Re: [iptables PATCH 00/18] nft: Sorted chain listing et al.

From: Phil Sutter <phil@nwl.cc>
To: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: netfilter-devel@vger.kernel.org
Subject: Re: [iptables PATCH 00/18] nft: Sorted chain listing et al.
Date: Sat, 25 Jul 2020 13:55:41 +0200	[thread overview]
Message-ID: <20200725115541.GA13697@orbyte.nwl.cc> (raw)
In-Reply-To: <20200723122257.GA22824@salvia>

Hi Pablo,

On Thu, Jul 23, 2020 at 02:22:57PM +0200, Pablo Neira Ayuso wrote:
> On Sat, Jul 11, 2020 at 12:18:13PM +0200, Phil Sutter wrote:
> > Work in this series centered around Harald's complaint about seemingly
> > random custom chain ordering in iptables-nft-save output. nftables
> > returns chains in the order they were created which differs from
> > legacy iptables which sorts by name.
> > 
> > The intuitive approach of simply sorting chains in tables'
> > nftnl_chain_lists is problematic since base chains, which shall be
> > dumped first, are contained in there as well. Patch 15 solves this by
> > introducing a per-table array of nftnl_chain pointers to hold only base
> > chains (the hook values determine the array index). The old
> > nftnl_chain_list now contains merely non-base chains and is sorted upon
> > population by the new nftnl_chain_list_add_sorted() function.
> > 
> > Having dedicated slots for base chains allows for another neat trick,
> > namely to create only immediately required base chains. Apart from the
> > obvious case, where adding a rule to OUTPUT chain doesn't cause creation
> > of INPUT or FORWARD chains, this means ruleset modifications can be
> > avoided completely when listing, flushing or zeroing counters (unless
> > chains exist).
> 
> Patches from 1 to 7, they look good to me. Would it be possible to
> apply these patches independently from this batch or they are a strong
> dependency?

I just pushed them after making sure they don't break any of the
testsuites. Fingers crossed I didn't miss a detail which breaks without
the other patches. :)

> I think it's better if we go slightly different direction?
> 
> https://patchwork.ozlabs.org/project/netfilter-devel/patch/20200723121553.7400-1-pablo@netfilter.org/

That's interesting. At least it would allow us to reorganize the
cache-related data structures, e.g. move the nft_cache->table array
items into nft_cache->table items.

> Instead of adding more functions into libnftnl for specific list
> handling, which are not used by nft, use linux list native handling.

OK.

> I think there is not need to cache the full nftnl_table object,
> probably it should be even possible to just use it to collect the
> attributes from the kernel to populate the nft_table object that I'm
> proposing.

Yes, for iptables-nft at least we should be completely fine with table
name alone.

> IIRC embedded people complained on the size of libnftnl, going this
> direction I suggest, we can probably deprecated iterators for a number
> of objects and get it slimmer in the midrun.

OK. I'll keep that in mind.

So I'll rework my changes based on your nft_table idea and introduce an
nft_chain struct to be organized in a standard list_head list. This will
allow me to perform the sorting in iptables-nft itself. Should I base
this onto your nft_table patch (and exploit it a bit further) or keep
them separate for now?

Thanks, Phil