Hi Janneke,

with our (gnu bootloader grub) already supporting multiboot, it would be easy
for us to add official support for the Xen hypervisor & Linux.

I've already packaged xen and it's ready to be used.

In order to boot Xen, the grub config should read something like this:

menuentry 'Guix with Xen Hypervisor' --class gnu-linux --class gnu --class os --class xen {
        insmod part_msdos
        insmod ext2
        set root='(hd0,msdos1)'
        search --no-floppy --fs-uuid --set=root c4291ab1-d3ad-4c70-ab97-e6c8cca0af2b
        echo    'Loading Xen 4.1-amd64 ...'
        multiboot       /xen-4.1-amd64.gz placeholder  
        echo    'Loading Linux 3.10-3-amd64 ...'
        module  /vmlinuz-3.10-3-amd64 placeholder root=/dev/mapper/disks-root ro resume=/dev/mapper/disks-swap quiet
        echo    'Loading initial ramdisk ...'
        module  /initrd.img-3.10-3-amd64
}

Note especially that "multiboot" is "/xen-4.1-amd64.gz", and that "module"
statements are used for the linux kernel and for the initrd.

The work you have been doing for the Hurd already fetches both the "multiboot"
and the "module" parameters from the boot-parameters via
boot-parameters->menu-entry.

But I can't find how I can set the multiboot-modules in my operating-system
definition.

Like,

(operating-system
  (kernel (file-append xen "/boot/xen.gz"))
  (multiboot-modules (list linux-libre initrd)))

(Or find where it is set for the Hurd in the first place)

Also, how do I get guix's usual initrd into that multiboot-modules list ?

Do you think it would make sense to adapt boot-parameters->menu-entry
slightly so one could specify both a multiboot kernel and a linux kernel
at the same time?  Or would that be too magical?