > OK, then the problem we discuss is mixing iptables-nft and nftables.
> > 
> > On Fri, Nov 18, 2022 at 10:47:48AM +0100, Phil Sutter wrote:
> > [...]
> > > > At this time I'd rather like a time machine to prevent nft_compat.c from
> > > > getting merged :-(
> > >
> > > If you do, please convince Pablo to not push iptables commit 384958620a.
> > > I think it opened the can of worms we're trying to confine here.
> > 
> > It could be worst, if iptables-nft would not be in place, then old
> > iptables-legacy and new nftables rules would have no visibility each
> > other.
> > 
> > With iptables-nft we have a way to move forward:
> > 
> > - Replace nft_compat by native expressions from iptables-nft.
> > - Extend iptables-nft to understand more complex expressions, worst
> >   case dump a native representation.
> > 
> > Why don't we just move ahead this path instead of spinning around the
> > compat layer? This only requires userspace updates on iptables-nft.
> 
> Sure! I'm just picking low hanging fruits first. With even translation
> support being still incomplete, I fear it will take a while until the
> tools are fluent enough for this to not matter anymore. And then there's
> still nftables without libxtables support.

Then perhaps its better to do following path:
1. Try ->xlate(), if that fails, then print a 'breaking' format?

As far as I understand the problem is the "# comment" - type syntax that
makes nft just skip the incomplete rule, so perhaps just use invalid
format?

Example:

counter packets 0 bytes 0 # name foo interval 250.0ms ewmalog 500.0ms
Instead make this something like
counter packets 0 bytes 0 nft_compat [ RATEEST name foo interval 250.0ms ewmalog 500.0ms ] # unsupported iptables-nft rule

?

I'd like to avoid exposure in the frontend with compatible-restore-approach if possible.