netdev - Re: [PATCH] virtio: don't set VIRTIO_NET_HDR_F_DATA

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Date:   Wed, 18 Jan 2017 11:54:21 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>,
        Rolf Neugebauer <rolf.neugebauer@...ker.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net,
        rppt@...ux.vnet.ibm.com
Subject: Re: [PATCH] virtio: don't set VIRTIO_NET_HDR_F_DATA_VALID on xmit



On 2017年01月18日 02:27, Michael S. Tsirkin wrote:
> On Tue, Jan 17, 2017 at 06:13:51PM +0000, Rolf Neugebauer wrote:
>> This patch part reverts fd2a0437dc33 and e858fae2b0b8 which introduced a
>> subtle change in how the virtio_net flags are derived from the SKBs
>> ip_summed field.
>>
>> With the above commits, the flags are set to VIRTIO_NET_HDR_F_DATA_VALID
>> when ip_summed == CHECKSUM_UNNECESSARY, thus treating it differently to
>> ip_summed == CHECKSUM_NONE, which should be the same.
>>
>> Further, the virtio spec 1.0 / CS04 explicitly says that
>> VIRTIO_NET_HDR_F_DATA_VALID must not be set by the driver.
>>
>> Signed-off-by: Rolf Neugebauer <rolf.neugebauer@...ker.com>
> Fixes: fd2a0437dc33 ("virtio_net: introduce virtio_net_hdr_{from,to}_skb")
> Fixes: e858fae2b0b8 (" virtio_net: use common code for virtio_net_hdr and skb GSO conversion")
> Acked-by: Michael S. Tsirkin <mst@...hat.com>
>
> Should be backported into stable as well.

Looks like a side effect is that we will never see this on receive path? 
We probably need a hint for virtio_net_hdr_from_skb().

Thanks

>
>
>> ---
>>   include/linux/virtio_net.h | 2 --
>>   1 file changed, 2 deletions(-)
>>
>> diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
>> index 66204007d7ac..56436472ccc7 100644
>> --- a/include/linux/virtio_net.h
>> +++ b/include/linux/virtio_net.h
>> @@ -91,8 +91,6 @@ static inline int virtio_net_hdr_from_skb(const struct sk_buff *skb,
>>   				skb_checksum_start_offset(skb));
>>   		hdr->csum_offset = __cpu_to_virtio16(little_endian,
>>   				skb->csum_offset);
>> -	} else if (skb->ip_summed == CHECKSUM_UNNECESSARY) {
>> -		hdr->flags = VIRTIO_NET_HDR_F_DATA_VALID;
>>   	} /* else everything is zero */
>>   
>>   	return 0;
>> -- 
>> 2.11.0