kernel-interface: Return bool for kernel interface registration

If the (un)registering of a kernel interface (net or ipsec) fails, the
plugin loader will never know, since the appropriate functions always
returns TRUE.  By making the (un)register functions return a boolean
value, the loader can detect a failure during initializing the kernel
interface and abort charon startup if desired.

src/libhydra/kernel/kernel_interface.c

@@ -738,44 +738,52 @@ METHOD(kernel_interface_t, get_address_by_ts, status_t,
 }
 
 
-METHOD(kernel_interface_t, add_ipsec_interface, void,
+METHOD(kernel_interface_t, add_ipsec_interface, bool,
 	private_kernel_interface_t *this, kernel_ipsec_constructor_t constructor)
 {
 	if (!this->ipsec)
 	{
 		this->ipsec_constructor = constructor;
 		this->ipsec = constructor();
+		return this->ipsec != NULL;
 	}
+	return FALSE;
 }
 
-METHOD(kernel_interface_t, remove_ipsec_interface, void,
+METHOD(kernel_interface_t, remove_ipsec_interface, bool,
 	private_kernel_interface_t *this, kernel_ipsec_constructor_t constructor)
 {
 	if (constructor == this->ipsec_constructor && this->ipsec)
 	{
 		this->ipsec->destroy(this->ipsec);
 		this->ipsec = NULL;
+		return TRUE;
 	}
+	return FALSE;
 }
 
-METHOD(kernel_interface_t, add_net_interface, void,
+METHOD(kernel_interface_t, add_net_interface, bool,
 	private_kernel_interface_t *this, kernel_net_constructor_t constructor)
 {
 	if (!this->net)
 	{
 		this->net_constructor = constructor;
 		this->net = constructor();
+		return this->net != NULL;
 	}
+	return FALSE;
 }
 
-METHOD(kernel_interface_t, remove_net_interface, void,
+METHOD(kernel_interface_t, remove_net_interface, bool,
 	private_kernel_interface_t *this, kernel_net_constructor_t constructor)
 {
 	if (constructor == this->net_constructor && this->net)
 	{
 		this->net->destroy(this->net);
 		this->net = NULL;
+		return TRUE;
 	}
+	return FALSE;
 }
 
 METHOD(kernel_interface_t, add_listener, void,

src/libhydra/kernel/kernel_interface.h

@@ -502,39 +502,49 @@ struct kernel_interface_t {
 	/**
 	 * Register an ipsec kernel interface constructor on the manager.
 	 *
-	 * @param create			constructor to register
+	 * @param create		constructor to register
+	 * @return				TRUE if the ipsec kernel interface was registered
+	 *						successfully, FALSE if an interface was already
+	 *						registered or the registration failed
 	 */
-	void (*add_ipsec_interface)(kernel_interface_t *this,
+	bool (*add_ipsec_interface)(kernel_interface_t *this,
 								kernel_ipsec_constructor_t create);
 
 	/**
 	 * Unregister an ipsec kernel interface constructor.
 	 *
-	 * @param create			constructor to unregister
+	 * @param create		constructor to unregister
+	 * @return				TRUE if the ipsec kernel interface was unregistered
+	 *						successfully, FALSE otherwise
 	 */
-	void (*remove_ipsec_interface)(kernel_interface_t *this,
+	bool (*remove_ipsec_interface)(kernel_interface_t *this,
 								   kernel_ipsec_constructor_t create);
 
 	/**
 	 * Register a network kernel interface constructor on the manager.
 	 *
-	 * @param create			constructor to register
+	 * @param create		constructor to register
+	 * @return				TRUE if the kernel net interface was registered
+	 *						successfully, FALSE if an interface was already
+	 *						registered or the registration failed
 	 */
-	void (*add_net_interface)(kernel_interface_t *this,
+	bool (*add_net_interface)(kernel_interface_t *this,
 							  kernel_net_constructor_t create);
 
 	/**
 	 * Unregister a network kernel interface constructor.
 	 *
-	 * @param create			constructor to unregister
+	 * @param create		constructor to unregister
+	 * @return				TRUE if the kernel net interface was unregistered
+	 *						successfully, FALSE otherwise
 	 */
-	void (*remove_net_interface)(kernel_interface_t *this,
+	bool (*remove_net_interface)(kernel_interface_t *this,
 								 kernel_net_constructor_t create);
 
 	/**
 	 * Add a listener to the kernel interface.
 	 *
-	 * @param listener			listener to add
+	 * @param listener		listener to add
 	 */
 	void (*add_listener)(kernel_interface_t *this,
 						 kernel_listener_t *listener);
@@ -542,7 +552,7 @@ struct kernel_interface_t {
 	/**
 	 * Remove a listener from the kernel interface.
 	 *
-	 * @param listener			listener to remove
+	 * @param listener		listener to remove
 	 */
 	void (*remove_listener)(kernel_interface_t *this,
 							kernel_listener_t *listener);

src/libhydra/kernel/kernel_ipsec.c

@@ -25,13 +25,14 @@ bool kernel_ipsec_register(plugin_t *plugin, plugin_feature_t *feature,
 {
 	if (reg)
 	{
-		hydra->kernel_interface->add_ipsec_interface(hydra->kernel_interface,
+		return hydra->kernel_interface->add_ipsec_interface(
+											hydra->kernel_interface,
 											(kernel_ipsec_constructor_t)data);
 	}
 	else
 	{
-		hydra->kernel_interface->remove_ipsec_interface(hydra->kernel_interface,
+		return hydra->kernel_interface->remove_ipsec_interface(
+											hydra->kernel_interface,
 											(kernel_ipsec_constructor_t)data);
 	}
-	return TRUE;
 }

src/libhydra/kernel/kernel_net.c

@@ -25,13 +25,14 @@ bool kernel_net_register(plugin_t *plugin, plugin_feature_t *feature,
 {
 	if (reg)
 	{
-		hydra->kernel_interface->add_net_interface(hydra->kernel_interface,
+		return hydra->kernel_interface->add_net_interface(
+											hydra->kernel_interface,
 											(kernel_net_constructor_t)data);
 	}
 	else
 	{
-		hydra->kernel_interface->remove_net_interface(hydra->kernel_interface,
+		return hydra->kernel_interface->remove_net_interface(
+											hydra->kernel_interface,
 											(kernel_net_constructor_t)data);
 	}
-	return TRUE;
 }