Thing to implement for using LVM on rootfs:
- if rootfs device have unsupported name then check if this is block device
  with major 58
- check PVDEVICES and if empty do:
-- run lvdisplay to determine volumen group (vg)
-- run pvscan to find physical volumens (pv) belong to determined vg
   (better write help application to parse /etc/lvmtab.d/[vgname] or
   /etc/lvmconf/[vgname].conf - ask malekith for help)
- for all found pvs find needed modules (support all devices that are
  supported for rootfs device)
- add to startup:
mount /proc
mount /tmp
mkdir /tmp/lvmtab.d
mkdir /tmp/lvmconf
lvm-initrd vgscan
lvm-initrd vgchange -a y
umount /tmp
umount /proc

NOTE: vgscan need writable /etc/lvmtab and /etc/lvmtab.d/. Distrib kernels are
built only with romfs, so mount tmpfs on /tmp and symlink writable files from
original location to /tmp.
But tmpfs are only in kernel series 2.4.x or later.

There is also problematic case with LVM on top of for example SOFTRAID. You would
need to find all pvdevices and set them up in initrd so there would be multiple
rootdevs with multiple dev_lists.