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: fs.go
    path of file: ./repos/trivy/pkg/fanal/walker
    
    the code of the file until where you have to start completion: package walker

import (
	"io/fs"
	"os"
	"path/filepath"

	swalker "github.com/saracen/walker"
	"golang.org/x/xe
    
func NewFS(skipFiles, skipDirs []string, parallel int, errCallback ErrorCallback) FS {
	if errCallback == nil {
		errCallback = func(pathname string, err error) error {
			// ignore permission errors
			if os.IsPermission(err) {
				return nil
			}
			// halt traversal on any other error
			return xerrors.Errorf("unknown error with %s: %w", pathname, err)
		}
	}

	return FS{
		walker:      newWalker(skipFiles, skipDirs),
		parallel:    parallel,
		errCallback: errCallback,
	}
}