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Re: grub.cfg and core.img getting out of sync

From: Colin Watson
Subject: Re: grub.cfg and core.img getting out of sync
Date: Thu, 13 Aug 2009 09:22:14 +0100
User-agent: Mutt/1.5.18 (2008-05-17)

On Thu, Aug 13, 2009 at 02:54:29AM -0400, Pavel Roskin wrote:
> On Wed, 2009-08-12 at 16:25 +0100, Colin Watson wrote:
> > I'm having persistent problems with grub.cfg and core.img getting out of
> > sync. The usual pattern is:
> > 
> >   * Some shiny new feature appears in core.img
> >   * We extend grub-mkconfig to use it
> >   * User runs update-grub but not grub-install (historically a perfectly
> >     sane thing to do, and indeed basically standard practice)
> >   * grub either falls over at boot or does something odd
> The assumption is that grub.cfg should be able to deal with it.  That's
> why it sets root before searching.

Hmm, it's sometimes tricky. For example:

> > This just bit me again today, and if it bites me it's going to bite the
> > users of the packages I upload too.
> By our today's standards, it's a bug, so it should be reported in a
> detailed way.

Well, this was in code I was writing. See the hiddenmenu and keystatus
patches I posted recently; with those, it is reasonable to do:

  if sleep --interruptible 0 ; then
    set timeout=0

(In other words, unless the Shift key is pressed when GRUB starts, boot
the default OS immediately.)

However, the effect of this if the keystatus patch is not applied (or
indeed if you're on a target with no support for keystatus) will be to
boot the default OS with no way to get at the menu. I'm open to ideas on
how to do this better; does it need something more complex than 'sleep
--interruptible 0'?

> > Is there any way we can do better? One thing I was thinking of is that
> > Ubuntu's carried a patch to GRUB Legacy for some time that stores the
> > package version at the point when grub-install was last run in
> > /boot/grub/installed-version. If we did something like that, then
> > grub-mkconfig could carry a bit of conditional code that says "only use
> > this feature if the installed version of GRUB is at least <foo>".
> > grub-mkconfig would end up carrying a bit of bloat, but at least the
> > bloat is in /usr, and I'm assuming that at this point things are stable
> > enough that we won't be talking about *too* many changes.
> > 
> > What do people think about this general approach?
> There is already a version hardcoded into the uncompressed part of
> core.img.  See kern/i386/pc/startup.S.  Unfortunately, there is no
> policy when the version should be updated.
> But I'm fine with a separate file in /boot/grub if we decide that the
> existing version in core.img cannot be used for that and we cannot keep
> grub.cfg backward compatible.

The version in core.img would be fine if there were a way to extract it
from userspace. It seems rather ugly to me to extract this using dd or
od directly - also, presumably grub-mkconfig ought to be at least
somewhat architecture-independent. Does this need a new tool?


Colin Watson                                       address@hidden

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