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Re: Set a bootdrive environment variable.

From: Andrei Borzenkov
Subject: Re: Set a bootdrive environment variable.
Date: Tue, 7 Jul 2015 06:48:29 +0300

В Mon, 6 Jul 2015 15:44:44 -0400
Mathieu Trudel-Lapierre <address@hidden> пишет:

> On Sun, May 31, 2015 at 2:42 AM, Andrei Borzenkov <address@hidden>
> wrote:
> >
> > The problem is that $cmdpath had been around for long enough. If
> > $cmdpath is used only after loading normal (that are cases I'm aware
> > of) we can make it compatibility variable set by normal without causing
> > more core bloat.
> >
> I'm not finding any uses of cmdpath in git, and when I went to dig in
> RH/Fedora packaging, it looks like there is already a patch that appears to
> rename it and change its meaning [1], along with two other related patches.

Well, it is up to RH. Moreover, the real problem as indicated in rhbz is

The issue comes from the fact that the original patch does not clear the 
grub_errno in case the grub.cfg is not found in the bootlocation. 

and it is unrelated to how variable is named. I have patch for it
somewhere, I hit this issue as well. Another issue is missing initial
'/' which is fixed in grub in the meantime as well.

> You mention you know of cases where it's used after loading normal, could
> you please point me to them?

I can think of some use cases and we never know how creative people
become in between.

> I'd like to try to come up with a patch that will work for everyone. FWIW,
> my requirement right now is only to have some way (aside from regexp, since
> we're concerned running regexp in the EFI context could increase attack
> exposure) to get just the GRUB boot device (ie. cd0, hd0, etc. without
> partition information), so that ISO images could boot and load a generic
> grub.cfg that doesn't need to encode a filesystem UUID or some other
> identifier.

If you set initial prefix in grub.efi to '()', grub will strip
partition part when setting $root; look at what grub-mkrescue does. Is
it good enough for your purpose?

> [1]
> Kind regards,
> / Matt

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