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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2011-12-01 at 15:09 +0000, 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.

Which toolstack are you using?

The weird thing is that, at least with xl, type=ioemu is the default for
an HVM guest.

What vif related entries do you get in xenstore, both front and backend?

Also what does your qemu-dm command line end up looking like?

> 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.

That is certainly the expectation.

> Is that something that can be seen with newer Xen versions, too (I am using 
> 4.1.1)?

I appear to have some other problem with xen-unstable at the moment.
I've never noticed a problem in that past, although I don't habitually
use type=XXX at all in my vif configuration.

Ian.

> -Stefan



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