Comment # 14 on bug 1011529 from Michael Chang

(In reply to Michal Suchanek from comment #13)
> 'firmware' here is Linux most likely

Sorry but I am confused here. I don't really get your idea in such a short
comment. (Please be more verbose to help me understand your thoughts :))

Any, In comment#12, the 'firmware' I was exactly inferring to Open Firmware,
which can only understand IEEE1275 device tree path for the disk (containing
PReP partition) translated by ofpathname. 

The ofpathname also takes care the Linux logical device to OFW path, and it
have trouble (Michel Normand created RFC patch for it). If firmware can't
really find a way to deal with the logical device, it has to report something
like "LVM Disk /dev/system/root is not support by "direct" firmware booting."
or such.

> The problem is with ofpathname and turned up by a change to grub scripts
> that started calling it afaik.

Again I am confused by the 'grub script'. :( Here listed my candidates :

1. grub2-install, but it's nothing a script
2. scripts under /etc/grub.d/ but they have nothing to do with ofpathname (ie
not calling it)
3. perl bootloader and/or YaST scripts, but they are not grub scripts
4. else ..

I presume 'grub2-install' is what you were talking about, but it has been
calling ofpathname since day one for booting powerpc-ieee1275.

Btw, grub2 has also grub2_ofpathname but is not used here, is it cause of
confusion here?

> So what does the grub script expect to get if there are multiple ways to
> reach the disk (provided it's not a deficiency of ofpath and there are in
> fact multiple equally canonical of names of the disk)?

In this case, it boots the the disk from which firmware loads it (aka the boot
disk). That is setting the $prefix to

'(,msdos3)/boot/grub2'

The msdos3 is set during grub2-install. As cross-disk installation (ie the PReP
and /boot partition are on different disk) is not allowed in grub2, it will
have identical result, even if you swap the disk order.

You can see this line in attachment #3 [details].

grub-mkimage --directory '/usr/lib/grub2/powerpc-ieee1275' --prefix
'(,msdos3)/boot/grub2' --output '/boot/grub2/powerpc-ieee1275/core.elf'
--format 'powerpc-ieee1275' --compression 'auto'  --config
'/boot/grub2/powerpc-ieee1275/load.cfg' 'btrfs' 'part_msdos'

Thanks.