Re: [Xen-devel] USB (virtualiation?) in PV and HVM

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> Another question and another pardon for getting your valuable development
> time.
>
> I want to assign specific USB ports to Specific DomU's in my Xen
> Setup. Am I able to do it in:
> - HVM domains (i.e. Windows)?

This sort-of works; there is a syntax for controlling USB passthrough to HVM 
domUs in the config file format.  However, I'm not sure anybody uses this; 
the one or two reports I've recently seen reported significant problems with 
this mode of operation.

You could test how it works for you, but please treat it with caution.  I'm 
not sure it's "officially" supported as a working configuration at all.

> - in PV domains (i.e. linux running a xen domu kernel)?

This is not supported at the moment; there were patches for paravirtualised 
USB available at one stage but they certainly wouldn't work on modern Xen 
releases without some modification.  There's no officially sanctioned way of 
doing this either, unfortunately.

> So that I can share my 8 USB ports to different domains.
>
> Is there any documentation? I checked xensource, mail lists etc. but
> maybe didn't search the right way and couldn't find anything to put
> inside the domain configuration files to enable this function.
>
> I remember seeing somewhere (maybe mailing lists) about this
> functionality and config like:
> usb:x:y:z:t
> to assign to a specific domain, but can't find it anymore...

This was probably a description of them PV USB interface, but that's not 
available anymore (IIRC it was included in Linux 2.4 on Xen 2.x releases - 
but that's ancient history now and not maintained.  In any case, it wasn't 
widely tested then so I wouldn't recommend trying it now other than to play 
around with.).

> I also 
> remember that it will be even possible to assign "specific devices" to
> specific domains regardless of the port (but this i don't need for the
> moment).

That sounds like something I might have said - was it me who made the post you 
were looking at?  Indeed this is something that shouldn't be too hard to 
implement given basic USB passthrough functionality; unfortunately we still 
don't have a stable and supported way of doing that.

Sorry to disappoint you.

You *could* pass through things like USB mass storage devices to PV and HVM 
guests using the standard blockfront/blockback driver, but USB hotplug will 
not work in a particularly sane way with this.  I'd recommend unmounting and 
removing the virtual block device corresponding to the USB device completely 
from all domains using it before removing it from the dom0 system.

Hope that helps you somewhat,
Cheers,
Mark

> Thanks alot beforehand for any link to a document to read,
>
> Best regards,
>
> Emre
>
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-- 
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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