[NET]: Remove gratuitous use of skb->tail in network drivers.

Many drivers use skb->tail unnecessarily.

In these situations, the code roughly looks like:

	dev = dev_alloc_skb(...);

	[optional] skb_reserve(skb, ...);

	... skb->tail ...

But even if the skb_reserve() happens, skb->data equals
skb->tail.  So it doesn't make any sense to use anything
other than skb->data in these cases.

Another case was the s2io.c driver directly mucking with
the skb->data and skb->tail pointers.  It really just wanted
to do an skb_reserve(), so that's what the code was changed
to do instead.

Another reason I'm making this change as it allows some SKB
cleanups I have planned simpler to merge.  In those cleanups,
skb->head, skb->tail, and skb->end pointers are removed, and
replaced with skb->head_room and skb->tail_room integers.

Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Jeff Garzik <jgarzik@pobox.com>

1 files changed, 3 insertions, 5 deletions

diff --git a/drivers/net/s2io.c b/drivers/net/s2io.c
index bb639a8794d4..ea638b162d3f 100644
--- a/drivers/net/s2io.c
+++ b/drivers/net/s2io.c
@@ -1699,11 +1699,9 @@ static int fill_rx_buffers(struct s2io_nic *nic, int ring_no)
 #else
                 ba = &nic->ba[ring_no][block_no][off];
                 skb_reserve(skb, BUF0_LEN);
-                tmp = (unsigned long) skb->data;
-                tmp += ALIGN_SIZE;
-                tmp &= ~ALIGN_SIZE;
-                skb->data = (void *) tmp;
-                skb->tail = (void *) tmp;
+                tmp = ((unsigned long) skb->data & ALIGN_SIZE);
+                if (tmp)
+                        skb_reserve(skb, (ALIGN_SIZE + 1) - tmp);
 
                 memset(rxdp, 0, sizeof(RxD_t));
                 rxdp->Buffer2_ptr = pci_map_single