bootloader/zipl in Debian

Hello,

I have a few questions regarding s390x bootloader on Debian, hope some
gurus in the list could help me out.

Says I have Debian installed in my disk. To make it bootable, I should
install the bootloader on the disk to make it bootable.
'bootable-system' virtual package on s390x should be 'zipl-installer'.
Looking up in zipl-installer source tree at
https://anonscm.debian.org/cgit/d-i/zipl-installer.git/tree/, I couldn't
find any possible code installing the bootloader on disk. I couldn't
find it in debian-installer neither. Am I missing something ?

I guess that code should contains zipl command and some other setups.
For example, I tried :

# zipl -V -t /boot -i /boot/vmlinuz -r /boot/initrd.img

# chreipl ccw 0.0.0001 -L 1
( device id collected from /dev/disk/by-path/ccw-0.0.0001 )

The commands run fine, and new 'bootmap' was installed in /boot but
reboot failed.

Here is the log at rebooting (running in KVM):
https://paste.debian.net/980399/. There definitely must be some other
setups/commands I am missing but I have no clue atm.

Thanks for reading,
Tuan