This conditionally gives all registered shutdown handlers a chance to
perform the reboot, with cpu_reset() being the fallback. The
debug.ddb.full_reboot sysctl/tunable restores the previous behaviour.
The motivation is that some platforms may not be able do anything
meaningful via cpu_reset(), due to a lack of standardized reset
mechanism and/or firmware shortcomings. However, they may have a
separate device driver attached that normally performs the reboot. Such
is the case for some versions of the Raspberry Pi.
Hm, should the nul input separater really be used for outputting matched lines?
And if so, shouldn't it also be used with oflag above?