[IPSEC]: Add xfrm_state_afinfo->init_flags

This patch adds the xfrm_state_afinfo->init_flags hook which allows
each address family to perform any common initialisation that does
not require a corresponding destructor call.

It will be used subsequently to set the XFRM_STATE_NOPMTUDISC flag
in IPv4.

It also fixes up the error codes returned by xfrm_init_state.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: James Morris <jmorris@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/xfrm.h

@@ -204,6 +204,7 @@ struct xfrm_state_afinfo {
 	rwlock_t		lock;
 	struct list_head	*state_bydst;
 	struct list_head	*state_byspi;
+	int			(*init_flags)(struct xfrm_state *x);
 	void			(*init_tempsel)(struct xfrm_state *x, struct flowi *fl,
 						struct xfrm_tmpl *tmpl,
 						xfrm_address_t *daddr, xfrm_address_t *saddr);

net/xfrm/xfrm_state.c

@@ -1058,10 +1058,26 @@ EXPORT_SYMBOL(xfrm_state_mtu);
 
 int xfrm_init_state(struct xfrm_state *x)
 {
+	struct xfrm_state_afinfo *afinfo;
+	int family = x->props.family;
 	int err;
 
-	err = -ENOENT;
-	x->type = xfrm_get_type(x->id.proto, x->props.family);
+	err = -EAFNOSUPPORT;
+	afinfo = xfrm_state_get_afinfo(family);
+	if (!afinfo)
+		goto error;
+
+	err = 0;
+	if (afinfo->init_flags)
+		err = afinfo->init_flags(x);
+
+	xfrm_state_put_afinfo(afinfo);
+
+	if (err)
+		goto error;
+
+	err = -EPROTONOSUPPORT;
+	x->type = xfrm_get_type(x->id.proto, family);
 	if (x->type == NULL)
 		goto error;