[Xen-devel] xen_emul_unplug on xen 4.1, HVM guest 2.6.38

[Alex Bligh <alex@xxxxxxxxxxx>]

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.

--
Alex Bligh

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