Re: [Xen-devel] Does XEN use TUN/TAP interface?

[Daniel Stodden <stodden@xxxxxxxxxx>]

On Sun, 2008-03-16 at 17:12 +0000, Daniel P. Berrange wrote:
> On Sun, Mar 16, 2008 at 05:50:19PM +0100, Daniel Stodden wrote:
> > On Sun, 2008-03-16 at 15:52 +0100, Pavel Muller wrote:
> > > Hello,
> > > I want to ask if XEN use TUP/TAP interfaces or use other interface?
> > 
> > No. TUN/TAP is typically used for hosted VMs. Broadly speaking, it's
> > only useful if a significant part of the VMM is running in user mode on
> > top of a native Linux, as is the case with VMware Workstation,
> > VirtualBox, UserModeLinux etc.
> > 
> > Xen is a hypervisor, running below all OSes on bare hardware. The
> > network virtualization is based on a Linux OS (dom0), but the guests
> > aren't running on top of that, but rather as siblings on a common
> > virtualization layer.
> 
> Whether it is a separate hypervisor / Dom0, or a combined HV+Dom0 is not
> really relevant to this question. In both cases the driver backends are 
> in the Linux host OS and not the hypervisor itself.

Using TUN/TAP is absolutely pointless if the peer is not running in
userland. Because connecting userspace to a network interface is the
whole point there. 

And this is why the VMM type matters to answer the question.

> > There's a dedicated interface class (vifN.M) in dom0. The purpose is
> > similar, but the interplay with guests is quite a different one.
> 
> This is correct for paravirt guest or PV drivers, but is wrong for fullvirt. 
> The QEMU device model used for fullvirt guests *does* use TUN/TAP devices 
> as the backend for its emulated ne2k/rtl8139 NICs.

Oh, I did not think about HVM, you're right. But that is a special case
which is different from most other solutions out there.

regards,
daniel

-- 
Daniel Stodden
LRR     -      Lehrstuhl fÃr Rechnertechnik und Rechnerorganisation
Institut fÃr Informatik der TU MÃnchen             D-85748 Garching
http://www.lrr.in.tum.de/~stodden         mailto:stodden@xxxxxxxxxx
PGP Fingerprint: F5A4 1575 4C56 E26A 0B33  3D80 457E 82AE B0D8 735B



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel