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Date: Tue, 27 Sep 2011 12:59:20 +0200
From: Jan Kiszka <jan.kiszka@siemens.com>
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Subject: Re: [Qemu-devel] [PATCH] slirp: Fix packet expiration
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To: Fabien Chouteau <chouteau@adacore.com>
Cc: Thomas Huth <thuth@linux.vnet.ibm.com>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

On 2011-09-27 12:56, Fabien Chouteau wrote:
> On 27/09/2011 11:20, Thomas Huth wrote:
>>
>> The two new variables "arp_requested" and "expiration_date" in the mbuf
>> structure have been added after the variable-sized "m_dat_" array. The
>> variables have to be added before the m_dat_ array instead.
>> Without this patch, the expiration_date gets clobbered by code that
>> accesses the m_dat_ array.
>> I experienced this problem with the code in slirp/tftp.c: The
>> tftp_send_data() function created a new packet with the m_get()
>> function (which fills-in a default expiration_date value). Then the
>> TFTP code cleared the data section of the packet, which accidentially
>> also cleared the expiration_date. This zeroed expiration_date then
>> finally causes the packet to be discarded during if_start(), so that
>> TFTP packets were not transmitted anymore.
>>
> 
> Thanks for the patch Thomas.
> 
> I think we can add a comment to avoid this kind of mistake in the
> future.
> 
> /* This is a "flexible array member". It should always remain
>  * the last member of the structure.
>  */

Good point, folded something like that in.

Thanks,
Jan

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