l3cfg: let NML3Cfg return a singleton NML3IPv4LL instance

NML3Cfg is the manager instance for one interface (ifindex). For one
interface, it is not supported (nor useful) to run IPv4LL multiple
times. Hence, let NML3Cfg manage and return a single instance.

src/nm-l3-ipv4ll.c

@@ -1028,6 +1028,9 @@ nm_l3_ipv4ll_unref(NML3IPv4LL *self)
     if (--self->ref_count > 0)
         return;
 
+    if (nm_l3cfg_get_ipv4ll(self->l3cfg) == self)
+        _nm_l3cfg_unregister_ipv4ll(self->l3cfg);
+
     _LOGT("finalize");
 
     nm_assert(c_list_is_empty(&self->reg_lst_head));

src/nm-l3cfg.c

@@ -147,6 +147,8 @@ typedef struct _NML3CfgPrivate {
     GArray *property_emit_list;
     GArray *l3_config_datas;
 
+    NML3IPv4LL *ipv4ll;
+
     const NML3ConfigData *combined_l3cd_merged;
 
     const NML3ConfigData *combined_l3cd_commited;
@@ -3608,6 +3610,47 @@ nm_l3cfg_has_commited_ip6_addresses_pending_dad(NML3Cfg *self)
 
 /*****************************************************************************/
 
+NML3IPv4LL *
+nm_l3cfg_get_ipv4ll(NML3Cfg *self)
+{
+    g_return_val_if_fail(NM_IS_L3CFG(self), NULL);
+
+    return self->priv.p->ipv4ll;
+}
+
+NML3IPv4LL *
+nm_l3cfg_access_ipv4ll(NML3Cfg *self)
+{
+    g_return_val_if_fail(NM_IS_L3CFG(self), NULL);
+
+    if (self->priv.p->ipv4ll)
+        return nm_l3_ipv4ll_ref(self->priv.p->ipv4ll);
+
+    /* We return the reference. But the NML3IPv4LL instance
+     * will call _nm_l3cfg_unregister_ipv4ll() when it gets
+     * destroyed.
+     *
+     * We don't have weak references, but NML3Cfg and NML3IPv4LL
+     * cooperate to handle this reference. */
+    self->priv.p->ipv4ll = nm_l3_ipv4ll_new(self);
+    return self->priv.p->ipv4ll;
+}
+
+void
+_nm_l3cfg_unregister_ipv4ll(NML3Cfg *self)
+{
+    nm_assert(NM_IS_L3CFG(self));
+
+    /* we don't own the refernce to "self->priv.p->ipv4ll", but
+     * when that instance gets destroyed, we get called back to
+     * forget about it. Basically, it's like a weak pointer. */
+
+    nm_assert(self->priv.p->ipv4ll);
+    self->priv.p->ipv4ll = NULL;
+}
+
+/*****************************************************************************/
+
 static void
 set_property(GObject *object, guint prop_id, const GValue *value, GParamSpec *pspec)
 {
@@ -3675,6 +3718,7 @@ finalize(GObject *object)
     NML3Cfg *self = NM_L3CFG(object);
 
     nm_assert(!self->priv.p->l3_config_datas);
+    nm_assert(!self->priv.p->ipv4ll);
 
     nm_assert(c_list_is_empty(&self->priv.p->commit_type_lst_head));
 

src/nm-l3cfg.h

@@ -345,4 +345,12 @@ gboolean nm_l3cfg_has_commited_ip6_addresses_pending_dad(NML3Cfg *self);
 
 /*****************************************************************************/
 
+struct _NML3IPv4LL *nm_l3cfg_get_ipv4ll(NML3Cfg *self);
+
+struct _NML3IPv4LL *nm_l3cfg_access_ipv4ll(NML3Cfg *self);
+
+void _nm_l3cfg_unregister_ipv4ll(NML3Cfg *self);
+
+/*****************************************************************************/
+
 #endif /* __NM_L3CFG_H__ */