[PATCH 2/4] x86/iommu: Make x86-iommu a singleton object

[Peter Xu]

X86 IOMMUs cannot be created more than one on a system yet.  Make it a
singleton so it guards the system from accidentally create yet another
IOMMU object when one already presents.

Now if someone tries to create more than one, e.g., via:

  ./qemu -M q35 -device intel-iommu -device intel-iommu

The error will change from:

  qemu-system-x86_64: -device intel-iommu: QEMU does not support multiple 
vIOMMUs for x86 yet.

To:

  qemu-system-x86_64: -device intel-iommu: Class 'intel-iommu' only supports 
one instance

Unfortunately, yet we can't remove the singleton check in the machine
hook (pc_machine_device_pre_plug_cb), because there can also be
virtio-iommu involved, which doesn't share a common parent class yet.

But with this, it should be closer to reach that goal to check singleton by
QOM one day.

Signed-off-by: Peter Xu <pet...@redhat.com>
---
 hw/i386/x86-iommu.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/hw/i386/x86-iommu.c b/hw/i386/x86-iommu.c
index 60af896225..4bfeb08705 100644
--- a/hw/i386/x86-iommu.c
+++ b/hw/i386/x86-iommu.c
@@ -26,6 +26,7 @@
 #include "qemu/error-report.h"
 #include "trace.h"
 #include "sysemu/kvm.h"
+#include "qom/object_interfaces.h"
 
 void x86_iommu_iec_register_notifier(X86IOMMUState *iommu,
                                      iec_notify_fn fn, void *data)
@@ -133,10 +134,19 @@ static Property x86_iommu_properties[] = {
     DEFINE_PROP_END_OF_LIST(),
 };
 
+static Object *x86_iommu_get_instance(Error **errp)
+{
+    return OBJECT(x86_iommu_get_default());
+}
+
 static void x86_iommu_class_init(ObjectClass *klass, void *data)
 {
     DeviceClass *dc = DEVICE_CLASS(klass);
+    SingletonClass *singleton = SINGLETON_CLASS(klass);
+
     dc->realize = x86_iommu_realize;
+    singleton->get_instance = x86_iommu_get_instance;
+
     device_class_set_props(dc, x86_iommu_properties);
 }
 
@@ -152,6 +162,10 @@ static const TypeInfo x86_iommu_info = {
     .class_init    = x86_iommu_class_init,
     .class_size    = sizeof(X86IOMMUClass),
     .abstract      = true,
+    .interfaces = (InterfaceInfo[]) {
+        { TYPE_SINGLETON },
+        { }
+    }
 };
 
 static void x86_iommu_register_types(void)
-- 
2.45.0