Installing to an Amiga HDF

[Intuition Amiga <intuitionamiga@gmail.com>]

Hi,

I created a 4GB empty file with dd then mounted it as /dev/loop7 using losetup.

Then I used fdisk-amiga-cross to create an RDB and one type 11 Linux
partition and one type 12 swap partition and wrote them out to the
loopback device.

I unmounted the file with losetup -d then remounted it as /dev/loop7
again to simulate a reboot.

This is where I get stuck....  I want to do the equivalent of
'mkfs.ext4 /dev/sda1' but 'mkfs.ext4 /dev/loop71 doesn't work because
no such partition exists.

GParted is of no use at all as it can't even see the RDB and when i
tried to use it to create an RDB and two partitions it fails to create
them at all.

I did a  hex dump of the HDF file and it shows that the RDB is correct
and both partitions have been created starting from offset 0000000989
up to 0000002236.

Can anyone offer me advice on how to create an ext4 filesystem on this
loopback device so I can then mount it and extract the Debian 68k base
image to it?

Kind regards,
Nik