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


On Friday 16 March 2012 11:34:37 Stefan Bader wrote:
> When using the xm/xend stack to manage instances there is a bug that causes
> the emulated interfaces to be unusable when the vif config contains
> type=ioemu.

I had a look at a similar problem some time ago, so some gereral comments:

Xens point of view:
If you specify model=XXX in Xen, you get that emulated NIC and also a second 
Xen-PV netfront interface as well.
When you specify type=ioemu, you only get the emulated NIC, netfront is 

libvirts point of view:
If you explicitly specify a model for the interface, you get exactly that 
model without the Xen-PV-companion interface, that is type=ioemu is added.
Without an explicit model, you get the default rtl8139 and netfront.

The problem with modern Linux kernels is, that unless you 
specify "xen_emul_unplug=never" on the Kernel command line, the kernel 
detects that you're running on Xen and disabled the emulated NIC leaving you 
without any network.

So currently with libvirt you can't specify the type of the emulated NIC (for 
example to get a more modern e1000) and also get the Xen-PV-interface as 
well. If I remeber corrently that forces you to change the NIC model when 
installing the Windows GPLPV drivers, 

I hope that little bit is helpful to others, since it cost my some time to 
find that out myself the hard way. Corrections are appreciated.

Philipp Hahn           Open Source Software Engineer      hahn 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

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