netdev - Re: [PATCH] netfilter: xtables: userspace notification target

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Date:	Tue, 13 Jul 2010 15:28:50 +0200
From:	Samuel Ortiz <sameo@...ux.intel.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	Patrick McHardy <kaber@...sh.net>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	netfilter-devel@...r.kernel.org,
	Luciano Coelho <luciano.coelho@...ia.com>
Subject: Re: [PATCH] netfilter: xtables: userspace notification target

On Tue, Jul 13, 2010 at 02:18:26PM +0800, Changli Gao wrote:
> On Tue, Jul 13, 2010 at 8:11 AM, Samuel Ortiz <sameo@...ux.intel.com> wrote:
> >
> > The userspace notification Xtables target sends a netlink notification
> > whenever a packet hits the target. Notifications have a label attribute
> > for userspace to match it against a previously set rule. The rules also
> > take a --all option to switch between sending a notification for all
> > packets or for the first one only.
> > Userspace can also send a netlink message to toggle this switch while the
> > target is in place. This target uses the nefilter netlink framework.
> >
> > This target combined with various matches (quota, rateest, etc..) allows
> > userspace to make decisions on interfaces handling. One could for example
> > decide to switch between power saving modes depending on estimated rate
> > thresholds.
> >
> 
> It much like the following iptables rules.
> 
> iptables -N log_and_drop
> iptables -A log_and_drop -j NFLOG --nflog-group 1 --nflog-prefix "log_and_drop"
> iptables -A log_and_drop -j DROP
> 
> ...
> iptables ... -m quota --quota-bytes 20000 -j log_and_drop
> ...
We'd still be missing the possibility of having only the first packet logged,
and we'd have to also send an initial netlink message to switch the copy_mode
to COPY_NONE. We're not interested in the actual packet, but just by the match
hit.
I know it's not big deal after all, I'm just trying to have one simple target
for that simple task of notifying userspace of a match hit.

> > +static unsigned int nfnotif_tg_target(struct sk_buff *skb,
> > +                                     const struct xt_action_param *par)
> > +{
> > +       const struct nfnotif_tg_info *info = par->targinfo;
> > +
> > +       BUG_ON(!info->notif);
> > +
> > +       if (!info->notif->send_notif)
> > +               return XT_CONTINUE;
> > +
> > +       pr_debug("Sending notification for %s\n", info->label);
> > +
> > +       schedule_work(&info->notif->work);
> > +
> 
> Why do you use another kernel activity: kernel thread? netlink
> messages can be sent in atomic context.
That's right, I should have used the ATOMIC gfp flags from my sending routine.
I'll fix that with my next revision of the patch.

Thanks for the review.

Cheers,
Samuel.

-- 
Intel Open Source Technology Centre
http://oss.intel.com/
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