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Re: Booting El Torito image from a partition table

From: Andrei Borzenkov
Subject: Re: Booting El Torito image from a partition table
Date: Tue, 1 Dec 2015 19:27:56 +0300
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0

30.11.2015 23:16, Emilio Lazo Zaia пишет:
>> Did you consider using syslinux loopback driver? This way ISO would
>> appear as ISO (or at least non-partitioned device) to GRUB. It may
>> work ...
> I don't know how loopback on syslinux works. I guess is like the GRUB
> loopback module, i.e. make a device from a file and boot from it. I'll
> try it...

Sorry, it is memdisk

> I have another idea: Make another -small and auxiliary- GRUB partition
> in the same USB drive and chainload it from syslinux's master partition.
> It worked in the sense of that I have the GRUB prompt/menu from the
> "auxiliary" new partition.
> What I thought is changing root=, prefix= to the Kaspersky partition (or
> SG2D if applies) and execute GRUB2's configfile directive to the main
> grub.cfg on that media. It didn't worked because of some 'unknown
> symbols' in the case of Kaspersky... Kaspersky includes other self-made
> GRUB modules (e.g. a module for displaying the EULA text) and these
> files were compiled against the version of GRUB included in their CD,
> naturally.

Yes. GRUB modules must match GRUB run-time (which is compiled into
single kernel.img).

> The core.img on that CD can be extracted to be concatenated with
> boot.img to be able to boot the same version of GRUB included in
> Kaspersky disk but from the helper partition? I mean installing on the
> 32MB helper partition the version of GRUB2 included on the Kaspersky CD.
> In that case I'll be able to change root and prefix variables pointing
> to the Kaspersky partition and loading the correct grub.cfg with
> 'configfile'.
> That way we can get rid of El Torito code, which don't understand
> partitioned devices, if I am right, and we'll not have unknown symbols
> because both GRUBs will be the same.

No, you misunderstand. The problem is not boot block, but core.img
itself - it lacks partition driver(s) and so is not able to access
partitions. It simply does not see them.

It is theoretically possible to decompose core.img (actually,
eltorito.img in this case) and add more drivers and adjust prefix as
needed and pack back into single executable. But I would try memdisk
first :)

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