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Re: [Xen-devel] [RFC] libxl hotplug / unplug emulated devices

On Fri, May 20, 2016 at 05:45:53PM +0100, Andrew Cooper wrote:
> On 20/05/16 17:42, Wei Liu wrote:
> > On Fri, May 20, 2016 at 05:38:44PM +0100, Ian Jackson wrote:
> >> Wei Liu writes ("[RFC] libxl hotplug / unplug emulated devices"):
> >>> Recently I got a report on xen-users@ about xl network-attach not
> >>> working for HVM guest.
> >>>
> >>> I try to use
> >>>   xl network-attach jessie-hvm 'bridge=xenbr0'
> >>> and vif-bridge script complains that it can't add vifXX-emu to bridge.
> >>>
> >>> The underlying issue is that the vif spec provided defaults to
> >>> emulated nic, but libxl only populates a pv nic but doesn't call out
> >>> via QMP to QEMU to populate one. Note that this issue not only affects
> >>> nic device but essentially all device types.
> >> Is it really sensible to offer emulated nic hotplug ?  That'd be
> >> presented to the guest as pci hotplug, I guess ?
> > Suppose you have a Windows guest doesn't have PV driver? Or any other
> > OSes that have PCI drivers with hotplug support but not Xen drivers?
> On qemu-trad, none of the devices support hotplug, so the option
> shouldn't be available in xl.
> I believe qemu-upstream does offer hotplug devices, but it still has to
> create empty PCIe slots at boot time to hotplug into later, along with
> appropriate ACPI tables.

I don't think it requires that much setup TBH. I tried to issue two QMP
commands and a nic shows up in the guest. Admittedly I only played with
it to see if it actually works so I could be missing a lot of things.


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