Re: [Qemu-devel] [PATCH RFC 0/2] s390x: cut down on unattached devices

[Cornelia Huck <cohuck@redhat.com>]

On Mon, 4 Dec 2017 15:47:37 +0100
Halil Pasic <pasic@linux.vnet.ibm.com> wrote:

> On 12/04/2017 10:22 AM, Cornelia Huck wrote:
> > On Fri, 1 Dec 2017 15:41:21 +0100
> > Halil Pasic <pasic@linux.vnet.ibm.com> wrote:
> >   
> >> On 11/28/2017 04:21 PM, Halil Pasic wrote:
> >> [..]  
> >>>>> Otherwise at first glance both patches seem sane.    
> >>>>
> >>>> Can I count this as an ack, or do you plan to do more review?
> >>>>    
> >>>
> >>> Yes I was planning to give it another look. And I do already
> >>> have questions. Isn't the QOM composition tree API? I mean
> >>> let's assume the QMP commands working on this tree are not completely
> >>> useless. How is client code (management software) supposed to work,
> >>> assumed it can rely on paths of e.g. properties being stable. Just
> >>> imagine we had this default-cssid property (for the sake of the
> >>> argument, not like we want it) on the css bridge.    
> >>
> >> Ping! I would like to get this clarified before proceeding with reviewing
> >> this series.  
> > 
> > [It might be helpful to not drop cc:s.]
> >   
> 
> Sorry. Wrong button.
> 
> > I don't think we really want a static tree. As long as the devices are
> > locateable, it should be fine.
> >   
> 
> What do you mean by locateable in particular?
> 
> Let's say I'm management software guy who want's to access a certain
> property of a certain device. For that I'm supposed to use qom-get. Now
> qom-get takes a path as input argument (absolute or relative). The question
> is, how I'm supposed to figure out this path as management software developer?
> In other words what is the algorithm?

I'd expect qom-tree to put out a path to the right object.

No idea if/how much management software relies on this. But hardcoded
paths sound fragile to me.

> 
> One naive approach would be, to assume that the path is stable between
> releases. So I have to figure it out when I'm implementing the stuff,
> and then it keeps working ever after. I read your answer as this naive
> approach is wrong.
> 
> (BTW I find static also confusing in this context.)
> 
> [..]
>