core: only use a shared lock for thin template overlays

When downloading a disk that is an overlay of a template, take only a
shared lock on the disk and skip the locked disk validation, this would
allow downloading disks of thin VMs without failing on the disk being
locked.

Bug-Url: Bug-Url: https://bugzilla.redhat.com/1879391
Signed-off-by: Benny Zlotnik <bzlotnik@redhat.com>

backend/manager/modules/bll/src/main/java/org/ovirt/engine/core/bll/storage/disk/image/TransferDiskImageCommand.java

@@ -444,15 +444,28 @@ protected Map<String, Pair<String, String>> getSharedLocks() {
             // StartVmBackup should handle locks
             return locks;
         }
-        if (!Guid.isNullOrEmpty(getParameters().getImageId()) && getDiskImage() != null) {
+
+        if (!Guid.isNullOrEmpty(getParameters().getImageId()) ||
+                getDiskImage() != null &&
+                        !isThinTemplate(getDiskImage())) {
             List<VM> vms = vmDao.getVmsListForDisk(getDiskImage().getId(), true);
             vms.forEach(vm -> locks.put(vm.getId().toString(),
                     LockMessagesMatchUtil.makeLockingPair(LockingGroup.VM, getDiskIsBeingTransferredLockMessage())));
         }
 
+        // Lock with a shared lock since we skip locking exclusively disks of thin VMs
+        if (isThinTemplate(getDiskImage())) {
+            locks.put(getDiskImage().getId().toString(),
+                    LockMessagesMatchUtil.makeLockingPair(LockingGroup.DISK, EngineMessage.ACTION_TYPE_FAILED_DISK_IS_LOCKED));
+        }
+
         return locks;
     }
 
+    private boolean isThinTemplate(DiskImage diskImage) {
+        return !Guid.isNullOrEmpty(diskImage.getImageTemplateId());
+    }
+
     private String getDiskIsBeingTransferredLockMessage() {
         return new LockMessage(EngineMessage.ACTION_TYPE_FAILED_DISK_IS_BEING_TRANSFERRED)
                 .withOptional("DiskName", getDiskImage().getDiskAlias() != null ? getDiskImage().getDiskAlias() : "")
@@ -466,7 +479,9 @@ protected Map<String, Pair<String, String>> getExclusiveLocks() {
             // StartVmBackup should handle locks
             return locks;
         }
-        if (getDiskImage() != null) {
+
+        // If the disk is a thin template overlay we only lock with a shared lock
+        if (getDiskImage() != null && !isThinTemplate(getDiskImage())) {
             locks.put(getDiskImage().getId().toString(),
                     LockMessagesMatchUtil.makeLockingPair(LockingGroup.DISK, getDiskIsBeingTransferredLockMessage()));
         }