Re: [PATCH] core/partmap: Add El Torito boot catalog parsing

[Ross Lagerwall <rosslagerwall@gmail.com>]

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On Mon, Jun 08, 2015 at 07:51:44PM +0300, Andrei Borzenkov wrote:
> В Sun,  7 Jun 2015 11:24:46 +0100
> Ross Lagerwall <rosslagerwall@gmail.com> пишет:
> 
> > Add a module, part_eltorito, to allow parsing of the El Torito boot
> > catalog into partitions. This follows the El Torito Bootable CD-ROM
> > Format Specification Version 1.0 and the UEFI Specification 2.5.
> > In cases where the specification is unclear, the code follows the UEFI
> > reference implementation.
> > 
> > This is useful when booting CDs in UEFI mode. Before, GRUB would not be
> > able to use the embedded ESP from which it was executed, so it would
> > have a root and prefix set to the top level of the CD. This could result
> > in subtle configuration bugs, because the same ISO booted from a USB
> > disk (using isohybrid) would have its root and prefix set to the
> > embedded ESP because it can find it through the MBR.
> 
> You can already access ESP on hybrid image using e.g. (cd0,msdos1); why
> is it not enough?

This is about booting a CD in UEFI mode; it may not be a hybrid disc in
which case it doesn't have an MBR.

Also, in the case of a hybrid image booted using a CD, the mismatch between
the 2048 byte sectors of the CD and the 512 byte sector values used in the
MBR means that GRUB is not able to access the correctly ESP anyway.

For these reasons, I think it is useful to parse the El Torito boot
catalog.

Regards,
-- 
Ross Lagerwall

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