}
sub nextFreeStepNr {
    my ($build) = @_;
    my $max = $build->buildsteps->find(
        {}, {select => {max => 'stepnr + 1'}, as => ['max']});
    return (defined $max && defined $max->get_column('max')) ? $max->get_column('max') : 1;

sub failDependents {
    my ($drvPath, $errorMsg) = @_;
    # Get the referrer closure of $drvPath.
    my @dependentDrvs = computeFSClosure(1, 0, $drvPath);
    my $time = time();
    txn_do($db, sub {

        my @dependentBuilds = $db->resultset('Builds')->search(
            { drvpath => [ @dependentDrvs ], finished => 0, busy => 0 });

        for my $d (@dependentBuilds) {
            print STDERR "failing dependent build ", $d->id, " of ", $d->project->name, ":", $d->jobset->name, ":", $d->job->name, "\n";
            $d->update(
                { finished => 1
                , logfile => ''
                , timestamp => time # !!! Why change the timestamp?
                , iscachedbuild => 0
                , buildstatus => $drvPath eq $d->drvpath ? 1 : 2
                , starttime => $time
                , stoptime => $time
                , errormsg => undef
                });
            my $step = $d->buildsteps->create(
                { stepnr => nextFreeStepNr($d)
                , type => 0 # = build
                , drvpath => $drvPath
                , busy => 0
                , status => 1
                , starttime => time
                , stoptime => time
                , errormsg => $errorMsg
                });
            addBuildStepOutputs($step);
        }
    });
}

        my $max = $build->buildsteps->find(
            {}, {select => {max => 'stepnr + 1'}, as => ['max']});
        my $buildStepNr = (defined $max && defined $max->get_column('max')) ? $max->get_column('max') : 1;

        my $buildStepNr = nextFreeStepNr($build);

                # Immediately fail all builds that depend on this derivation.
                failDependents($drvPathStep, $errorMsg);