vl: clean up global property registration

It's not that clear on how the global properties are registered to
global_props (and also its priority relationship). Let's provide a
single function to be called in main() for that, with comment to explain
it a bit.
Signed-off-by: NPeter Xu <peterx@redhat.com>
Message-Id: <1498536619-14548-4-git-send-email-peterx@redhat.com>
Reviewed-by: NEduardo Habkost <ehabkost@redhat.com>
Signed-off-by: NJuan Quintela <quintela@redhat.com>

vl.c

@@ -2969,6 +2969,25 @@ static int qemu_read_default_config_file(void)
     return 0;
 }
 
+static void user_register_global_props(void)
+{
+    qemu_opts_foreach(qemu_find_opts("global"),
+                      global_init_func, NULL, NULL);
+}
+
+/*
+ * Note: we should see that these properties are actually having a
+ * priority: accel < machine < user. This means e.g. when user
+ * specifies something in "-global", it'll always be used with highest
+ * priority than either machine/accelerator compat properties.
+ */
+static void register_global_properties(MachineState *ms)
+{
+    accel_register_compat_props(ms->accelerator);
+    machine_register_compat_props(ms);
+    user_register_global_props();
+}
+
 int main(int argc, char **argv, char **envp)
 {
     int i;
@@ -4571,11 +4590,11 @@ int main(int argc, char **argv, char **envp)
             exit (i == 1 ? 1 : 0);
     }
 
-    accel_register_compat_props(current_machine->accelerator);
-    machine_register_compat_props(current_machine);
-
-    qemu_opts_foreach(qemu_find_opts("global"),
-                      global_init_func, NULL, NULL);
+    /*
+     * Register all the global properties, including accel properties,
+     * machine properties, and user-specified ones.
+     */
+    register_global_properties(current_machine);
 
     /* This checkpoint is required by replay to separate prior clock
        reading from the other reads, because timer polling functions query