Re: GRUB and the risk of block list corruption in extX

[Andrey Borzenkov]

On Thu, Feb 7, 2013 at 2:47 PM, Martin Wilck
<address@hidden> wrote:
> Hello,
>
Hi Martin

> this is a question about the long-running topic of installing GRUB in
> partitions or partitionless disks.
>
> Recently I have been involved in discussions about this on
> https://bugzilla.redhat.com/show_bug.cgi?id=872826. The Fedora boot
> loader can't be installed in partition headers any more. The major
> reason given by the Fedora developers is the famous GRUB warning
> "blocklists are UNRELIABLE and their use is discouraged."
>
> The Grub manual says "installing to a filesystem means that GRUB is
> vulnerable to its blocks being moved around by filesystem features such
> as tail packing, or even by aggressive fsck implementations".
>
> I'd like to understand how this blocklist corruption might come to pass
> (except for cases where "core.img" itself is moved, deleted, or
> overwritten by user space tools). Also, it has been recommended to
> prevent accidental corruption by setting the IMMUTABLE flag on core.img,
> and I'd like to ask for the GRUB experts' opinion about that.
> Finally I'd like to know if it's true that the GRUB team plans to drop
> block list support altogether in a future version.
>


I think this is simply the wrong question for upstream. The primary
consideration is, what happens inside filesystem is outside of grub
scope, so grub simply cannot commit itself to saying "it's fine and we
support it everywhere". Because grub has no control over what happens.

If you are sure in your environment corruption cannot happen (e.g.
because you use filesystem that is known to be not susceptible to such
corruption) then by all means do it.

grub2 does not stop you from doing it. It just wants you to do it consciously :)