From 663ead3bb8d5b561e70fc3bb3861c9220b5a77eb Mon Sep 17 00:00:00 2001 From: Herbert Xu Date: Mon, 9 Apr 2007 11:59:07 -0700 Subject: [NET]: Use csum_start offset instead of skb_transport_header The skb transport pointer is currently used to specify the start of the checksum region for transmit checksum offload. Unfortunately, the same pointer is also used during receive side processing. This creates a problem when we want to retransmit a received packet with partial checksums since the skb transport pointer would be overwritten. This patch solves this problem by creating a new 16-bit csum_start offset value to replace the skb transport header for the purpose of checksums. This offset is calculated from skb->head so that it does not have to change when skb->data changes. No extra space is required since csum_offset itself fits within a 16-bit word so we can use the other 16 bits for csum_start. For backwards compatibility, just before we push a packet with partial checksums off into the device driver, we set the skb transport header to what it would have been under the old scheme. Signed-off-by: Herbert Xu Signed-off-by: David S. Miller --- net/ipv4/tcp_ipv4.c | 2 ++ 1 file changed, 2 insertions(+) (limited to 'net/ipv4/tcp_ipv4.c') diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index e11eaf4cc269..a091a99ad263 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -504,6 +504,7 @@ void tcp_v4_send_check(struct sock *sk, int len, struct sk_buff *skb) if (skb->ip_summed == CHECKSUM_PARTIAL) { th->check = ~tcp_v4_check(len, inet->saddr, inet->daddr, 0); + skb->csum_start = skb_transport_header(skb) - skb->head; skb->csum_offset = offsetof(struct tcphdr, check); } else { th->check = tcp_v4_check(len, inet->saddr, inet->daddr, @@ -526,6 +527,7 @@ int tcp_v4_gso_send_check(struct sk_buff *skb) th->check = 0; th->check = ~tcp_v4_check(skb->len, iph->saddr, iph->daddr, 0); + skb->csum_start = skb_transport_header(skb) - skb->head; skb->csum_offset = offsetof(struct tcphdr, check); skb->ip_summed = CHECKSUM_PARTIAL; return 0; -- cgit v1.2.3