bus_generic_read_ivar(9) on FreeBSD
The text cfa1a595d9d1, as FreeBSD 5.5-RELEASE, FreeBSD 5.4-RELEASE, FreeBSD 5.3-RELEASE, FreeBSD 5.2.1-RELEASE, FreeBSD 5.2-RELEASE, FreeBSD 5.1-RELEASE, FreeBSD 5.0-RELEASE shipped it.
generic implementation of BUS_READ_IVAR and BUS_WRITE_IVAR for busses