Bind mounts in make-disk-image

[danjujan]

Currently make-disk-image only mounts the filesystems specified in disko's config. However, there might be other mounts specified in a nixosConfiguration that need to be mounted in order to build a valid VM image. For my use case (XBOOTLDR partition), I need the following bind mounts to be available before nixos-install installs the bootloader/kernel.

Mount commands

mkdir -p /mnt/efi/EFI/{Linux,nixos,shell}
mkdir -p /mnt/boot/EFI/{Linux,nixos,shell}
mkdir -p /mnt/{efi,boot}/loader/entries
mount --bind /mnt/boot/EFI/Linux /mnt/efi/EFI/Linux
mount --bind /mnt/boot/EFI/nixos /mnt/efi/EFI/nixos
mount --bind /mnt/boot/EFI/shell /mnt/efi/EFI/shell
mount --bind /mnt/boot/loader/entries /mnt/efi/loader/entries

I solved the issue by hardcoding these commands in make-disk-image's installer but would prefer a more maintainable solution. Ideally one would try to mount the remaining filesystems specified in the nixosConfiguration. However, that would require running or emulating parts of the stage1 script (mountFS) which is probably too complex. Would you be open for a PR that adds some pre-install commands configurable by the user? Or is there maybe a better solution?