Reboot-Shutdown signal through net device.

Within our PCI Network Device there is a special feature, that allows
out-of-band signaling-messeging (by using special interrupt and shared
registers) to control system state: Reboot, Shutdown.
What would be an acceptable method of executing such controls?
So, the sequence is: 
     1. Device Driver receives Reboot-or-Shutdown message.
     2. Device Driver initiates Reboot-or-Shutdown sequence (how?).
I have cosidere usermode helper, looks like this solution is favored...
Any recommendations?