src/client/pkg/tracing/tracing.go
func AddSpanToAnyExisting(ctx context.Context, operation string, kvs ...interface{}) (opentracing.Span, context.Context) {
	if parentSpan := opentracing.SpanFromContext(ctx); parentSpan != nil {
		span := opentracing.StartSpan(operation, opentracing.ChildOf(parentSpan.Context()))
		tagSpan(span, kvs)
		return span, opentracing.ContextWithSpan(ctx, span)
	}
	return nil, ctx
}
func AddSpanToAnyExisting(ctx context.Context, operation string, kvs ...interface{}) (opentracing.Span, context.Context) {
	if parentSpan := opentracing.SpanFromContext(ctx); parentSpan != nil {
		span := opentracing.StartSpan(operation, opentracing.ChildOf(parentSpan.Context()))
		tagSpan(span, kvs)
		return span, opentracing.ContextWithSpan(ctx, span)
	}
	return nil, ctx
}
// AddSpanToAnyExisting checks 'ctx' for Jaeger tracing information, and if
// tracing metadata is present, it generates a new span for 'operation', marks
// it as a child of the existing span, and returns it.