netdev - Re: i386 vs x86_64 struct tpacket

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Date:	Fri, 20 Dec 2013 22:22:52 +0100
From:	Norbert van Bolhuis <nvbolhuis@...valley.nl>
To:	Daniel Borkmann <dborkman@...hat.com>
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: i386 vs x86_64 struct tpacket_hdr layout

On 12/20/13 19:45, Daniel Borkmann wrote:
> On 12/20/2013 07:38 PM, David Miller wrote:
>> From: Norbert van Bolhuis <nvbolhuis@...valley.nl>
>> Date: Fri, 20 Dec 2013 14:30:06 +0100
>>
>>>
>>> I'm compiling my 32bit application with -m32 on a x86_64
>>> system/kernel.
>>>
>>> Things aren't working because for my application tp_len is at offset 4
>>> but for the kernel it is at offset 8.
>>>
>>> struct tpacket_hdr {
>>> unsigned long tp_status;
>>> unsigned int tp_len;
>>> unsigned int tp_snaplen;
>>> unsigned short tp_mac;
>>> unsigned short tp_net;
>>> unsigned int tp_sec;
>>> unsigned int tp_usec;
>>> };
>>>
>>> How is this suppose to work ?
>>
>> This is why you should use tpacket layout v2 or v3, rather than v1,
>> they fix these issues.
>
> Norbert, please also read Documentation/networking/packet_mmap.txt
>
> Thanks !


Ah... thanks guys, now I see. struct tpacket2_hdr has fixed layout. I will use v2 (or v3).

I could not find this info in [linux-3.6.8/]Documentation/networking/packet_mmap.txt
though.

---
Norbert.





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