4 files changed, 39 insertions, 5 deletions

diff --git a/hw/hw.h b/hw/hw.h
index 2d39724..fc2d184 100644
--- a/hw/hw.h
+++ b/hw/hw.h
@@ -758,5 +758,9 @@ extern void vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
                                void *opaque);
 extern int vmstate_register(int instance_id, const VMStateDescription *vmsd,
                             void *base);
+extern int vmstate_register_with_alias_id(int instance_id,
+                                          const VMStateDescription *vmsd,
+                                          void *base, int alias_id,
+                                          int required_for_version);
 void vmstate_unregister(const VMStateDescription *vmsd, void *opaque);
 #endif
diff --git a/hw/qdev.c b/hw/qdev.c
index d3bf0fa..af17486 100644
--- a/hw/qdev.c
+++ b/hw/qdev.c
@@ -93,6 +93,7 @@ static DeviceState *qdev_create_from_info(BusState *bus, DeviceInfo *info)
         assert(bus->allow_hotplug);
         dev->hotplugged = 1;
     }
+    dev->instance_id_alias = -1;
     dev->state = DEV_STATE_CREATED;
     return dev;
 }
@@ -278,12 +279,23 @@ int qdev_init(DeviceState *dev)
         return rc;
     }
     qemu_register_reset(qdev_reset, dev);
-    if (dev->info->vmsd)
-        vmstate_register(-1, dev->info->vmsd, dev);
+    if (dev->info->vmsd) {
+        vmstate_register_with_alias_id(-1, dev->info->vmsd, dev,
+                                       dev->instance_id_alias,
+                                       dev->alias_required_for_version);
+    }
     dev->state = DEV_STATE_INITIALIZED;
     return 0;
 }
 
+void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
+                                 int required_for_version)
+{
+    assert(dev->state == DEV_STATE_CREATED);
+    dev->instance_id_alias = alias_id;
+    dev->alias_required_for_version = required_for_version;
+}
+
 int qdev_unplug(DeviceState *dev)
 {
     if (!dev->parent_bus->allow_hotplug) {
diff --git a/hw/qdev.h b/hw/qdev.h
index d8fbc73..a44060e 100644
--- a/hw/qdev.h
+++ b/hw/qdev.h
@@ -44,6 +44,8 @@ struct DeviceState {
     QLIST_HEAD(, BusState) child_bus;
     int num_child_bus;
     QLIST_ENTRY(DeviceState) sibling;
+    int instance_id_alias;
+    int alias_required_for_version;
 };
 
 typedef void (*bus_dev_printfn)(Monitor *mon, DeviceState *dev, int indent);
@@ -112,6 +114,8 @@ int qdev_device_help(QemuOpts *opts);
 DeviceState *qdev_device_add(QemuOpts *opts);
 int qdev_init(DeviceState *dev) QEMU_WARN_UNUSED_RESULT;
 void qdev_init_nofail(DeviceState *dev);
+void qdev_set_legacy_instance_id(DeviceState *dev, int alias_id,
+                                 int required_for_version);
 int qdev_unplug(DeviceState *dev);
 void qdev_free(DeviceState *dev);
 int qdev_simple_unplug_cb(DeviceState *dev);
diff --git a/savevm.c b/savevm.c
index 74e553c..dc20390 100644
--- a/savevm.c
+++ b/savevm.c
@@ -991,6 +991,7 @@ typedef struct SaveStateEntry {
     QTAILQ_ENTRY(SaveStateEntry) entry;
     char idstr[256];
     int instance_id;
+    int alias_id;
     int version_id;
     int section_id;
     SaveSetParamsHandler *set_params;
@@ -1079,11 +1080,16 @@ void unregister_savevm(const char *idstr, void *opaque)
     }
 }
 
-int vmstate_register(int instance_id, const VMStateDescription *vmsd,
-                     void *opaque)
+int vmstate_register_with_alias_id(int instance_id,
+                                   const VMStateDescription *vmsd,
+                                   void *opaque, int alias_id,
+                                   int required_for_version)
 {
     SaveStateEntry *se;
 
+    /* If this triggers, alias support can be dropped for the vmsd. */
+    assert(alias_id == -1 || required_for_version >= vmsd->minimum_version_id);
+
     se = qemu_mallocz(sizeof(SaveStateEntry));
     pstrcpy(se->idstr, sizeof(se->idstr), vmsd->name);
     se->version_id = vmsd->version_id;
@@ -1093,6 +1099,7 @@ int vmstate_register(int instance_id, const VMStateDescription *vmsd,
     se->load_state = NULL;
     se->opaque = opaque;
     se->vmsd = vmsd;
+    se->alias_id = alias_id;
 
     if (instance_id == -1) {
         se->instance_id = calculate_new_instance_id(vmsd->name);
@@ -1104,6 +1111,12 @@ int vmstate_register(int instance_id, const VMStateDescription *vmsd,
     return 0;
 }
 
+int vmstate_register(int instance_id, const VMStateDescription *vmsd,
+                     void *opaque)
+{
+    return vmstate_register_with_alias_id(instance_id, vmsd, opaque, -1, 0);
+}
+
 void vmstate_unregister(const VMStateDescription *vmsd, void *opaque)
 {
     SaveStateEntry *se, *new_se;
@@ -1433,7 +1446,8 @@ static SaveStateEntry *find_se(const char *idstr, int instance_id)
 
     QTAILQ_FOREACH(se, &savevm_handlers, entry) {
         if (!strcmp(se->idstr, idstr) &&
-            instance_id == se->instance_id)
+            (instance_id == se->instance_id ||
+             instance_id == se->alias_id))
             return se;
     }
     return NULL;