[PATCH v8 08/17] qdev: add "check if address free" callback for buses

[Paolo Bonzini]

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         | 17 +++++++++++++++--
 hw/net/virtio-net.c    |  2 +-
 hw/sd/core.c           |  3 ++-
 include/hw/qdev-core.h | 13 ++++++++++++-
 4 files changed, 30 insertions(+), 5 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);
     }
diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index 7bf27b9db7..268cecc498 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -3142,7 +3142,7 @@ 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)) {
diff --git a/hw/sd/core.c b/hw/sd/core.c
index 957d116f1a..08c93b5903 100644
--- a/hw/sd/core.c
+++ b/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);
 }
diff --git a/include/hw/qdev-core.h b/include/hw/qdev-core.h
index 72064f4dd4..14d476c587 100644
--- a/include/hw/qdev-core.h
+++ b/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;
-- 
2.26.2