ipv4: introduce frag_expire_skip_icmp()

Improve readability of skip ICMP for de-fragmentation expiration logic.
This change will also make the logic easier to maintain when the
following patches in this series are applied.

Signed-off-by: Andy Zhou <azhou@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ip.h

@@ -478,6 +478,16 @@ enum ip_defrag_users {
 	IP_DEFRAG_MACVLAN,
 };
 
+/* Return true if the value of 'user' is between 'lower_bond'
+ * and 'upper_bond' inclusively.
+ */
+static inline bool ip_defrag_user_in_between(u32 user,
+					     enum ip_defrag_users lower_bond,
+					     enum ip_defrag_users upper_bond)
+{
+	return user >= lower_bond && user <= upper_bond;
+}
+
 int ip_defrag(struct sk_buff *skb, u32 user);
 #ifdef CONFIG_INET
 struct sk_buff *ip_check_defrag(struct sk_buff *skb, u32 user);

net/ipv4/ip_fragment.c

@@ -173,6 +173,13 @@ static void ipq_kill(struct ipq *ipq)
 	inet_frag_kill(&ipq->q, &ip4_frags);
 }
 
+static bool frag_expire_skip_icmp(u32 user)
+{
+	return user == IP_DEFRAG_AF_PACKET ||
+	       ip_defrag_user_in_between(user, IP_DEFRAG_CONNTRACK_IN,
+					 __IP_DEFRAG_CONNTRACK_IN_END);
+}
+
 /*
  * Oops, a fragment queue timed out.  Kill it and send an ICMP reply.
  */
@@ -217,10 +224,8 @@ static void ip_expire(unsigned long arg)
 		/* Only an end host needs to send an ICMP
 		 * "Fragment Reassembly Timeout" message, per RFC792.
 		 */
-		if (qp->user == IP_DEFRAG_AF_PACKET ||
-		    ((qp->user >= IP_DEFRAG_CONNTRACK_IN) &&
-		     (qp->user <= __IP_DEFRAG_CONNTRACK_IN_END) &&
-		     (skb_rtable(head)->rt_type != RTN_LOCAL)))
+		if (frag_expire_skip_icmp(qp->user) &&
+		    (skb_rtable(head)->rt_type != RTN_LOCAL))
 			goto out_rcu_unlock;
 
 		/* Send an ICMP "Fragment Reassembly Timeout" message. */