netfilter: nf_defrag_ipv4: use net_generic infra

This allows followup patch to remove the defrag_ipv4 member from struct
net.  It also allows to auto-remove the hooks later on by adding a
_disable() function.  This will be done later in a follow patch series.
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/ipv4/netfilter/nf_defrag_ipv4.c

@@ -20,8 +20,13 @@
 #endif
 #include <net/netfilter/nf_conntrack_zones.h>
 
+static unsigned int defrag4_pernet_id __read_mostly;
 static DEFINE_MUTEX(defrag4_mutex);
 
+struct defrag4_pernet {
+	unsigned int users;
+};
+
 static int nf_ct_ipv4_gather_frags(struct net *net, struct sk_buff *skb,
 				   u_int32_t user)
 {
@@ -106,15 +111,19 @@ static const struct nf_hook_ops ipv4_defrag_ops[] = {
 
 static void __net_exit defrag4_net_exit(struct net *net)
 {
-	if (net->nf.defrag_ipv4) {
+	struct defrag4_pernet *nf_defrag = net_generic(net, defrag4_pernet_id);
+
+	if (nf_defrag->users) {
 		nf_unregister_net_hooks(net, ipv4_defrag_ops,
 					ARRAY_SIZE(ipv4_defrag_ops));
-		net->nf.defrag_ipv4 = false;
+		nf_defrag->users = 0;
 	}
 }
 
 static struct pernet_operations defrag4_net_ops = {
 	.exit = defrag4_net_exit,
+	.id   = &defrag4_pernet_id,
+	.size = sizeof(struct defrag4_pernet),
 };
 
 static int __init nf_defrag_init(void)
@@ -129,21 +138,22 @@ static void __exit nf_defrag_fini(void)
 
 int nf_defrag_ipv4_enable(struct net *net)
 {
+	struct defrag4_pernet *nf_defrag = net_generic(net, defrag4_pernet_id);
 	int err = 0;
 
 	might_sleep();
 
-	if (net->nf.defrag_ipv4)
+	if (nf_defrag->users)
 		return 0;
 
 	mutex_lock(&defrag4_mutex);
-	if (net->nf.defrag_ipv4)
+	if (nf_defrag->users)
 		goto out_unlock;
 
 	err = nf_register_net_hooks(net, ipv4_defrag_ops,
 				    ARRAY_SIZE(ipv4_defrag_ops));
 	if (err == 0)
-		net->nf.defrag_ipv4 = true;
+		nf_defrag->users = 1;
 
  out_unlock:
 	mutex_unlock(&defrag4_mutex);