net: Add skb_unclone() helper function.

This function will be used in next GRE_GSO patch. This patch does
not change any functionality.

Signed-off-by: Pravin B Shelar <[e-mail]>
Acked-by: Eric Dumazet <[e-mail]>

drivers/net/ppp/ppp_generic.c

···
 		/* the filter instructions are constructed assuming
 		   a four-byte PPP header on each packet */
 		if (ppp->pass_filter || ppp->active_filter) {
-			if (skb_cloned(skb) &&
-			    pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+			if (skb_unclone(skb, GFP_ATOMIC))
 				goto err;
 
 			*skb_push(skb, 2) = 0;

include/linux/skbuff.h

···
 	       (atomic_read(&skb_shinfo(skb)->dataref) & SKB_DATAREF_MASK) != 1;
 }
 
+static inline int skb_unclone(struct sk_buff *skb, gfp_t pri)
+{
+	might_sleep_if(pri & __GFP_WAIT);
+
+	if (skb_cloned(skb))
+		return pskb_expand_head(skb, 0, 0, pri);
+
+	return 0;
+}
+
 /**
  *	skb_header_cloned - is the header a clone
  *	@skb: buffer to check

net/ipv4/ah4.c

···
 
 	/* We are going to _remove_ AH header to keep sockets happy,
 	 * so... Later this can change. */
-	if (skb_cloned(skb) &&
-	    pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+	if (skb_unclone(skb, GFP_ATOMIC))
 		goto out;
 
 	skb->ip_summed = CHECKSUM_NONE;

net/ipv4/ip_fragment.c

···
 		goto out_oversize;
 
 	/* Head of list must not be cloned. */
-	if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
+	if (skb_unclone(head, GFP_ATOMIC))
 		goto out_nomem;
 
 	/* If the first fragment is fragmented itself, we split

net/ipv4/tcp_output.c

···
 /* Remove acked data from a packet in the transmit queue. */
 int tcp_trim_head(struct sock *sk, struct sk_buff *skb, u32 len)
 {
-	if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+	if (skb_unclone(skb, GFP_ATOMIC))
 		return -ENOMEM;
 
 	__pskb_trim_head(skb, len);

net/ipv4/xfrm4_input.c

···
 	 * header and optional ESP marker bytes) and then modify the
 	 * protocol to ESP, and then call into the transform receiver.
 	 */
-	if (skb_cloned(skb) && pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+	if (skb_unclone(skb, GFP_ATOMIC))
 		goto drop;
 
 	/* Now we can update and verify the packet length... */

net/ipv4/xfrm4_mode_tunnel.c

···
 	for_each_input_rcu(rcv_notify_handlers, handler)
 		handler->handler(skb);
 
-	if (skb_cloned(skb) &&
-	    (err = pskb_expand_head(skb, 0, 0, GFP_ATOMIC)))
+	if (err = skb_unclone(skb, GFP_ATOMIC))
 		goto out;
 
 	if (x->props.flags & XFRM_STATE_DECAP_DSCP)

net/ipv6/ah6.c

···
 
 	/* We are going to _remove_ AH header to keep sockets happy,
 	 * so... Later this can change. */
-	if (skb_cloned(skb) &&
-	    pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+	if (skb_unclone(skb, GFP_ATOMIC))
 		goto out;
 
 	skb->ip_summed = CHECKSUM_NONE;

net/ipv6/netfilter/nf_conntrack_reasm.c

···
 	}
 
 	/* Head of list must not be cloned. */
-	if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC)) {
+	if (skb_unclone(head, GFP_ATOMIC)) {
 		pr_debug("skb is cloned but can't expand head");
 		goto out_oom;
 	}

net/ipv6/reassembly.c

···
 		goto out_oversize;
 
 	/* Head of list must not be cloned. */
-	if (skb_cloned(head) && pskb_expand_head(head, 0, 0, GFP_ATOMIC))
+	if (skb_unclone(head, GFP_ATOMIC))
 		goto out_oom;
 
 	/* If the first fragment is fragmented itself, we split

net/ipv6/xfrm6_mode_tunnel.c

···
 	if (!pskb_may_pull(skb, sizeof(struct ipv6hdr)))
 		goto out;
 
-	if (skb_cloned(skb) &&
-	    (err = pskb_expand_head(skb, 0, 0, GFP_ATOMIC)))
+	if (err = skb_unclone(skb, GFP_ATOMIC))
 		goto out;
 
 	if (x->props.flags & XFRM_STATE_DECAP_DSCP)

net/sched/act_ipt.c

···
 	struct tcf_ipt *ipt = a->priv;
 	struct xt_action_param par;
 
-	if (skb_cloned(skb)) {
-		if (pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
-			return TC_ACT_UNSPEC;
-	}
+	if (skb_unclone(skb, GFP_ATOMIC))
+		return TC_ACT_UNSPEC;
 
 	spin_lock(&ipt->tcf_lock);
 

net/sched/act_pedit.c

···
 	int i, munged = 0;
 	unsigned int off;
 
-	if (skb_cloned(skb) &&
-	    pskb_expand_head(skb, 0, 0, GFP_ATOMIC))
+	if (skb_unclone(skb, GFP_ATOMIC))
 		return p->tcf_action;
 
 	off = skb_network_offset(skb);