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

[Cornelia Huck <cohuck@redhat.com>]

On Fri, 24 Nov 2017 16:30:24 +0100
Halil Pasic <pasic@linux.vnet.ibm.com> wrote:

> On 11/24/2017 03:58 PM, Christian Borntraeger wrote:
> > 
> > 
> > On 11/24/2017 02:27 PM, Cornelia Huck wrote:  
> >> On Fri, 24 Nov 2017 14:01:20 +0100
> >> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> >>  
> >>> I first liked the idea to have it as a property of the css, but 
> >>> this is all pretty unclear how to do right. I start to think that going with
> >>> Halils first patch (a property per virtio device) is going to be the most
> >>> simple solution without causing any harm. After all as of today we only want 
> >>> to have a way to tell libvirt that devices can be everywhere. Specifying the
> >>> default css might be something that we want to have in the future, but here
> >>> future might even mean never.  
> >>
> >> I still don't like the idea of a per-device property, but I agree that
> >> adding a css property would need too much discussion to get to a
> >> solution in the near future.
> >>
> >> Is there anything that speaks against a machine property, though? While
> >> not ideal, I like it better than the per-device one.  
> > 
> > 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?

(Unless we simply make this a "default cssid" prop after all - then it
would be more than just a simple indication for libvirt...)

> 
> BTW one can do -machine s390-ccw-virtio-2.11,help and get a list of properties,
> so the command line introspection would work similar.
> 
> I've already brought some other arguments against the machine property.
> Won't repeat them here.

I have not read them yet.

> 
> > Not sure if there are
> > easier ways to do it. (e.g. QOM-only things, but then we have no command line
> > way of doing it)
> > 
> >   
>  
> If we don't care about if it can be introspected on the command line my
> trait type approach is pretty minimal. But the least surprise is probably
> still the device property (IMHO).

I think it's the other way around.