RE: HVMAssist BIOS boot device problem

RE: HVMAssist BIOS boot device problem

[Stephen Quintero]

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.

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@eu.citrix.com] 
Sent: Tuesday, July 08, 2008 2:12 AM
To: Stephen Quintero; xen-devel@lists.xensource.com
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@3tera.com> 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

Re: HVMAssist BIOS boot device problem

[Keir Fraser]

On 8/7/08 14:52, "Stephen Quintero" <stephen@3tera.com> wrote:

> See example B in my original post where hda|hdb|hdc all contain active
> partitions but the guest boots from hdc.

I checked an example where hda was not bootable yet hdd was. In that case
the BIOS wanted to boot from hda, and failed, and that was that. I'm afraid
that, plus reading the BIOS code, was as far as I went in trying to repro
this oddness.

 -- Keir

Re: HVMAssist BIOS boot device problem

[Steve Ofsthun]

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@eu.citrix.com] 
> Sent: Tuesday, July 08, 2008 2:12 AM
> To: Stephen Quintero; xen-devel@lists.xensource.com
> 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@3tera.com> 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
> 
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

RE: HVMAssist BIOS boot device problem

[Stephen Quintero]

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@virtualiron.com] 
Sent: Tuesday, July 08, 2008 7:05 AM
To: Stephen Quintero
Cc: Keir Fraser; xen-devel@lists.xensource.com; 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@eu.citrix.com] 
> Sent: Tuesday, July 08, 2008 2:12 AM
> To: Stephen Quintero; xen-devel@lists.xensource.com
> 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@3tera.com> 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
> 
> 
> 
> _______________________________________________
> Xen-devel mailing list
> Xen-devel@lists.xensource.com
> http://lists.xensource.com/xen-devel

HVMAssist BIOS boot device problem

[Stephen Quintero]

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Hello,

The xm config option boot="c" is intended to boot from the "first" harddrive; however, the enumeration of harddrives is independent of device enumeration (hda|hdb|hdc|hdd), leading to unreliable boot device selection.

Example A:  

I am building a Windows HVM appliance which performs file-system level operations over mounted NTFS volumes - for example a file-system level copy.

hda is the boot disk of the appliance and contains a single active (bootable) primary partition.  If hdb also contains a single active primary partition, sometimes the appliance boots from hda and properly mounts the hdb partition and sometimes it misfires and boots from the hdb partition, causing a disaster (the contents of hdb are unknown to the appliance prior to boot).

Example B:

Make three copies of a bootable Windows image and set them up as hda, hdb, and hdc.  "xm create" boots from the active partition of hda.  Shutdown and reorder the devices, switching the images for hda and hdc.  "xm create" now boots from the active partition of hdc.

Is there any method to cause an HVM guest to reliably boot from hda?

Any insight would be appreciated.

Thank you,

Stephen Quintero

[-- Attachment #2: Type: text/plain, Size: 138 bytes --]

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Re: HVMAssist BIOS boot device problem

[Keir Fraser]

On 8/7/08 01:24, "Stephen Quintero" <stephen@3tera.com> wrote:

> Example A:  
> 
> I am building a Windows HVM appliance which performs file-system level
> operations over mounted NTFS volumes - for example a file-system level copy.
> 
> hda is the boot disk of the appliance and contains a single active (bootable)
> primary partition.  If hdb also contains a single active primary partition,
> sometimes the appliance boots from hda and properly mounts the hdb partition
> and sometimes it misfires and boots from the hdb partition, causing a disaster
> (the contents of hdb are unknown to the appliance prior to boot).
> 
> Example B:
> 
> Make three copies of a bootable Windows image and set them up as hda, hdb, and
> hdc.  "xm create" boots from the active partition of hda.  Shutdown and
> reorder the devices, switching the images for hda and hdc.  "xm create" now
> boots from the active partition of hdc.
> 
> Is there any method to cause an HVM guest to reliably boot from hda?

Is the selected disc deterministic for any particular config file, or does
it change randomly across reboots, with no changes to the guest config file?

 -- Keir

Re: HVMAssist BIOS boot device problem

[Keir Fraser]

On 8/7/08 01:24, "Stephen Quintero" <stephen@3tera.com> 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