Try to delete also the metadata of an incomplete layer

Account for the "diff != nil" path; try to remove even
the metadata of a layer on a failure saving.

Not that there's _much_ hope to be able to save
the version without the new layer when we weren't able
to save the version with the new layer.

Signed-off-by: Miloslav Trmač <mitr@redhat.com>

layers.go

@@ -795,6 +795,7 @@ func (r *layerStore) Put(id string, parentLayer *Layer, names []string, mountLab
 		for flag, value := range flags {
 			layer.Flags[flag] = value
 		}
+		savedIncompleteLayer := false
 		if diff != nil {
 			layer.Flags[incompleteFlag] = true
 			err = r.Save()
@@ -806,6 +807,7 @@ func (r *layerStore) Put(id string, parentLayer *Layer, names []string, mountLab
 				}
 				return nil, -1, err
 			}
+			savedIncompleteLayer = true
 			size, err = r.applyDiffWithOptions(layer.ID, moreOptions, diff)
 			if err != nil {
 				if err2 := r.Delete(layer.ID); err2 != nil {
@@ -820,10 +822,19 @@ func (r *layerStore) Put(id string, parentLayer *Layer, names []string, mountLab
 		}
 		err = r.Save()
 		if err != nil {
+			if savedIncompleteLayer {
+				if err2 := r.Delete(layer.ID); err2 != nil {
+					// Either a driver error or an error saving.
+					// We now have a layer that's been marked for
+					// deletion but which we failed to remove.
+					logrus.Errorf("While recovering from a failure applying layer diff, error deleting layer %#v: %v", layer.ID, err2)
+				}
+			} else {
 				// We don't have a record of this layer, but at least
 				// try to clean it up underneath us.
 				if err2 := r.driver.Remove(id); err2 != nil {
-				logrus.Errorf("While recovering from a failure saving finished layer metadata, error deleting layer %#v: %v", id, err2)
+					logrus.Errorf("While recovering from a failure saving finished layer metadata, error deleting layer %#v in graph driver: %v", id, err2)
+				}
 			}
 			return nil, -1, err
 		}