Loggers specify what log messages they want to receive during registration.

This also allows us to generate the log message only once for all
loggers that need it (avoids calls to custom printf specifier callbacks).

To update the log levels loggers can simply be registered again.

src/libcharon/plugins/smp/smp.c

@@ -349,7 +349,7 @@ static void request_query_config(xmlTextReaderPtr reader, xmlTextWriterPtr write
  * callback which logs to a XML writer
  */
 static bool xml_callback(xmlTextWriterPtr writer, debug_t group, level_t level,
-						 ike_sa_t* ike_sa, char* format, va_list args)
+						 ike_sa_t* ike_sa, char* message)
 {
 	if (level <= 1)
 	{
@@ -358,7 +358,7 @@ static bool xml_callback(xmlTextWriterPtr writer, debug_t group, level_t level,
 		xmlTextWriterWriteFormatAttribute(writer, "level", "%d", level);
 		xmlTextWriterWriteFormatAttribute(writer, "source", "%N", debug_names, group);
 		xmlTextWriterWriteFormatAttribute(writer, "thread", "%u", thread_current_id());
-		xmlTextWriterWriteVFormatString(writer, format, args);
+		xmlTextWriterWriteString(writer, message);
 		xmlTextWriterEndElement(writer);
 		/* </item> */
 	}