Re: [Qemu-devel] [PATCH v8 6/7] s390x/cpu: Add error handling to cpu creation

[Bharata B Rao]

On Fri, Mar 04, 2016 at 12:07:28PM +0100, David Hildenbrand wrote:
> 
> > >      cpu_exec_init(cs, &err);
> > >      if (err != NULL) {
> > >          error_propagate(errp, err);
> > >          return;
> > >      }
> > > +    scc->next_cpu_id = cs->cpu_index + 1;  
> > 
> > It appears that scc->next_cpu_id (and hence cpu->id) is some sort of arch_id
> > for you. If it is just going to be monotonically increasing like 
> > cs->cpu_index,
> > couldn't you just use cs->cpu_index instead of introducing additional IDs ?
> > 
> > Note that cpu_exec_init(cs, &err) returns with the next available cpu_index
> > which can be compared against max_cpus directly.
> > 
> > Regards,
> > Bharata.
> 
> I don't think that we should mix the id setting and cpu_index for now.
> 
> We can't simply set cpu_index before the device is realized. That logic
> belongs to cpu_exec_init().

Yes, I see that, but apart from the following obvious uses of the id
property from realizefn, are there other uses ?

1 Checking against max_cpus
  cpu_index can be used for this.

2 Checking if cpu with such an id exists
  cpu_exec_init() would never return with an in-use index. Hence cpu_index
  can be used here too given that you don't define ->get_arch_id()

3 Checking if the id is the next expected one
  cpu_exec_init/cpu_exec_exit take care of deletion too, so I guess you will
  always have the next available id to be used in cpu_index.

Did I miss any other use other than these which makes it necessary to have
an explicit id property here ?

Regards,
Bharata.