[PATCH-for-5.2 v4] hw/core/qdev: Increase qdev_realize() kindness

["Philippe Mathieu-Daudé" <f4bug@amsat.org>]

Since commit 510ef98dca5, qdev_realize() aborts if bus-less
device is realized on a bus. While commits 514db7710b..007d1dbf72
took care of converting all mainstream uses, QEMU forks weren't
converted.

These forks are usually maintained by hobbyist with interest in
following mainstream development, but with limited time, so usually
rebase from time to time. To avoid them to spend time on debugging
and reading git-log history, display a kind hint about what is wrong.

Before:

  qemu-system-mipsel: hw/core/qdev.c:376: qdev_realize: Assertion `!DEVICE_GET_CLASS(dev)->bus_type' failed.
  Aborted (core dumped)

After:

  Unexpected error in qdev_realize() at hw/core/qdev.c:376:
  qemu-system-mipsel: Unexpected bus 'System' for bus-less device 'unimplemented-device'
  Aborted (core dumped)

Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
 hw/core/qdev.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index 2131c7f951..a16f1270f1 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -392,8 +392,11 @@ bool qdev_realize(DeviceState *dev, BusState *bus, Error **errp)
 
     if (bus) {
         qdev_set_parent_bus(dev, bus);
-    } else {
-        assert(!DEVICE_GET_CLASS(dev)->bus_type);
+    } else if (DEVICE_GET_CLASS(dev)->bus_type) {
+        error_setg(errp, "Unexpected bus '%s' for bus-less device '%s'",
+                   DEVICE_GET_CLASS(dev)->bus_type,
+                   object_get_typename(OBJECT(dev)));
+        return false;
     }
 
     object_property_set_bool(OBJECT(dev), true, "realized", &err);
-- 
2.21.3