In OpenBSD and DragonFly BSD, sysctl is also used as the transport layer for the hw.sensors framework for hardware monitoring, whereas NetBSD uses the ioctl system call for its sysmon envsys counterpart. Both sysctl and ioctl are the two system calls which can be used to add extra functionality to the kernel without adding yet another system call; for example, in 2004 with OpenBSD 3.6, when the tcpdrop utility was introduced, sysctl was used as the underlying system call. In FreeBSD, although there is no sensors framework, the individual temperature and other sensors are still commonly exported through the sysctl tree through Newbus, for example, as is the case with the codice_1 driver that's available in all the 4 BSD systems, including FreeBSD.