code: func checkMountDestination(rootfs, dest string) error {
  	if filepath.Clean(rootfs) == filepath.Clean(dest) {
  		return fmt.Errorf("mounting into / is prohibited")
  	}
  	invalidDestinations := []string{
  		"/proc",
  	}
  	for _, invalid := range invalidDestinations {
  		path, err := filepath.Rel(filepath.Join(rootfs, invalid), dest)
  		if err != nil {
  			return err
  		}
  		if path == "." || !strings.HasPrefix(path, "..") {
  			return fmt.Errorf("%q cannot be mounted because it is located inside %q", dest, invalid)
  		}
  	}
  	return nil
  }
docs: // checkMountDestination checks to ensure that the mount destination is not over the
  // top of /proc or /sys.
  // dest is required to be an abs path and have any symlinks resolved before calling this function.