RE: [Xen-devel] HVMAssist BIOS boot device problem

["Stephen Quintero" <stephen@xxxxxxxxx>]

Steve,

Okay, I get it.  The BIOS is picking the MBR of hda and the windows boot
loader is deciding to boot from the active partition of hdc.

A boot loader problem.

Thanks you,

Stephen 

-----Original Message-----
From: Steve Ofsthun [mailto:sofsthun@xxxxxxxxxxxxxxx] 
Sent: Tuesday, July 08, 2008 7:05 AM
To: Stephen Quintero
Cc: Keir Fraser; xen-devel@xxxxxxxxxxxxxxxxxxx; Apoorva Kulkarni; Minh
Quach; Eric Tessler
Subject: Re: [Xen-devel] HVMAssist BIOS boot device problem

Stephen Quintero wrote:
> Keir,
> 
> Thank you for your reply.
> 
> I agree it should be deterministic, according to the enumeration of
the
> devices (hda-hdd), but, alas, it is not.

Realize that Xen (QEMU BIOS) is only determining which MBR is loaded and
executed.  After that you are at the mercy of the boot loader in
question.  Windows in particular doesn't "support" multiple visible
system partitions, or rather, doesn't specify the selection of the
appropriate system partition.  In your example B below, if you destroy
the boot block on hda, you will fail to boot anything.  If you "hide"
all windows partitions on hdb/hdc/hdd, you will indeed boot the system
volume on hda.  This is exactly what many multiboot boot loaders do.
The partition tables are usually modified in memory only, not on the
physical disk itself.

Steve

> See example B in my original post where hda|hdb|hdc all contain active
> partitions but the guest boots from hdc.
> 
> See also example A in my post where hda is always a bootable image but
> sometimes the guest boots from hdb (you may not easily recreate this
> scenario yourself, but example B is simple to reproduce).
> 
> Stephen
> 
> 
> -----Original Message-----
> From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx] 
> Sent: Tuesday, July 08, 2008 2:12 AM
> To: Stephen Quintero; xen-devel@xxxxxxxxxxxxxxxxxxx
> Cc: Apoorva Kulkarni; Minh Quach; Eric Tessler
> Subject: Re: [Xen-devel] HVMAssist BIOS boot device problem
> 
> On 8/7/08 01:24, "Stephen Quintero" <stephen@xxxxxxxxx> wrote:
> 
>> Is there any method to cause an HVM guest to reliably boot from hda?
>>
>> Any insight would be appreciated.
> 
> Reading the BIOS code, my understanding is that 'boot from hard disk'
> means
> to boot from the first connected hard drive enumerated in the
following
> order: primary master, primary slave, secondary master, secondary
slave
> (i.e., hda-hdd). I confirmed this with a few simple tests -- attach a
> bootable image to hdd boots fine, but if I connect a non-bootable
image
> on
> any of hha-hdc then the system fails to boot. This is all entirely
> deterministic. Selection of boot device should not be random, nor
change
> across reboots.
> 
>  -- Keir
> 
> 
> 
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