Skip overlay2 diff tests when using naivediff

Naivediff fails when layers are created directly on top of
each other. Other graphdrivers which use naivediff already
skip these tests. Until naivediff is fixed, skip with overlay2
when running tests on a kernel which causes naivediff fallback.
Fix applydiff to never use the naivediff size when not applying
changes with naivediff.

Signed-off-by: Derek McGowan <derek@mcgstyle.net> (github: dmcgowan)

daemon/graphdriver/overlay2/overlay.go

@@ -608,7 +608,7 @@ func (d *Driver) ApplyDiff(id string, parent string, diff io.Reader) (size int64
 		return 0, err
 	}
 
-	return d.DiffSize(id, parent)
+	return directory.Size(applyDir)
 }
 
 func (d *Driver) getDiffPath(id string) string {

daemon/graphdriver/overlay2/overlay_test.go

@@ -3,6 +3,7 @@
 package overlay2
 
 import (
+	"io/ioutil"
 	"os"
 	"syscall"
 	"testing"
@@ -33,6 +34,18 @@ func cdMountFrom(dir, device, target, mType, label string) error {
 	return syscall.Mount(device, target, mType, 0, label)
 }
 
+func skipIfNaive(t *testing.T) {
+	td, err := ioutil.TempDir("", "naive-check-")
+	if err != nil {
+		t.Fatalf("Failed to create temp dir: %v", err)
+	}
+	defer os.RemoveAll(td)
+
+	if useNaiveDiff(td) {
+		t.Skipf("Cannot run test with naive diff")
+	}
+}
+
 // This avoids creating a new driver for each test if all tests are run
 // Make sure to put new tests between TestOverlaySetup and TestOverlayTeardown
 func TestOverlaySetup(t *testing.T) {
@@ -56,10 +69,12 @@ func TestOverlay128LayerRead(t *testing.T) {
 }
 
 func TestOverlayDiffApply10Files(t *testing.T) {
+	skipIfNaive(t)
 	graphtest.DriverTestDiffApply(t, 10, driverName)
 }
 
 func TestOverlayChanges(t *testing.T) {
+	skipIfNaive(t)
 	graphtest.DriverTestChanges(t, driverName)
 }