Filter based on disk space

    use Filesys::DiskSpace;
    ...

    my ($used, $avail) = (df "/")[2,3];

    if ($avail < 100 &&                 # less than 100k free?
        $tcp->{dest_port} == 119 &&     # NNTP
        ($tcp->{flags} & SYN) &&        # SYN
        !($tcp->{flags} & ACK)          # !ACK
        $msg->indev_name)               # incoming
    {
        $ipq->set_verdict($msg->packet_id, NF_DROP);
        syslog "crit", "Throttling inbound connections";
    }