This reverts commit 4263d7617f.
Still I think this is the way to go. But the change was merged after -rc2,
and still discussion is continued. So, at least now let's revert it,
and do that after v256-final is released if approved.
Otherwise, at the time systemd-soft-reboot.service succeeds,
services which has Conflicts= and Before=soft-reboot.target may
not be stopped yet, and may be SIGKILLed.
Especially, systemd-journald.service has the dependencies, thus
journal may be corrupted. See #32223.
Follow-up for 13ffc60749.
Fixes#32834.
This adds a new mechanism for rebooting, a form of "userspace reboot"
hereby dubbed "soft-reboot". It will stop all services as in a usual
shutdown, possibly transition into a new root fs and then issue a fresh
initial transaction. The kernel is not replaced.
File descriptors can be passed over, thus opening the door for leaving
certain resources around between such reboots.
Usecase: this is an extremely quick way to reset userspace fully when
updating image based systems, without going through a full
hardware/firmware/boot loader/kernel/initrd cycle. It minimizes "grayout time"
for OS updates. (In particular when combined with kernel live patching)
