skb: Add inline helper for getting the skb end offset from head

With the recent changes for how we compute the skb truesize it occurs to me
we are probably going to have a lot of calls to skb_end_pointer -
skb->head.  Instead of running all over the place doing that it would make
more sense to just make it a separate inline skb_end_offset(skb) that way
we can return the correct value without having gcc having to do all the
optimization to cancel out skb->head - skb->head.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/atm/ambassador.c

@@ -802,7 +802,7 @@ static void fill_rx_pool (amb_dev * dev, unsigned char pool,
     }
     // cast needed as there is no %? for pointer differences
     PRINTD (DBG_SKB, "allocated skb at %p, head %p, area %li",
-	    skb, skb->head, (long) (skb_end_pointer(skb) - skb->head));
+	    skb, skb->head, (long) skb_end_offset(skb));
     rx.handle = virt_to_bus (skb);
     rx.host_address = cpu_to_be32 (virt_to_bus (skb->data));
     if (rx_give (dev, &rx, pool))

drivers/atm/idt77252.c

@@ -1258,7 +1258,7 @@ idt77252_rx_raw(struct idt77252_dev *card)
 	tail = readl(SAR_REG_RAWCT);
 
 	pci_dma_sync_single_for_cpu(card->pcidev, IDT77252_PRV_PADDR(queue),
-				    skb_end_pointer(queue) - queue->head - 16,
+				    skb_end_offset(queue) - 16,
 				    PCI_DMA_FROMDEVICE);
 
 	while (head != tail) {

drivers/net/wimax/i2400m/usb-rx.c

@@ -277,7 +277,7 @@ retry:
 		d_printf(1, dev, "RX: size changed to %d, received %d, "
 			 "copied %d, capacity %ld\n",
 			 rx_size, read_size, rx_skb->len,
-			 (long) (skb_end_pointer(new_skb) - new_skb->head));
+			 (long) skb_end_offset(new_skb));
 		goto retry;
 	}
 		/* In most cases, it happens due to the hardware scheduling a

drivers/staging/octeon/ethernet-tx.c

@@ -344,7 +344,7 @@ int cvm_oct_xmit(struct sk_buff *skb, struct net_device *dev)
 	}
 	if (unlikely
 	    (skb->truesize !=
-	     sizeof(*skb) + skb_end_pointer(skb) - skb->head)) {
+	     sizeof(*skb) + skb_end_offset(skb))) {
 		/*
 		   printk("TX buffer truesize has been changed\n");
 		 */

include/linux/skbuff.h

@@ -645,11 +645,21 @@ static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
 {
 	return skb->head + skb->end;
 }
+
+static inline unsigned int skb_end_offset(const struct sk_buff *skb)
+{
+	return skb->end;
+}
 #else
 static inline unsigned char *skb_end_pointer(const struct sk_buff *skb)
 {
 	return skb->end;
 }
+
+static inline unsigned int skb_end_offset(const struct sk_buff *skb)
+{
+	return skb->end - skb->head;
+}
 #endif
 
 /* Internal */
@@ -2558,7 +2568,7 @@ static inline bool skb_is_recycleable(const struct sk_buff *skb, int skb_size)
 		return false;
 
 	skb_size = SKB_DATA_ALIGN(skb_size + NET_SKB_PAD);
-	if (skb_end_pointer(skb) - skb->head < skb_size)
+	if (skb_end_offset(skb) < skb_size)
 		return false;
 
 	if (skb_shared(skb) || skb_cloned(skb))

net/core/skbuff.c

@@ -829,7 +829,7 @@ static void copy_skb_header(struct sk_buff *new, const struct sk_buff *old)
 struct sk_buff *skb_copy(const struct sk_buff *skb, gfp_t gfp_mask)
 {
 	int headerlen = skb_headroom(skb);
-	unsigned int size = (skb_end_pointer(skb) - skb->head) + skb->data_len;
+	unsigned int size = skb_end_offset(skb) + skb->data_len;
 	struct sk_buff *n = alloc_skb(size, gfp_mask);
 
 	if (!n)
@@ -930,7 +930,7 @@ int pskb_expand_head(struct sk_buff *skb, int nhead, int ntail,
 {
 	int i;
 	u8 *data;
-	int size = nhead + (skb_end_pointer(skb) - skb->head) + ntail;
+	int size = nhead + skb_end_offset(skb) + ntail;
 	long off;
 
 	BUG_ON(nhead < 0);
@@ -2727,14 +2727,13 @@ struct sk_buff *skb_segment(struct sk_buff *skb, netdev_features_t features)
 			if (unlikely(!nskb))
 				goto err;
 
-			hsize = skb_end_pointer(nskb) - nskb->head;
+			hsize = skb_end_offset(nskb);
 			if (skb_cow_head(nskb, doffset + headroom)) {
 				kfree_skb(nskb);
 				goto err;
 			}
 
-			nskb->truesize += skb_end_pointer(nskb) - nskb->head -
-					  hsize;
+			nskb->truesize += skb_end_offset(nskb) - hsize;
 			skb_release_head_state(nskb);
 			__skb_push(nskb, doffset);
 		} else {
@@ -2883,7 +2882,8 @@ int skb_gro_receive(struct sk_buff **head, struct sk_buff *skb)
 		skb_frag_size_sub(frag, offset);
 
 		/* all fragments truesize : remove (head size + sk_buff) */
-		delta_truesize = skb->truesize - SKB_TRUESIZE(skb_end_pointer(skb) - skb->head);
+		delta_truesize = skb->truesize -
+				 SKB_TRUESIZE(skb_end_offset(skb));
 
 		skb->truesize -= skb->data_len;
 		skb->len -= skb->data_len;