# Creation of a COMPUTE data source is not contemplated in the
	# documentation, nor it is in the code. That's why we use an
	# object in dry-run mode: we'll get a reference to the function
	# and arguments that were about to be called, and add our
	# resource. Finally, we run the call.
	# Pretty bad it didn't have the function already...
	my $dsdef =
	  q{DS:aggregate:COMPUTE:}.
	    join(",",@dsources).",ADDNAN"x$#dsources ;

	$rrdbuilder->create(@rrd_parms) ;

	# Get references to the RRD function and arguments
	# Push the COMPUTE data source in it
	# Run the create command, see what happens
	my ($subref,$args) = $rrdbuilder->get_exec_env();
	push @$args,$dsdef ;

	eval {
	  $subref->(@$args) ;
	} ;