Re: [PATCH net-next 6/8] net: gre: Implement LCO for GRE over IPv4

Alexander Duyck [off-list ref] wrote:

Actually you may want to go the other way on that.  If they weren't
flipping the checksum value for GRE before why should we start doing
that now?  I'm pretty sure the checksum mangling is a very UDP centric
thing.  There is no need to introduce it to other protocols.

If different checksum representations are needed, then there really should  
be an explicit indication of whether it is a UDP-style checksum or other in  
the skb I would think rather than guessing it based on the offset. Of  
course it would be convenient if all the protocols that use a one's  
complement checksum would tolerate the UDP representation. I have a long  
(and now old) history working with real one's complement machines, and so I  
would want to believe that any correct implementation would tolerate it,  
but I don't know for a fact that they do.