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From: Phil Sutter <phil@nwl.cc>
To: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: netfilter-devel@vger.kernel.org
Subject: Re: [iptables PATCH v2 02/10] nft: Implement nft_chain_foreach()
Date: Tue, 13 Oct 2020 11:40:09 +0200
Message-ID: <20201013094009.GT13016@orbyte.nwl.cc> (raw)
In-Reply-To: <20201012120118.GB26845@salvia>

Hi,

On Mon, Oct 12, 2020 at 02:01:18PM +0200, Pablo Neira Ayuso wrote:
> On Wed, Sep 23, 2020 at 07:48:41PM +0200, Phil Sutter wrote:
> > This is just a fancy wrapper around nftnl_chain_list_foreach() with the
> > added benefit of detecting invalid table names or uninitialized chain
> > lists. This in turn allows to drop the checks in flush_rule_cache() and
> > ignore the return code of nft_chain_foreach() as it fails only if the
> > dropped checks had failed, too.
> 
> At quick glance, this is reducing the LoC.
> 
> However, I'm not sure this is better, before this code:
> 
> 1) You fetch the list
> 2) You use it from several spots in the function
> 
> with this patch you might look up for the chain list several times in
> the same function.

Hmm. There might be exceptions, but typically we should have a function
that takes an optional chain name and the body roughly looks like this:

| if (chain) {
| 	return do_something(nft_chain_find(..., chain));
| }
| return nft_chain_foreach(..., do_something);

[...]
> I can also see calls to:
> 
> nft_chain_find(h, table, chain);
> 
> and
> 
> nft_chain_foreach(...)
> 
> from the same function.
> 
> This patch also updates paths in very different ways, there is no
> common idiom being replaced.

Which in particular are those?

The overall agenda is that looking up a chain won't be a trivial
nftnl_chain_list lookup anymore. And iterating over a table's chains
won't be a matter of iterating over a list, because I split base-chains
from user-defined ones:

* Base-chains sit in an array of size NF_INET_NUMHOOKS.
* User-defined chains sit in an (open-coded) list ordered by name.

So the old nft_chain_list_get() is not possible anymore, therefore I
replace everything by either nft_chain_find() or nft_chain_foreach().
Functions should not use both in the same code-path, so if you spot that
I should have a close look again.

Cheers, Phil

  reply index

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-23 17:48 [iptables PATCH v2 00/10] nft: Sorted chain listing et al Phil Sutter
2020-09-23 17:48 ` [iptables PATCH v2 01/10] nft: Fix selective chain compatibility checks Phil Sutter
2020-10-12 11:54   ` Pablo Neira Ayuso
2020-10-13  9:29     ` Phil Sutter
2020-09-23 17:48 ` [iptables PATCH v2 02/10] nft: Implement nft_chain_foreach() Phil Sutter
2020-10-12 12:01   ` Pablo Neira Ayuso
2020-10-13  9:40     ` Phil Sutter [this message]
2020-09-23 17:48 ` [iptables PATCH v2 03/10] nft: cache: Introduce nft_cache_add_chain() Phil Sutter
2020-10-12 12:02   ` Pablo Neira Ayuso
2020-09-23 17:48 ` [iptables PATCH v2 04/10] nft: Eliminate nft_chain_list_get() Phil Sutter
2020-10-12 12:03   ` Pablo Neira Ayuso
2020-10-13  9:44     ` Phil Sutter
2020-09-23 17:48 ` [iptables PATCH v2 05/10] nft: cache: Move nft_chain_find() over Phil Sutter
2020-09-23 17:48 ` [iptables PATCH v2 06/10] nft: Introduce struct nft_chain Phil Sutter
2020-10-12 12:08   ` Pablo Neira Ayuso
2020-10-13  9:56     ` Phil Sutter
2020-09-23 17:48 ` [iptables PATCH v2 07/10] nft: Introduce a dedicated base chain array Phil Sutter
2020-09-23 17:48 ` [iptables PATCH v2 08/10] nft: cache: Sort custom chains by name Phil Sutter
2020-09-23 17:48 ` [iptables PATCH v2 09/10] tests: shell: Drop any dump sorting in place Phil Sutter
2020-09-23 17:48 ` [iptables PATCH v2 10/10] nft: Avoid pointless table/chain creation Phil Sutter

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