Message-ID: <4468F5A0.3040404@trash.net>
Date: Mon, 15 May 2006 23:41:52 +0200
From: Patrick McHardy <kaber@trash.net>
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To: "David S. Miller" <davem@davemloft.net>
CC: ranjitm@google.com, akpm@osdl.org, linux-kernel@vger.kernel.org,
       netdev@vger.kernel.org
Subject: Re: [PATCH] tcpdump may trace some outbound packets twice.
References: <20060514031034.5d0396e7.akpm@osdl.org>	<20060514.134231.101346572.davem@davemloft.net>	<Pine.LNX.4.56.0605151409110.25064@ranjit.corp.google.com> <20060515.142645.94689626.davem@davemloft.net>
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David S. Miller wrote:
> From: Ranjit Manomohan <ranjitm@google.com>
> Date: Mon, 15 May 2006 14:19:06 -0700 (PDT)
> 
> 
>>Heres a new version which does a copy instead of the clone to avoid
>>the double cloning issue.
> 
> 
> I still very much dislike this patch because it is creating
> 1 more clone per packet than is actually necessary and that
> is very expensive.
> 
> dev_queue_xmit_nit() is going to clone whatever SKB you send into
> there, so better to just bump the reference count (with skb_get())
> instead of cloning or copying.


I think this would break the tc actions. Some actions call
pskb_expand_head() on input, which BUGs on skb_shared(skb).
They can't clone the skb instead because the functions
doing that don't own it, the caller would continue with the
old skb.
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