is "unsigned" guaranteed to always be a byte here?

Do you expect to need to extend this in the future, adding other event type handling? If so, maybe consider a jump table struct, or a switch here, to make it easier.

Also, that buffer pointer math looks error prone, so consider simplifying that. You could simply pass the whole buffer down instead, and use a union to get the vendor data you need.

Is the EPOW shutdown request a request, or an order? Unless this is the hypervisor saying that the partition will be shut down, I think this could instead be propagated up to devd (devctl_notify()) to let the user decide how to handle it, and add an entry to devd.conf (or, better yet, create a pseries devd.conf) to default to shutdown.

the only other one i think we definitely want to handle is hotplug events, but i'm not planning on looking at that any time soon. so a jump table is probably over kill, but i'll try a switch and see if it looks nicer.

it depends on the type/reason code, but i think in all cases, the user will want to shut down here:

• if the user interacted with the power button or the BMC, they obviously want the system to shut down
• if a temperature threshold is exceeded or the UPS requested a shutdown, we are going to turn off anyway (because either the hardware is about to melt or the UPS battery is about to run out), so we should do it cleanly
• if the VM host is shutting down / rebooting, we are going to turn off anyway, so as above

i'm not opposed to making this a devd event, but i don't think any other architecture works that way, and we'd want to make sure the event was at least roughly portable between platforms, so it's probably out of scope for this diff.

incidentally, OPAL does this the same way, see sys/powerpc/powernv/opal_dev.c:opal_handle_shutdown_message().

cc: @imp

OPAL does it this way because the message is reporting that the machine is going down shortly, there's no way to stop it. The only safe thing to do in that case is to shutdown from the kernel, and hope that it cleans up before power is removed.