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>

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);
     }

hw/net/virtio-net.c

@@ -3138,7 +3138,7 @@ static bool failover_replug_primary(VirtIONet *n, Error **errp)
         error_setg(errp, "virtio_net: couldn't find primary bus");
         return false;
     }
-    qdev_set_parent_bus(n->primary_dev, n->primary_bus);
+    qdev_set_parent_bus(n->primary_dev, n->primary_bus, &error_abort);
     n->primary_should_be_hidden = false;
     if (!qemu_opt_set_bool(n->primary_device_opts,
                            "partially_hotplugged", true, errp)) {

hw/sd/core.c

@@ -23,6 +23,7 @@
 #include "hw/qdev-core.h"
 #include "hw/sd/sd.h"
 #include "qemu/module.h"
+#include "qapi/error.h"
 #include "trace.h"
 
 static inline const char *sdbus_name(SDBus *sdbus)
@@ -240,7 +241,7 @@ void sdbus_reparent_card(SDBus *from, SDBus *to)
     readonly = sc->get_readonly(card);
 
     sdbus_set_inserted(from, false);
-    qdev_set_parent_bus(DEVICE(card), &to->qbus);
+    qdev_set_parent_bus(DEVICE(card), &to->qbus, &error_abort);
     sdbus_set_inserted(to, true);
     sdbus_set_readonly(to, readonly);
 }

include/hw/qdev-core.h

@@ -210,13 +210,24 @@ struct BusClass {
     /* FIXME first arg should be BusState */
     void (*print_dev)(Monitor *mon, DeviceState *dev, int indent);
     char *(*get_dev_path)(DeviceState *dev);
+
     /*
      * This callback is used to create Open Firmware device path in accordance
      * with OF spec http://forthworks.com/standards/of1275.pdf. Individual bus
      * bindings can be found at http://playground.sun.com/1275/bindings/.
      */
     char *(*get_fw_dev_path)(DeviceState *dev);
+
     void (*reset)(BusState *bus);
+
+    /*
+     * Return whether the device can be added to @bus,
+     * based on the address that was set (via device properties)
+     * before realize.  If not, on return @errp contains the
+     * human-readable error message.
+     */
+    bool (*check_address)(BusState *bus, DeviceState *dev, Error **errp);
+
     BusRealize realize;
     BusUnrealize unrealize;
 
@@ -788,7 +799,7 @@ const char *qdev_fw_name(DeviceState *dev);
 Object *qdev_get_machine(void);
 
 /* FIXME: make this a link<> */
-void qdev_set_parent_bus(DeviceState *dev, BusState *bus);
+bool qdev_set_parent_bus(DeviceState *dev, BusState *bus, Error **errp);
 
 extern bool qdev_hotplug;
 extern bool qdev_hot_removed;