MXS-1929: Load global configuration as soon as possible

There exists a dependency on the configuration for the workers: the total
number of worker thread is defined by the `threads` parameter. This means
that the global configuration section must be read before workers are
started.

Commit 411b70e25656317909e54f748f8012593120041f broke MaxScale and turned
it into a single threaded application as the default configuration value
of one worker was used.

server/core/config.cc

@@ -570,6 +570,11 @@ static bool is_maxscale_section(const char* section)
 
 static bool is_root_config_file = true;
 
+static int ini_global_handler(void *userdata, const char *section, const char *name, const char *value)
+{
+    return is_maxscale_section(section) ? handle_global_item(name, value) : 1;
+}
+
 /**
  * Config item handler for the ini file reader
  *
@@ -673,11 +678,7 @@ static int ini_handler(void *userdata, const char *section, const char *name, co
 
     if (is_maxscale_section(section))
     {
-        if (is_root_config_file || is_persisted_config)
+        if (!is_root_config_file && !is_persisted_config)
-        {
-            return handle_global_item(name, value);
-        }
-        else
         {
             MXS_ERROR("The [maxscale] section must only be defined in the root configuration file.");
             return 0;
@@ -687,6 +688,29 @@ static int ini_handler(void *userdata, const char *section, const char *name, co
     return 1;
 }
 
+static void log_config_error(const char* file, int rval)
+{
+    char errorbuffer[1024 + 1];
+
+    if (rval > 0)
+    {
+        snprintf(errorbuffer, sizeof(errorbuffer),
+                 "Failed to parse configuration file %s. Error on line %d.", file, rval);
+    }
+    else if (rval == -1)
+    {
+        snprintf(errorbuffer, sizeof(errorbuffer),
+                 "Failed to parse configuration file %s. Could not open file.", file);
+    }
+    else
+    {
+        snprintf(errorbuffer, sizeof(errorbuffer),
+                 "Failed to parse configuration file %s. Memory allocation failed.", file);
+    }
+
+    MXS_ERROR("%s", errorbuffer);
+}
+
 /**
  * Load single configuration file.
  *
@@ -710,25 +734,7 @@ static bool config_load_single_file(const char* file,
     {
         if ((rval = ini_parse(file, ini_handler, ccontext)) != 0)
         {
-            char errorbuffer[1024 + 1];
+            log_config_error(file, rval);
-
-            if (rval > 0)
-            {
-                snprintf(errorbuffer, sizeof(errorbuffer),
-                         "Failed to parse configuration file %s. Error on line %d.", file, rval);
-            }
-            else if (rval == -1)
-            {
-                snprintf(errorbuffer, sizeof(errorbuffer),
-                         "Failed to parse configuration file %s. Could not open file.", file);
-            }
-            else
-            {
-                snprintf(errorbuffer, sizeof(errorbuffer),
-                         "Failed to parse configuration file %s. Memory allocation failed.", file);
-            }
-
-            MXS_ERROR("%s", errorbuffer);
         }
     }
 
@@ -1075,6 +1081,18 @@ config_load_and_process(const char* filename, bool (*process_config)(CONFIG_CONT
     return rval;
 }
 
+bool config_load_global(const char *filename)
+{
+    int rval;
+
+    if ((rval = ini_parse(filename, ini_global_handler, NULL)) != 0)
+    {
+        log_config_error(filename, rval);
+    }
+
+    return rval == 0;
+}
+
 /**
  * @brief Load the configuration file for the MaxScale
  *

server/core/gateway.cc

@@ -1890,6 +1890,12 @@ int main(int argc, char **argv)
         }
     }
 
+    if (!config_load_global(cnf_file_path))
+    {
+        rc = MAXSCALE_BADCONFIG;
+        goto return_main;
+    }
+
     if (daemon_mode)
     {
         if (!change_cwd())

server/core/internal/config.h

@@ -75,6 +75,7 @@ void config_add_defaults(CONFIG_CONTEXT *ctx, const MXS_MODULE_PARAM *params);
 char*                 config_clean_string_list(const char* str);
 MXS_CONFIG_PARAMETER* config_clone_param(const MXS_CONFIG_PARAMETER* param);
 bool                  config_load(const char *);
+bool                  config_load_global(const char *filename);
 void                  config_parameter_free(MXS_CONFIG_PARAMETER* p1);
 
 /**