code: func (m *ProcessManager) Open(u *url.URL, mode int32) (hgfs.File, error) {
  	info, err := m.Stat(u)
  	if err != nil {
  		return nil, err
  	}
  
  	pinfo, ok := info.(*ProcessFile)
  
  	if !ok {
  		return nil, os.ErrNotExist // fall through to default os.Open
  	}
  
  	switch path.Base(u.Path) {
  	case "stdin":
  		if mode != hgfs.OpenModeWriteOnly {
  			return nil, vix.Error(vix.InvalidArg)
  		}
  	case "stdout", "stderr":
  		if mode != hgfs.OpenModeReadOnly {
  			return nil, vix.Error(vix.InvalidArg)
  		}
  	}
  
  	return pinfo, nil
  }
docs: // Open implements hgfs.FileHandler.Open