Re: [Qemu-devel] [RFC PATCH 1/1] s390x/css: unresrict cssids

[Halil Pasic]

On 11/27/2017 01:56 PM, Cornelia Huck wrote:
> On Fri, 24 Nov 2017 17:39:04 +0100
> Halil Pasic <address@hidden> wrote:
> 
>> On 11/24/2017 05:15 PM, Cornelia Huck wrote:
>>>>> In theory this should work. 
>>>>>
>>>>> In reality it seems more complicated. A per-device property is easy and 
>>>>> can be
>>>>> inspected on the command line (e.g. -device virtio-blk-ccw,help), while a 
>>>>> new 
>>>>> machine property would require to change the qemu help output and 
>>>>> qemu-options 
>>>>> file (which makes it visible for all architectures).    
>>>> And then we have the fun of describing, that this property is weird, and 
>>>> can
>>>> not be set, and it's value does not matter.  
>>> Well, that's the case for both, no?  
>>
>>
>> I don't think we have to document _device_ properites in qemu-options.hx
>> I don't see any documented neither for virtio-ccw nor for vfio-ccw. The
>> machine properties, on the contrary, are documented in this file.
> 
> But not having to describe it does not make it any less weird.
> 

The user won't make big eyes should she read the documentation. The
weirdness isn't less but is less exposed.

>>>
>>> (Unless we simply make this a "default cssid" prop after all - then it
>>> would be more than just a simple indication for libvirt...)
>>>   
>>
>> We are now talking about the "cssid-unrestricted" property. The default
>> cssid is not something I would like to do any time soon.
> 
> What's so bad about this? As said above, I think it would be much more
> useful. If libvirt can detect r/o vs. r/w for properties, we can simply
> start out with a r/o variant now...
> 

I'm not sure I understand you. Are you proposing the following:
Drop the restriction, but don't indicate this via a read only
"cssid-unrestricted" device property but via a "default-css"
read only machine property.

Libvirt then should know that if "default-css" is present then
we don't have this virtual into 0xfe and non virtual into 0xfd
restriction any more.

Please confirm that I understood correctly or describe your
idea more verbosely.