[IPSEC]: Set skb->data to payload in x->mode->output

This patch changes the calling convention so that on entry from
x->mode->output and before entry into x->type->output skb->data
will point to the payload instead of the IP header.

This is essentially a redistribution of skb_push/skb_pull calls
with the aim of minimising them on the common path of tunnel +
ESP.

It'll also let us use the same calling convention between IPv4
and IPv6 with the next patch.

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

1 files changed, 7 insertions, 6 deletions

diff --git a/net/ipv6/xfrm6_mode_tunnel.c b/net/ipv6/xfrm6_mode_tunnel.c
index 3dd40af75e81..01bd7d11ea1b 100644
--- a/net/ipv6/xfrm6_mode_tunnel.c
+++ b/net/ipv6/xfrm6_mode_tunnel.c
@@ -41,8 +41,8 @@ static inline void ip6ip_ecn_decapsulate(struct sk_buff *skb)
  * filled in by x->type->output and the mac header will be set to the
  * nextheader field of the extension header directly preceding the
  * encapsulation header, or in its absence, that of the top IP header.
- * The value of skb->data and the network header will always point to the
- * top IP header.
+ * The value of the network header will always point to the top IP header
+ * while skb->data will point to the payload.
  */
 static int xfrm6_tunnel_output(struct xfrm_state *x, struct sk_buff *skb)
 {
@@ -51,12 +51,13 @@ static int xfrm6_tunnel_output(struct xfrm_state *x, struct sk_buff *skb)
         struct ipv6hdr *iph, *top_iph;
         int dsfield;
 
-        skb_push(skb, x->props.header_len);
         iph = ipv6_hdr(skb);
 
-        skb_set_mac_header(skb, offsetof(struct ipv6hdr, nexthdr));
-        skb_reset_network_header(skb);
-        skb_set_transport_header(skb, sizeof(struct ipv6hdr));
+        skb_set_mac_header(skb, offsetof(struct ipv6hdr, nexthdr) -
+                                x->props.header_len);
+        skb_set_network_header(skb, -x->props.header_len);
+        skb_set_transport_header(skb, sizeof(struct ipv6hdr) -
+                                      x->props.header_len);
         top_iph = ipv6_hdr(skb);
 
         top_iph->version = 6;