[SK_BUFF]: Introduce skb_set_mac_header()

For the cases where we want to set skb->mac.raw to an offset from skb->data.

Simple cases first, the memmove ones and specially pktgen will be left for later.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/loopback.c

@@ -90,7 +90,7 @@ static void emulate_large_send_offload(struct sk_buff *skb)
 		if (!nskb)
 			break;
 		skb_reserve(nskb, 32);
-		nskb->mac.raw = nskb->data - 14;
+		skb_set_mac_header(nskb, -ETH_HLEN);
 		nskb->nh.raw = nskb->data;
 		iph = nskb->nh.iph;
 		memcpy(nskb->data, skb->nh.raw, doffset);

drivers/net/myri_sbus.c

@@ -368,7 +368,7 @@ static __be16 myri_type_trans(struct sk_buff *skb, struct net_device *dev)
 	struct ethhdr *eth;
 	unsigned char *rawp;
 
-	skb->mac.raw = skb->data + MYRI_PAD_LEN;
+	skb_set_mac_header(skb, MYRI_PAD_LEN);
 	skb_pull(skb, dev->hard_header_len);
 	eth = eth_hdr(skb);
 

drivers/s390/net/qeth_eddp.c

@@ -486,7 +486,7 @@ qeth_eddp_fill_context_tcp(struct qeth_eddp_context *ctx,
 		return -ENOMEM;
 	}
 	if (qhdr->hdr.l2.id == QETH_HEADER_TYPE_LAYER2) {
-		skb->mac.raw = skb->data + sizeof(struct qeth_hdr);
+		skb_set_mac_header(skb, sizeof(struct qeth_hdr));
 		memcpy(&eddp->mac, eth_hdr(skb), ETH_HLEN);
 #ifdef CONFIG_QETH_VLAN
 		if (eddp->mac.h_proto == __constant_htons(ETH_P_8021Q)) {

drivers/s390/net/qeth_main.c

@@ -2306,7 +2306,7 @@ qeth_rebuild_skb_fake_ll_tr(struct qeth_card *card, struct sk_buff *skb,
 	struct iphdr *ip_hdr;
 
 	QETH_DBF_TEXT(trace,5,"skbfktr");
-	skb->mac.raw = skb->data - QETH_FAKE_LL_LEN_TR;
+	skb_set_mac_header(skb, -QETH_FAKE_LL_LEN_TR);
 	/* this is a fake ethernet header */
 	fake_hdr = tr_hdr(skb);
 
@@ -2359,7 +2359,7 @@ qeth_rebuild_skb_fake_ll_eth(struct qeth_card *card, struct sk_buff *skb,
 	struct iphdr *ip_hdr;
 
 	QETH_DBF_TEXT(trace,5,"skbfketh");
-	skb->mac.raw = skb->data - QETH_FAKE_LL_LEN_ETH;
+	skb_set_mac_header(skb, -QETH_FAKE_LL_LEN_ETH);
 	/* this is a fake ethernet header */
 	fake_hdr = eth_hdr(skb);
 

include/linux/skbuff.h

@@ -965,6 +965,11 @@ static inline void skb_reset_mac_header(struct sk_buff *skb)
 	skb->mac.raw = skb->data;
 }
 
+static inline void skb_set_mac_header(struct sk_buff *skb, const int offset)
+{
+	skb->mac.raw = skb->data + offset;
+}
+
 /*
  * CPUs often take a performance hit when accessing unaligned memory
  * locations. The actual performance hit varies, it can be small if the

net/atm/br2684.c

@@ -458,7 +458,7 @@ static void br2684_push(struct atm_vcc *atmvcc, struct sk_buff *skb)
 	/* FIXME: tcpdump shows that pointer to mac header is 2 bytes earlier,
 	   than should be. What else should I set? */
 	skb_pull(skb, plen);
-	skb->mac.raw = skb->data - ETH_HLEN;
+	skb_set_mac_header(skb, -ETH_HLEN);
 	skb->pkt_type = PACKET_HOST;
 #ifdef CONFIG_BR2684_FAST_TRANS
 	skb->protocol = ((u16 *) skb->data)[-1];