Re: [Xen-devel] Xen 4.x / Linux 3.x (dom0 and HVM domU) and NIC handling

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Thu, Dec 01, 2011 at 04:09:38PM +0100, Stefan Bader wrote:
> Moving to public discussion...
> 
> This was found with Xen hypervisor version supporting device unplugging and 
> the
> domU kernel having net-/blkfront and pci platform built-in (or as module).
> 
> The block device is defined as hda and the NIC type=ioemu (so theoretically
> guests without pv support would work, too).
> 
> Since both drivers are present, the kernel tries to unplug the emulated 
> devices
> and succeeds. The blkfront driver detects the xvda device available in 
> parallel
> and is working ok.
> 
> However the network interface does not work. There are entries present under
> sysfs for the xenbus but trying to bring it up fails with errors. And also 
> there
> seems to be no mac address set (all zeros in sysfs).
> When the type=ioemu is removed in the configuration, this works.
> 
> I have not much more debugging information beyond that, yet. But it sounds a 
> bit
> like NICs should behave the same as block devices. So if there is an emulated
> device defined there will be an alternate paravirt interface for it and after
> unplugging the emulated ones we end up with the pv ones.
> Is that something that can be seen with newer Xen versions, too (I am using 
> 4.1.1)?
> 

Hey,

Have you seen?: 
http://wiki.xen.org/xenwiki/XenLinuxPVonHVMdrivers

Especially the following note:
"NOTE! If you have "type=ioemu" specified for the "vif"-line, PVHVM drivers 
WILL NOT work! Don't specify "type" parameter for the vif. (with type=ioemu the 
pvhvm nic in the VM will have mac address full of zeroes - and thus won't 
work!)."

"type=ioemu" is not needed, at least with xm/xend toolstack both HVM and PVHVM 
guests work OK without it.

-- Pasi


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