object: add object_property_set_default

Add a default value to ObjectProperty and an implementation of
ObjectPropertyInit that uses it.  This will make it easier to show the
default in help messages.

Also provide convenience functions object_property_set_default_{bool,
str, int, uint}().

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20200110153039.1379601-11-marcandre.lureau@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

include/qom/object.h

@@ -378,6 +378,7 @@ struct ObjectProperty
     ObjectPropertyRelease *release;
     ObjectPropertyInit *init;
     void *opaque;
+    QObject *defval;
 };
 
 /**
@@ -1055,6 +1056,42 @@ ObjectProperty *object_class_property_add(ObjectClass *klass, const char *name,
                                           ObjectPropertyRelease *release,
                                           void *opaque, Error **errp);
 
+/**
+ * object_property_set_default_bool:
+ * @prop: the property to set
+ * @value: the value to be written to the property
+ *
+ * Set the property default value.
+ */
+void object_property_set_default_bool(ObjectProperty *prop, bool value);
+
+/**
+ * object_property_set_default_str:
+ * @prop: the property to set
+ * @value: the value to be written to the property
+ *
+ * Set the property default value.
+ */
+void object_property_set_default_str(ObjectProperty *prop, const char *value);
+
+/**
+ * object_property_set_default_int:
+ * @prop: the property to set
+ * @value: the value to be written to the property
+ *
+ * Set the property default value.
+ */
+void object_property_set_default_int(ObjectProperty *prop, int64_t value);
+
+/**
+ * object_property_set_default_uint:
+ * @prop: the property to set
+ * @value: the value to be written to the property
+ *
+ * Set the property default value.
+ */
+void object_property_set_default_uint(ObjectProperty *prop, uint64_t value);
+
 /**
  * object_property_find:
  * @obj: the object

qom/object.c

@@ -19,8 +19,10 @@
 #include "qapi/visitor.h"
 #include "qapi/string-input-visitor.h"
 #include "qapi/string-output-visitor.h"
+#include "qapi/qobject-input-visitor.h"
 #include "qapi/qapi-builtin-visit.h"
 #include "qapi/qmp/qerror.h"
+#include "qapi/qmp/qjson.h"
 #include "trace.h"
 
 /* TODO: replace QObject with a simpler visitor to avoid a dependency
@@ -268,6 +270,10 @@ static void object_property_free(gpointer data)
 {
     ObjectProperty *prop = data;
 
+    if (prop->defval) {
+        qobject_unref(prop->defval);
+        prop->defval = NULL;
+    }
     g_free(prop->name);
     g_free(prop->type);
     g_free(prop->description);
@@ -1438,6 +1444,45 @@ int64_t object_property_get_int(Object *obj, const char *name,
     return retval;
 }
 
+static void object_property_init_defval(Object *obj, ObjectProperty *prop)
+{
+    Visitor *v = qobject_input_visitor_new(prop->defval);
+
+    assert(prop->set != NULL);
+    prop->set(obj, v, prop->name, prop->opaque, &error_abort);
+
+    visit_free(v);
+}
+
+static void object_property_set_default(ObjectProperty *prop, QObject *defval)
+{
+    assert(!prop->defval);
+    assert(!prop->init);
+
+    prop->defval = defval;
+    prop->init = object_property_init_defval;
+}
+
+void object_property_set_default_bool(ObjectProperty *prop, bool value)
+{
+    object_property_set_default(prop, QOBJECT(qbool_from_bool(value)));
+}
+
+void object_property_set_default_str(ObjectProperty *prop, const char *value)
+{
+    object_property_set_default(prop, QOBJECT(qstring_from_str(value)));
+}
+
+void object_property_set_default_int(ObjectProperty *prop, int64_t value)
+{
+    object_property_set_default(prop, QOBJECT(qnum_from_int(value)));
+}
+
+void object_property_set_default_uint(ObjectProperty *prop, uint64_t value)
+{
+    object_property_set_default(prop, QOBJECT(qnum_from_uint(value)));
+}
+
 void object_property_set_uint(Object *obj, uint64_t value,
                               const char *name, Error **errp)
 {
@@ -2549,6 +2594,9 @@ void object_property_add_alias(Object *obj, const char *name,
         goto out;
     }
     op->resolve = property_resolve_alias;
+    if (target_prop->defval) {
+        op->defval = qobject_ref(target_prop->defval);
+    }
 
     object_property_set_description(obj, op->name,
                                     target_prop->description,