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

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 */
}