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Re: [RFC][PATCH] unique sigs in the msdos label

From: Andrew Clausen
Subject: Re: [RFC][PATCH] unique sigs in the msdos label
Date: Sat, 3 Jul 2004 22:53:53 +1000
User-agent: Mutt/

I'll answer for Matt :)

On Mon, Jun 28, 2004 at 03:46:21PM -0700, John Gilmore wrote:
> I think writing 'unique signatures into disk labels' is a terrible idea.
> Intel is working on a Legacy-BIOS-free spec.

GPT, yeah.  (Parted and Linux even support it :)
There are plenty of legacy users left though.

> It should provide a way
> to determine exactly what device is the boot device -- without this
> hocus pocus about storing different magic numbers in every partition
> table, retrieving them via different routes to compare and contrast.
> By getting involved in the writing of this spec, we should be able to
> put a stake through the heart of this issue once and for all, in new
> hardware.  Like the concept of cylinders, 'BIOS drive numbers' should
> hsve been d-e-a-d two decades ago.
> As far as I know, nobody cares what device numbers the BIOS assigned
> to devices other than the boot disk.  The main question is, "What
> disk and partition did I, this kernel/bootstrapper/etc, get read in from?"

With the current BIOS setup, we need to have unique hard disks to
answer this question.

We can ask the BIOS which disk is the boot disk, but it will give
an identifier that "BIOS-only".  i.e. we can't match it up to an IDE
controller or whatever.  (Reason: the BIOS can do funky remapping
tricks)  What we can do is ask the BIOS to read sectors from this
boot device.  If they are unique, we can figure out which disk it is.

Matt: is this what you had in mind?


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