[#339] Count how many settings remain unchanged in configuration reload.

The internal function `transfer_configuration` now returns a negative
value in the case of unchanged settings: such value counts the number
of parameters that has remained untouched, for example because they
require a restart.
The idea is that there are parameter that cannot be changed on the fly
and that do not prevent the configuration to be swapped, but it could
be interesting to take the count of unchanged configuration settings.

Close #339

src/libpgagroal/configuration.c

@@ -1935,7 +1935,7 @@ pgagroal_reload_configuration(void)
       goto error;
    }
 
-   if (transfer_configuration(config, reload))
+   if (transfer_configuration(config, reload) > 0)
    {
       goto error;
    }
@@ -2467,18 +2467,31 @@ extract_value(char* str, int offset, char** value)
    return -1;
 }
 
+/**
+ * Utility function to copy all the settings from the source configuration
+ * to the destination one. This is useful for example when a reload
+ * command is issued.
+ *
+ * @param config the new (clean) configuration
+ * @param reload the one loaded from the configuration (i.e., the one to apply)
+ * @return 0 on success, a negative number in the case some parameters cannot be changed
+ * because require a restart (in such case, the value indicates the number of untouched
+ * parameters), a positive value in the case of a dramatic error.
+ */
 static int
 transfer_configuration(struct configuration* config, struct configuration* reload)
 {
 #ifdef HAVE_LINUX
    sd_notify(0, "RELOADING=1");
 #endif
 
+   int unchanged = 0;
+
    memcpy(config->host, reload->host, MISC_LENGTH);
    config->port = reload->port;
    config->metrics = reload->metrics;
    config->metrics_cache_max_age = reload->metrics_cache_max_age;
-   restart_int("metrics_cache_max_size", config->metrics_cache_max_size, reload->metrics_cache_max_size);
+   unchanged -= restart_int("metrics_cache_max_size", config->metrics_cache_max_size, reload->metrics_cache_max_size);
    config->management = reload->management;
 
    config->update_process_title = reload->update_process_title;
@@ -2488,7 +2501,7 @@ transfer_configuration(struct configuration* config, struct configuration* reloa
    /* disabled */
 
    /* pipeline */
-   restart_int("pipeline", config->pipeline, reload->pipeline);
+   unchanged -= restart_int("pipeline", config->pipeline, reload->pipeline);
 
    config->failover = reload->failover;
    memcpy(config->failover_script, reload->failover_script, MISC_LENGTH);
@@ -2538,7 +2551,7 @@ transfer_configuration(struct configuration* config, struct configuration* reloa
 
    /* active_connections */
    /* max_connections */
-   restart_int("max_connections", config->max_connections, reload->max_connections);
+   unchanged -= restart_int("max_connections", config->max_connections, reload->max_connections);
    config->allow_unknown_users = reload->allow_unknown_users;
 
    config->blocking_timeout = reload->blocking_timeout;
@@ -2550,22 +2563,22 @@ transfer_configuration(struct configuration* config, struct configuration* reloa
    config->disconnect_client = reload->disconnect_client;
    config->disconnect_client_force = reload->disconnect_client_force;
    /* pidfile */
-   restart_string("pidfile", config->pidfile, reload->pidfile);
+   unchanged -= restart_string("pidfile", config->pidfile, reload->pidfile);
 
    /* libev */
-   restart_string("libev", config->libev, reload->libev);
+   unchanged -= restart_string("libev", config->libev, reload->libev);
    config->buffer_size = reload->buffer_size;
    config->keep_alive = reload->keep_alive;
    config->nodelay = reload->nodelay;
    config->non_blocking = reload->non_blocking;
    config->backlog = reload->backlog;
    /* hugepage */
-   restart_int("hugepage", config->hugepage, reload->hugepage);
+   unchanged -= restart_int("hugepage", config->hugepage, reload->hugepage);
    config->tracker = reload->tracker;
    config->track_prepared_statements = reload->track_prepared_statements;
 
    /* unix_socket_dir */
-   restart_string("unix_socket_dir", config->unix_socket_dir, reload->unix_socket_dir);
+   unchanged -= restart_string("unix_socket_dir", config->unix_socket_dir, reload->unix_socket_dir);
 
    /* su_connection */
 
@@ -2602,7 +2615,7 @@ transfer_configuration(struct configuration* config, struct configuration* reloa
 
    /* number_of_limits */
    /* limits */
-   restart_limit("limits", config, reload);
+   unchanged -= restart_limit("limits", config, reload);
 
    memset(&config->users[0], 0, sizeof(struct user) * NUMBER_OF_USERS);
    for (int i = 0; i < reload->number_of_users; i++)
@@ -2635,7 +2648,12 @@ transfer_configuration(struct configuration* config, struct configuration* reloa
    sd_notify(0, "READY=1");
 #endif
 
-   return 0;
+   if (unchanged < 0)
+   {
+      pgagroal_log_warn("%d settings cannot be applied", unchanged * -1);
+   }
+
+   return unchanged;
 }
 
 /**