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

From: Halil Pasic
Subject: Re: [Qemu-devel] [RFC PATCH 1/1] s390x/css: unresrict cssids
Date: Mon, 27 Nov 2017 14:11:57 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.4.0

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.

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