On Mon, Jun 27, 2016 at 2:47 PM, Tom Herbert <t...@herbertland.com> wrote:
> On Mon, Jun 27, 2016 at 2:44 PM, Cong Wang <xiyou.wangc...@gmail.com> wrote:
>> On Mon, Jun 27, 2016 at 2:08 PM, Or Gerlitz <gerlitz...@gmail.com> wrote:
>>> On Mon, Jun 27, 2016 at 9:22 PM, Cong Wang <xiyou.wangc...@gmail.com> wrote:
>>>> The stack doesn't trust the complete csum by hardware
>>>> even when it is correct.
>>>
>>> Can you explain that a little further?
>>
>> Sure, here is the code in __skb_checksum_complete():
>>
>> /* skb->csum holds pseudo checksum */
>> sum = csum_fold(csum_add(skb->csum, csum));
>> if (likely(!sum)) {
>> if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE) &&
>> !skb->csum_complete_sw)
>> netdev_rx_csum_fault(skb->dev);
>> }
>>
>> So when sum == 0, it means the checksum is correct. And
>> we already set ->ip_summed to CHECKSUM_COMPLETE
>> after check_csum(), and ->csum_complete_sw is initialized
>> to 0 when we allocate the skb. This is why we trigger
>> netdev_rx_csum_fault().
>>
> Yes, but this also means that the driver gave the stack a checksum
> complete value that was incorrect. That's an error.
That is the whole purpose of commit f8c6455bb04b944edb69e,
isn't it?
