Re: [PATCH 1/4] pch_gbe: Fix the checksum fill to the error location

[Eric Dumazet <eric.dumazet@gmail.com>]

On Tue, 2012-07-17 at 16:04 +0800, Zhong Hongbo wrote:

> Hi Eric,
> 
> When forwarding network packages at the network layer, the variable
> value of skb->transport_header is unknown. In my test, the variable
> value of skb->transport_header is equal to skb->network_header. So
> When you count the checksum as following:
> 
> offset = skb_transport_offset(skb);
> 
> skb->csum = skb_checksum(skb, offset, skb->len - offset, 0);
> We should only count the TCP checksum, But it maybe include IP part.
> 
> tcp_hdr(skb)->check = csum_tcpudp_magic(iph->saddr, iph->daddr,
> skb->len - offset, IPPROTO_TCP, skb->csum);
> We should fill the checksum in TCP package, But maybe fill it in other
> location and cover the useful information, such as source ip.
> 
> So We should count the TCP checksum and fill it in the correct
> location. Or else the forwarding network package will be drop for the
> error checksum.
> 



So maybe you should instead test 

if (skb->ip_summed == CHECKSUM_PARTIAL) {
	...
	skb_checksum_start_offset(skb); /* is valid */
}