install grub on img file

### on linux (works) ###
truncate -s 100MiB rootfs.img
losetup /dev/loop0 rootfs.img
parted -a optimal -s /dev/loop0 mklabel msdos
parted -a optimal -s /dev/loop0 -- mkpart primary ext2 32k -1
parted -s /dev/loop0 -- set 1 boot on
kpartx -a -v /dev/loop0
mkfs.ext2 -o hurd -m 1 -v /dev/mapper/loop0p1
mount /dev/mapper/loop0p1 /mnt/rpi/
grub-install --target=i386-pc --boot-directory=/mnt/rpi/boot /dev/loop0
umount /mnt/rpi
kpartx -d /dev/loop0
losetup -d /dev/loop0
qemu-system-i386 rootfs.img


### on hurd (doesn't work) ###
truncate -s 100MiB rootfs.img
settrans -ca /tmp/rootfs /hurd/storeio -T file rootfs.img
parted -a optimal -s /tmp/rootfs mklabel msdos
parted -a optimal -s /tmp/rootfs -- mkpart primary ext2 32k -1
parted -s /tmp/rootfs -- set 1 boot on
settrans -ca /tmp/rootfs_s1 /hurd/storeio -T typed part:1:file:rootfs.img
mkfs.ext2 -o hurd -m 1 -v /tmp/rootfs_s1
mount /tmp/rootfs_s1 /tmp/rootfs_mount
grub-install --target=i386-pc --boot-directory=/tmp/rootfs_mount/boot /tmp/rootfs
umount /tmp/rootfs_mount
settrans -g /tmp/rootfs
settrans -g /tmp/rootfs_s1