I'm afraid it's not that simple.
The source device is given to the initramfs script when it is executing,
and the initramfs script needs to figure out how to create said device
if it doesn't exist.
Now, if it is handed a random device name such as /dev/X/Y, there is no
way to tell what steps are necessary to create said node. If the script
is handed /dev/mapper/X-Y, it is almost certainly a LVM node.
/dev/VG/LV devices are not supported by initramfs-tools either, see bug
reports #402931 and #378332.
I'm inclined to simply document that the LVM symlinks are not supported
as device nodes.
--
David Härdeman
