Re: [Xen-devel] [PATCH] Network Checksum Removal

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 21 May 2005, at 00:30, Jon Mason wrote:

> Traffic generated externally, if rx hardware checksum is available and
> enabled, then dom0 will notify domU that it is unnecessary to validate
> this checksum (providing the checksum is valid) by enabling the csum
> bit.  If domU is not notified that it is unnecessary to vaildate the
> checksum, then domU will do it.
Unfortunately you can't trust the ip_summed flag because, as you point 
out yourself, the bridge and IP forwarding paths both clobber it to 
CHECKSUM_NONE. This puts us in a pickle: without hacking in some more 
info we have no way to know whether the physical interface (eth0, say) 
summed the packet or not. And, if it did, whether it was a 
CHECKSUM_UNNECESSARY or a CHECKSUM_HW kind of summing (they differ in 
how you interpret the result).
Your patch as its stands is only correct if eth0 sets 
ip_summed==CHECKSUM_UNNECESSARY on received packets.
 -- Keir


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