[systemd-devel] Unmount / right before reboot/shutdown/kexec

[Lorenzo Pistone]

Hello,
the cloud provider I'm testing has rather strange setup. All volumes are 
provided through nbd, including /, and they have to be unmounted cleanly 
for reboot to work successfully, because the rebooted or kexec'd kernel 
will retry to attach them and if there host thinks there's already a 
connection mounting will fail. However, unmounting needs to happen as 
the very last thing before rebooting, because after that / will 
disappear. They currently have an unholy hack: they replace 
systemd-reboot.service with their own version that simply disconnects / 
and calls 'echo b > /proc/sysrq-trigger'. I believe this is far from the 
correct way of doing things (among the other things, an update of 
systemd replaces systemd-reboot.service). How can this be done more cleanly?

Please don't argue whether having / as a ndb device is a good thing. It 
is not my call.

Cheers.
Lorenzo