Remove Windows' Readlink fork

.travis.yml

@@ -2,9 +2,8 @@ language: go
 sudo: required
 
 go:
-  - 1.11.x
-  - 1.12.x
   - 1.13.x
+  - 1.14.x
   - tip
 
 go_import_path: github.com/containerd/continuity

driver/driver.go

@@ -138,6 +138,10 @@ func (d *driver) Lstat(p string) (os.FileInfo, error) {
 	return os.Lstat(p)
 }
 
+func (d *driver) Readlink(p string) (string, error) {
+	return os.Readlink(p)
+}
+
 func (d *driver) Mkdir(p string, mode os.FileMode) error {
 	return os.Mkdir(p, mode)
 }

driver/driver_unix.go

@@ -131,8 +131,3 @@ func (d *driver) LSetxattr(path string, attrMap map[string][]byte) error {
 func (d *driver) DeviceInfo(fi os.FileInfo) (maj uint64, min uint64, err error) {
 	return devices.DeviceInfo(fi)
 }
-
-// Readlink was forked on Windows to fix a Golang bug, use the "os" package here
-func (d *driver) Readlink(p string) (string, error) {
-	return os.Readlink(p)
-}

driver/driver_windows.go

@@ -14,12 +14,16 @@
    limitations under the License.
 */
 
+// +build go1.13
+
+// Go 1.13 is the minimally supported version for Windows.
+// Earlier golang releases have bug in os.Readlink
+// (see https://github.com/golang/go/issues/30463).
+
 package driver
 
 import (
 	"os"
-
-	"github.com/containerd/continuity/sysx"
 )
 
 func (d *driver) Mknod(path string, mode os.FileMode, major, minor int) error {
@@ -35,9 +39,3 @@ func (d *driver) Lchmod(path string, mode os.FileMode) (err error) {
 	// TODO: Use Window's equivalent
 	return os.Chmod(path, mode)
 }
-
-// Readlink is forked in order to support Volume paths which are used
-// in container layers.
-func (d *driver) Readlink(p string) (string, error) {
-	return sysx.Readlink(p)
-}