[syslinux] embedded fs access?, was Re: Booting ISOs

[Douglas McClendon]

Hello, my name is Douglas McClendon.  I just joined this list.  The 
question that prompted me to join, is actually quite timely, as it 
related to the Booting ISOs thread, which unfortunately, I can't just 
continue.

I think the answer the "Booting ISOs" question got, regarding the 
knoppix cheatcode, was relevant, but not quite optimal.

Unless I am misunderstanding, using the knoppix cheatcode, requires that 
the user duplicate the initramfs and kernel, *outside* the iso image, so 
that isolinux will have access to it.  I.e. they(knoppix) just put 
support in their initramfs to deal with the .iso in the vfat filesystem.

What would be ideal, and what I would *really like*, is if sys/isolinux 
would support referencing kernels and initrds that live *within* a .iso 
image, that is either residing on a vfat fs on a usbstick, or a .iso 
image that is residing in the iso9660 filesystem of the cdrom boot media.

One perhaps controversial use-case of this, would be to take a Fedora 
LiveCD iso image, and redistribute it *intact and unmodified* inside 
another iso9660 filesystem, along with custom modifications, and a 
bootloader that can *efficiently* utilize the kernel inside the 
'embedded' iso filesystem, rather than duplicating those bits in the 
primary iso filesystem.  (and then boot the embedded LiveCD, but adding 
the custom patches immediately, before transferring control to the 
normal boot scripts)

I believe this could be implemented in a fairly elegant way in syslinux, 
and would actually be useful in a multitude of situations.

If I were to start to invest the time, I'd start looking at the isodump 
utilitity which now appears to be able to dump the bits from a 
particular file from an iso image specified by path.  Then try to glue 
that code into isolinux so that it could dump the bits of the kernel and 
  the initrd into memory from the embedded iso image, rather than 
reading them from the primary iso9660 (or vfat) filesystem.

I guess my best hope with this message is to inspire someone to do the 
work for me.  The next best hope would I guess be comments off the top 
of peoples heads as to gotchas to expect during implementation, or 
otherwise supportive or intelligently critical advice.

Thanks,

-dmc