[NETFILTER]: nf_conntrack: introduce extension infrastructure

Old space allocator of conntrack had problems about extensibility.
- It required slab cache per combination of extensions.
- It expected what extensions would be assigned, but it was impossible
  to expect that completely, then we allocated bigger memory object than
  really required.
- It needed to search helper twice due to lock issue.

Now basic informations of a connection are stored in 'struct nf_conn'.
And a storage for extension (helper, NAT) is allocated by kmalloc.

Signed-off-by: Yasuyuki Kozakai <yasuyuki.kozakai@toshiba.co.jp>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netfilter/nf_conntrack.h

@@ -131,6 +131,9 @@ struct nf_conn
 	/* Storage reserved for other modules: */
 	union nf_conntrack_proto proto;
 
+	/* Extensions */
+	struct nf_ct_ext *ext;
+
 	/* features dynamically at the end: helper, nat (both optional) */
 	char data[0];
 };

include/net/netfilter/nf_conntrack_extend.h

@@ -0,0 +1,80 @@
+#ifndef _NF_CONNTRACK_EXTEND_H
+#define _NF_CONNTRACK_EXTEND_H
+
+#include <net/netfilter/nf_conntrack.h>
+
+enum nf_ct_ext_id
+{
+	NF_CT_EXT_NUM,
+};
+
+/* Extensions: optional stuff which isn't permanently in struct. */
+struct nf_ct_ext {
+	u8 offset[NF_CT_EXT_NUM];
+	u8 len;
+	u8 real_len;
+	char data[0];
+};
+
+static inline int nf_ct_ext_exist(const struct nf_conn *ct, u8 id)
+{
+	return (ct->ext && ct->ext->offset[id]);
+}
+
+static inline void *__nf_ct_ext_find(const struct nf_conn *ct, u8 id)
+{
+	if (!nf_ct_ext_exist(ct, id))
+		return NULL;
+
+	return (void *)ct->ext + ct->ext->offset[id];
+}
+#define nf_ct_ext_find(ext, id)	\
+	((id##_TYPE *)__nf_ct_ext_find((ext), (id)))
+
+/* Destroy all relationships */
+extern void __nf_ct_ext_destroy(struct nf_conn *ct);
+static inline void nf_ct_ext_destroy(struct nf_conn *ct)
+{
+	if (ct->ext)
+		__nf_ct_ext_destroy(ct);
+}
+
+/* Free operation. If you want to free a object referred from private area,
+ * please implement __nf_ct_ext_free() and call it.
+ */
+static inline void nf_ct_ext_free(struct nf_conn *ct)
+{
+	if (ct->ext)
+		kfree(ct->ext);
+}
+
+/* Add this type, returns pointer to data or NULL. */
+void *
+__nf_ct_ext_add(struct nf_conn *ct, enum nf_ct_ext_id id, gfp_t gfp);
+#define nf_ct_ext_add(ct, id, gfp) \
+	((id##_TYPE *)__nf_ct_ext_add((ct), (id), (gfp)))
+
+#define NF_CT_EXT_F_PREALLOC	0x0001
+
+struct nf_ct_ext_type
+{
+	/* Destroys relationships (can be NULL). */
+	void (*destroy)(struct nf_conn *ct);
+	/* Called when realloacted (can be NULL).
+	   Contents has already been moved. */
+	void (*move)(struct nf_conn *ct, void *old);
+
+	enum nf_ct_ext_id id;
+
+	unsigned int flags;
+
+	/* Length and min alignment. */
+	u8 len;
+	u8 align;
+	/* initial size of nf_ct_ext. */
+	u8 alloc_size;
+};
+
+int nf_ct_extend_register(struct nf_ct_ext_type *type);
+void nf_ct_extend_unregister(struct nf_ct_ext_type *type);
+#endif /* _NF_CONNTRACK_EXTEND_H */