Re: [PATCH net] enic: fix rx skb checksum

[Jiri Benc <jbenc@redhat.com>]

On Fri, 19 Dec 2014 16:22:34 +0530 (IST), Govindarajulu Varadarajan wrote:
> Hardware returns 0xffff for non tcp/udp packets.

That explains that I saw that with ICMP packets.

> For tcp/udp packet it returns
> pseudo checksum. Not the _whole_ pkt checksum.

I see. I didn't get this from your patch, although you wrote it there,
sorry. And I didn't dig that deep while debugging, I was satisfied with
seeing 0xffff for the packets that caused problems :-)

> Dec 18 11:13:18 a163 kernel: enic: saddr=96d8690a, daddr=a3ba6a0a, length=40, proto=6
> Dec 18 11:13:18 a163 kernel: enic: hw_checksum = c457, pseudo_checksum_32=3a930115, pseudo_checksum_fold=c457
> 
> Dec 18 11:13:18 a163 kernel: enic: saddr=a37410a, daddr=a3ba6a0a, length=32, proto=6
> Dec 18 11:13:18 a163 kernel: enic: hw_checksum = 80f9, pseudo_checksum_32=adf1d114, pseudo_checksum_fold=80f9
> 
> Dec 18 11:13:18 a163 kernel: enic: saddr=a37410a, daddr=a3ba6a0a, length=32, proto=6
> Dec 18 11:13:18 a163 kernel: enic: hw_checksum = 80f9, pseudo_checksum_32=adf1d114, pseudo_checksum_fold=80f9
> 
> Clearly hw is returning folded pseudo checksum.

Indeed.

> > I have no idea whether the hardware verified the checksum for the
> > 0xffff case and is just not returning the checksum or whether such
> > packets come completely unverified.
> 
> Yes, hardware verifies the checksum and sets tcp_udp_csum_ok flag to 1.
> If pkt verification fails or pkt is not tcp/udp, tcp_udp_csum_ok is 0. And we
> send the pkt to stack with CHECKSUM_NONE.

Thanks for the confirmation.

> Driver should use CHECKSUM_COMPLETE only if it can produce _whole_ pkt checksum.
> as described in include/linux/skbuff.h:75

Sure. I just misunderstood what the hardware provides.

> I am trying to fix "Do not set CHECKSUM_COMPLETE, when driver does not have
> checksum of whole pkt."
> 
> Is my understanding correct?

With the information you've just written (thanks for your patience),
I think your patch is correct.

Thanks a lot!

 Jiri

-- 
Jiri Benc