netdev - Re: [PATCH nf-next-2.6] netfilter: add xt

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Date:	Thu, 22 Jul 2010 17:39:34 +0200 (CEST)
From:	Jan Engelhardt <jengelh@...ozas.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Patrick McHardy <kaber@...sh.net>,
	Netfilter Development Mailinglist 
	<netfilter-devel@...r.kernel.org>, netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH nf-next-2.6] netfilter: add xt_cpu match

On Thursday 2010-07-22 17:18, Eric Dumazet wrote:

>Le jeudi 22 juillet 2010 à 16:19 +0200, Jan Engelhardt a écrit :
>> On Thursday 2010-07-22 16:03, Eric Dumazet wrote:
>> 
>> >This match is a bit strange, being packet content agnostic...
>> >+/*
>> >+ * Yes, packet content is not interesting for us, we only take care
>> >+ * of cpu handling this packet
>> >+ */
>> 
>> That is not so strange after all, we have many packet agnostic matches: 
>> xt_time, xt_condition, xt_IDLETIMER, xt_iface.
>> So this little comment looks a bit redundant.
>> 
>> Or it seems that academia can't come up with enough new protocols in time that
>> we have to resort to do -m coffeemaker :)
>> 
>> >@@ -0,0 +1,8 @@
>> >+#ifndef _XT_CPU_H
>> >+#define _XT_CPU_H
>> >+
>> >+struct xt_cpu_info {
>> >+	unsigned int	cpu;
>> >+	int		invert;
>> >+};
>> >+#endif /*_XT_MAC_H*/
>> 
>> Please take a read in "Writing Netfilter Modules" e-book :-)
>> It will tell you that types other than fixed ones are a no-no.
>
>Ok, let's do that, but I doubt sizeof(int) can be different than 4 on a
>Linux 2.6 host right now.

Never say never. "long" already bit people in the past, and now we
have that CONFIG_COMPAT stuff.

If invert is the only flag, perhaps it makes sense to use __u8 
for it. 

>I prefer not doing the !!info->invert, and do the check only once.

>+static int cpu_mt_check(const struct xt_mtchk_param *par)
>+{
>+	const struct xt_cpu_info *info = par->matchinfo;
>+
>+	if (info->invert & ~1)
>+		return -EINVAL;
>+	return 0;
>+}
>+
>+static bool cpu_mt(const struct sk_buff *skb, struct xt_action_param *par)
>+{
>+	const struct xt_cpu_info *info = par->matchinfo;
>+
>+	return (info->cpu == smp_processor_id()) ^ info->invert;
>+}

That works nicely indeed. Do you anticipate any future flags?

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