Re: Set a bootdrive environment variable.

[Andrei Borzenkov <arvidjaar@gmail.com>]

В Mon, 6 Jul 2015 15:44:44 -0400
Mathieu Trudel-Lapierre <mathieu.tl@gmail.com> пишет:

> On Sun, May 31, 2015 at 2:42 AM, Andrei Borzenkov <arvidjaar@gmail.com>
> 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]
> http://pkgs.fedoraproject.org/cgit/grub2.git/tree/0090-Add-fw_path-variable-revised.patch
> 
> Kind regards,
> 
> / Matt