Add SUM sysctl

[John Baldwin]

On Saturday, April 16, 2011 10:24:44 am rank1seeker at gmail.com wrote:
> After compilation of kernel and world in MUM, kernel is installed in MUM, 
> but to install world, we reboot into SUM, then install world. (HANDBOOK)
> Now, in case of GELI usage AND if upgrading is taking place, i.e; 8.2 -> 
> 8.3, once you reboot into SUM to install world, you are doomed, BECAUSE 
> ...
> Kernel will bitch (GELI part), about world->kernel mismatch and you won't 
> be able to install world as you cant decrypt geom providers!!
> The only way to save yourself in that case is to restore /boot/kernel.old, 
> or one is doomed.

This seems broken to me.  An 8.3 kernel+modules should be able to handle GELI 
devices with an 8.2 world.  If they can't, it means someone broke the ABI.  
Even a 9.0 kernel should work fine with an 8.x-stable world.

-- 
John Baldwin