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SubjectRe: [PATCH] tcpdump may trace some outbound packets twice.
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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