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Re: [Xen-devel] Virtualization project idea

To: Pasi Kärkkäinen <pasik@xxxxxx>
Subject: Re: [Xen-devel] Virtualization project idea
From: Michal Novotny <minovotn@xxxxxxxxxx>
Date: Fri, 27 Aug 2010 15:47:29 +0200
Cc: Dhananjay Goel <dhananjaygoel123@xxxxxxxxx>, James Harper <james.harper@xxxxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
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On 08/27/2010 03:30 PM, 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.


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 
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

Ok Pasi, I know what you mean. I was talking about physical machines since Dhananjay compared this to physical machines. I know sharing between VMs is possible using specific paths like the xenbus one.


Michal Novotny<minovotn@xxxxxxxxxx>, RHCE
Virtualization Team (xen userspace), Red Hat

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