You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: followerreads.go
    path of file: ./repos/cockroach/pkg/ccl/kvccl/kvfollowerreadsccl
    
    the code of the file until where you have to start completion: // Copyright 2019 The Cockroach Authors.
//
// Licensed as a CockroachDB En
    
func evalFollowerReadOffset(st *cluster.Settings) (time.Duration, error) {
	if err := checkEnterpriseEnabled(st); err != nil {
		return 0, err
	}
	// NOTE: we assume that at least some of the ranges being queried use a
	// LAG_BY_CLUSTER_SETTING closed timestamp policy. Otherwise, there would
	// be no reason to use AS OF SYSTEM TIME follower_read_timestamp().
	return getFollowerReadLag(st), nil
}