susi:~ # mount /space/FACTORY.iso /mnt/ -oloop
mount: Could not find any loop device. Maybe this kernel does not know
about the loop device? (If so, recompile or `modprobe loop'.)
WTF? That never happened to me before, so I assumed (obviously) that something was broken in current FACTORY and filed a bug.
Finally we found out, that the loop module was always unconditionally loaded on every machine by boot.localfs, which is no longer run since I switched to systemd.
As Kay pointed out in the bug, it is very easy to fix:
susi:~ # echo loop > /etc/modules-load.d/loop.confAt least until someone fixes the Kernel's loop device behaviour ;)