[UDP]: Clean up UDP-Lite receive checksum

This patch eliminates some duplicate code for the verification of
receive checksums between UDP-Lite and UDP.  It does this by
introducing __skb_checksum_complete_head which is identical to
__skb_checksum_complete_head apart from the fact that it takes
a length parameter rather than computing the first skb->len bytes.

As a result UDP-Lite will be able to use hardware checksum offload
for packets which do not use partial coverage checksums.  It also
means that UDP-Lite loopback no longer does unnecessary checksum
verification.

If any NICs start support UDP-Lite this would also start working
automatically.

This patch removes the assumption that msg_flags has MSG_TRUNC clear
upon entry in recvmsg.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 8 insertions, 2 deletions

diff --git a/net/core/datagram.c b/net/core/datagram.c
index 186212b5b7da..cb056f476126 100644
--- a/net/core/datagram.c
+++ b/net/core/datagram.c
@@ -411,11 +411,11 @@ fault:
         return -EFAULT;
 }
 
-__sum16 __skb_checksum_complete(struct sk_buff *skb)
+__sum16 __skb_checksum_complete_head(struct sk_buff *skb, int len)
 {
         __sum16 sum;
 
-        sum = csum_fold(skb_checksum(skb, 0, skb->len, skb->csum));
+        sum = csum_fold(skb_checksum(skb, 0, len, skb->csum));
         if (likely(!sum)) {
                 if (unlikely(skb->ip_summed == CHECKSUM_COMPLETE))
                         netdev_rx_csum_fault(skb->dev);
@@ -423,6 +423,12 @@ __sum16 __skb_checksum_complete(struct sk_buff *skb)
         }
         return sum;
 }
+EXPORT_SYMBOL(__skb_checksum_complete_head);
+
+__sum16 __skb_checksum_complete(struct sk_buff *skb)
+{
+        return __skb_checksum_complete_head(skb, skb->len);
+}
 EXPORT_SYMBOL(__skb_checksum_complete);
 
 /**