Use tryRelocate to fall back to symlink if rename fails

graphdriver/aufs/migrate.go

@@ -1,6 +1,7 @@
 package aufs
 
 import (
+	"fmt"
 	"io/ioutil"
 	"os"
 	"path"
@@ -20,7 +21,7 @@ func (a *AufsDriver) Migrate(pth string) error {
 	}
 	for _, fi := range fis {
 		if fi.IsDir() && exists(path.Join(pth, fi.Name(), "layer")) && !a.Exists(fi.Name()) {
-			if err := os.Symlink(path.Join(pth, fi.Name(), "layer"), path.Join(a.rootPath(), "diff", fi.Name())); err != nil {
+			if err := tryRelocate(path.Join(pth, fi.Name(), "layer"), path.Join(a.rootPath(), "diff", fi.Name())); err != nil {
 				return err
 			}
 			if err := a.Create(fi.Name(), ""); err != nil {
@@ -30,3 +31,14 @@ func (a *AufsDriver) Migrate(pth string) error {
 	}
 	return nil
 }
+
+// tryRelocate will try to rename the old path to the new pack and if
+// the operation fails, it will fallback to a symlink
+func tryRelocate(oldPath, newPath string) error {
+	if err := os.Rename(oldPath, newPath); err != nil {
+		if sErr := os.Symlink(oldPath, newPath); sErr != nil {
+			return fmt.Errorf("Unable to relocate %s to %s: Rename err %s Symlink err %s", oldPath, newPath, err, sErr)
+		}
+	}
+	return nil
+}