[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, 5 deletions

diff --git a/drivers/usb/atm/usbatm.c b/drivers/usb/atm/usbatm.c
index ec63b0ee074..4d8f282b23d 100644
--- a/drivers/usb/atm/usbatm.c
+++ b/drivers/usb/atm/usbatm.c
@@ -335,15 +335,15 @@ static void usbatm_extract_one_cell(struct usbatm_data *instance, unsigned char
 
         sarb = instance->cached_vcc->sarb;
 
-        if (sarb->tail + ATM_CELL_PAYLOAD > sarb->end) {
+        if (skb_tail_pointer(sarb) + ATM_CELL_PAYLOAD > sarb->end) {
                 atm_rldbg(instance, "%s: buffer overrun (sarb->len %u, vcc: 0x%p)!\n",
                                 __func__, sarb->len, vcc);
                 /* discard cells already received */
                 skb_trim(sarb, 0);
-                UDSL_ASSERT(sarb->tail + ATM_CELL_PAYLOAD <= sarb->end);
+                UDSL_ASSERT(skb_tail_pointer(sarb) + ATM_CELL_PAYLOAD <= sarb->end);
         }
 
-        memcpy(sarb->tail, source + ATM_CELL_HEADER, ATM_CELL_PAYLOAD);
+        memcpy(skb_tail_pointer(sarb), source + ATM_CELL_HEADER, ATM_CELL_PAYLOAD);
         __skb_put(sarb, ATM_CELL_PAYLOAD);
 
         if (pti & 1) {
@@ -370,7 +370,7 @@ static void usbatm_extract_one_cell(struct usbatm_data *instance, unsigned char
                         goto out;
                 }
 
-                if (crc32_be(~0, sarb->tail - pdu_length, pdu_length) != 0xc704dd7b) {
+                if (crc32_be(~0, skb_tail_pointer(sarb) - pdu_length, pdu_length) != 0xc704dd7b) {
                         atm_rldbg(instance, "%s: packet failed crc check (vcc: 0x%p)!\n",
                                   __func__, vcc);
                         atomic_inc(&vcc->stats->rx_err);
@@ -396,7 +396,7 @@ static void usbatm_extract_one_cell(struct usbatm_data *instance, unsigned char
                         goto out;       /* atm_charge increments rx_drop */
                 }
 
-                memcpy(skb->data, sarb->tail - pdu_length, length);
+                memcpy(skb->data, skb_tail_pointer(sarb) - pdu_length, length);
                 __skb_put(skb, length);
 
                 vdbg("%s: sending skb 0x%p, skb->len %u, skb->truesize %u",