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

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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