code: void linkEntry(FatLfnDirectoryEntry entry) throws IOException {
          checkUniqueName(entry.getName());
  
          final ShortName sn = makeShortName(entry.getName());
          entry.realEntry.setShortName(sn);
          
          this.longNameIndex.put(entry.getName().toLowerCase(Locale.ROOT), entry);
          this.shortNameIndex.put(entry.realEntry.getShortName(), entry);
          
          updateLFN();
      }
docs: Links the specified entry to this directory, updating the entrie's
  short name.
  
  @param entry the entry to be linked (added) to this directory
  @see #unlinkEntry(de.waldheinz.fs.fat.FatLfnDirectoryEntry)