fix validation

Author: JoaoJandre

engine/storage/snapshot/src/main/java/org/apache/cloudstack/storage/vmsnapshot/DefaultVMSnapshotStrategy.java

@@ -479,11 +479,17 @@ public boolean deleteVMSnapshotFromDB(VMSnapshot vmSnapshot, boolean unmanage) {
     @Override
     public StrategyPriority canHandle(Long vmId, Long rootPoolId, boolean snapshotMemory) {
         UserVmVO vm = userVmDao.findById(vmId);
-        if (State.Running.equals(vm.getState()) && (!snapshotMemory || vmHasKvmDiskOnlySnapshot(vm))) {
+        if (State.Running.equals(vm.getState()) && !snapshotMemory) {
             logger.debug("Default VM snapshot cannot handle VM snapshot for [{}] as it is running and its memory will not be affected.", vm);
             return StrategyPriority.CANT_HANDLE;
         }
 
+        if (vmHasKvmDiskOnlySnapshot(vm)) {
+            logger.debug("Default VM snapshot cannot handle VM snapshot for [{}] as it has a disk-only VM snapshot using kvmFileBasedStorageSnapshot strategy." +
+                    "These two strategies are not compatible, as reverting a disk-only VM snapshot will erase newer disk-and-memory VM snapshots.", vm);
+            return StrategyPriority.CANT_HANDLE;
+        }
+
         List<VolumeVO> volumes = volumeDao.findByInstance(vmId);
         for (VolumeVO volume : volumes) {
             if (volume.getFormat() != ImageFormat.QCOW2) {
@@ -501,9 +507,7 @@ private boolean vmHasKvmDiskOnlySnapshot(UserVm vm) {
 
         for (VMSnapshotVO vmSnapshotVO : vmSnapshotDao.findByVmAndByType(vm.getId(), VMSnapshot.Type.Disk)) {
             List<VMSnapshotDetailsVO> vmSnapshotDetails = vmSnapshotDetailsDao.listDetails(vmSnapshotVO.getId());
-            if (vmSnapshotDetails.stream().
-                    anyMatch(vmSnapshotDetailsVO -> vmSnapshotDetailsVO.getName().equals(KVM_FILE_BASED_STORAGE_SNAPSHOT) ||
-                            vmSnapshotDetailsVO.getName().equals(STORAGE_SNAPSHOT))) {
+            if (vmSnapshotDetails.stream().anyMatch(vmSnapshotDetailsVO -> vmSnapshotDetailsVO.getName().equals(KVM_FILE_BASED_STORAGE_SNAPSHOT))) {
                 return true;
             }
         }