You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: import.go
    path of file: ./repos/docker-ce/components/engine/vendor/github.com/Microsoft/hcsshim/pkg/ociwclayer
    
    the code of the file until where you have to start completion: package ociwclayer

import (
	"archive/tar"
	"bufio"
	"context"
	"io"
	"os"
	"path"
	"path/filepath"
	"strings"

	winio "github.com/Microsoft/go-winio"
	"github.com/Microsoft/go-winio/backuptar"
	"github.com/Microsoft/hcsshim"
)

const whiteoutPrefix = ".wh."

var (
	// mutatedFiles is a list of files that are mutated by the import process
	// and must be backed up and restored.
	mutatedFiles = map[string]string{
		"UtilityVM/Files/EFI/Microsoft/Boot/BCD":    
    
func writeBackupStreamFromTarAndSaveMutatedFiles(buf *bufio.Writer, w io.Writer, t *tar.Reader, hdr *tar.Header, root string) (nextHdr *tar.Header, err error) {
	var bcdBackup *os.File
	var bcdBackupWriter *winio.BackupFileWriter
	if backupPath, ok := mutatedFiles[hdr.Name]; ok {
		bcdBackup, err = os.Create(filepath.Join(root, backupPath))
		if err != nil {
			return nil, err
		}
		defer func() {
			cerr := bcdBackup.Close()
			if err == nil {
				err = cerr
			}
		}()

		bcdBackupWriter = winio.NewBackupFileWriter(bcdBackup, false)
		defer func() {
			cerr := bcdBackupWriter.Close()
			if err == nil {
				err = cerr
			}
		}()

		buf.Reset(io.MultiWriter(w, bcdBackupWriter))
	} else {
		buf.Reset(w)
	}

	defer func() {
		ferr := buf.Flush()
		if err == nil {
			err = ferr
		}
	}()

	return backuptar.WriteBackupStreamFromTarFile(buf, t, hdr)
}