RE: [Xen-users] Xen as virtual KVM

["Petersson, Mats" <Mats.Petersson@xxxxxxx>]

> -----Original Message-----
> From: xen-users-bounces@xxxxxxxxxxxxxxxxxxx 
> [mailto:xen-users-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf Of 
> Brandon Reno
> Sent: 26 June 2007 15:28
> To: xen-users@xxxxxxxxxxxxxxxxxxx
> Subject: [Xen-users] Xen as virtual KVM
> 
> I'm looking at doing something that may seem a little bit 
> odd, I would like to use xen to virtualize several desktop 
> environments, with a specific keystroke configured to switch 
> to that environment.
> I will have either gentoo or debian as a dom0.  this will be 
> used only for management of the virtual machines. 
> I will have several full desktop environments for different users.  
> For example, I will be using Gentoo with KDE/Beryl (soon to 
> be Fusion or whatever they are changing their name to)
> I'd like to have a test environment for various trials of 
> different other flavours and for development 
> Additionally, I will be buying a new computer, supporting 
> AMD-V, will want to have 3 additional environments, Windows 
> XP and Vista, for application testing, and one Windows DE for my Wife.
> 
> To accellerate as much as possible the different 
> environments,  I would need to setup the PCI video card to 
> passthrough to whichever domU is active.  It is not necessary 
> for more than one environment to be active and running at any 
> given time. 
> My theory is to simply configure each environment to pass 
> through the video card, and drop one environment (suspend?), 
> and switch to the next.  Do you see any problems with this 
> configuration, or have any advice?

You can do it with VNC/SDL in fully-virtual domains with a virtual
graphics card. That's a (nearly) no-brainer. 

But unless you have at least two graphics cards in the machine, Dom0
will need to own the graphics card - it uses the VGA as console during
startup at the very least. So you need a second graphics card to start
with. I've seen complaints that pass-through of graphics doesn't work,
but don't take my word for it. 

Using PCI passthrough, you would definitely have to suspend ("xm save")
the domain and resume another ("xm resstore") when switching from one
domain to another. Note that this takes several seconds per save/restore
cycle for any reasonable size domain - just writing 128MB to the disk at
50MB/s takes 2.5s or so, and there is more work than this involved in
the save-process. 

HVM domains (Windows for example) can't use PCI passthrough, at all, at
this time (there's work to allow ONE instance of Windows to do that -
but that's still some way off, and I wouldn't rely on this for the next
3-6 months at least, although I'm not sure how far off it really is). 

> 
> Additionally, I would need to write a program or series of 
> scripts to manage the switching of DEs, which doesn't seem to 
> be too much of a problem, except that it would need to 
> capture a few specific keystrokes (i.e. win+f1 thru win+f5) 
> to actually call the switch. 

Why? What's wrong with clicking buttons/menus or typing into a window
someplace? 

> I'm not sure where I would need to start to do this should 
> this program monitor /dev/input for the keypress, or would 
> this need to go into the hypervisor?

That's a good question - Dom0 doesn't (strictly) own the keyboard, but
you'd certainly have an easier task intercepting this in Dom0 than you'd
have in the Hypervisor, since the hypervisor won't actually be able to
make the switch happen anyways, so you NEED to get to Dom0 someway
anywyas to achieve this. 

--
Mats

> 
> I currently have a few VMs on my server computer running 
> things like a webserver, samba share, Kerberos 
> Authentication, etc. and have been very happy with xen.  I'd 
> like to take the chance to document my findings on this 
> unique setup in case someone else would be interested. 
> 
> Any advice would be appreciated, or better yet, if someone 
> has done something like this, I'd like to hear about their 
> successes/failures.
> Thanks,
> Brandon Reno
> 
> 



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