libvirt users - May 2010 - Host should not touch passed-through USB device, how?

Hello list, 

this may be off topic but it is closely related to my Libvirt adventures 
so maybe you can help me.

I want to pass a USB device (a USB Huawei E620 modem) through to a KVM 
guest. Pass-through in general works fine and the modem is visible in 
the guest. However, the host still sees it and sometimes tries to access 
it (such modems seem to also be USB storage devices). This naturally 
leads to conflicts and I believe this crashed the guest very badly 
yesterday.

So I am looking for a way to make sure the host passes through the USB 
device (in its entirety) without trying to touch it and claim it as its 
own. Preferably without disabling the USB storage subsystem completely 
on the host.

Any ideas? Is there a best practice for such things in the Libvirt 
world? Or any other world? 

Thanks!

Andreas
-- 
Andreas Ntaflos 

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On 05/28/2010 02:09 PM, Andreas Ntaflos wrote:
> Hello list, 
> 
> this may be off topic but it is closely related to my Libvirt adventures 
> so maybe you can help me.
> 
> I want to pass a USB device (a USB Huawei E620 modem) through to a KVM 
> guest. Pass-through in general works fine and the modem is visible in 
> the guest. However, the host still sees it and sometimes tries to access 
> it (such modems seem to also be USB storage devices). This naturally 
> leads to conflicts and I believe this crashed the guest very badly 
> yesterday.
> 
> So I am looking for a way to make sure the host passes through the USB 
> device (in its entirety) without trying to touch it and claim it as its 
> own. Preferably without disabling the USB storage subsystem completely 
> on the host.
> 
> Any ideas? Is there a best practice for such things in the Libvirt 
> world? Or any other world? 
> 
For PCI devices, libvirt automatically performs a device reset and some
other voodoo to make sure the host doesn't try to use the device. Maybe
there is something similar that libvirt can do for USB devices as well?
I'm not very knowledgable about that stuff so I can't say for certain.

- Cole