Hybrid MBR support in GRUB2!

[Erlend Hoel]

### IF BORED OR IMPATIENT, SKIP THIS PART! :-) ###

First of all, hello everybody!  This is my first post to grub-devel.
I've done a bit of reading in the archives and tried some searches,
but I couldn't find that the question I am about to asked has been
asked already, or indeed, whether it's been answered.

Is it possible to "force" GRUB to do old-style parttool operations on
the MBR header even if a GPT is detected?  In other words, to
manipulate a Hybrid MBR.

Lest you ask yourself "Who would want to do that and why?" let me
describe my situation:  I'm trying to multiboot Windows XP, Windows 7
(32-bit), Windows 7 (64-bit), Mac OS X Snow Leopard 10.6.6, Ubuntu
Desktop 10.10 (64-bits), CentOS 5.5 ... for starters. :-)

I'm going to pause for a moment just to address any potential "Well
that's just crazy" and/or "That's not what we intended GRUB for" type
of comments.  Although if that's your first impulse, then, fair
enough.  But really, isn't GRUB about providing choice?  And if that's
(at least partially) true, then isn't *more* choice an even *better*
choice? :-P  I bring this up because I've seen signs that GRUB is
trying to move away from chainloading, and while I understand that
from a "purity of design" point of view, the reality is that booting
several "impure" operating systems in parallel on the same computer
seems to give at least this user a greater satisfaction than a pure
design.

So, with all that groundwork in place (and forgive me for wasting your
time thus far):

### SKIP TO HERE! ###

It seems to me that GRUB detects a GUID partition table and
automatically prefers it over the MBR even if the latter is a
so-called "Hybrid MBR", and that is even if I specifically do not
"insmod part_gpt".

The problem with that is that I can't use parttool to perform
operations on the (fake) MBR entries so that I can hide/unhide the
only-MBR-aware OS'es from each other.

### SKIP THE REST IF YOU LIKE, IT'S MORE CHATTY STUFF ###

I'm aware of the possible workaround of basically dropping GPT and
going back to MBR.  But ... The reason I'm using GPT in the first
place is ... well, I like it! :-)

And Mac OS X required GPT when I was installing.  I've seen (mentioned
here:  http://refit.sourceforge.net/myths/ at the part that says
"Myth: Mac OS X requires GPT") that I could do my install on a GPT
partition and then clone the whole thing back to a MBR partition,
though I haven't tested it, and I don't know if it means that Mac OS X
would boot from a logical partition within an extended MBR partition.
In any case, that seems like a bigger step backward than getting GRUB
to do what I'd like.

### EMAIL ENDS BELOW! ###

Is something like this already possible today, in ways I haven't
discovered?  If not, is something like this planned?  If not, how much
work would it be to enable it?  (if I'm lucky, it's just a question of
disabling a "are we on a GPT or an MBR" inside parttool -- if I'm
unlucky, it means duplication of data structures if GRUB currently
either only loads and relates to the MBR _or_ the GPT table)

Thanks for your time.  Sorry for my long-windedness;  I tried to
mitigate it with helpful clauses. :-)

Best regards,
Erlend