Re: [Xen-users] xen in in the stock linux kernel...

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> > The 2.6.23 development tree (which has just passed -rc1) includes support
> > for Xen.  If you select a Xen capable host architecture (Pentium Pro and
> > above) then there'll be an option to support Xen under the
> > paravirtualisation support section.
> >
> > The resulting kernel build will be capable of booting native or on Xen.
> > However you'll need to use the vmlinux / vmlinuz on Xen, whereas native
> > booting will still need the bzImage.  There's work underway to allow Xen
> > to boot bzImages directly, so you'll only need to keep one image around.
> >
> > Cheers,
> > Mark
>
> Can we get more info about this? I assume this means that you can compile
> a stock linux kernel for use as a domU...

Yep.  The code is different from that shipped in the sparse tree, and 
therefore not quite as widely used / tested, but it's been through a fair 
amount of review now so hopefully it'll work reasonably well.

Suspend / resume, live migration and ballooning are not currently supported.  
Nor is the virtual framebuffer (and maybe some other stuff I forget).

> how about a dom0?

Nope.  The Xen <-> dom0 interface isn't in mainline yet.  It's not entirely 
clear whether it ever will be, or if it'll be shipped as a patch against 
mainline.  I think Jeremy is looking at something like this.

> And since the  
> kernel compile is separate from the current xen packaged compile which
> builds the hypervisor, I guess this will imply a fairly formal/strict API?

The Xen <-> domU ABI has been pretty strict since the 3.0 release.  Any 
3.x-aware guest will run on an equally new, or newer hypervisor.  You can't 
in general guarantee that a newer kernel will run on an older hypervisor, 
unless it supports appropriate compatibility APIs.  The default build for the 
XenLinux tree kernels (the kernel tree built by Xen, by default) also 
includes compatibility support so that they may run on older hypervisors as 
well as newer ones.

The Xen <-> dom0 ABI has been fixed since uhhhh around 3.0.4 / 3.1, I can't 
remember which.  However, you may sacifice some functionality if you use an 
older kernel for dom0.

> or should I just go download it and try it out? I'll try to find time for
> that.

You can grab it from Linus' git tree, or you can probably download a snapshot 
of that tree.  Remember that you need to set your architecture to be PPro or 
newer, otherwise the Xen option won't show up - that confused me for some 
time a couple of days ago ;-)

For the moment, the XenLinux repository at XenSource contains a more full 
featured port of Linux to Xen than what is available in mainline.  This is 
downloaded and built by default when you build Xen.  I think you might now be 
able to get the Xen build system to grab mainline Linux and build it as a 
domU kernel automagically though...

Eventually I expect that the main XenLinux repository will move to be closer 
to mainline Linux, as feature from the former are merged upstream, or 
refactored into patches against upstream.

I hope this makes some sense!

Cheers,
Mark

-- 
Dave: Just a question. What use is a unicyle with no seat?  And no pedals!
Mark: To answer a question with a question: What use is a skateboard?
Dave: Skateboards have wheels.
Mark: My wheel has a wheel!

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