Lock devices during OVF export as this could cause a race otherwise

Closes: oVirt#797

During the creation of the ovf config export, oVirt does modifications
to the VmDevices.
Now another thread cleans those entries again, and if you are unlucky it
happens during the ovf generation itself.

DEBUG [org.ovirt.engine.core.vdsbroker.monitoring.VmDevicesMonitoring]
(EE-ManagedScheduledExecutorService-engineScheduledThreadPool-Thread-60)
[] VM 'xxxx' unmanaged device was marked for remove : {1}

And this causes the export to be skipped.

So we add a device lock during the ovf export to resolve this.

Signed-off-by: Jean-Louis Dupond <jean-louis@dupond.be>

backend/manager/modules/bll/src/main/java/org/ovirt/engine/core/bll/GetVmOvfByVmIdQuery.java

@@ -9,6 +9,7 @@
 import org.ovirt.engine.core.common.queries.GetVmOvfByVmIdParameters;
 import org.ovirt.engine.core.dao.SnapshotDao;
 import org.ovirt.engine.core.dao.VmDao;
+import org.ovirt.engine.core.vdsbroker.ResourceManager;
 
 public class GetVmOvfByVmIdQuery<P extends GetVmOvfByVmIdParameters> extends QueriesCommandBase<P> {
     @Inject
@@ -23,6 +24,9 @@ public class GetVmOvfByVmIdQuery<P extends GetVmOvfByVmIdParameters> extends Que
     @Inject
     private VmDeviceUtils vmDeviceUtils;
 
+    @Inject
+    private ResourceManager resourceManager;
+
     public GetVmOvfByVmIdQuery(P parameters, EngineContext engineContext) {
         super(parameters, engineContext);
     }
@@ -35,10 +39,16 @@ protected void executeQueryCommand() {
             return;
         }
 
+        // We want to lock the devices to make sure no other thread modifies them during the ovf export.
+        // Otherwise we end up without ovf in the export
+        resourceManager.getVmManager(getParameters().getId()).getVmDevicesLock().lock();
+
         vm.setSnapshots(snapshotDao.getAllWithConfiguration(vm.getId()));
         vmDeviceUtils.setVmDevices(vm.getStaticData());
         String ovfData = generateOvfConfig(vm, getParameters().isAsOva());
 
+        resourceManager.getVmManager(getParameters().getId()).getVmDevicesLock().unlock();
+
         if (ovfData == null) {
             return;
         }