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

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.


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