netfilter: add API to manage NAT helpers.

The API allows a conntrack helper to indicate its corresponding
NAT helper which then can be loaded and reference counted.

Signed-off-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_conntrack_helper.h

@@ -15,7 +15,8 @@
 #include <net/netfilter/nf_conntrack_extend.h>
 #include <net/netfilter/nf_conntrack_expect.h>
 
-#define NF_NAT_HELPER_NAME(name)	"ip_nat_" name
+#define NF_NAT_HELPER_PREFIX		"ip_nat_"
+#define NF_NAT_HELPER_NAME(name)	NF_NAT_HELPER_PREFIX name
 #define MODULE_ALIAS_NF_NAT_HELPER(name) \
 	MODULE_ALIAS(NF_NAT_HELPER_NAME(name))
 
@@ -58,6 +59,8 @@ struct nf_conntrack_helper {
 	unsigned int queue_num;
 	/* length of userspace private data stored in nf_conn_help->data */
 	u16 data_len;
+	/* name of NAT helper module */
+	char nat_mod_name[NF_CT_HELPER_NAME_LEN];
 };
 
 /* Must be kept in sync with the classes defined by helpers */
@@ -157,4 +160,21 @@ nf_ct_helper_expectfn_find_by_symbol(const void *symbol);
 extern struct hlist_head *nf_ct_helper_hash;
 extern unsigned int nf_ct_helper_hsize;
 
+struct nf_conntrack_nat_helper {
+	struct list_head list;
+	char mod_name[NF_CT_HELPER_NAME_LEN];	/* module name */
+	struct module *module;			/* pointer to self */
+};
+
+#define NF_CT_NAT_HELPER_INIT(name) \
+	{ \
+	.mod_name = NF_NAT_HELPER_NAME(name), \
+	.module = THIS_MODULE \
+	}
+
+void nf_nat_helper_register(struct nf_conntrack_nat_helper *nat);
+void nf_nat_helper_unregister(struct nf_conntrack_nat_helper *nat);
+int nf_nat_helper_try_module_get(const char *name, u16 l3num,
+				 u8 protonum);
+void nf_nat_helper_put(struct nf_conntrack_helper *helper);
 #endif /*_NF_CONNTRACK_HELPER_H*/