why does virtio not support IPv4 CKSUM?

[jiangheng (G)]

>> Hi 
>> 
>> why does virtio not support IPv4 CKSUM? But support TCP/UDP cksum.

> Because virtio is a software driver developed on Linux and Linux doesn't need/want IP checksum offload.
> It takes longer to look at offload bits then to compute checksum in SW.

However, Virtio supports LRO. Is it possible to merge packets with incorrect cksum?
Must cksum offload be enabled when LRO enabled?

>> 
>> If not support ipv4 cksum, when I use GRO, the ip cksum of the packets transmitted to ip layer will be incorrect.
>> I have to calculate ip cksum before packet was transmiited to ip layer.
>> So why does virtio not support ipv4 cksum ?