netdev - Re: [PATCH] netfilter: Remove skb_is_nonlinear check from nf_conntrack

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Message-ID: <4BED230A.8020002@trash.net>
Date:	Fri, 14 May 2010 12:16:42 +0200
From:	Patrick McHardy <kaber@...sh.net>
To:	Jan Engelhardt <jengelh@...ozas.de>
CC:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	netfilter-devel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH] netfilter: Remove skb_is_nonlinear check from nf_conntrack_sip

Jan Engelhardt wrote:
> On Friday 2010-05-14 02:38, Jason Gunthorpe wrote:
> 
>> At least the XEN net front driver always produces non linear skbs,
>> so the SIP module does nothing at all when used with that NIC.
>>
>> Copy the hacky technique for accessing SKB data from the ftp conntrack,
>> better than nothing..
>>
>> Signed-off-by: Jason Gunthorpe <jgunthorpe@...idianresearch.com>
>>
>> +/* This is slow, but it's simple. --RR */
>> +static char *sip_buffer;
>> +static DEFINE_SPINLOCK(nf_sip_lock);
>> +
> 
> skb_linearize seems simpler. (What about the cost?)

Yeah, we have to use skb_linearize(). The SIP NAT helper might mangle
the packet and alter its size, at which point we'd have to make a new
copy of the data area to get the offsets right.
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