func (f *fs) Mkdir(name string, perm os.FileMode) error {
	p, err := f.strip(name)
	if err != nil {
		return err
	}
	return f.backend.Mkdir(p, perm)
}
Mkdir creates a directory in the filesystem, return an error if any
happens.
package stripprefix
import (
	"os"
	"path/filepath"
	"strings"
	"time"
	"github.com/spf13/afero"
)
type fs struct {
	prefix  string
	backend afero.Fs
}
func New(prefix string, backend afero.Fs) afero.Fs {
	return &fs{
		prefix:  prefix,
		backend: backend,
	}
}
func (f *fs) strip(name string) (string, error) {
	if !filepath.IsAbs(name) {
		return name, nil
	}
	p := strings.TrimPrefix(name, f.prefix)
	if len(p) == len(name) {
		return "", os.ErrNotExist
	}
	if p == "" {
		return ".", nil
	}
	return p, nil
}
func (f *fs) Create(name string) (afero.File, error) {
	p, err := f.strip(name)
	if err != nil {
		return nil, err
	}
	return f.backend.Create(p)
}