RX checksum offloading problem

[Michael Tuexen]

On 13 May 2014, at 07:21, Yonghyeon PYUN <pyunyh at gmail.com> wrote:

> On Mon, May 12, 2014 at 01:22:03PM +0200, Michael Tuexen wrote:
>> On 12 May 2014, at 03:36, Yonghyeon PYUN <pyunyh at gmail.com> wrote:
>> 
>>> On Fri, May 09, 2014 at 12:46:48PM +0200, Michael Tuexen wrote:
>>>> On 09 May 2014, at 03:35, Yonghyeon PYUN <pyunyh at gmail.com> wrote:
>>>> 
> 
> [...]
> 
>>> Oops, sorry. You're right.  Probably I was confused with old memory
>>> when I worked on that area.  I've quickly read IP reassembly code
>>> again and as you said, it should work.  However it seems there is a
>>> checksumming bug here.
>>> 
>>> 	/*
>>> 	 * In order to do checksumming faster we do 'end-around carry' here
>>> 	 * (and not in for{} loop), though it implies we are not going to
>>> 	 * reassemble more than 64k fragments.
>>> 	 */
>>> 	m->m_pkthdr.csum_data =
>>> 	    (m->m_pkthdr.csum_data & 0xffff) + (m->m_pkthdr.csum_data >> 16);
>>> 
>>> I guess the line above didn't account possible carry happened after
>>> the computation.  Probably it could be rewritten as the following.
>>> 
>>> 	while (m->m_pkthdr.csum_data & 0xffff0000)
>>> 		m->m_pkthdr.csum_data = (m->m_pkthdr.csum_data & 0xffff) +
>>> 		    (m->m_pkthdr.csum_data >> 16);
>> I think you are right here. Good catch. Will you fix it?
>> 
> 
> Done in r265942.
Great. Thanks.
Michael
>