Re: xen_emul_unplug on xen 4.1, HVM guest 2.6.38

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

On Wed, Oct 26, 2011 at 02:17:25PM +0100, Alex Bligh wrote:
> I am running Xen 4 and want users to be able to install arbitrary HVM
> images. We want both PV and emulated drivers to appear. The reason
> for this is for compatibility with images that were prepared for
> Xen 3.3, which assume emulated devices exist at boot time (particularly
> for running the boot loader).
> 
> If I do not specify on the boot line xen_emul_unplug=never, then
> under some guest OS's (e.g. Ubuntu Natty (2.6.38)), the domU kernel
> unplugs the non-PV devices, which is undesirable in my application.
> 
> I cannot arbitrarily change the kernel command line because it is
> in effect set by the user's image.
> 
> Therefore what I need to do is prevent Xen4 offering the facility
> to unplug the devices in the first place. Setting "(unpluggable 0)"
> in the config for the emulated NICs and disks does not appear
> to prevent them getting unplugged; what may be happening is that
> domU tries to unplug them (but fails) but still doesn't use them.
> Is there a way to signal from dom0 that the kernel really shouldn't
> unplug this stuff.

xen_pci_platform=0 in your guest config should do it.