linux-kernel - Re: Protocol handler using dev_add

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Message-ID: <1342016239.3265.8007.camel@edumazet-glaptop>
Date:	Wed, 11 Jul 2012 16:17:19 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jerry Yu <jerryy@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Protocol handler using dev_add_pack

On Wed, 2012-07-11 at 10:38 -0300, Jerry Yu wrote:
> I am working on a kernel module to monitor all TCP packets. I created a protocol
> handler with protocol code ETH_P_ALL to handle all incoming and outgoing
> TCP packets. The code worked fine on 2.6.14 kernel, but in current 3.2.0-26
> kernel, I am no longer able to get the TCP payload for outgoing packets.
> The data in TCP payload section of skb->data are mainly 0x00. I am still
> able to get incoming TCP packets' payloads though.
> 
> Is there any change in 3.2.0 or other early kernel versions that will cause
> this issue?

Maybe you make wrong assumptions in your code.

skb->data doesnt exactly contains tcp payload of locally generated TCP
packets, unless you disabled scatter-gather on the NIC

ehtool -K eth0 sg off



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