[Pkg-xen-devel] Several xen problems in Debian Etch

[Ralph Passgang]

Am Dienstag, 27. November 2007 16:05:42 schrieb Richard W.M. Jones:
> Henning Sprang wrote:
> >>Ian Jackson wrote:
> >> If you want to cleanly shut down a Windows guest without appropriate
> >> PV drivers (which aren't generally Freely available I think)
>
> Red Hat are sponsoring the development of free PV drivers for Xen.  I
> cannot say when they'll be available at the moment.  The license cannot
> be GPL (because M$'s DDK license, which we link against, would forbid us
> to distribute the binaries), but will be a properly Free license, most
> likely BSD.

James Harper is trying to develop a gpl'ed set of pv drivers for windows. 
But I haven't checked them in any way, so I don't know if they are working 
stable or even worth trying. I also don't know if they are really free 
(because of the linking problem) or if there is the same problem with the 
windows DDK license.

At least there is some alternative movement and maybe worth testing in 
future :)

> > There are, for example from SuSE (see a thread some while ago in this
> > list, I never tested them... not sure if they apply to Windows or Linux
> > HVM guests, or both) as GPL, and I heard, but not checked, that the
> > same goes for Redhat.
> >
> > Not sure if they are somehow/at all usable from a Debian dom0, but I
> > don't see why not.

I tried the novell and the xensource pv drivers on a debian xen system. both 
driverpacks didn't worked as expexted. The novell drivers installed, but 
after the neccessary reboot the system hung directly with a blue screen, 
telling me something about an irq problem.

The xensource drivers were not that bad, but not all devices were working. 
For example the pv block driver was listed broken within the windows device 
manager. Furthermore "xm top" started to showed 100% cpu consumtion for the 
windows hvm guest all the time, so this wasn't what I wanted of course and 
I stopped trying more.

I don't know what is the exact reason, but I guess novell and xensource 
added some lines to the hypervisor or dom0 kernel for their own pv drivers. 
Furthermore, both are interessted to have something that the other's might 
not already have, so a pv driver that only works on their hypervisor/dom0 
should be what they want anyways.

> > Then again, are you sure that using a PV disk/net IO driver (the
> > primary purpose of those is to get better performance and circumvent
> > the need for qemu emulation of some devices) in a HVM domU makes it
> > possible to send the shutdown command to the guest?
>
> Red Hat's PV drivers for Windows allow you to send a graceful shutdown
> command to the guest.  Novell's don't ...

I also noticed that "xm shutdown" destroys a hvm guest without shutting it 
down before. I am not sure about the "it is not possible without the pv 
driver part within the guest" theory, because every acpi-capable OS is able 
to recieve a signal to shutdown (normally when the power button is 
pressed). Xen isn't able to "virtualise" this acpi signal, but in general 
it should be possible.

Almost every major virtualisation solution offers this. Virtualbox for 
example (available as open source edition) is a good example.

--Ralph

> Rich.