@@ -1,7 +1,6 @@

 package graphdriver

 import (

-	"errors"

 	"fmt"

 	"io"

 	"os"

@@ -28,13 +27,6 @@ const (

 var (

 	// All registered drivers

 	drivers map[string]InitFunc

-

-	// ErrNotSupported returned when driver is not supported.

-	ErrNotSupported = errors.New("driver not supported")

-	// ErrPrerequisites returned when driver does not meet prerequisites.

-	ErrPrerequisites = errors.New("prerequisites for driver not satisfied (wrong filesystem?)")

-	// ErrIncompatibleFS returned when file system is not supported.

-	ErrIncompatibleFS = fmt.Errorf("backing file system is unsupported for this graph driver")

 )

 //CreateOpts contains optional arguments for Create() and CreateReadWrite()

@@ -248,7 +240,7 @@ func New(name string, pg plugingetter.PluginGetter, config Options) (Driver, err

 	for _, name := range list {

 		driver, err := getBuiltinDriver(name, config.Root, config.DriverOptions, config.UIDMaps, config.GIDMaps)

 		if err != nil {

-			if isDriverNotSupported(err) {

+			if IsDriverNotSupported(err) {

 				continue

 			}

 			return nil, err

@@ -260,7 +252,7 @@ func New(name string, pg plugingetter.PluginGetter, config Options) (Driver, err

 	for name, initFunc := range drivers {

 		driver, err := initFunc(filepath.Join(config.Root, name), config.DriverOptions, config.UIDMaps, config.GIDMaps)

 		if err != nil {

-			if isDriverNotSupported(err) {

+			if IsDriverNotSupported(err) {

 				continue

 			}

 			return nil, err

@@ -270,12 +262,6 @@ func New(name string, pg plugingetter.PluginGetter, config Options) (Driver, err

 	return nil, fmt.Errorf("No supported storage backend found")

 }

-// isDriverNotSupported returns true if the error initializing

-// the graph driver is a non-supported error.

-func isDriverNotSupported(err error) bool {

-	return err == ErrNotSupported || err == ErrPrerequisites || err == ErrIncompatibleFS

-}

-

 // scanPriorDrivers returns an un-ordered scan of directories of prior storage drivers

 func scanPriorDrivers(root string) map[string]bool {

 	driversMap := make(map[string]bool)

new file mode 100644

@@ -0,0 +1,36 @@

+package graphdriver

+

+const (

+	// ErrNotSupported returned when driver is not supported.

+	ErrNotSupported NotSupportedError = "driver not supported"

+	// ErrPrerequisites returned when driver does not meet prerequisites.

+	ErrPrerequisites NotSupportedError = "prerequisites for driver not satisfied (wrong filesystem?)"

+	// ErrIncompatibleFS returned when file system is not supported.

+	ErrIncompatibleFS NotSupportedError = "backing file system is unsupported for this graph driver"

+)

+

+// ErrUnSupported signals that the graph-driver is not supported on the current configuration

+type ErrUnSupported interface {

+	NotSupported()

+}

+

+// NotSupportedError signals that the graph-driver is not supported on the current configuration

+type NotSupportedError string

+

+func (e NotSupportedError) Error() string {

+	return string(e)

+}

+

+// NotSupported signals that a graph-driver is not supported.

+func (e NotSupportedError) NotSupported() {}

+

+// IsDriverNotSupported returns true if the error initializing

+// the graph driver is a non-supported error.

+func IsDriverNotSupported(err error) bool {

+	switch err.(type) {

+	case ErrUnSupported:

+		return true

+	default:

+		return false

+	}

+}

@@ -42,7 +42,7 @@ func newDriver(t testing.TB, name string, options []string) *Driver {

 	d, err := graphdriver.GetDriver(name, nil, graphdriver.Options{DriverOptions: options, Root: root})

 	if err != nil {

 		t.Logf("graphdriver: %v\n", err)

-		if err == graphdriver.ErrNotSupported || err == graphdriver.ErrPrerequisites || err == graphdriver.ErrIncompatibleFS {

+		if graphdriver.IsDriverNotSupported(err) {

 			t.Skipf("Driver %s not supported", name)

 		}

 		t.Fatal(err)

@@ -138,11 +138,19 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap

 	}

 	switch fsMagic {

-	case graphdriver.FsMagicAufs, graphdriver.FsMagicBtrfs, graphdriver.FsMagicOverlay, graphdriver.FsMagicZfs, graphdriver.FsMagicEcryptfs, graphdriver.FsMagicNfsFs:

+	case graphdriver.FsMagicAufs, graphdriver.FsMagicBtrfs, graphdriver.FsMagicEcryptfs, graphdriver.FsMagicNfsFs, graphdriver.FsMagicOverlay, graphdriver.FsMagicZfs:

 		logrus.Errorf("'overlay' is not supported over %s", backingFs)

 		return nil, graphdriver.ErrIncompatibleFS

 	}

+	supportsDType, err := fsutils.SupportsDType(testdir)

+	if err != nil {

+		return nil, err

+	}

+	if !supportsDType {

+		return nil, overlayutils.ErrDTypeNotSupported("overlay", backingFs)

+	}

+

 	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)

 	if err != nil {

 		return nil, err

@@ -156,15 +164,6 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap

 		return nil, err

 	}

-	supportsDType, err := fsutils.SupportsDType(home)

-	if err != nil {

-		return nil, err

-	}

-	if !supportsDType {

-		// not a fatal error until v17.12 (#27443)

-		logrus.Warn(overlayutils.ErrDTypeNotSupported("overlay", backingFs))

-	}

-

 	d := &Driver{

 		home:          home,

 		uidMaps:       uidMaps,

@@ -153,9 +153,8 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap

 		backingFs = fsName

 	}

-	// check if they are running over btrfs, aufs, zfs, overlay, or ecryptfs

 	switch fsMagic {

-	case graphdriver.FsMagicAufs, graphdriver.FsMagicZfs, graphdriver.FsMagicOverlay, graphdriver.FsMagicEcryptfs, graphdriver.FsMagicNfsFs:

+	case graphdriver.FsMagicAufs, graphdriver.FsMagicEcryptfs, graphdriver.FsMagicNfsFs, graphdriver.FsMagicOverlay, graphdriver.FsMagicZfs:

 		logrus.Errorf("'overlay2' is not supported over %s", backingFs)

 		return nil, graphdriver.ErrIncompatibleFS

 	case graphdriver.FsMagicBtrfs:

@@ -174,12 +173,19 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap

 		if opts.overrideKernelCheck {

 			logrus.Warn("Using pre-4.0.0 kernel for overlay2, mount failures may require kernel update")

 		} else {

-			if err := supportsMultipleLowerDir(filepath.Dir(home)); err != nil {

+			if err := supportsMultipleLowerDir(testdir); err != nil {

 				logrus.Debugf("Multiple lower dirs not supported: %v", err)

 				return nil, graphdriver.ErrNotSupported

 			}

 		}

 	}

+	supportsDType, err := fsutils.SupportsDType(testdir)

+	if err != nil {

+		return nil, err

+	}

+	if !supportsDType {

+		return nil, overlayutils.ErrDTypeNotSupported("overlay2", backingFs)

+	}

 	rootUID, rootGID, err := idtools.GetRootUIDGID(uidMaps, gidMaps)

 	if err != nil {

@@ -194,15 +200,6 @@ func Init(home string, options []string, uidMaps, gidMaps []idtools.IDMap) (grap

 		return nil, err

 	}

-	supportsDType, err := fsutils.SupportsDType(home)

-	if err != nil {

-		return nil, err

-	}

-	if !supportsDType {

-		// not a fatal error until v17.12 (#27443)

-		logrus.Warn(overlayutils.ErrDTypeNotSupported("overlay2", backingFs))

-	}

-

 	d := &Driver{

 		home:          home,

 		uidMaps:       uidMaps,

@@ -3,8 +3,9 @@

 package overlayutils

 import (

-	"errors"

 	"fmt"

+

+	"github.com/docker/docker/daemon/graphdriver"

 )

 // ErrDTypeNotSupported denotes that the backing filesystem doesn't support d_type.

@@ -13,6 +14,7 @@ func ErrDTypeNotSupported(driver, backingFs string) error {

 	if backingFs == "xfs" {

 		msg += " Reformat the filesystem with ftype=1 to enable d_type support."

 	}

-	msg += " Running without d_type support will no longer be supported in Docker 17.12."

-	return errors.New(msg)

+	msg += " Backing filesystems without d_type support are not supported."

+

+	return graphdriver.NotSupportedError(msg)

 }