Xen users - Aug 2005 - Question about stability 32bit chroot and xen 2.0.7

I want to run a stable system with Xen, so my best choice
is the xen-2.0.7 installation. I have however a AMD opteron
which is 64 bit.

Will i be able to run a stable Xen server in a 32 bit chroot enviroment
on Debian 3.1 amd64 stable?

Or would my best bet be, install Debian i386 on my amd64
and run xen-2.0.7 from there.

The last option however needs a complete reinstall of the
entire system if i want to replace Xen 2.0.7 with Xen 3.0
if it becomes stable. So i''d rather go with the first option.

But, otoh, my primary objective is to have a STABLE system.
So what should i do?

Kind regards,

Robin van Leeuwen

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I want to run a stable system with Xen, so my best choice
is the xen-2.0.7 installation. I have however a AMD opteron
which is 64 bit.

Will i be able to run a stable Xen server in a 32 bit chroot enviroment
on Debian 3.1 amd64 stable?

Or would my best bet be, install Debian i386 on my amd64
and run xen-2.0.7 from there.

The last option however needs a complete reinstall of the
entire system if i want to replace Xen 2.0.7 with Xen 3.0
if it becomes stable. So i''d rather go with the first option.

But, otoh, my primary objective is to have a STABLE system.
So what should i do?

Kind regards,

Robin van Leeuwen


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Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

> Will i be able to run a stable Xen server in a 32 bit chroot
> enviroment on Debian 3.1 amd64 stable?
I think you are confused about what Xen does. Xen is a hypervisor: it
goes between the kernel and the hardware. You can''t run Xen
"on" Debian;
you might run a Debian guest on Xen though. Xen can''t run in a chroot
environment because Xen itself does not care about filesystems and such
high level things: it cares about letting the guest operating systems
use the hardware in a safe way (FSVO safe).

You can''t run dom0 in a chroot because there is nothing to set up the
chroot environment for it: Xen boots it just as a normal bootloader
would. Similarly, you wouldn''t want to run a domU in a chroot because
the domain already gets its own filesystem. Of course, in both cases you
can run *applications* in a chroot just as you would on a native Linux
(or NetBSD or FreeBSD) system.

To answer what you actually want to do rather than what you asked, Xen
does not support mixing 32-bit and 64-bit guests. Either Xen and all
guest operating systems are 64-bit, or they are all 32-bit. The same
applies to PAE/non-PAE. This support is planned, but not for some time
yet.
> The last option however needs a complete reinstall of the
> entire system if i want to replace Xen 2.0.7 with Xen 3.0
> if it becomes stable. So i''d rather go with the first option.
> But, otoh, my primary objective is to have a STABLE system.
> So what should i do?
It depends on whether you want a stable system right now. The unstable
tree (with PAE and 64-bit support) is expected to go into testing Real
Soon Now, and once it does and the number of people trying it out
increases, a stable 3.0 release should follow. If you can''t wait that
long, go with 2.0.7 and 32-bit for now, and be ready to upgrade once you
are happy with the stability. If changing your arch and reinstalling the
packages is that much of a headache for you, consider changing your
backup and installation procedure. On production systems, it is
generally a good idea to set things up so if the system goes down with
all hands you can install an identical replacement and restore backed-up
data onto it with minimal administrator interaction. Of course, I
appreciate that it isn''t always as easy as this...

-- 
"And  what if  I assign  a  hundred  programmers  to  it?"   The 
master
programmer shrugged. "Then the design will never be completed," he
said.
http://www.google.com/search?q=%22pgp+singing%22  <-- childish but funny
http://surreal.istic.org/ <-- It''s like a DEATH CIRCUS! | keyid
885b170d


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Daniel Hulme wrote:
>>Will i be able to run a stable Xen server in a 32 bit chroot
>>enviroment on Debian 3.1 amd64 stable?
>>    
>>
>I think you are confused about what Xen does. Xen is a hypervisor: it
>goes between the kernel and the hardware. You can''t run Xen
"on" Debian;
>you might run a Debian guest on Xen though. Xen can''t run in a
chroot
>environment because Xen itself does not care about filesystems and such
>high level things: it cares about letting the guest operating systems
>use the hardware in a safe way (FSVO safe).
>  
>
i''m familiar enough with xen and it''s internals, currently
i''m
setup 32bit servers, and 64 bit servers with errors, submitting
my bugreports etc, helping out where i can.
>You can''t run dom0 in a chroot because there is nothing to set up
the
>chroot environment for it: Xen boots it just as a normal bootloader
>would. Similarly, you wouldn''t want to run a domU in a chroot
because
>the domain already gets its own filesystem. Of course, in both cases you
>can run *applications* in a chroot just as you would on a native Linux
>(or NetBSD or FreeBSD) system.
>  
>
I can compile xen 3.0 to boot DomU in 64 bit mode.
and set Linux-2.6-xenU to architecture x86 instead
of x86_64? Question is if i can boot with the xen3 kernel
64 bit and the domU xen32 bit. That''s not possible as
i understand from your answer.

My solution, could work, indeed you don''t need a chroot,
but you should just setup your domU partitions with a
x86 release of linux. But your stuck with a unstable kernel
in that way.

To answer what you actually want to do rather than what you asked, Xen
>does not support mixing 32-bit and 64-bit guests. Either Xen and all
>guest operating systems are 64-bit, or they are all 32-bit. The same
>applies to PAE/non-PAE. This support is planned, but not for some time
>yet.
>
So for now my only option is to install the whole thing 32 bit,
debian + xen.

tnx



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Daniel Hulme wrote:
>>Will i be able to run a stable Xen server in a 32 bit chroot
>>enviroment on Debian 3.1 amd64 stable?
>>    
>>
>I think you are confused about what Xen does. Xen is a hypervisor: it
>goes between the kernel and the hardware. You can''t run Xen
"on" Debian;
>you might run a Debian guest on Xen though. Xen can''t run in a
chroot
>environment because Xen itself does not care about filesystems and such
>high level things: it cares about letting the guest operating systems
>use the hardware in a safe way (FSVO safe).
>  
>
i''m familiar enough with xen and it''s internals, currently
i''m
setup 32bit servers, and 64 bit servers with errors, submitting
my bugreports etc, helping out where i can.
>You can''t run dom0 in a chroot because there is nothing to set up
the
>chroot environment for it: Xen boots it just as a normal bootloader
>would. Similarly, you wouldn''t want to run a domU in a chroot
because
>the domain already gets its own filesystem. Of course, in both cases you
>can run *applications* in a chroot just as you would on a native Linux
>(or NetBSD or FreeBSD) system.
>  
>
I can compile xen 3.0 to boot DomU in 64 bit mode.
and set Linux-2.6-xenU to architecture x86 instead
of x86_64? Question is if i can boot with the xen3 kernel
64 bit and the domU xen32 bit. That''s not possible as
i understand from your answer.

My solution, could work, indeed you don''t need a chroot,
but you should just setup your domU partitions with a
x86 release of linux. But your stuck with a unstable kernel
in that way.

To answer what you actually want to do rather than what you asked, Xen
>does not support mixing 32-bit and 64-bit guests. Either Xen and all
>guest operating systems are 64-bit, or they are all 32-bit. The same
>applies to PAE/non-PAE. This support is planned, but not for some time
>yet.
>
So for now my only option is to install the whole thing 32 bit,
debian + xen.

tnx




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Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users

> I can compile xen 3.0 to boot DomU in 64 bit mode.
> and set Linux-2.6-xenU to architecture x86 instead of x86_64? 
> Question is if i can boot with the xen3 kernel
> 64 bit and the domU xen32 bit. That''s not possible as i 
> understand from your answer.
> 
> My solution, could work, indeed you don''t need a chroot, but 
> you should just setup your domU partitions with a
> x86 release of linux. But your stuck with a unstable kernel 
> in that way.
Running a 64b guest kernel on a 32b file system works just fine. "uname
-a" reports x86_64, but other than that you wouldn''t know the
difference.

Ian 

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Ian Pratt wrote:
>>I can compile xen 3.0 to boot DomU in 64 bit mode.
>>and set Linux-2.6-xenU to architecture x86 instead of x86_64? 
>>Question is if i can boot with the xen3 kernel
>>64 bit and the domU xen32 bit. That''s not possible as i 
>>understand from your answer.
>>
>>My solution, could work, indeed you don''t need a chroot, but 
>>you should just setup your domU partitions with a
>>x86 release of linux. But your stuck with a unstable kernel 
>>in that way.
>>    
>>
>
>Running a 64b guest kernel on a 32b file system works just fine. "uname
>-a" reports x86_64, but other than that you wouldn''t know the
>difference.
>
>Ian 
>  
>
But i want it the other way around. I want to run a stable 64 bit server
(debian-amd64 stable) with a stable xen (2.0.7) but, 2.0.7
doesn''t support 64 bit''s. Is there a way i still can use 2.0.7
AND make
use of debian-amd64-stable.

There is another catch (maybe an advantage) I have to recompile it
myself to
change some kernel-config settings and recompile at least the kernels.

Can this be done?

kind regards,

Robin van Leeuwen




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> But i want it the other way around. I want to run a stable 64 
> bit server
> (debian-amd64 stable) with a stable xen (2.0.7) but, 2.0.7 
> doesn''t support 64 bit''s. Is there a way i still can use 
> 2.0.7 AND make use of debian-amd64-stable.
There is no way you can run a 64-bit OS on top of a 32-bit hypervisor,
stable, unstable or otherwise. The reason, primarily, is that the
hypervisor has to understand entire processor architecture, and AMD64
has 8 more gp registers than the 32-bit x86 architecture. These
registers are not accessible in 32-bit mode, so you would end up with
unsaved registers. Since some of these registers are of the type that
doesn''t automatically get saved by the OS or C calling convention
(ABI),
they absolutely need to be saved and restored with Xen''s context
switches. 

So you need a Xen hypervisor that understands 64-bit processors, or you
have to run a 32-bit OS. 

[Aside from that, amd64 also uses 4 level page tables in combination
with PAE mode, none of which I believe are supported in 2.0.x].
> 
> There is another catch (maybe an advantage) I have to 
> recompile it myself to change some kernel-config settings and 
> recompile at least the kernels.
> 
> Can this be done?
No. 

--
Mats
> 
> kind regards,
> 
> Robin van Leeuwen
> 
> 
> 
> 
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
> 

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