Re: about rx checksum flags

[Olivier MATZ <olivier.matz@6wind.com>]

Hi Stephen,

On 05/31/2016 10:28 PM, Stephen Hemminger wrote:
> On Tue, 31 May 2016 21:11:59 +0200
> Olivier MATZ <olivier.matz@6wind.com> wrote:
> 
>>
>>
>> On 05/31/2016 10:09 AM, Yuanhan Liu wrote:
>>> On Mon, May 30, 2016 at 05:26:21PM +0200, Olivier Matz wrote:
>>>>  PKT_RX_L4_CKSUM_NONE: the L4 checksum is not correct in the packet
>>>>  data, but the integrity of the L4 header is verified.
>>>>   -> the application can process the packet but must not verify the
>>>>      checksum by sw. It has to take care to recalculate the cksum
>>>>      if the packet is transmitted (either by sw or using tx offload)
>>>
>>> I like the explanation you made at [1] better :)
>>>
>>> So in general, I think this proposal is good to have.
>>
>> Thanks everyone for your feedback.
>>
>> I'll try to send a first patch proposition soon.
>>
>> Regards,
>> Olivier
> 
> I think it is time to ditch the old definitions of Rx checksum and instead
> use something more compatiable with virtio (and Linux). I.e have three values
>   1) checksum is know good for packet contents
>   2) checksum value one's complement for packet contents
>   3) checksum is undetermined
> The original definition seems to be Intel HW centric and applies to a limited
> range of devices making it unusable by general application.
> 
> Break the ABI, and ditch the old values (ok mark PKT_RX_L4_CKSUM_BAD as __deprecated
> and remove all usage).
> 

Don't you think knowing that a checksum is bad could be useful?
In that case the application can drop/log the packet without any
additional cpu cost.

What do you mean by beeing unusable by general application?

I think the "2)" also requires a csum_start + csum_offset in
mbuf structure, right?

Do you also suggest to drop IP checksum flags?

Will it be possible to manage tunnel checksums?

I think this would be a pretty big change. If there is no additional
argument than beeing more compatible with virtio/linux, I'm wondering
if it's worth breaking the API. Let's wait for other opinions.

Thanks for your feedback.
Olivier