[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>

3 files changed, 10 insertions, 7 deletions

diff --git a/drivers/atm/he.c b/drivers/atm/he.c
index 8510026b690a..d33aba6864c2 100644
--- a/drivers/atm/he.c
+++ b/drivers/atm/he.c
@@ -1901,13 +1901,13 @@ he_service_rbrq(struct he_dev *he_dev, int group)
                         case ATM_AAL0:
                                 /* 2.10.1.5 raw cell receive */
                                 skb->len = ATM_AAL0_SDU;
-                                skb->tail = skb->data + skb->len;
+                                skb_set_tail_pointer(skb, skb->len);
                                 break;
                         case ATM_AAL5:
                                 /* 2.10.1.2 aal5 receive */
 
                                 skb->len = AAL5_LEN(skb->data, he_vcc->pdu_len);
-                                skb->tail = skb->data + skb->len;
+                                skb_set_tail_pointer(skb, skb->len);
 #ifdef USE_CHECKSUM_HW
                                 if (vcc->vpi == 0 && vcc->vci >= ATM_NOT_RSV_VCI) {
                                         skb->ip_summed = CHECKSUM_COMPLETE;
diff --git a/drivers/atm/idt77252.c b/drivers/atm/idt77252.c
index b4b80140c398..1e49799cd6cf 100644
--- a/drivers/atm/idt77252.c
+++ b/drivers/atm/idt77252.c
@@ -1816,7 +1816,8 @@ push_rx_skb(struct idt77252_dev *card, struct sk_buff *skb, int queue)
         u32 handle;
         u32 addr;
 
-        skb->data = skb->tail = skb->head;
+        skb->data = skb->head;
+        skb_reset_tail_pointer(skb);
         skb->len = 0;
 
         skb_reserve(skb, 16);
diff --git a/drivers/atm/nicstar.c b/drivers/atm/nicstar.c
index aab9b3733d52..26f4b7033494 100644
--- a/drivers/atm/nicstar.c
+++ b/drivers/atm/nicstar.c
@@ -2208,7 +2208,7 @@ static void dequeue_rx(ns_dev *card, ns_rsqe *rsqe)
          if (i == 1 && ns_rsqe_eopdu(rsqe))
             *((u32 *) sb->data) |= 0x00000002;
          skb_put(sb, NS_AAL0_HEADER);
-         memcpy(sb->tail, cell, ATM_CELL_PAYLOAD);
+         memcpy(skb_tail_pointer(sb), cell, ATM_CELL_PAYLOAD);
          skb_put(sb, ATM_CELL_PAYLOAD);
          ATM_SKB(sb)->vcc = vcc;
          __net_timestamp(sb);
@@ -2252,7 +2252,8 @@ static void dequeue_rx(ns_dev *card, ns_rsqe *rsqe)
       vc->rx_iov = iovb;
       NS_SKB(iovb)->iovcnt = 0;
       iovb->len = 0;
-      iovb->tail = iovb->data = iovb->head;
+      iovb->data = iovb->head;
+      skb_reset_tail_pointer(iovb);
       NS_SKB(iovb)->vcc = vcc;
       /* IMPORTANT: a pointer to the sk_buff containing the small or large
                     buffer is stored as iovec base, NOT a pointer to the 
@@ -2265,7 +2266,8 @@ static void dequeue_rx(ns_dev *card, ns_rsqe *rsqe)
       recycle_iovec_rx_bufs(card, (struct iovec *) iovb->data, NS_MAX_IOVECS);
       NS_SKB(iovb)->iovcnt = 0;
       iovb->len = 0;
-      iovb->tail = iovb->data = iovb->head;
+      iovb->data = iovb->head;
+      skb_reset_tail_pointer(iovb);
       NS_SKB(iovb)->vcc = vcc;
    }
    iov = &((struct iovec *) iovb->data)[NS_SKB(iovb)->iovcnt++];
@@ -2489,7 +2491,7 @@ static void dequeue_rx(ns_dev *card, ns_rsqe *rsqe)
             {
                lb = (struct sk_buff *) iov->iov_base;
                tocopy = min_t(int, remaining, iov->iov_len);
-               memcpy(hb->tail, lb->data, tocopy);
+               memcpy(skb_tail_pointer(hb), lb->data, tocopy);
                skb_put(hb, tocopy);
                iov++;
                remaining -= tocopy;