netdev - Re: pskb_copy() in tcp_transmit

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Message-ID: <CAL4Wiirw1kjBEDVHDNETb7MwEenq0x2XOtQKdzYtNkp1m3nrrA@mail.gmail.com>
Date:	Tue, 13 Sep 2011 14:51:16 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	christoph.paasch@...ouvain.be
Cc:	Gaofeng <gaofeng@...fujitsu.com>, netdev@...r.kernel.org
Subject: Re: pskb_copy() in tcp_transmit_skb()

Le 13 septembre 2011 14:41, Christoph Paasch
<christoph.paasch@...ouvain.be> a écrit :
> Eric,
>
> On Tuesday 13 September 2011 wrote Eric Dumazet:
>> I suggest you read dev_queue_xmit_nit() : Every xmit packet can be
>> cloned right here.
>>
>> By the time tcp_retransmit_skb() is called, cloned skb might still be
>> in a AF_PACKET queue (or even a device TX queue)
>
> Thanks for the clear answer.
>
> So, basically every call to tcp_retransmit_skb on an skb that is also still
> hold in an AF_PACKET queue will end up in pskb_copy, because:
> 1. it has been cloned previously in tcp_transmit_skb()
> 2. The data_ref > 1 because it's clone is still in an AF_PACKET queue.
>
> Please correct me, if I'm wrong.

Thats correct.
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