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To: Stephen Hemminger <stephen@networkplumber.org>,
 Yuanhan Liu <yuanhan.liu@linux.intel.com>
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From: Olivier Matz <olivier.matz@6wind.com>
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Date: Tue, 18 Oct 2016 16:07:03 +0200
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Subject: Re: [dpdk-dev] [PATCH v2 12/12] virtio: add Tso support
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Hi Stephen,

On 10/14/2016 01:33 AM, Stephen Hemminger wrote:
> On Thu, 13 Oct 2016 16:18:39 +0800
> Yuanhan Liu <yuanhan.liu@linux.intel.com> wrote:
> 
>> On Mon, Oct 03, 2016 at 11:00:23AM +0200, Olivier Matz wrote:
>>> +/* When doing TSO, the IP length is not included in the pseudo header
>>> + * checksum of the packet given to the PMD, but for virtio it is
>>> + * expected.
>>> + */
>>> +static void
>>> +virtio_tso_fix_cksum(struct rte_mbuf *m)
>>> +{
>>> +	/* common case: header is not fragmented */
>>> +	if (likely(rte_pktmbuf_data_len(m) >= m->l2_len + m->l3_len +
>>> +			m->l4_len)) {  
>> ...
>>> +		/* replace it in the packet */
>>> +		th->cksum = new_cksum;
>>> +	} else {  
>> ...
>>> +		/* replace it in the packet */
>>> +		*rte_pktmbuf_mtod_offset(m, uint8_t *,
>>> +			m->l2_len + m->l3_len + 16) = new_cksum.u8[0];
>>> +		*rte_pktmbuf_mtod_offset(m, uint8_t *,
>>> +			m->l2_len + m->l3_len + 17) = new_cksum.u8[1];
>>> +	}  
>>
>> The tcp header will always be in the mbuf, right? Otherwise, you can't
>> update the cksum field here. What's the point of introducing the "else
>> clause" then?
>>
>> 	--yliu
> 
> You need to check the reference count before updating any data in mbuf.
> 

That's correct, I'll fix that.

Thanks for the comment,
Olivier