Replace cf_on_config_change() with "config_change" trigger

This is required to support feature-driven linking, in which the exact
list of which functions to call in response to a configuration re-load
is not known until link time.

The "config_change_log" trigger is called before "config_change", so
that the logger can respond to the change before other subsystems.

conf.c

@@ -236,12 +236,27 @@ static int reload_and_parse(int permissive, int strict)
   cf_limbo = 0; // let log messages out
   logFlush();
   if (changed) {
-    logConfigChanged();
-    cf_on_config_change();
+    CALL_TRIGGER(config_change_log);
+    CALL_TRIGGER(config_change);
   }
   return ret;
 }
 
+// Put a dummy no-op trigger callback into the "config_change" and "config_change_log" trigger
+// sections, otherwise if no other object provides one, the link will fail with errors like:
+// undefined reference to `__start_tr_config_change'
+// undefined reference to `__stop_tr_config_change'
+
+static void __dummy_on_config_change_log();
+DEFINE_TRIGGER(config_change_log, __dummy_on_config_change_log);
+static void __dummy_on_config_change_log() {}
+
+static void __dummy_on_config_change();
+DEFINE_TRIGGER(config_change, __dummy_on_config_change);
+static void __dummy_on_config_change() {}
+
+// The configuration API entry points.
+
 int cf_load()
 {
   conffile_meta = config_meta = FILE_META_UNKNOWN;

conf.h

@@ -233,6 +233,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 #include "rhizome_types.h"
 #include "strbuf.h"
 #include "httpd.h"
+#include "trigger.h"
 
 #define CONFIG_FILE_MAX_SIZE        (32 * 1024)
 #define INTERFACE_NAME_STRLEN       40
@@ -713,6 +714,7 @@ int cf_reload(void);
 int cf_reload_strict(void);
 int cf_reload_permissive(void);
 
-void cf_on_config_change(void);
+DECLARE_TRIGGER(config_change_log);
+DECLARE_TRIGGER(config_change);
 
 #endif //__SERVAL_DNA__CONF_H

directory_service.c

@@ -191,10 +191,6 @@ static void resolve_request(){
   }
 }
 
-void cf_on_config_change()
-{
-}
-
 int main(void){
   struct pollfd fds[2];
   int mdp_sockfd;

fakeradio.c

@@ -60,8 +60,6 @@ struct radio_state {
 #define STATE_PLUSPLUSPLUS 3
 #define STATE_COMMAND 4
 
-void cf_on_config_change(){}
-
 void log_time(){
   struct timeval tv;
   struct tm tm;

log.c

@@ -669,7 +669,9 @@ void vlogMessage(int level, struct __sourceloc whence, const char *fmt, va_list
   }
 }
 
-void logConfigChanged()
+static void logConfigChanged();
+DEFINE_TRIGGER(config_change_log, logConfigChanged);
+static void logConfigChanged()
 {
   _log_iterator it;
   _log_iterator_start(&it);

log.h

@@ -1,4 +1,6 @@
 /*
+Serval DNA logging
+Copyright (C) 2016 Flinders University
 Copyright (C) 2012-2015 Serval Project Inc.
  
 This program is free software; you can redistribute it and/or
@@ -52,7 +54,6 @@ extern int logLevel_NoLogFileConfigured;
 void close_log_file();
 void redirect_stderr_to_log();
 void logFlush();
-void logConfigChanged();
 
 // Logging context string.
 struct strbuf;

log_on_config_change.c

@@ -1,25 +0,0 @@
-/*
-Serval DNA logging
-Copyright 2016 Flinders University
-
-This program is free software; you can redistribute it and/or
-modify it under the terms of the GNU General Public License
-as published by the Free Software Foundation; either version 2
-of the License, or (at your option) any later version.
-
-This program is distributed in the hope that it will be useful,
-but WITHOUT ANY WARRANTY; without even the implied warranty of
-MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-GNU General Public License for more details.
-
-You should have received a copy of the GNU General Public License
-along with this program; if not, write to the Free Software
-Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
-*/
-
-// This compilation unit provides an on_log_config_change() function for
-// clients that do not define their own.
-
-#include "log.h"
-
-void cf_on_config_change() {}

log_stderr.c

@@ -88,7 +88,3 @@ void logFlush()
 {
   fflush(stderr);
 }
-
-void logConfigChanged()
-{
-}

server.c

@@ -36,6 +36,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 #include "server.h"
 #include "serval.h"
 #include "conf.h"
+#include "log.h"
 #include "str.h"
 #include "numeric_str.h"
 #include "strbuf.h"
@@ -273,7 +274,7 @@ int server_bind()
 
 void server_loop(time_ms_t (*waiting)(time_ms_t, time_ms_t, time_ms_t), void (*wokeup)())
 {
-  cf_on_config_change();
+  CALL_TRIGGER(config_change);
   
   // This log message is used by tests to wait for the server to start.
   INFOF("Server initialised, entering main loop");
@@ -512,7 +513,11 @@ void rhizome_clean_db(struct sched_ent *alarm)
   RESCHEDULE(alarm, now + 30*60*1000, TIME_MS_NEVER_WILL, TIME_MS_NEVER_WILL);
 }
 
-void cf_on_config_change()
+static void server_on_config_change();
+
+DEFINE_TRIGGER(config_change, server_on_config_change);
+
+static void server_on_config_change()
 {
   if (!serverMode)
     return;

simulator.c

@@ -109,10 +109,6 @@ struct command_state *stdin_state;
 struct network *networks=NULL;
 static void unicast_alarm(struct sched_ent *alarm);
 
-void cf_on_config_change()
-{
-}
-
 static void recv_packet(int fd, struct network *network, struct peer *destination)
 {
   struct socket_address addr;