netdev - Re: [PATCH] net: increase skb->users instead of skb

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Date:	Thu, 16 Dec 2010 22:20:59 +0800
From:	Junchang Wang <junchangwang@...il.com>
To:	Changli Gao <xiaosuo@...il.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	Tom Herbert <therbert@...gle.com>,
	Jiri Pirko <jpirko@...hat.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	Xinan Tang <xinan.tang@...el.com>, netdev@...r.kernel.org
Subject: Re: [PATCH] net: increase skb->users instead of skb_clone()

On Thu, Dec 16, 2010 at 3:23 PM, Changli Gao <xiaosuo@...il.com> wrote:

>> You beat me, but I was thinking of a different way, adding a new
>> pt_prev->xmit_func(), handling all the details (no need for atomic ops
>> on skb users if packet is not delivered at all).
>>
>> By the way, your patch is not 100% safe/OK, because af_packet rcv()
>> handler writes on skb (skb_pull() and all)
>>
>
> But af_packet_rcv() restores skbs at last.
>
>        if (skb_head != skb->data && skb_shared(skb)) {
>                skb->data = skb_head;
>                skb->len = skb_len;
>        }
>
If af packet_rcv invokes skb_clone, this skb is differ from the original one.
Eric's warning is right.


-- 
--Junchang
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