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Re: GRUB doesn't recognize partitions on El-Torito image during EFI boot

From: Andrey Borzenkov
Subject: Re: GRUB doesn't recognize partitions on El-Torito image during EFI boot from CD
Date: Mon, 11 Nov 2013 23:15:50 +0400

В Mon, 11 Nov 2013 18:58:20 +0100
Jacek Konieczny <address@hidden> пишет:

> Hi,
> I have a system as a disk image. It can be booted directly from an USB
> stick both via legacy BIOS and EFI. I wanted the same image to be usable
> on a CD.
> For EFI boot it should be straightforward – use the disk image as
> a hard-disk-emulation El-Torito EFI boot image.

Do you mean - in addition to EFI boot image? Because EFI requires ESP
in "no emulation" mode to boot.

>                                                I have done that with
> other EFI boot loaders and it worked right.

> With GRUB there is a problem – it is unable to find the boot partition.
> In rescue mode I can see only:
> (hd0) (cd0)
> however, I would expect too see (hd0,msdos1) too – with the first
> partition of the El-Torito image.

Why "msdos"? El-Torito CD does not have standard DOS label, so it would
be wrong name. And if you place whole image of partitioned disk there,
it becomes nested partition (dos label in El-Torito "partition").

Something like (cd,eltorito0,msdos1) probably.

> Is it a bug? Am I doing something wrong?

No. As it stands currently grub does not expose El-Torito image as 
partition of CD media. It is completely invisible unless you use hybrid
CD which contains other partition labels referring to it.

> I made a workaround by using GRUB loopback in the embedded config for
> the EFI loader:
> echo "starting grub"
> search.fs_uuid 8101-917C root
> set prefix=($root)/grub
> configfile $prefix/go_normal.cfg
> echo "boot partition not found falling back to loopback device"
> search.fs_uuid 2013-11-11-18-32-41-96 cd
> loopback loop ($cd)/pld-nr-32.img
> set root=(loop,msdos1)
> set prefix=($root)/grub
> It works, but I don't like this.

But you need to place image on CD either way. Are you using this image
for anything else, like directly booting on non-EFI?

>                                  GRUB should be able to see the El-Torito
> contents, shouldn't it?

So far there was not any use case. But yes, technically EFI does expose
it as "partition" so grub probably should too.

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