Re: [Xen-devel] Virtualization project idea

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Fri, Aug 27, 2010 at 03:17:39PM +0200, Michal Novotny wrote:
> On 08/27/2010 03:08 PM, Pasi Kärkkäinen wrote:
>> On Fri, Aug 27, 2010 at 06:33:35PM +0530, Dhananjay Goel wrote:
>>    
>>>     Yes, exactly. So, we wanted to know if it is possible to *share USB*
>>>     across VMs.
>>>
>>>      
>> I don't think USB protocol has been designed for *sharing*.
>> I'm pretty certain only one computer/device/VM can use USB device at a time.
>>
>> -- Pasi
>>
>>    
>
> Pasi, I agree. I think the think here is that Dhananjay confused the USB  
> device sharing with the file system sharing. I guess the USB protocol  
> was not designed for sharing nevertheless sharing the filesystem on a  
> USB stick is a completely different think.
>
> Dhananajay, you need to plug in the USB stick onto one computer (and  
> it's impossible to plug it into multiple computer at one time, of  
> course) and then setup the sharing. Everybody here is talking about the  
> hardware abstraction and virtualization and what you wrote is a  
> completely different thing - it's software-related and this has nothing  
> to do with the hardware emulation/abstraction what-so-ever.
>
> Considering the NFS and all the sharing protocols there was something  
> why it doesn't corrupt the data. I'm no expert on this subject but I  
> think this is because they run in the server-client mode. All the  
> clients are talking to the server and the server itself is one computer  
> that's having the just one operating system working with this particular  
> device - no matter what the underlaying device is - it may be everything  
> - USB stick, IDE/SCSI/SAS drive or just a relay workstation to save all  
> the data into one remote media (e.g. for replication). What I mean is  
> that the basic thing is that it's running on only one operating system  
> (because of it's connected to this one machine *only*) so it takes care  
> of everything and it's aware of the write-cache and data operations  
> being done to this media.
>

Yep.

If you want to share files from the hypervisor-host (from USB stick or from 
actual disk)
to the VMs you *can* do it today over-the-network (nfs,cifs,webdav,ftp) using 
the standard
client-server tools that have been used for over 20 years.

If you don't want to do it over-the-network, but somehow 'through' the 
hypervisor,
then you'd need to build some kind of special filesystem protocol that is able
to do the client-server communication over the hypervisor specific paths 
(xenbus etc).
And have drivers for it in the hypervisor-host, and in the VMs.

-- Pasi


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