code: def check_disk_usage(filehandle, meta):
      
      # limit it at twenty kilobytes if no default is provided
      MAX_DISK_USAGE = current_app.config.get('MAX_DISK_USAGE', 20 * 1024)
      CURRENT_USAGE = really_bad_du(current_app.config['UPLOAD_PATH'])
      filehandle.seek(0, os.SEEK_END)
  
      if CURRENT_USAGE + filehandle.tell() > MAX_DISK_USAGE:
          filehandle.close()
          raise UploadError("Upload exceeds allotment.")
      filehandle.seek(0)
      return filehandle
docs: Checks the upload directory to see if the uploaded file would exceed
      the total disk allotment. Meant as a quick and dirty example.