It occurred to me, in an email elsewhere, that parts of the kernel might
like to be "notified" when an event occurs in another part of the kernel.
For example, a network interface going up/down or changing IP address might
be of interest to another part of the kernel.  My motivation here is that
IP Filter would do well to know when these events occur, but maybe there
would be other benefits too.

Is this a resonable idea ?