From: Pablo Neira Ayuso <pablo@netfilter.org>
To: Florian Westphal <fw@strlen.de>
Cc: netfilter-devel <netfilter-devel@vger.kernel.org>
Subject: Re: [PATCH 3/3] netfilter: ctnetlink: allow userspace to set labels
Date: Fri, 30 Nov 2012 19:34:50 +0100 [thread overview]
Message-ID: <20121130183450.GA27138@1984> (raw)
In-Reply-To: <20121130140254.GB31969@breakpoint.cc>
On Fri, Nov 30, 2012 at 03:02:54PM +0100, Florian Westphal wrote:
> Pablo Neira Ayuso <pablo@netfilter.org> wrote:
> > Quick idea: I think we can also support atomic replacement at word
> > size using xchg, so the replacement operation can still happen at word
> > level. Setting many bits at once would be also faster with that.
>
> Unfortunately, no -- the interface is too rudimentary.
> Example: You want to set bis 0, 2, 6; but leave all other
> bit that are set intact.
>
> So you first need to make a dump to fetch the current labels set.
> Then, you set bits 0, 2, 6 and send the new state to the kernel.
>
> But between the dump and the set operation, a new bit might
> have been set. So even when using xchg it will be un-set again...
what about cmpxchg inside a loop? I think we can assume that the
probability of interference while updating a word is low.
next prev parent reply other threads:[~2012-11-30 18:34 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-11-15 15:55 [PATCH 0/3] netfilter: add connlabel conntrack extension Florian Westphal
2012-11-15 15:55 ` [PATCH 1/3] " Florian Westphal
2012-11-15 15:55 ` [PATCH 2/3] netfilter: ctnetlink: deliver labels to userspace via CTA_LABELS attribute Florian Westphal
2012-11-15 15:55 ` [PATCH 3/3] netfilter: ctnetlink: allow userspace to set labels Florian Westphal
2012-11-27 11:18 ` Pablo Neira Ayuso
2012-11-27 11:50 ` Florian Westphal
2012-11-27 12:31 ` Pablo Neira Ayuso
2012-11-27 13:09 ` Florian Westphal
2012-11-27 14:13 ` Pablo Neira Ayuso
2012-11-27 14:24 ` Florian Westphal
2012-11-30 13:58 ` Pablo Neira Ayuso
2012-11-30 14:02 ` Florian Westphal
2012-11-30 18:34 ` Pablo Neira Ayuso [this message]
2012-11-30 21:36 ` Florian Westphal
2012-12-03 11:04 ` Pablo Neira Ayuso
2012-12-03 11:13 ` Florian Westphal
2012-12-03 12:58 ` Pablo Neira Ayuso
2012-11-27 12:39 ` Pablo Neira Ayuso
2012-11-16 10:02 ` [PATCH 0/3] netfilter: add connlabel conntrack extension Pablo Neira Ayuso
2012-11-16 11:31 ` Florian Westphal
2012-11-16 11:52 ` Pablo Neira Ayuso
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