DragonflyBSD has done some kernel 'virtualisation' in userland.
Meaning running kernel and network interface drivers in userland,
maybe take a look at that.
It would be nice to have that ability in FreeBSD/NetBSD too.

On Dec 15, 2007 1:06 PM, Masao Uebayashi <uebayasi@gmail.com> wrote:
> > I am mostly curious about this for developing and testing without
> > rebooting kernels.
>
> If what you need is trying a new driver without reboot, LKM *should
> be* the way to go.
>
> (I say *should be* because I have never tried that. :)
>
> Masao
>