Re: [Qemu-devel] [PATCH 1/1] s390x: create a compat s390 phb for <=2.10

[David Hildenbrand]

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 <address@hidden> wrote:
>>
>>> 在 2017/9/27 下午5:47, Cornelia Huck 写道:
>>>> On Tue, 26 Sep 2017 20:40:25 +0200
>>>> David Hildenbrand <address@hidden> 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?

-- 

Thanks,

David