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Re: [libvirt] [PATCH v3 21/26] qemu: Use PHBs to fill holes in PCI bus numbering

On Tue, 2017-06-27 at 11:59 -0400, Laine Stump wrote:
> > @@ -23,10 +23,9 @@
> >        <target index='1'/>
> >      </controller>
> >      <controller type='usb' index='0' model='none'/>
> > -    <controller type='pci' index='1' model='pci-bridge'>
> > -      <model name='pci-bridge'/>
> > -      <target chassisNr='1'/>
> > -      <address type='pci' domain='0x0000' bus='0x00' slot='0x01' function='0x0'/>
> > +    <controller type='pci' index='1' model='pci-root'>
> > +      <model name='spapr-pci-host-bridge'/>
> > +      <target index='2'/>
> Interesting - since we initially had one with controller index=2 that
> was automatically given target index=1, now that this PHB controller is
> being automatically added at index=1, it uses the next free target
> index, which is '2'. I assume that works correctly?

Yes. The test case was crafted specifically to show that
controller index and target index don't have to match.

> Although I think (in a separate patch) someone should eliminate all this
> cruft about filling in empty places in the bus numbering with unused
> controllers - it's pointless, and in the case of pci-bridge at least, I
> think it creates controllers that are unusable (because they have no io
> space allocated).

The only drawback I can think of at the moment is that it
might be confusing for the user to have controllers numbered
eg. 0, 42 and 1337, even though of course the guest OS would
not care at all.

Andrea Bolognani / Red Hat / Virtualization

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