// assume an array of (offset,length,status) records

// allocate n new pages
PageId allocate_pages(int n) {
   if (no existing free chunks are large enough) {
      int endfile = lseek(db->fd, 0, SEEK_END);
      addNewEntry(db->map, endfile, n);
   } else {
      grab "worst fit" chunk
      split off unused section as new chunk
   }
   // note that file itself is not changed
}