Re: [Xen-devel] [PATCH] Fix checksum errors when firewalling in domU

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

On 10 May 2006, at 16:39, Keir Fraser wrote:

> > Right, that was hiding more brokenness. Fixed below.
> >
> > Signed-off-by: Jim Dykman <dykman@xxxxxxxxxx>
> > Fix checksum errors when firewalling in domU
> Two more questions:
>  1. Why do you need to check proto_csum_blank in the start_xmit() 
> handling paths of netfront and netback? skb_checksum_setup() will have 
> set ip_summed=CHECKSUM_HW in all cases won't it?
>  2. The change to not aggressively clear proto_csum_blank appears to 
> make sense. However, why not clear it inside skb_checksum_help(), 
> rather than modifying two of its callers to do so? Because it'll be in 
> one place we can wrap in ifdef XEN rather than needing to add yet 
> another wrapper function to do the clearing.
Ah, now I *think* I understand where all these problems are emanating 
from. You added code to copy proto_csum_blank when we copy a packet in 
the start_xmit handler of netback. However, what you *really* want to 
copy is ip_summed, as it's that which we use to determine if 
checksum-offload is required or not (not proto_csum_blank).
I bet that, with copying of ip_summed added to netback, the rest of 
your patch will not be required.
A similar patch is also needed in two(!) places in netfront. I've 
applied a patch to fix all of them. Let's see how far that gets us.
 Thanks,
 Keir


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