sysctl_ctx_init(9) on FreeBSD

The text f88747a084d5, as FreeBSD 5.2.1-RELEASE, FreeBSD 5.2-RELEASE, FreeBSD 5.1-RELEASE, FreeBSD 5.0-RELEASE shipped it.

sysctl context for managing dynamically created sysctl oids

sysctl_ctx_init(9) on FreeBSD now