Comment 29 for bug 1895192

@slyon: You nailed it!
I've used curtin/block/lvm.py and curtin/commands/curthooks.py from your first MP and curtin/block/__init__.py from your second MP.

That finally led me complete an FCP impish installation with LUKS using protected keys (paes_s390)!

$ sudo cryptsetup status $(awk '{ print $1 }' /etc/crypttab )
/dev/mapper/dm_crypt-0 is active and is in use.
  type: LUKS2
  cipher: paes-xts-plain64
  keysize: 1024 bits
  key location: keyring
  device: /dev/mapper/mpatha-part2
  sector size: 4096
  offset: 32768 sectors
  size: 132083712 sectors
  mode: read/write
$ sudo dmsetup ls --tree -o nodevice
mpatha-part1
 └─mpatha
ubuntu--vg-ubuntu--lv
 └─dm_crypt-0
    └─mpatha-part2
       └─mpatha

Great - many thx!!