Re: [Qemu-devel] Managing architectural restrictions with -device and libvirt

["Daniel P. Berrange" <berrange@redhat.com>]

On Tue, Jul 04, 2017 at 07:25:41PM +0100, Mark Cave-Ayland wrote:
> Hi all,
> 
> I've been working on a patchset that brings the sun4u machine on
> qemu-system-sparc64 much closer to a real Ultra 5, however due to
> various design restrictions I need to be able to restrict how devices
> are added to the machine with -device.
> 
> On a real Ultra 5, the root PCI bus (sabre) has 2 PCI bridges (simba A
> and simba B) with the onboard devices attached to simba A with 2 free
> slots, and an initially empty simba B.
> 
> Firstly, is it possible to restrict the machine so that devices cannot
> be directly plugged into the root PCI bus, but only behind one of the
> PCI bridges? There is also an additional restriction in that slot 0
> behind simba A must be left empty to ensure that the ebus (containing
> the onboard devices) is the first device allocated.
> 
> Secondly, how does libvirt handle these type of restrictions? Is it able
> to get the information from QEMU or is there some kind of libvirt
> profile that needs to be updated? And do newer versions of libvirt have
> the ability to attach devices behind PCI bridges using a GUI such as
> virt-manager, or is that only something that can only be done by
> directly editing the domain XML?

Libvirt has a bunch of code that provides different logic for various
machine types when doing addressing & setting up default PCI controllers.
Libvirt support for sparc machine types almost certainly broken since
I'm not aware of anyone having looked at it forever. Probably best to
re-ask your Q's on the libvir-list to get info from the people familiar
with this, since I'm fuzzy on precise details of what you'd need todo.


Regards,
Daniel
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