From: Phil Sutter <phil@nwl.cc>
To: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: netfilter-devel@vger.kernel.org
Subject: Re: [iptables PATCH] nft: Eliminate table list from cache
Date: Fri, 31 Jul 2020 13:21:34 +0200 [thread overview]
Message-ID: <20200731112134.GA13697@orbyte.nwl.cc> (raw)
In-Reply-To: <20200730192554.GA5322@salvia>
Hi Pablo,
On Thu, Jul 30, 2020 at 09:25:54PM +0200, Pablo Neira Ayuso wrote:
> On Thu, Jul 30, 2020 at 03:57:10PM +0200, Phil Sutter wrote:
> > The full list of tables in kernel is not relevant, only those used by
> > iptables-nft and for those, knowing if they exist or not is sufficient.
> > For holding that information, the already existing 'table' array in
> > nft_cache suits well.
> >
> > Consequently, nft_table_find() merely checks if the new 'exists' boolean
> > is true or not and nft_for_each_table() iterates over the builtin_table
> > array in nft_handle, additionally checking the boolean in cache for
> > whether to skip the entry or not.
> >
> > Signed-off-by: Phil Sutter <phil@nwl.cc>
> > ---
> > iptables/nft-cache.c | 73 +++++++++++---------------------------------
> > iptables/nft-cache.h | 9 ------
> > iptables/nft.c | 55 +++++++++------------------------
> > iptables/nft.h | 2 +-
> > 4 files changed, 34 insertions(+), 105 deletions(-)
>
> This diffstat looks interesting :-)
As promised, I wanted to leverage your change for further optimization,
but ended up optimizing your code out along with the old one. :D
> One question:
>
> c->table[i].exists = true;
>
> then we assume this table is still in the kernel and we don't recheck?
Upon each COMMIT line, nft_action() calls nft_release_cache(). This will
also reset the 'exists' value to false.
> I mean, if you pipe command to an open process running
> iptables-restore (which has been the recommended interface for years
> to avoid of the overhead of system() invocation and to ensure atomic
> updates), is there any cache this new approach might get out of sync?
This is not just a problem of iptables-restore running in a pipe -
restoring a large ruleset (or just pure coincidence) could lead to the
same result.
Playing with 'iptables-nft-restore --noflush' reading from stdin and
calling 'nft flush ruleset' in a second shell right before entering
'COMMIT' leads to funny errors. This is not related to the table list
elimination though. I'll investigate.
Cheers, Phil
next prev parent reply other threads:[~2020-07-31 11:21 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-30 13:57 [iptables PATCH] nft: Eliminate table list from cache Phil Sutter
2020-07-30 19:25 ` Pablo Neira Ayuso
2020-07-31 11:21 ` Phil Sutter [this message]
2020-07-31 11:25 ` Pablo Neira Ayuso
2020-07-31 11:26 ` Pablo Neira Ayuso
2020-07-31 11:36 ` Phil Sutter
2020-07-31 11:31 ` Phil Sutter
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