Ability to specify root directory with grub-mkconfig command?

[Grabben D]

After successfully building a OSTree system to a dedicated disk which is mounted in /mnt directory, the final rootfs looks like this:

  $ ls /mnt

  boot  ostree

Generating bootloader to /mnt/boot/efi works as intended:

  $ grub-install --target=x86_64-efi --efi-directory=/mnt/boot/efi --removable --boot-directory=/mnt/boot/efi/EFI --bootloader-id=archlinux /dev/sda1

However, generation of grub.cfg doesn't support switching root, because of this it generates boot entries which uses the disk of the parent system and not /mnt:

  $ grub-mkconfig -o /mnt/boot/efi/EFI/grub/grub.cfg

Currently the only workaround is to mount: the OSTree system (/mnt/ostree/deploy/archlinux/deploy/*), bootloader (/mnt/boot), device nodes from parent (/dev /proc /sys) and use chroot to finalize generation of grub.cfg

Ability to use a different root as the reference point while generating grub.cfg would be tremendously useful to build OSTree systems and even when rescuing a regular installation which has a broken bootloader.

Would love to hear what you guys think about this

Regards