Re: Docs on UEFI support in Debian 7 CDs

["Thomas Schmitt" <scdbackup@gmx.net>]

Hi,

i wrote:
> > [real MBR combined with GPT] [MBR partition type 0x00]
> > One will have to watch out whether these violations, or the fact
> > that MBR partition 2 is nested in MBR partition 1, cause any
> > trouble.

Andreas Heinlein wrote:
> Do you think this might cause trouble, i.e. older machines which
> used to boot with "plain" (MBR only) isohybrid will not boot with such a
> dual UEFI/MBR image?

I myself am not into boot loaders. I only provide features on
request of the boot loader developers and/or producers of
bootable images. (You can see from my methods of testing that
i do not even operate SYSLINUX or GRUB, but rather act as
parasite of the produced bootable images.)

I can report about some opinions of skilled people.
Vladimir Serbinenko puts much emphasis on a "protective MBR" for
GPT and on disjoint partitions.
H.Peter Anvin and Matthew Garrett are willing to deviate from MBR
traditions and GPT specs, as long as it works. E.g. the partition
type of the big MBR partition is ok for them either as 0x00 or as
0x17. Peter mainly refers to the reactions of running operating
systems than to the reactions of BIOS, when discussing the type
question.

I serve both opinions by different xorrisofs options.
And there is room for more alternatives. :))


> the whole UEFI stuff is on the amd64 images only, and you would rarely want
> to use these with old Pentium IV machines.

So it is only about MBR partition type and nesting.
And only when not booting the ISO image from CD, DVD, or BD
but from hard disk or from USB stick.


> But we definitely would want a single image (32bit) to boot on current
> machines with UEFI as well as on machines as old as Pentium IV/Pentium M
> class.

Testing is needed. We deal with a large set of different BIOS
implementations and versions.
So everybody should copy a Debian image on USB stick and try
as many machines as possible whether they boot into the usual
menu.

I am watching debian-cd for problem reports and will do my
best to help with finding the reason for any trouble.


Have a nice day :)

Thomas