ALT_BREAK_TO_DEBUGGER. In addition to "Enter ~ ctrl-B" (to enter the
debugger), there is now "Enter ~ ctrl-P" (force panic) and
"Enter ~ ctrl-R" (request clean reboot, ala ctrl-alt-del on syscons).
We've used variations of this at work. The force panic sequence is
best used with KDB_UNATTENDED for when you just want it to dump and
get on with it.
The reboot request is a safer way of getting into single user than
a power cycle. eg: you've hosed the ability to log in (pam, rtld, etc).
It gives init the reboot signal, which causes an orderly reboot.
I've taken my best guess at what the !x86 and non-sio code changes
should be.
This also makes sio release its spinlock before calling KDB/DDB.
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