Function serve_read_only 

pub fn serve_read_only<D: Directory + ?Sized>(
    directory: Arc<D>,
) -> DirectoryProxy

Helper function to serve a new connection to directory as read-only (i.e. with [fio::PERM_READABLE]). Errors will be communicated via epitaph on the returned proxy. A new crate::execution_scope::ExecutionScope will be created for the request.