vl: Document dependencies hiding in global and compat props

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190401090827.20793-5-armbru@redhat.com>
Reviewed-by: Igor Mammedov <imammedo@redhat.com>

1 files changed, 22 insertions, 2 deletions

diff --git a/vl.c b/vl.c
index 0d517a09e1..c696ad2a13 100644
--- a/vl.c
+++ b/vl.c
@@ -4286,16 +4286,36 @@ int main(int argc, char **argv, char **envp)
     current_machine->maxram_size = maxram_size;
     current_machine->ram_slots = ram_slots;
 
+    /*
+     * Note: uses machine properties such as kernel-irqchip, must run
+     * after machine_set_property().
+     */
     configure_accelerator(current_machine, argv[0]);
 
+    /*
+     * Beware, QOM objects created before this point miss global and
+     * compat properties.
+     *
+     * Global properties get set up by qdev_prop_register_global(),
+     * called from user_register_global_props(), and certain option
+     * desugaring.  Also in CPU feature desugaring (buried in
+     * parse_cpu_model()), which happens below this point, but may
+     * only target the CPU type, which can only be created after
+     * parse_cpu_model() returned the type.
+     *
+     * Machine compat properties: object_set_machine_compat_props().
+     * Accelerator compat props: object_set_accelerator_compat_props(),
+     * called from configure_accelerator().
+     */
+
     if (!qtest_enabled() && machine_class->deprecation_reason) {
         error_report("Machine type '%s' is deprecated: %s",
                      machine_class->name, machine_class->deprecation_reason);
     }
 
     /*
-     * Migration object can only be created after global properties
-     * are applied correctly.
+     * Note: creates a QOM object, must run only after global and
+     * compat properties have been set up.
      */
     migration_object_init();