Re: [Xen-devel] Virtualization project idea

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Fri, Aug 27, 2010 at 04:30:42PM +0300, Pasi Kärkkäinen wrote:
> 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.
> 

Oh, and as mentioned on irc, something like VirtFS 
(http://www.linuxplumbersconf.org/2010/ocw/proposals/603)
could be implemented over xenbus.. to make 'filesystem sharing', or 
'paravirtual filesystem' 
through the hypervisor.

-- Pasi


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