Re: [Qemu-ppc] [PATCH] spapr: Correctly set query_hotpluggable_cpus hook based on machine version

[Bharata B Rao]

On Fri, Aug 05, 2016 at 05:50:29PM +1000, David Gibson wrote:
> Prior to c8721d3 "spapr: Error out when CPU hotplug is attempted on older
> pseries machines", attempting to use query-hotpluggable-cpus on pseries-2.6
> and earlier machine types would SEGV.
> 
> That change fixed that, but due to some unexpected interactions in init
> order and a brown-paper-bag worthy failure to test, it accidentally
> disabled query-hotpluggable-cpus for all pseries machine types, including
> the current one which should allow it.
> 
> In fact, query_hotpluggable_cpus needs to be non-NULL when and only when
> the dr_cpu_enabled flag in sPAPRMachineClass is set, which makes
> dr_cpu_enabled itself redundant.
> 
> This patch removes dr_cpu_enabled, instead directly setting
> query_hotpluggable_cpus from the machine class_init functions, and using
> that to determine the availability of CPU hotplug when necessary.

dr_cpu_enabled actually determines if CPU hotplug feature is present
or not. It also controls the creation of DRC-specific properties
in /cpus DT node like ibm,drc-indexes etc

query_hotpluggable_cpus just tells us if the machine supports the
querying of hotpluggable CPUS. query_hotpluggable_cpus definitely
implies dr_cpu_enabled but dr_cpu_enabled can exist on its own
(theoretically at the least) without query_hotpluggable_cpus.

So I think we should not replace dr_cpu_enabled with query_hotpluggable_cpus.

However, I tested this patch and it works as intended.

Regards,
Bharata.