[libvirt] [PATCH] libvirt: xen: do not use ioemu type for any emulated NIC

[Philipp Hahn]

Hello Stefan,

On Wednesday 21 March 2012 09:24:04 Stefan Bader wrote:
> Unfortunately not true. You always get the enulated NIC, whatever you do
> with type=ioemu.
...
> From what I see (and at least from Xen side expect) is that you always get
> both. Whether you use default or a specific NIC type. The only way for your
> guest not to get an emulated device is to disable the pci-platform device
> in the config.
> Otherwise the Xen approach is to always present both and let the guest
> decide whether it is capable of using the pv devices (which are faster).
> Then the guest unplugs the emulated devices so there is no confusion. The
> goal there is to have one configuration on the hosting side which allows
> the guest to switch as it is capable.
>
> So currently with the default setting for the NIC, you get the implicit
> model or rtl8139 and the paravirt NIC. Newer Linux guests will, if they
> think they can handle paravirt devices, unplug the emulated interfaces
> (NICs and disks). I would expect a similar behavior from the Windows
> drivers. So with the default, there should be no need to change the model.
>
> However with the current libvirt, when you do select something like e1000,
> then the Xen configuration gets a type=ioemu added. But that does _not_
> prevent the paravirt interface to be present, its "just" unusable because
> it does not have a MAC address.

Yes, you're correct. Now that you mention the MAC adress, I remember seeing 
the netfront device with an all-zero-MAC-adress. I started writing the 
attached email some time ago, but never sent it because the libvirt behaviour 
was understandable and consistent: "If you specify a model, you only what 
that model (and not the netfront as well)".
That this behaviour makes switching from emulated to PV more complicates, is a 
different matter. I would appreciate a change in that behaviour as well, so 
+1 for your work.

Sincerely
Philipp
-- 
Philipp Hahn           Open Source Software Engineer      hahn at univention.de
Univention GmbH        be open.                       fon: +49 421 22 232- 0
Mary-Somerville-Str.1  D-28359 Bremen                 fax: +49 421 22 232-99
                                                   http://www.univention.de/
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Subject: FYI Xen-4.1.2+libvirt-0-8-7: type=ioemu and PV on HVM guests
Date: Thu, 22 Dec 2011 10:34:22 +0100
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