Comment # 35 on bug 1187264 from Ruediger Oertel

for comments 22 ... there is no libvirt involved, this is plain qemu.

cmdline looks like this: /usr/bin/qemu-system-s390x -nodefaults -no-reboot
-nographic -vga none -cpu host -enable-kvm -object
rng-random,filename=/dev/random,id=rng0 -device virtio-rng-ccw,rng=rng0 -runas
qemu -net none -kernel /var/cache/obs/worker/root_1/.mount/boot/kernel -initrd
/var/cache/obs/worker/root_1/.mount/boot/initrd -append
"root=/dev/disk/by-id/virtio-0 rootfstype=ext4 rootflags=noatime
ext4.allow_unsupported=1 mitigations=off panic=1 quiet no-kvmclock
elevator=noop nmi_watchdog=0 rw rd.driver.pre=binfmt_misc console=hvc0
init=/.build/build" -m 8192 -drive
file=/var/cache/obs/worker/root_1/root,format=raw,if=none,id=disk,cache=unsafe
-device virtio-blk-ccw,drive=disk,serial=0 -drive
file=/var/cache/obs/worker/root_1/swap,format=raw,if=none,id=swap,cache=unsafe
-device virtio-blk-ccw,drive=swap,serial=1 -device virtio-serial-ccw -device
virtconsole,chardev=virtiocon0 -chardev stdio,mux=on,id=virtiocon0 -mon
chardev=virtiocon0 -chardev
socket,id=monitor,server,nowait,path=/var/cache/obs/worker/root_1/root.qemu/monitor
-mon chardev=monitor,mode=readline -smp 4

now after looking up kernel parameters I've added a "loglevel=4" to maybe also
get the KERN_WARNING messages