ah so you're claiming something like this would work out of the box: label ubuntu1104 kernel memdisk append iso initrd=ubuntu.iso
This is one entry from my multiboot USB drive's GRUB menu:
title Ubuntu Netinstall x86 find --set-root /iso/ubuntunetinstall.iso.gz map --mem /iso/ubuntunetinstall.iso.gz (hd32) map --hook chainloader (hd32)
To my knowledge, Linux ISO booting consisted of [A] booting kernel [B] processing INITRD [C] mounting CD/DVD/BluRay, or ISO [D] continuing.
This is another entry in my menu.lst:
title Kubuntu 10.04 find --set-root /iso/kubuntu-10.04-desktop-i386.iso map /iso/kubuntu-10.04-desktop-i386.iso (0xff) map --hook root (0xff) kernel /casper/vmlinuz file=/cdrom/preseed/kubuntu.seed boot=casper persistent iso-scan/filename=/iso/kubuntu-10.04-desktop-i386.iso splash initrd /casper/initrd.lz
Both boot methods work just fine.
What I mean is only doing C and D, everything has to be self-contained in 1 single file For DOS this goes fine as it doesn't enter protected mode.
Not entirely true. This is another of the entries in my list:
title FreeDOS Balder Floppy map --mem /iso/balder10.img.gz (fd0) map (hd1) (hd0) map (hd0) (hd1) map --hook chainloader --force (fd0)+1 rootnoverify (fd0)
This works fine, as long as I don't boot with HIMEM.