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

[Pablo Neira Ayuso <pablo@netfilter.org>]

Hi Phil,

On Sat, Jul 25, 2020 at 01:55:41PM +0200, Phil Sutter wrote:
> 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. :)

Good.

> > 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.

Good.

> > 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.

Good.

> Should I base this onto your nft_table patch (and exploit it a bit
> further) or keep them separate for now?

I'll push it out so you can rebase on top, OK?

Thanks.