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

From: Martin Wilck
Subject: Re: GRUB and the risk of block list corruption in extX
Date: Mon, 18 Feb 2013 18:16:46 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130110 Thunderbird/17.0.2


> Why do you specifically want a blocklist method of getting the primary 
> bootloader to load the second? 

I may have expressed myself unclearly.

What I want is the *secondary* boot loader to be able to load *its own
code* from a partition header (e.g. ext4) using block lists. The primary
boot loader in the setup I prefer is actually embedded in the MBR and
thus doesn't use block lists. It will use "chainloader" command to
access the boot sector of the secondary boot loader (well I guess that's
also a primitve "block list" if you want to see it that way).

> If the primary boot loader is GRUB2, it's capable of reading many
> file systems, and then finding a distribution specific grub
> configuration file and consuming it. Even legacy formats.

Using chainloading has the advantage that the primary bootloader (it's
indeed GRUB 0.9x in my case) doesn't have to understand the more
advanced filesystems of newer distros. It's no problem to boot a btrfs
distro in this way, and when Fedora 31 comes out with KlingonFS as
default filesystem, my stupid Grub 0.9X will still be able to chainload
it, as long as KlingonFS supports embedding a boot loader in its
partition header. Fedora 18's GRUB2 will not be able to do that using a
secondary "grub.cfg", unless someone backports a KlingonFS module for it
(fortunately, GRUB2 would be able to chainload, too).

I like the fact that GRUB2 is able to detect foreign installations and
offer auto-generated boot menu entries for them. But there are some
scenarios for which the primitive chainloading mechanism is better suited.

> If the enhancement in bug 886502 were to happen, would this enable your 
> primary boot loader to find either Fedora's grub.cfg, or core.img instead of 
> depending on a blocklist?

As long as I install F18 on extX, yes. But as explained above, it
wouldn't be my preferred solution.


Dr. Martin Wilck
PRIMERGY System Software Engineer
x86 Server Engineering

Fujitsu Technology Solutions GmbH
Heinz-Nixdorf-Ring 1
33106 Paderborn, Germany
Phone:                  ++49 5251 525 2796
Fax:                    ++49 5251 525 2820
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