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

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

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.

> 
> 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.

Dan.
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