netdev - Re: [Patch net] net: invert the check of detecting hardware RX checksum fault

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Message-ID: <CAM_iQpX8jpfq1CtavmsOvcfTW=ecPeUn5gJFNG1Z4NU+_urv6Q@mail.gmail.com>
Date:   Fri, 16 Nov 2018 12:15:01 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Herbert Xu <herbert@...dor.apana.org.au>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Tom Herbert <tom@...bertland.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Saeed Mahameed <saeedm@...lanox.com>
Subject: Re: [Patch net] net: invert the check of detecting hardware RX
 checksum fault

On Thu, Nov 15, 2018 at 8:52 PM Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> It is very possible NIC provides an incorrect CHECKSUM_COMPLETE, in the
> case non zero trailer bytes were added by a buggy switch (or host)
>
> Saeed can comment/confirm, but the theory is that the NIC does header analysis and
> computes a checksum only on the bytes of the IP frame, not including the tail bytes
> that were added by a switch.


This theory seems can't explain why Pawel saw this warning so often,
which is beyond the probability of a buggy switch. I don't know.


>
> You could use trafgen to cook such a frame and confirm the theory.
>
> Something like :

I will try it.

Thanks.