RE: Xen compatibility interface numbering

RE: Xen compatibility interface numbering

[Ian Pratt]

> Questions about compatibility between dom0 and domU kernels.   In the 
> ideal situation, all domU kernels would be patched to the 
> same level of 
> Xen in dom0.   What happens if they are not?
> 
> 1.  Can an incompatible domU take down or in any way 
> interfere with dom0?

No.
 
> 2.  Does Xen/dom0/Xend perform version checking on domUs?

Yes.

> 3.  Can a binary Xen kernel be queried for its compatibility version?

There's a dom0 op that queries the interface version.

> 4.  How frequently does the Xen compatibility interface change?

Only when there's a major release number change.

> 5.  Can I run a 2.4 domU against a 2.6 dom0 and vice-versa, 
> if both are 
> patched to the same level of Xen?

Yes. You can play with this on the Demo CD.

Ian


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Re: Xen compatibility interface numbering

[Rich Persaud]

Ian Pratt wrote:

>>2.  Does Xen/dom0/Xend perform version checking on domUs?
>>    
>>
>
>Yes.
>  
>
Out of curiosity, what happens in dom0 if a domU spoofs its interface 
version?

>>3.  Can a binary Xen kernel be queried for its compatibility version?
>>    
>>
>
>There's a dom0 op that queries the interface version.
>  
>
Is this accessible to the management tools, i.e. can Xend report the 
dom0 interface version to userland? 

If I have a domU binary kernel image (vmlinuz), is there any way to 
query its interface version (even a search string for strings+grep)?

>>4.  How frequently does the Xen compatibility interface change?
>>    
>>
>
>Only when there's a major release number change.
>  
>
Major = 1.x, 2.x, 3.x, not 2.0.4 to 2.0.5-pre, right? So the Xen 
interface is compatible between 2.0.4 and the testing/unstable tree.

Rich


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Re: Xen compatibility interface numbering

[John Kelly]

On Mon, 07 Mar 2005 07:50:17 +0000, Ian Pratt
<m+Ian.Pratt@cl.cam.ac.uk> wrote:

>> Can I run a 2.4 domU against a 2.6 dom0 and vice-versa, 
>> if both are patched to the same level of Xen?
>
> Yes. You can play with this on the Demo CD.

How does that work when dom0 is 100 Hz 2.4 kernel and domU is 1000 Hz
2.6 kernel?




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Re: Xen compatibility interface numbering

[Grzegorz Milos]

> >> Can I run a 2.4 domU against a 2.6 dom0 and vice-versa,
> >> if both are patched to the same level of Xen?
> >
> > Yes. You can play with this on the Demo CD.
>
> How does that work when dom0 is 100 Hz 2.4 kernel and domU is 1000 Hz
> 2.6 kernel?

I will answer this question, although there might be better people to explain 
this.
The scheduling code in both 2.4 and 2.6 kernels relay on hardware timer (to 
interrupt with 100 or 1000 Hz frequency). But the timers had to be 
virtualised, and therefore the parts of the code responsible for scheduling 
patched up as well. This way both linux kernels can work just fine. 
(BTW remember that Xen also has a scheduler which decides which domain should 
be run, but then the domains have freedom of scheduling their own processes).

Cheers
Gregor

>
>
>
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-- 
Quidquid latine dictum sit, altum viditur --- Anon


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Re: Xen compatibility interface numbering

[Mark Williamson]

> How does that work when dom0 is 100 Hz 2.4 kernel and domU is 1000 Hz
> 2.6 kernel?

The dom0 kernel requests timer interrupts from Xen at 100HZ, the domU requests 
them at 1000HZ, Xen just delivers events when timers expire without caring 
what the domain does with them.

In the situation you describe, the 2.4 kernel in dom0 would also be granted 
access to hardware devices.  The 2.6 kernel would use virtual devices 
provided to it by dom0.  The virtual device interfaces are independent of OS.

HTH,
Mark


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RE: Xen compatibility interface numbering

[Ian Pratt]

> Out of curiosity, what happens in dom0 if a domU spoofs its interface 
> version?

The domU probably ends up crashing itself. It's not a concern of dom0 or
Xen anyhow, 
 
> >>3.  Can a binary Xen kernel be queried for its 
> compatibility version?
> >There's a dom0 op that queries the interface version.
> Is this accessible to the management tools, i.e. can Xend report the 
> dom0 interface version to userland? 

Yes.

> If I have a domU binary kernel image (vmlinuz), is there any way to 
> query its interface version (even a search string for strings+grep)?

As I recall, there's a version identifier in the header.

> >>4.  How frequently does the Xen compatibility interface change?

> >Only when there's a major release number change.
> >  
> >
> Major = 1.x, 2.x, 3.x, not 2.0.4 to 2.0.5-pre, right? So the Xen 
> interface is compatible between 2.0.4 and the testing/unstable tree.

2.0.x and 2.0-testing are compatible.

Unstable is something entirely different, and is not guaranteed to be
compatible with anything (other than the same version of itself).

The original plan was to have 2.1.x compatible with 2.0.x, but I'm
currently thinking that this will *not* be the case. Given current usage
models, I don't think that this is going to upset too many people. We'll
have to be much more careful to be backward compatible post 3.0.

Ian




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Xen compatibility interface numbering

[Rich Persaud]

Questions about compatibility between dom0 and domU kernels.   In the 
ideal situation, all domU kernels would be patched to the same level of 
Xen in dom0.   What happens if they are not?

1.  Can an incompatible domU take down or in any way interfere with dom0?

2.  Does Xen/dom0/Xend perform version checking on domUs?

3.  Can a binary Xen kernel be queried for its compatibility version?

4.  How frequently does the Xen compatibility interface change?

5.  Can I run a 2.4 domU against a 2.6 dom0 and vice-versa, if both are 
patched to the same level of Xen?

Thanks,
Rich


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