code: func (ms *FileMsgStore) lockFiles(fslice *fileSlice) error {
  	return ms.doLockFiles(fslice, false)
  }
docs: // lockFiles locks the data and index files of the given file slice.
  // If files were closed they are opened in this call, and if so,
  // and if this slice is the write slice, the writer and offset are reset.