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

[Bharata B Rao]

On Fri, Mar 04, 2016 at 05:01:29PM +0530, Bharata B Rao wrote:
> 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 ?

Oops, Sorry this is not device_add, but cpu-add that gets the id from the
user. So ignore the above :(

> 
> Regards,
> Bharata.