func getWalkRoot(srcPath string, include string) string {
	return filepath.Join(srcPath, include)
}
getWalkRoot calculates the root path when performing a TarWithOptions.
We use a separate function as this is platform specific.
package archive
import (
	"archive/tar"
	"fmt"
	"os"
	"path/filepath"
	"strings"
	"github.com/docker/docker/pkg/idtools"
	"github.com/docker/docker/pkg/longpath"
)
func CanonicalTarNameForPath(p string) (string, error) {
	if strings.Contains(p, "/") {
		return "", fmt.Errorf("Windows path contains forward slash: %s", p)
	}
	return strings.Replace(p, string(os.PathSeparator), "/", -1), nil
}
func fixVolumePathPrefix(srcPath string) string {
	return longpath.AddPrefix(srcPath)
}