I think we need to look at the journal for the reboot/shutdown to have
direct evidence whether the right or wrong thing is happening. In the
case of Btrfs, there is no journal replay. But also, you'd need to
track down why journal replay is happening anyway.
I'm pretty sure systemd does not umount sysroot, but rather remounts
it ro at shutdown time. That clears the journal and dirty bit.
But I agree there should be a test to make sure sysroot is ro
remounted; and that everything else is unmounted, before the reboot.
--
Chris Murphy