nixos/installer: add sd-image-powerpc64le.nix

This builds on top of nixpkgs mainline 00d83471803a8a308a52fc4b09b6ec41dfb36453
with the following two PRs cherry-picked:

- https://github.com/NixOS/nixpkgs/pull/192670
- https://github.com/NixOS/nixpkgs/pull/192668

using the following command:

```
nix build -f nixos -L \
  -I nixos-config=nixos/modules/installer/sd-card/sd-image-powerpc64le.nix \
  config.system.build.sdImage
```

I was able to successfully boot the image, although it boots to a login prompt
rather than a shell, and won't accept the empty password for `root`.  I guess
I'll have to figure out why that is.

To boot the image: `zstd`-decompress the it, mount it, and use `kexec`:

```
cd boot/nixos
kexec -l \
  *-vmlinux \
  --initrd *-initrd \
  --dt-no-old-root \
  --command-line="$(grep APPEND ../extlinux/extlinux.conf | sed 's_^ *APPEND *__')"
```

The machine I used for testing has only one storage device which is completely
allocated to LVM.  It appears that the NixOS ISO loader doesn't look for
partition tables within LVM volumes.  To work aroundn this, I had to extract the
`ext4` image within the partition table within the `sd-card` image and put that
in its own LVM volume.  This likely won't be an obstacle for users who write the
image to a USB stick or similar.

0 files changed, 0 insertions, 0 deletions