=== load stock chain ===
=== create the controllable child (direct device_add_child) ===
dfctl failchild: kernel rc=0 v0=0x0 v1=0x0 v2=0x0
=== make the child refuse to detach ===
hw.df5632.childbusy: 0 -> 1
=== detach the bus: STOCK swallows the child's EBUSY (rc must be 0) ===
dfctl detach_bus: kernel rc=0 v0=0x0 v1=0x0 v2=0x0
=== state witness (iicbus0 driverless, softc NULL, child attached) ===
dfctl stat: kernel rc=0 v0=0x0 v1=0x0 v2=0x0
=== now use the bus like the attached child would: NULL-softc deref ===