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authorEdward Cree <ecree@solarflare.com>2016-02-11 20:48:04 +0000
committerDavid S. Miller <davem@davemloft.net>2016-02-12 05:52:15 -0500
commit179bc67f69b6cb53ad68cfdec5a917c2a2248355 (patch)
tree9c3251d5226c75826a19f10d33e3b7279d6f0969 /include/linux/skbuff.h
parente51271d4ce7b229f5c02903e3c44bf92c0dbef6b (diff)
net: local checksum offload for encapsulation
The arithmetic properties of the ones-complement checksum mean that a correctly checksummed inner packet, including its checksum, has a ones complement sum depending only on whatever value was used to initialise the checksum field before checksumming (in the case of TCP and UDP, this is the ones complement sum of the pseudo header, complemented). Consequently, if we are going to offload the inner checksum with CHECKSUM_PARTIAL, we can compute the outer checksum based only on the packed data not covered by the inner checksum, and the initial value of the inner checksum field. Signed-off-by: Edward Cree <ecree@solarflare.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/linux/skbuff.h')
-rw-r--r--include/linux/skbuff.h24
1 files changed, 24 insertions, 0 deletions
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index 6ec86f1a2ed9..cf906d1ce8a7 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3702,5 +3702,29 @@ static inline unsigned int skb_gso_network_seglen(const struct sk_buff *skb)
return hdr_len + skb_gso_transport_seglen(skb);
}
+/* Local Checksum Offload.
+ * Compute outer checksum based on the assumption that the
+ * inner checksum will be offloaded later.
+ * Fill in outer checksum adjustment (e.g. with sum of outer
+ * pseudo-header) before calling.
+ * Also ensure that inner checksum is in linear data area.
+ */
+static inline __wsum lco_csum(struct sk_buff *skb)
+{
+ char *inner_csum_field;
+ __wsum csum;
+
+ /* Start with complement of inner checksum adjustment */
+ inner_csum_field = skb->data + skb_checksum_start_offset(skb) +
+ skb->csum_offset;
+ csum = ~csum_unfold(*(__force __sum16 *)inner_csum_field);
+ /* Add in checksum of our headers (incl. outer checksum
+ * adjustment filled in by caller)
+ */
+ csum = skb_checksum(skb, 0, skb_checksum_start_offset(skb), csum);
+ /* The result is the checksum from skb->data to end of packet */
+ return csum;
+}
+
#endif /* __KERNEL__ */
#endif /* _LINUX_SKBUFF_H */