Re: Announcing mkisofs 1.13

[Robert Millan <rmh@aybabtu.com>]

On Sat, Jan 09, 2010 at 11:03:39PM +0100, Thomas Schmitt wrote:
> Hi,
> 
> > I happen to be maintainer of GNU GRUB, so yes ;-)
> 
> Nice incidence. I will leech you for the final
> boot loader of the emerging libburnia OS farm.

Be my guest.  You can also try grub-devel@gnu.org.

> > > (The question is about how one has to patch
> > >  the boot image and/or the MBR after the block
> > >  address of the boot image is determined.)
> 
> > I don't understand your question.  First 32 kiBs are used to embed a chunk
> > of arbitrary data.
> 
> The System Area as of ECMA-119. The first 512
> bytes can be used as MBR. So depending on the
> media the BIOS can either boot via the El Torito
> block or via the MBR.

Yeah, that'd be it.

> With ISOLINUX/isohybrid i have to tell the MBR
> where the boot image isolinux.bin is located on
> the media. The method and the MBR template stems
> from 
>   syslinux-3.72/utils/isohybrid
> which operates on a El Torito enhanced ISO 9660
> image in a disk file.

Ah, I see.  Well, GRUB uses an entirely different approach:

  - System area contains GRUB core.img image
    (GRUB's kernel plus a few modules like filesystem driver).

  - core.img is instructed to search in /boot/grub/ for
    grub.cfg and other modules, etc.

So, it'd seem that unlike ISOLINUX, GRUB makes use of the whole
System area (well, not all of it, but close: just as much as occupied by
core.img).

So if you'd like to create a GRUB bootable disk, you'd do something
like:

  cat boot.img core.img > tmp
  mkisofs --embedded-boot tmp -o grub.iso -r somedir

Of course, if you put together all the details (like building core.img and
filling up /boot/grub structure), it gets a bit hairy, so grub-mkrescue utility
is provided with GRUB:

  grub-mkrescue --output=grub.iso [somedir]

which as of recent Bazaar produces images that are bootable as HD media.

> (genisofs would be our mkisofs emulator. But i
>  deem the architecture of separate ISO generator
>  and burn program quite suboptimal. So i rather
>  started an integrated ISO+burn tool.)

You don't like pipes!?  What kind of Un*x hacker are you ;-)

-- 
Robert Millan

  "Be the change you want to see in the world" -- Gandhi