Enable PVC as DataSource for PVC creation

This enables the ability to specify and existing PVC as a DataSource in
a new PVC Spec (eg "clone" and existing volume).

pkg/apis/core/validation/validation_test.go

@@ -13288,3 +13288,48 @@ func TestValidateWindowsSecurityContextOptions(t *testing.T) {
 		})
 	}
 }
+
+func testDataSourceInSpec(name string, kind string, apiGroup string) *core.PersistentVolumeClaimSpec {
+	scName := "csi-plugin"
+	dataSourceInSpec := core.PersistentVolumeClaimSpec{
+		AccessModes: []core.PersistentVolumeAccessMode{
+			core.ReadOnlyMany,
+		},
+		Resources: core.ResourceRequirements{
+			Requests: core.ResourceList{
+				core.ResourceName(core.ResourceStorage): resource.MustParse("10G"),
+			},
+		},
+		StorageClassName: &scName,
+		DataSource: &core.TypedLocalObjectReference{
+			APIGroup: &apiGroup,
+			Kind:     kind,
+			Name:     name,
+		},
+	}
+
+	return &dataSourceInSpec
+}
+
+func TestAlphaVolumeDataSource(t *testing.T) {
+	successTestCases := []core.PersistentVolumeClaimSpec{
+		*testDataSourceInSpec("test_snapshot", "VolumeSnapshot", "snapshot.storage.k8s.io"),
+		*testDataSourceInSpec("test_pvc", "PersistentVolumeClaim", ""),
+	}
+	failedTestCases := []core.PersistentVolumeClaimSpec{
+		*testDataSourceInSpec("", "VolumeSnapshot", "snapshot.storage.k8s.io"),
+		*testDataSourceInSpec("test_snapshot", "PersistentVolumeClaim", "snapshot.storage.k8s.io"),
+		*testDataSourceInSpec("test_snapshot", "VolumeSnapshot", "storage.k8s.io"),
+	}
+
+	for _, tc := range successTestCases {
+		if errs := ValidatePersistentVolumeClaimSpec(&tc, field.NewPath("spec")); len(errs) != 0 {
+			t.Errorf("expected success: %v", errs)
+		}
+	}
+	for _, tc := range failedTestCases {
+		if errs := ValidatePersistentVolumeClaimSpec(&tc, field.NewPath("spec")); len(errs) == 0 {
+			t.Errorf("expected failure: %v", errs)
+		}
+	}
+}