qom: Add check() argument to object_property_add_link()

There are currently three types of object_property_add_link() callers:

1. The link property may be set at any time.
2. The link property of a DeviceState instance may only be set before
   realize.
3. The link property may never be set, it is read-only.

Something similar can already be achieved with
object_property_add_str()'s set() argument.  Follow its example and add
a check() argument to object_property_add_link().

Also provide default check() functions for case #1 and #2.  Case #3 is
covered by passing a NULL function pointer.

Cc: Peter Crosthwaite <peter.crosthwaite@petalogix.com>
Cc: Alexander Graf <agraf@suse.de>
Cc: Anthony Liguori <aliguori@amazon.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
[AF: Tweaked documentation comment]
Signed-off-by: Andreas Färber <afaerber@suse.de>

2 files changed, 18 insertions, 2 deletions

diff --git a/hw/core/qdev-properties.c b/hw/core/qdev-properties.c
index 77d0c66635..c67acf58b5 100644
--- a/hw/core/qdev-properties.c
+++ b/hw/core/qdev-properties.c
@@ -21,6 +21,18 @@ void qdev_prop_set_after_realize(DeviceState *dev, const char *name,
     }
 }
 
+void qdev_prop_allow_set_link_before_realize(Object *obj, const char *name,
+                                             Object *val, Error **errp)
+{
+    DeviceState *dev = DEVICE(obj);
+
+    if (dev->realized) {
+        error_setg(errp, "Attempt to set link property '%s' on device '%s' "
+                   "(type '%s') after it was realized",
+                   name, dev->id, object_get_typename(obj));
+    }
+}
+
 void *qdev_get_prop_ptr(DeviceState *dev, Property *prop)
 {
     void *ptr = dev;
diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index a182917222..97acf62906 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -97,7 +97,10 @@ static void bus_add_child(BusState *bus, DeviceState *child)
     snprintf(name, sizeof(name), "child[%d]", kid->index);
     object_property_add_link(OBJECT(bus), name,
                              object_get_typename(OBJECT(child)),
-                             (Object **)&kid->child, 0, NULL);
+                             (Object **)&kid->child,
+                             NULL, /* read-only property */
+                             0, /* return ownership on prop deletion */
+                             NULL);
 }
 
 void qdev_set_parent_bus(DeviceState *dev, BusState *bus)
@@ -823,7 +826,7 @@ static void device_initfn(Object *obj)
     } while (class != object_class_by_name(TYPE_DEVICE));
 
     object_property_add_link(OBJECT(dev), "parent_bus", TYPE_BUS,
-                             (Object **)&dev->parent_bus, 0,
+                             (Object **)&dev->parent_bus, NULL, 0,
                              &error_abort);
 }
 
@@ -945,6 +948,7 @@ static void qbus_initfn(Object *obj)
     object_property_add_link(obj, QDEV_HOTPLUG_HANDLER_PROPERTY,
                              TYPE_HOTPLUG_HANDLER,
                              (Object **)&bus->hotplug_handler,
+                             object_property_allow_set_link,
                              OBJ_PROP_LINK_UNREF_ON_RELEASE,
                              NULL);
     object_property_add_bool(obj, "realized",