code: func (file *GridFile) SetName(name string) {
  	file.assertMode(gfsWriting)
  	file.m.Lock()
  	file.doc.Filename = name
  	file.m.Unlock()
  }
docs: // SetName changes the optional file name.  An empty string may be used to
  // unset it.
  //
  // It is a runtime error to call this function when the file is not open
  // for writing.