code: def linked(prefix):
          
          logger.debug(str(prefix))
  
          if not isdir(prefix):
              return set()
  
          meta_dir = join(prefix, 'conda-meta')
          if not isdir(meta_dir):
              # We might have nothing in linked (and no conda-meta directory)
              return set()
  
          return set(fn[:-5] for fn in os.listdir(meta_dir)
                     if fn.endswith('.json'))
docs: Return set of canonical names of linked packages in `prefix`.