Re: Beware using modules from different grub versions (was error: cannot allocate real mode pages)

[Andrey Borzenkov]

В Mon, 9 Sep 2013 21:27:31 -0500
Glenn Washburn <address@hidden> пишет:

> I originally started writing this to request help from the grub-help
> list in solving this problem that has been plaguing me for days.  I just
> solved the issue and thought others might be able to benefit.  And
> perhaps this issue indicates a need for module versioning as the linux
> kernel has.  I'm sending to the devel list, because I think much is
> related to development.
> 
> I'd been having some problems trying to get grub to boot my
> x86_64 ubuntu server installation lately.  I've attached some
> screenshots of relevant grub output with some debugging on.  I'm using
> grub compiled from HEAD and tried both the x86_64 and i386 platforms
> for the "pc" target. Actually, I'm curious to know if there's actually
> a difference in those platforms.
> 
> It turns out this error was a result of loading the linux module (and
> many of its dependants, ie mmap) from a different (older) grub
> install.  I presume this is not infact because of a bug (otherwise the
> original install wouldn't have booted), rather the fact that the
> versions are different.
> 
> One might suggest chainloading the ubuntu grub installation instead of
> using "configfile" to just load its config.  This won't work for me (in
> general) because the other grub install doesn't necessarily have the
> capability to boot the system (ie doesn't have cryptmount/lvm/raid
> support).
> 
> Should grub implement some kind of module versioning to eliminate this
> issue?  Ideally, this seems the right thing.  However, I'm not sure if
> versioning as restrictive as limiting loading to modules of the same
> grub version.  In my experience, loading modules from other grub
> versions hasn't caused much issue, so this could cause a different pain
> for people using this "feature".
> 
> Regardless, there's another issue, the difficulty in ensuring where
> modules are being loaded from.  Currently, modules are searched for in
> the $prefix directory.  But $prefix is used for many other things as
> well, like config loading and font loading.  So if you want the fonts
> coming from the ubuntu install, but the modules coming from a newer
> grub, you have problems.
> 

grub is using whatever font is loaded using loadfont command. So just
load it from your preferred location.

> I see two potential, non-mutually exclusive solutions. 

I'm afraid I miss the problem.

>                                                         One, have
> another $moduledir variable for dividing up the multi-use $prefix
> ($prefix would be used as a fallback). And two, have $prefix (and
> potentially $moduledir) be a list of paths, much like the bash $PATH
> variable.  The first suggestion would be almost trivial to implement,
> while the second for $prefix will be a pain because potentially all
> uses of $prefix would need to be modified.
> 
> Comments and suggestions appreciated.
> Glenn