RFC: multi-os configuration

[lode leroy]

I just thought of the following solution to the problem mentioned
here lately about OS's generating "/boot/grub/grub.cfg" from templates.

Would it not be better for grub to do this instead of the OS?

If the user asks the OS to *install* grub, the installing OS should install
a default grub.cfg, as is done now.

If the user asks the OS to *register* with grub, the installing OS should
install a file "/boot/grub/grub.sub" with an entry for booting itself,
on whatever it considers it's "/boot" partition.
(a provision could be made to add a number in the .sub file to indicate
the order of the menu entries, to be entered by the user.)

When reading grub.cfg, grub would find a function call 
"insert_dynamic_menuentries()"
it should then scan all known partitions, and see if a file 
"/boot/grub/grub.sub" exist, 
if it does, it sets the variable "root" to the partition name, and includes the 
file.


This way, an OS should only manage it's own entry...



a more elaborate example below:

cat (hd0,0)/boot/grub/grub.cfg
==========================================

insmod gfxterm
background_image (hd0,0)/boot/grub/splash.jpg

insert_dynamic_menuentries()

menuentry "Boot first partition" 
{
  set root=(hd0,1)
  chainloader +1
}
==========================================


cat (hd0,1)/boot/grub/grub.sub
==========================================
# For booting GNU/Hurd
menuentry "GNU (aka GNU/Hurd)" 2 {
    multiboot /boot/gnumach.gz root=device:hd0s1
    module /hurd/ext2fs.static ext2fs --readonly \
            --multiboot-command-line='${kernel-command-line}' \
            --host-priv-port='${host-port}' \
            --device-master-port='${device-port}' \
            --exec-server-task='${exec-task}' -T typed '${root}' \
            '$(task-create)' '$(task-resume)'
    module /lib/ld.so.1 exec /hurd/exec '$(exec-task=task-create)'
}
==========================================


cat (hd0,2)/boot/grub/grub.sub
==========================================
# For booting GNU/Linux
menuentry "GNU/Linux" 1 {
    linux /boot/vmlinuz root=/dev/sda3
    initrd /boot/initrd.img
}

==========================================









equivalent grub.cfg
==========================================

insmod gfxterm

background_image (hd0,0)/boot/grub/splash.jpg

menuentry "GNU/Linux" {
    set root=(hd0,2)
    linux /boot/vmlinuz root=/dev/sda3
    initrd /boot/initrd.img
}

menuentry "GNU (aka GNU/Hurd)" {
    set root=(hd0,1)
    multiboot /boot/gnumach.gz root=device:hd0s1
    module /hurd/ext2fs.static ext2fs --readonly \
            --multiboot-command-line='${kernel-command-line}' \
            --host-priv-port='${host-port}' \
            --device-master-port='${device-port}' \
            --exec-server-task='${exec-task}' -T typed '${root}' \
            '$(task-create)' '$(task-resume)'
    module /lib/ld.so.1 exec /hurd/exec '$(exec-task=task-create)'
}

menuentry "Boot first partition" 
{
  set root=(hd0,1)
  chainloader +1
}


==========================================