On 09/27/2017 02:21 PM, David Hildenbrand wrote: > On 27.09.2017 12:59, Christian Borntraeger wrote: >> >> >> On 09/27/2017 12:56 PM, Cornelia Huck wrote: >>> On Wed, 27 Sep 2017 18:25:00 +0800 >>> Yi Min Zhao <zyi...@linux.vnet.ibm.com> wrote: >>> >>>> 在 2017/9/27 下午5:47, Cornelia Huck 写道: >>>>> On Tue, 26 Sep 2017 20:40:25 +0200 >>>>> David Hildenbrand <da...@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. >>>>> 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)? >>>>> >>>>> >>>> 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... >> >> For this particular case your initial patch might be less problematic than >> a dummy device, because the code that does the migration is NOT contained >> in s390 specific code but in common PCI code instead. We would need to keep >> the dummy device always in a way that it will work with the common PCI >> code. >> > > Interesting, so how is migration then handled for e.g. x86 or other > architectures that can work without CONFIG_PCI? I assume their migration > should also break?
If you migrate from a QEMU with CONFIG_PCI to a QEMU without CONFIG_PCI I assume it will break. But maybe there is really some clever way to do the right thing. PS: Is really anybody disabling CONFIG_PCI and why?
