devctl (alike?) for devfs

[Jille]

Andriy Gapon wrote:
> Maybe this is a crazy idea or maybe we already have something like this.
> Is it possible to get notifications about changes in devfs - appearance
> and disappearance of devices (in devfs sense of the word)?
> devctl currently notifies about real (hardware) devices handled by
> device drivers and some notifications about hardware/driver events.
> But what if I want to automatically run some action if
> /dev/ufs/magic-label appears?
> Or if I want to monitor appearance and disappearance of ad* and da*
> devices (without having to monitor low level drivers like umass)?
> 

I don't know whether it is what you are looking for, but take a look at 
devd(8).

-- Jille