code: def get_readonly_instance(cls, working_dir, expected_snapshots={}):
          
          import virtualchain_hooks
          db_path = virtualchain.get_db_filename(virtualchain_hooks, working_dir)
          db = BlockstackDB(db_path, DISPOSITION_RO, working_dir, get_genesis_block(), expected_snapshots={})
          rc = db.db_setup()
          if not rc:
              log.error("Failed to set up virtualchain state engine")
              return None
          
          return db
docs: Get a read-only handle to the blockstack-specific name db.
          Multiple read-only handles may exist.
  
          Returns the handle on success.
          Returns None on error