[systemd-devel] New reboot flag: -c for 'power cycle'

[Jonathan de Boyne Pollard]

Warner Losh, FreeBSD and embedded systems developer, has just invented a 
new shutdowngoal, in addition to the ones that we already know.  In 
addition to the conventional reset, power off, halt, and kexec goals; xe 
has added a power-off-and-then-on-again goal.  Xe has named it power 
cycle, and its use case is systems with hardware that can trigger a full 
power cycle under the kernel's controland where an ACPI reset or even an 
EFI ResetSystem() of type EfiResetColdjust do not cutthe mustard.

It involvesanew flag to the FreeBSD reboot() system call, RB_POWERCYCLE; 
new FreeBSD kernel functionality for enacting this with hardwares that 
support it; new -c (for "cycle") flags to the various reboot, halt, 
poweroff, and shutdown commands; and a new signal sent to process #1.

* https://marc.info/?l=freebsd-arch&m=150886821625848&w=2

* https://reviews.freebsd.org/D12777

This of course impacts those of us who write process #1 programs.

Since SIGWINCH to process #1 is already taken by Linux, I have adjusted 
my softwares to use SIGRTMIN+7 and SIGRTMIN+17 for the signals to 
process #1 for this, ready for when Linux eventually catches up with 
this idea.  (-:

(There is an on-going discussion of whether FreeBSD's old init program 
should use real-time signals, too.  It currently does not.But that is a 
side issue here. I have also added to my softwares powercycle and 
fastpowercycle commands and subcommands, a "c" or "C" argument to the 
compatibility telinit program (by analogy to the existing letters, 
although I might have to pick another letter), a powercycle target 
(again by analogy to existing targets), and a --powercycle long option 
equivalent for -c .)

Please do not use SIGRTMIN+7 and SIGRTMIN+17 for an incompatible purpose.