[libvirt] [Question] About ivshmemory device and slot number confliction.

[Daniel P. Berrange]

On Tue, Jan 28, 2014 at 09:17:46AM +0000, Wangyufei (James) wrote:
> Hello,
> 
> I want to use ivshmemory device which is supported by qemu, but libvirt
> does not support it. 
> So I use qemu:commandline to make ivshmemory device in qemu command
> pass-through. 
> But then hot-plug a virtio-net device failed. 
> The reason is that a qemu:commandline pci device's slot number is
> assigned by qemu not libvirt.
> And hot-plug device's slot is assigned by libvirt.
> So it failed beacause of slot confliction.

Yes, that's pretty much expected behaviour if you use qemu:commandline
for adding more devices, since this is all invisible as far as libvirt
is concerned.

> I have two questions to ask:
> 1. Why libvirt does not support ivshmemory device? If libvirt intends
> to support it, when?

No one has ever done the work required to support it. We need two
things to handle it. First we need to be able to configure the
guest, but second we need to actually have a ivmshm daemon in the
host to support it. The existing ivmshm daemon was just a proof
of concept demo by the original developers and not something that
is intended for real world use. Their recommendation is that libvirt
provide a daemon for this role. We'd love to see someone work on
this....

> 2. Can libvirt handle with qemu:commandline pci device's slot
> number? Just like pci:commandline to assign a slot number. what's
> your opinion?

No, qemu:commandline is intended to be completely opaque to libvirt.
We don't want to get into the business of parsing command line strings
to guess PCI slot numbers. The right solution is to propperly support
ivmshm.

Daniel
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