tracer.go
func AppendOptionWithPrefix(options []string, prefix string, v string) []string {
	for i, opt := range options {
		if strings.HasPrefix(opt, prefix) == true {
			new_opt := opt + "," + v
			options[i] = new_opt
			return options
		}
	}
	return append(options, prefix + v)
}
func AppendOptionWithPrefix(options []string, prefix string, v string) []string {
	for i, opt := range options {
		if strings.HasPrefix(opt, prefix) == true {
			new_opt := opt + "," + v
			options[i] = new_opt
			return options
		}
	}
	return append(options, prefix + v)
}
// Append to an option with given prefix