From: Pablo Neira Ayuso <pablo@netfilter.org>
To: Phil Sutter <phil@nwl.cc>, netfilter-devel@vger.kernel.org
Subject: Re: [iptables PATCH] nft: Eliminate table list from cache
Date: Fri, 31 Jul 2020 13:25:37 +0200 [thread overview]
Message-ID: <20200731112537.GA10915@salvia> (raw)
In-Reply-To: <20200731112134.GA13697@orbyte.nwl.cc>
On Fri, Jul 31, 2020 at 01:21:34PM +0200, Phil Sutter wrote:
> 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.
Thanks for explaining.
I think the chain cache can also be converted to use linux list,
right?
> > 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.
There is a generation number that the userspace sends to the kernel to
validate that it's working with a stale cache to retry. This should
help catch the interference scenario to basically (transparently)
restart from scratch.
next prev parent reply other threads:[~2020-07-31 11:25 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
2020-07-31 11:25 ` Pablo Neira Ayuso [this message]
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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