kubeadm: fix a bug during kubeadm upgrade, where it is not possible to mount a new device and create a symbolic link for /etc/kubernetes (or a sub-directory) so that kubeadm stores its information on the mounted device

cmd/kubeadm/app/phases/upgrade/staticpods.go

@@ -123,7 +123,7 @@ func NewKubeStaticPodPathManagerUsingTempDirs(kubernetesDir, patchesDir string,
 
 // MoveFile should move a file from oldPath to newPath
 func (spm *KubeStaticPodPathManager) MoveFile(oldPath, newPath string) error {
-	return os.Rename(oldPath, newPath)
+	return kubeadmutil.MoveFile(oldPath, newPath)
 }
 
 // KubernetesDir should point to the directory Kubernetes owns for storing various configuration files

cmd/kubeadm/app/util/copy.go

@@ -17,19 +17,56 @@ limitations under the License.
 package util
 
 import (
+	"io"
 	"os"
+	"strings"
+
+	"github.com/pkg/errors"
+
+	"k8s.io/klog/v2"
 )
 
 // CopyFile copies a file from src to dest.
 func CopyFile(src, dest string) error {
-	fileInfo, err := os.Stat(src)
+	sourceFileInfo, err := os.Stat(src)
 	if err != nil {
 		return err
 	}
-	contents, err := os.ReadFile(src)
+
+	sourceFile, err := os.Open(src)
 	if err != nil {
 		return err
 	}
-	err = os.WriteFile(dest, contents, fileInfo.Mode())
+	defer func() {
+		_ = sourceFile.Close()
+	}()
+
+	destFile, err := os.OpenFile(dest, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, sourceFileInfo.Mode())
+	if err != nil {
+		return err
+	}
+	defer func() {
+		_ = destFile.Close()
+	}()
+
+	_, err = io.Copy(destFile, sourceFile)
+
+	return err
+}
+
+// MoveFile moves a file from src to dest.
+func MoveFile(src, dest string) error {
+	err := os.Rename(src, dest)
+	if err != nil && strings.Contains(err.Error(), "invalid cross-device link") {
+		// When calling os.Rename(), an "invalid cross-device link" error may occur
+		// if the source and destination files are on different file systems.
+		// In this case, the file is moved by copying and then deleting the source file,
+		// although it is less efficient than os.Rename().
+		klog.V(4).Infof("cannot rename %v to %v due to %v, attempting an alternative method", src, dest, err)
+		if err := CopyFile(src, dest); err != nil {
+			return errors.Wrapf(err, "failed to copy file %v to %v", src, dest)
+		}
+		return os.Remove(src)
+	}
 	return err
 }