[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, 6 insertions, 4 deletions

diff --git a/drivers/media/dvb/dvb-core/dvb_net.c b/drivers/media/dvb/dvb-core/dvb_net.c
index c6b004182d91..9de177a5b9f1 100644
--- a/drivers/media/dvb/dvb-core/dvb_net.c
+++ b/drivers/media/dvb/dvb-core/dvb_net.c
@@ -600,6 +600,7 @@ static void dvb_net_ule( struct net_device *dev, const u8 *buf, size_t buf_len )
                         /* Check CRC32, we've got it in our skb already. */
                         unsigned short ulen = htons(priv->ule_sndu_len);
                         unsigned short utype = htons(priv->ule_sndu_type);
+                        const u8 *tail;
                         struct kvec iov[3] = {
                                 { &ulen, sizeof ulen },
                                 { &utype, sizeof utype },
@@ -613,10 +614,11 @@ static void dvb_net_ule( struct net_device *dev, const u8 *buf, size_t buf_len )
                         }
 
                         ule_crc = iov_crc32(ule_crc, iov, 3);
-                        expected_crc = *((u8 *)priv->ule_skb->tail - 4) << 24 |
-                                       *((u8 *)priv->ule_skb->tail - 3) << 16 |
-                                       *((u8 *)priv->ule_skb->tail - 2) << 8 |
-                                       *((u8 *)priv->ule_skb->tail - 1);
+                        tail = skb_tail_pointer(priv->ule_skb);
+                        expected_crc = *(tail - 4) << 24 |
+                                       *(tail - 3) << 16 |
+                                       *(tail - 2) << 8 |
+                                       *(tail - 1);
                         if (ule_crc != expected_crc) {
                                 printk(KERN_WARNING "%lu: CRC32 check FAILED: %08x / %08x, SNDU len %d type %#x, ts_remain %d, next 2: %x.\n",
                                        priv->ts_count, ule_crc, expected_crc, priv->ule_sndu_len, priv->ule_sndu_type, ts_remain, ts_remain > 2 ? *(unsigned short *)from_where : 0);