[NET]: Avoid allocating skb in skb_pad

First of all it is unnecessary to allocate a new skb in skb_pad since
the existing one is not shared.  More importantly, our hard_start_xmit
interface does not allow a new skb to be allocated since that breaks
requeueing.

This patch uses pskb_expand_head to expand the existing skb and linearize
it if needed.  Actually, someone should sift through every instance of
skb_pad on a non-linear skb as they do not fit the reasons why this was
originally created.

Incidentally, this fixes a minor bug when the skb is cloned (tcpdump,
TCP, etc.).  As it is skb_pad will simply write over a cloned skb.  Because
of the position of the write it is unlikely to cause problems but still
it's best if we don't do it.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/3c527.c

@@ -1031,8 +1031,7 @@ static int mc32_send_packet(struct sk_buff *skb, struct net_device *dev)
 		return 1;
 	}
 
-	skb = skb_padto(skb, ETH_ZLEN);
-	if (skb == NULL) {
+	if (skb_padto(skb, ETH_ZLEN)) {
 		netif_wake_queue(dev);
 		return 0;
 	}

drivers/net/82596.c

@@ -1070,8 +1070,7 @@ static int i596_start_xmit(struct sk_buff *skb, struct net_device *dev)
 				skb->len, (unsigned int)skb->data));
 
 	if (skb->len < ETH_ZLEN) {
-		skb = skb_padto(skb, ETH_ZLEN);
-		if (skb == NULL)
+		if (skb_padto(skb, ETH_ZLEN))
 			return 0;
 		length = ETH_ZLEN;
 	}

drivers/net/a2065.c

@@ -573,8 +573,7 @@ static int lance_start_xmit (struct sk_buff *skb, struct net_device *dev)
 	
 	if (len < ETH_ZLEN) {
 		len = ETH_ZLEN;
-		skb = skb_padto(skb, ETH_ZLEN);
-		if (skb == NULL)
+		if (skb_padto(skb, ETH_ZLEN))
 			return 0;
 	}
 

drivers/net/ariadne.c

@@ -607,8 +607,7 @@ static int ariadne_start_xmit(struct sk_buff *skb, struct net_device *dev)
     /* FIXME: is the 79C960 new enough to do its own padding right ? */
     if (skb->len < ETH_ZLEN)
     {
-    	skb = skb_padto(skb, ETH_ZLEN);
-    	if (skb == NULL)
+    	if (skb_padto(skb, ETH_ZLEN))
     	    return 0;
     	len = ETH_ZLEN;
     }

drivers/net/arm/ether1.c

@@ -700,8 +700,7 @@ ether1_sendpacket (struct sk_buff *skb, struct net_device *dev)
 	}
 
 	if (skb->len < ETH_ZLEN) {
-		skb = skb_padto(skb, ETH_ZLEN);
-		if (skb == NULL)
+		if (skb_padto(skb, ETH_ZLEN))
 			goto out;
 	}
 

drivers/net/arm/ether3.c

@@ -518,8 +518,7 @@ ether3_sendpacket(struct sk_buff *skb, struct net_device *dev)
 
 	length = (length + 1) & ~1;
 	if (length != skb->len) {
-		skb = skb_padto(skb, length);
-		if (skb == NULL)
+		if (skb_padto(skb, length))
 			goto out;
 	}
 

drivers/net/atarilance.c

@@ -804,8 +804,7 @@ static int lance_start_xmit( struct sk_buff *skb, struct net_device *dev )
 		++len;
 		
 	if (len > skb->len) {
-		skb = skb_padto(skb, len);
-		if (skb == NULL)
+		if (skb_padto(skb, len))
 			return 0;
 	}
 		

drivers/net/cassini.c

@@ -2915,8 +2915,7 @@ static int cas_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	 */
 	static int ring; 
 
-	skb = skb_padto(skb, cp->min_frame_size);
-	if (!skb)
+	if (skb_padto(skb, cp->min_frame_size))
 		return 0;
 
 	/* XXX: we need some higher-level QoS hooks to steer packets to

drivers/net/declance.c

@@ -885,8 +885,7 @@ static int lance_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	len = skblen;
 	
 	if (len < ETH_ZLEN) {
-		skb = skb_padto(skb, ETH_ZLEN);
-		if (skb == NULL)
+		if (skb_padto(skb, ETH_ZLEN))
 			return 0;
 		len = ETH_ZLEN;
 	}

drivers/net/depca.c

@@ -938,11 +938,8 @@ static int depca_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	if (skb->len < 1)
 		goto out;
 
-	if (skb->len < ETH_ZLEN) {
-		skb = skb_padto(skb, ETH_ZLEN);
-		if (skb == NULL)
-			goto out;
-	}
+	if (skb_padto(skb, ETH_ZLEN))
+		goto out;
 	
 	netif_stop_queue(dev);
 

drivers/net/eepro.c

@@ -1154,8 +1154,7 @@ static int eepro_send_packet(struct sk_buff *skb, struct net_device *dev)
 		printk(KERN_DEBUG  "%s: entering eepro_send_packet routine.\n", dev->name);
 
 	if (length < ETH_ZLEN) {
-		skb = skb_padto(skb, ETH_ZLEN);
-		if (skb == NULL)
+		if (skb_padto(skb, ETH_ZLEN))
 			return 0;
 		length = ETH_ZLEN;
 	}

drivers/net/eexpress.c

@@ -677,8 +677,7 @@ static int eexp_xmit(struct sk_buff *buf, struct net_device *dev)
 #endif
 
 	if (buf->len < ETH_ZLEN) {
-		buf = skb_padto(buf, ETH_ZLEN);
-		if (buf == NULL)
+		if (skb_padto(buf, ETH_ZLEN))
 			return 0;
 		length = ETH_ZLEN;
 	}

drivers/net/epic100.c

@@ -1027,11 +1027,8 @@ static int epic_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	u32 ctrl_word;
 	unsigned long flags;
 
-	if (skb->len < ETH_ZLEN) {
-		skb = skb_padto(skb, ETH_ZLEN);
-		if (skb == NULL)
-			return 0;
-	}
+	if (skb_padto(skb, ETH_ZLEN))
+		return 0;
 
 	/* Caution: the write order is important here, set the field with the
 	   "ownership" bit last. */

drivers/net/eth16i.c

@@ -1064,8 +1064,7 @@ static int eth16i_tx(struct sk_buff *skb, struct net_device *dev)
 	unsigned long flags;
 
 	if (length < ETH_ZLEN) {
-		skb = skb_padto(skb, ETH_ZLEN);
-		if (skb == NULL)
+		if (skb_padto(skb, ETH_ZLEN))
 			return 0;
 		length = ETH_ZLEN;
 	}

drivers/net/hp100.c

@@ -1487,11 +1487,8 @@ static int hp100_start_xmit_bm(struct sk_buff *skb, struct net_device *dev)
 	if (skb->len <= 0)
 		return 0;
 		
-	if (skb->len < ETH_ZLEN && lp->chip == HP100_CHIPID_SHASTA) {
-		skb = skb_padto(skb, ETH_ZLEN);
-		if (skb == NULL)
-			return 0;
-	}
+	if (lp->chip == HP100_CHIPID_SHASTA && skb_padto(skb, ETH_ZLEN))
+		return 0;
 
 	/* Get Tx ring tail pointer */
 	if (lp->txrtail->next == lp->txrhead) {

drivers/net/lance.c

@@ -968,8 +968,7 @@ static int lance_start_xmit(struct sk_buff *skb, struct net_device *dev)
 	/* The old LANCE chips doesn't automatically pad buffers to min. size. */
 	if (chip_table[lp->chip_version].flags & LANCE_MUST_PAD) {
 		if (skb->len < ETH_ZLEN) {
-			skb = skb_padto(skb, ETH_ZLEN);
-			if (skb == NULL)
+			if (skb_padto(skb, ETH_ZLEN))
 				goto out;
 			lp->tx_ring[entry].length = -ETH_ZLEN;
 		}

drivers/net/lasi_82596.c

@@ -1083,8 +1083,7 @@ static int i596_start_xmit(struct sk_buff *skb, struct net_device *dev)
 				skb->len, skb->data));
 
 	if (length < ETH_ZLEN) {
-		skb = skb_padto(skb, ETH_ZLEN);
-		if (skb == NULL)
+		if (skb_padto(skb, ETH_ZLEN))
 			return 0;
 		length = ETH_ZLEN;
 	}

drivers/net/lp486e.c

@@ -877,8 +877,7 @@ static int i596_start_xmit (struct sk_buff *skb, struct net_device *dev) {
 	length = skb->len;
 	
 	if (length < ETH_ZLEN) {
-		skb = skb_padto(skb, ETH_ZLEN);
-		if (skb == NULL)
+		if (skb_padto(skb, ETH_ZLEN))
 			return 0;
 		length = ETH_ZLEN;
 	}

drivers/net/myri10ge/myri10ge.c

@@ -1939,8 +1939,7 @@ again:
 
 		/* pad frames to at least ETH_ZLEN bytes */
 		if (unlikely(skb->len < ETH_ZLEN)) {
-			skb = skb_padto(skb, ETH_ZLEN);
-			if (skb == NULL) {
+			if (skb_padto(skb, ETH_ZLEN)) {
 				/* The packet is gone, so we must
 				 * return 0 */
 				mgp->stats.tx_dropped += 1;

drivers/net/pcmcia/fmvj18x_cs.c

@@ -831,8 +831,7 @@ static int fjn_start_xmit(struct sk_buff *skb, struct net_device *dev)
     
     if (length < ETH_ZLEN)
     {
-    	skb = skb_padto(skb, ETH_ZLEN);
-    	if (skb == NULL)
+    	if (skb_padto(skb, ETH_ZLEN))
     		return 0;
     	length = ETH_ZLEN;
     }