[ARP]: Introduce the arp_hdr_len helper.

There are some place, that calculate the ARP header length. These
calculations are correct, but 
 a) some operate with "magic" constants,
 b) enlarge the code length (sometimes at the cost of coding style),
 c) are not informative from the first glance.

The proposal is to introduce a helper, that includes all the good
sides of these calculations.
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/bonding/bond_main.c

@@ -2646,10 +2646,7 @@ static int bond_arp_rcv(struct sk_buff *skb, struct net_device *dev, struct pack
 	if (!slave || !slave_do_arp_validate(bond, slave))
 		goto out_unlock;
 
-	/* ARP header, plus 2 device addresses, plus 2 IP addresses.  */
-	if (!pskb_may_pull(skb, (sizeof(struct arphdr) +
-				 (2 * dev->addr_len) +
-				 (2 * sizeof(u32)))))
+	if (!pskb_may_pull(skb, arp_hdr_len(dev)))
 		goto out_unlock;
 
 	arp = arp_hdr(skb);

include/linux/if_arp.h

@@ -156,6 +156,12 @@ static inline struct arphdr *arp_hdr(const struct sk_buff *skb)
 {
 	return (struct arphdr *)skb_network_header(skb);
 }
+
+static inline int arp_hdr_len(struct net_device *dev)
+{
+	/* ARP header, plus 2 device addresses, plus 2 IP addresses. */
+	return sizeof(struct arphdr) + (dev->addr_len + sizeof(u32)) * 2;
+}
 #endif
 
 #endif	/* _LINUX_IF_ARP_H */

net/core/netpoll.c

@@ -384,9 +384,7 @@ static void arp_reply(struct sk_buff *skb)
 	if (skb->dev->flags & IFF_NOARP)
 		return;
 
-	if (!pskb_may_pull(skb, (sizeof(struct arphdr) +
-				 (2 * skb->dev->addr_len) +
-				 (2 * sizeof(u32)))))
+	if (!pskb_may_pull(skb, arp_hdr_len(skb->dev)))
 		return;
 
 	skb_reset_network_header(skb);
@@ -414,7 +412,7 @@ static void arp_reply(struct sk_buff *skb)
 	    ipv4_is_loopback(tip) || ipv4_is_multicast(tip))
 		return;
 
-	size = sizeof(struct arphdr) + 2 * (skb->dev->addr_len + 4);
+	size = arp_hdr_len(skb->dev);
 	send_skb = find_skb(np, size + LL_RESERVED_SPACE(np->dev),
 			    LL_RESERVED_SPACE(np->dev));
 

net/ipv4/arp.c

@@ -570,14 +570,13 @@ struct sk_buff *arp_create(int type, int ptype, __be32 dest_ip,
 	 *	Allocate a buffer
 	 */
 
-	skb = alloc_skb(sizeof(struct arphdr)+ 2*(dev->addr_len+4)
-				+ LL_RESERVED_SPACE(dev), GFP_ATOMIC);
+	skb = alloc_skb(arp_hdr_len(dev) + LL_RESERVED_SPACE(dev), GFP_ATOMIC);
 	if (skb == NULL)
 		return NULL;
 
 	skb_reserve(skb, LL_RESERVED_SPACE(dev));
 	skb_reset_network_header(skb);
-	arp = (struct arphdr *) skb_put(skb,sizeof(struct arphdr) + 2*(dev->addr_len+4));
+	arp = (struct arphdr *) skb_put(skb, arp_hdr_len(dev));
 	skb->dev = dev;
 	skb->protocol = htons(ETH_P_ARP);
 	if (src_hw == NULL)
@@ -916,9 +915,7 @@ static int arp_rcv(struct sk_buff *skb, struct net_device *dev,
 		goto freeskb;
 
 	/* ARP header, plus 2 device addresses, plus 2 IP addresses.  */
-	if (!pskb_may_pull(skb, (sizeof(struct arphdr) +
-				 (2 * dev->addr_len) +
-				 (2 * sizeof(u32)))))
+	if (!pskb_may_pull(skb, arp_hdr_len(dev)))
 		goto freeskb;
 
 	arp = arp_hdr(skb);

net/ipv4/ipconfig.c

@@ -459,10 +459,7 @@ ic_rarp_recv(struct sk_buff *skb, struct net_device *dev, struct packet_type *pt
 	if (rarp->ar_pro != htons(ETH_P_IP))
 		goto drop;
 
-	if (!pskb_may_pull(skb,
-			   sizeof(struct arphdr) +
-			   (2 * dev->addr_len) +
-			   (2 * 4)))
+	if (!pskb_may_pull(skb, arp_hdr_len(dev)))
 		goto drop;
 
 	/* OK, it is all there and looks valid, process... */

net/ipv4/netfilter/arp_tables.c

@@ -233,10 +233,7 @@ unsigned int arpt_do_table(struct sk_buff *skb,
 	void *table_base;
 	struct xt_table_info *private;
 
-	/* ARP header, plus 2 device addresses, plus 2 IP addresses.  */
-	if (!pskb_may_pull(skb, (sizeof(struct arphdr) +
-				 (2 * skb->dev->addr_len) +
-				 (2 * sizeof(u32)))))
+	if (!pskb_may_pull(skb, arp_hdr_len(skb->dev)))
 		return NF_DROP;
 
 	indev = in ? in->name : nulldevname;