qdev: add "check if address free" callback for buses

Check if an address is free on the bus before plugging in the
device.  This makes it possible to do the check without any
side effects, and to detect the problem early without having
to do it in the realize callback.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20201006123904.610658-5-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 15 insertions, 2 deletions

diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index 96772a15bd..74db78df36 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -94,13 +94,23 @@ static void bus_add_child(BusState *bus, DeviceState *child)
                              0);
 }
 
-void qdev_set_parent_bus(DeviceState *dev, BusState *bus)
+static bool bus_check_address(BusState *bus, DeviceState *child, Error **errp)
+{
+    BusClass *bc = BUS_GET_CLASS(bus);
+    return !bc->check_address || bc->check_address(bus, child, errp);
+}
+
+bool qdev_set_parent_bus(DeviceState *dev, BusState *bus, Error **errp)
 {
     BusState *old_parent_bus = dev->parent_bus;
     DeviceClass *dc = DEVICE_GET_CLASS(dev);
 
     assert(dc->bus_type && object_dynamic_cast(OBJECT(bus), dc->bus_type));
 
+    if (!bus_check_address(bus, dev, errp)) {
+        return false;
+    }
+
     if (old_parent_bus) {
         trace_qdev_update_parent_bus(dev, object_get_typename(OBJECT(dev)),
             old_parent_bus, object_get_typename(OBJECT(old_parent_bus)),
@@ -126,6 +136,7 @@ void qdev_set_parent_bus(DeviceState *dev, BusState *bus)
         object_unref(OBJECT(old_parent_bus));
         object_unref(OBJECT(dev));
     }
+    return true;
 }
 
 DeviceState *qdev_new(const char *name)
@@ -371,7 +382,9 @@ bool qdev_realize(DeviceState *dev, BusState *bus, Error **errp)
     assert(!dev->realized && !dev->parent_bus);
 
     if (bus) {
-        qdev_set_parent_bus(dev, bus);
+        if (!qdev_set_parent_bus(dev, bus, errp)) {
+            return false;
+        }
     } else {
         assert(!DEVICE_GET_CLASS(dev)->bus_type);
     }