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Date: Wed, 27 Sep 2017 12:56:06 +0200
From: Cornelia Huck <cohuck@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for
 <=2.10
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To: Yi Min Zhao <zyimin@linux.vnet.ibm.com>
Cc: David Hildenbrand <david@redhat.com>, qemu-devel@nongnu.org, borntraeger@de.ibm.com, agraf@suse.de, pasic@linux.vnet.ibm.com, jjherne@linux.vnet.ibm.com, dgilbert@redhat.com

On Wed, 27 Sep 2017 18:25:00 +0800
Yi Min Zhao <zyimin@linux.vnet.ibm.com> wrote:

> =E5=9C=A8 2017/9/27 =E4=B8=8B=E5=8D=885:47, Cornelia Huck =E5=86=99=E9=81=
=93:
> > On Tue, 26 Sep 2017 20:40:25 +0200
> > David Hildenbrand <david@redhat.com> wrote:

> >> I'd really really really (did I mention really?) favor something like a
> >> dummy device, because we could easily handle the !CONFIG_PCI case then.
> >>
> >> All these compat options and conditions will kill us someday... we're
> >> already patching around that whole stuff way too much.
> >>
> >> If we ever unconditionally created a device, we should keep doing so. =
=20
> > Yes, that whole thing is horrible, especially interaction with compat
> > machines.
> >
> > Do you have an idea on how to create such a dummy device (without
> > having to effectively copy a lot of configured-out code)?
> >
> > =20
> How about in s390_pcihost_hot_plug() we check s390_has_feat(zpci)?
> If no zpci feature, we avoid plugging any pci device.
> Then we could always create phb.
> I think pcibus's vmstate is only data to migrate.

That's still problematic if CONFIG_PCI is off. I currently don't have a
better idea than either disallowing compat machines on builds without
pci, or using a dummy device...