migration: allow unplug during migration for failover devices

In "b06424de62 migration: Disable hotplug/unplug during migration" we
added a check to disable unplug for all devices until we have figured
out what works. For failover primary devices qdev_unplug() is called
from the migration handler, i.e. during migration.

This patch adds a flag to DeviceState which is set to false for all
devices and makes an exception for PCI devices that are also
primary devices in a failover pair.

Signed-off-by: Jens Freimann <jfreimann@redhat.com>
Message-Id: <20191029114905.6856-8-jfreimann@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

hw/core/qdev.c

@@ -996,6 +996,7 @@ static void device_initfn(Object *obj)
 
     dev->instance_id_alias = -1;
     dev->realized = false;
+    dev->allow_unplug_during_migration = false;
 
     object_property_add_bool(obj, "realized",
                              device_get_realized, device_set_realized, NULL);

hw/pci/pci.c

@@ -2130,6 +2130,7 @@ static void pci_qdev_realize(DeviceState *qdev, Error **errp)
             pci_qdev_unrealize(DEVICE(pci_dev), NULL);
             return;
         }
+        qdev->allow_unplug_during_migration = true;
     }
 
     /* rom loading */

include/hw/qdev-core.h

@@ -156,6 +156,7 @@ struct DeviceState {
     bool pending_deleted_event;
     QemuOpts *opts;
     int hotplugged;
+    bool allow_unplug_during_migration;
     BusState *parent_bus;
     QLIST_HEAD(, NamedGPIOList) gpios;
     QLIST_HEAD(, BusState) child_bus;

qdev-monitor.c

@@ -851,7 +851,7 @@ void qdev_unplug(DeviceState *dev, Error **errp)
         return;
     }
 
-    if (!migration_is_idle()) {
+    if (!migration_is_idle() && !dev->allow_unplug_during_migration) {
         error_setg(errp, "device_del not allowed while migrating");
         return;
     }