[SK_BUFF]: Convert skb->tail to sk_buff_data_t

So that it is also an offset from skb->head, reduces its size from 8 to 4 bytes
on 64bit architectures, allowing us to combine the 4 bytes hole left by the
layer headers conversion, reducing struct sk_buff size to 256 bytes, i.e. 4
64byte cachelines, and since the sk_buff slab cache is SLAB_HWCACHE_ALIGN...
:-)

Many calculations that previously required that skb->{transport,network,
mac}_header be first converted to a pointer now can be done directly, being
meaningful as offsets or pointers.

Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 5 insertions, 3 deletions

diff --git a/net/ipv4/esp4.c b/net/ipv4/esp4.c
index de019f9fbfe1..5e5613930ffb 100644
--- a/net/ipv4/esp4.c
+++ b/net/ipv4/esp4.c
@@ -21,6 +21,7 @@ static int esp_output(struct xfrm_state *x, struct sk_buff *skb)
         struct blkcipher_desc desc;
         struct esp_data *esp;
         struct sk_buff *trailer;
+        u8 *tail;
         int blksize;
         int clen;
         int alen;
@@ -49,12 +50,13 @@ static int esp_output(struct xfrm_state *x, struct sk_buff *skb)
                 goto error;
 
         /* Fill padding... */
+        tail = skb_tail_pointer(trailer);
         do {
                 int i;
                 for (i=0; i<clen-skb->len - 2; i++)
-                        *(u8*)(trailer->tail + i) = i+1;
+                        tail[i] = i + 1;
         } while (0);
-        *(u8*)(trailer->tail + clen-skb->len - 2) = (clen - skb->len)-2;
+        tail[clen - skb->len - 2] = (clen - skb->len) - 2;
         pskb_put(skb, trailer, clen - skb->len);
 
         __skb_push(skb, skb->data - skb_network_header(skb));
@@ -62,7 +64,7 @@ static int esp_output(struct xfrm_state *x, struct sk_buff *skb)
         esph = (struct ip_esp_hdr *)(skb_network_header(skb) +
                                      top_iph->ihl * 4);
         top_iph->tot_len = htons(skb->len + alen);
-        *(u8*)(trailer->tail - 1) = top_iph->protocol;
+        *(skb_tail_pointer(skb) - 1) = top_iph->protocol;
 
         /* this is non-NULL only with UDP Encapsulation */
         if (x->encap) {