netdev - Re: pskb_copy() in tcp_transmit

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Message-Id: <201109131355.55588.christoph.paasch@uclouvain.be>
Date:	Tue, 13 Sep 2011 13:55:55 +0300
From:	Christoph Paasch <christoph.paasch@...ouvain.be>
To:	Gaofeng <gaofeng@...fujitsu.com>
Cc:	netdev@...r.kernel.org
Subject: Re: pskb_copy() in tcp_transmit_skb()

Hi,

On Tuesday 13 September 2011 wrote Gaofeng:
> > I'm trying to understand the reason for the possible call to pskb_copy()
> > in tcp_transmit_skb().
> > I don't find, where we may have a cloned skb entering tcp_transmit_skb().
> > 
> > The original pskb_copy() came from tcp_retransmit_skb() (commit
> > dfb4b9dceb35c567a595ae5e9d035cfda044a103).
> > But from that point, the git-history does not show where the pskb_copy()
> > is coming from.
> > 
> > 
> > Does somebody has an idea, how a cloned skb can be passed to
> > tcp_transmit_skb() and thus trigger this call to pskb_copy().
>
> maybe nat,nat can change the tcp packet header

although NAT may change the TCP header, it is not doing an skb_clone() - (at 
least I don't find it).
Thus, we will not call pskb_copy() in tcp_transmit_skb() due to NAT.

Christoph

--
Christoph Paasch
PhD Student

IP Networking Lab --- http://inl.info.ucl.ac.be
MultiPath TCP in the Linux Kernel --- http://inl.info.ucl.ac.be/mptcp
Université Catholique de Louvain

www.rollerbulls.be
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