how to skip partitioning with preseed?

[Riccardo Murri <riccardo.murri@gmail.com>]

Hello,

first of all, thanks for the great D-I!

I'd like to (re)install a system using a totally automated preseed
install, re-using existing partitions if they fit a given schema.

I would like it to be partitioned with a minimal /boot
partition, and the rest of the disk setup up as a LVM VG, within which
"root" and "swap" LVs are created.

Partman recipes handle this just fine when the disk is blank or can be
reformatted; however I cannot find a way to preseed D-I so that it
just re-uses the existing partitions if they are found: all my
attempts ended up in D-I asking for permission to remove the entire VG
and start partitioning over.

Is there a way to tell D-I to skip partitioning altogether, and
instead run a shell script that will just mount /target and swap from
the existing LVs? (Or any other way to tell D-I "use this LV as /"?)

I cannot find any documentation or examples around, so I'll appreciate
any pointers.

Thank you very much!

Riccardo