# https://www.gnu.org/software/grub/manual/html_node/Device-map.html
e grub-bios-setup -d $mount_point/grub/i386-pc -s -m $mount_point/grub/device.map $boot_disk
+# todo, mount_point needs subvolid=0
+e grub-editenv $mount_point/grub2/grubenv set default_subvol=/boot_$distro
+
e umount $mount_point
e rmdir $mount_point