machine: export register_compat_prop()

We have HW_COMPAT_*, however that's only bound to machines, not other
things (like accelerators).  Behind it, it was register_compat_prop()
that played the trick.  Let's export the function for further use
outside HW_COMPAT_* magic.

Meanwhile, move it to qdev-properties.c where seems more proper (since
it'll be used not only in machine codes).

Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <1498536619-14548-2-git-send-email-peterx@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

hw/core/machine.c

@@ -770,19 +770,6 @@ static void machine_class_finalize(ObjectClass *klass, void *data)
     g_free(mc->name);
 }
 
-static void register_compat_prop(const char *driver,
-                                 const char *property,
-                                 const char *value)
-{
-    GlobalProperty *p = g_new0(GlobalProperty, 1);
-    /* Machine compat_props must never cause errors: */
-    p->errp = &error_abort;
-    p->driver = driver;
-    p->property = property;
-    p->value = value;
-    qdev_prop_register_global(p);
-}
-
 static void machine_register_compat_for_subclass(ObjectClass *oc, void *opaque)
 {
     GlobalProperty *p = opaque;

hw/core/qdev-properties.c

@@ -1084,6 +1084,20 @@ void qdev_prop_register_global(GlobalProperty *prop)
     global_props = g_list_append(global_props, prop);
 }
 
+void register_compat_prop(const char *driver,
+                          const char *property,
+                          const char *value)
+{
+    GlobalProperty *p = g_new0(GlobalProperty, 1);
+
+    /* Any compat_props must never cause error */
+    p->errp = &error_abort;
+    p->driver = driver;
+    p->property = property;
+    p->value = value;
+    qdev_prop_register_global(p);
+}
+
 void qdev_prop_register_global_list(GlobalProperty *props)
 {
     int i;

include/hw/qdev-properties.h

@@ -209,6 +209,29 @@ void qdev_prop_set_globals(DeviceState *dev);
 void error_set_from_qdev_prop_error(Error **errp, int ret, DeviceState *dev,
                                     Property *prop, const char *value);
 
+/**
+ * register_compat_prop:
+ *
+ * Register internal (not user-provided) global property, changing the
+ * default value of a given property in a device type.  This can be used
+ * for enabling machine-type compatibility or for enabling
+ * accelerator-specific defaults in devices.
+ *
+ * The property values set using this function must be always valid and
+ * never report setter errors, as the property will have
+ * GlobalProperty::errp set to &error_abort.
+ *
+ * User-provided global properties should override internal global
+ * properties, so callers of this function should ensure that it is
+ * called before user-provided global properties are registered.
+ *
+ * @driver: Device type to be affected
+ * @property: Property whose default value is going to be changed
+ * @value: New default value for the property
+ */
+void register_compat_prop(const char *driver, const char *property,
+                          const char *value);
+
 /**
  * qdev_property_add_static:
  * @dev: Device to add the property to.