Re: GRUB device names wrt. ieee1275

[David Miller]

From: Robert Millan <address@hidden>
Date: Sun, 15 Mar 2009 16:45:31 +0100

> It's not an absolute must that device names are unique.  You can still
> identify partitions by their filesystem UUID or label, and in fact this
> is what our default scripts (grub-mkconfig) do anyway.

Things like UUID and labels are not an option for the 512-byte
boot block where I have to know the exact OBP path of the boot
device, and this is what the GRUB kernel fetches from the
'bootpath' environment variable to compose the root device
and path.

So the point is that we need this information anyways.

> Making GRUB specify partitions differently depending on the platform we're
> on seems troublesome, specially if we end up with such long an ugly names.

If there are commas in the openfirmware paths, which there are,
there are only two ways to resolve the conflict between how
GRUB uses comma characters (to delimit partition specifications)
and how the firmware uses them:

1) My suggestion, which is to use ":" on openfirmware platforms.
   To me this is the best because people using openfirmware
   platforms are familiar with this syntax.  We gain nothing by
   giving them something else to learn, on top of openfirmware
   path naming, just for the sake of GRUB.

2) Munge the openfirmware path back and forth, for example changing
   the openfirmware "," characters into something else.

   We'd need to do this back and forth, as device paths go in and
   out of GRUB's realm.  I don't really think that is maintainable.

> If we really need this, can't we just assign names dynamically like
> hd0, hd1, etc, and keep a memory structure that matches them with the
> actual OFW device?

I need the fully expanded path for things like the boot block
anyways.  Here is the devicemap file on my workstation:

(/address@hidden,600000/address@hidden/address@hidden/address@hidden/address@hidden/address@hidden)
        /dev/sda
(/address@hidden,600000/address@hidden/address@hidden/address@hidden/address@hidden/address@hidden)
        /dev/sdb

And that looks just fine to me.

We could enhance this (and I planned on implementing this) by
using the shorter devalias names which match the above paths.