[PATCH 1/2] qemu: Add some cpu hotpluggable inforamtion in vm xml when run "virsh setvcpus vm --count <current> --live".

[Peter Krempa]

On Thu, Apr 09, 2020 at 20:38:47 +0800, Jidong Xia wrote:
> From: xiajidong <xiajidong at cmss.chinamobile.com>
> 
> The optional cpu attribute current can be used to specify whether
> fewer than the maximum number of virtual CPUs should be enabled.
> when run "virsh setvcpus vm --count <current> --live", it can
> display cpu hotpluggable information when run "virsh dumpxml vm
> | grep vcpu". so we can know the value of enabled and hotpluggable
> attributes of the current vcpus.
> 
> Signed-off-by: Jidong Xia <xiajidong at cmss.chinamobile.com>
> ---
>  src/qemu/qemu_hotplug.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/src/qemu/qemu_hotplug.c b/src/qemu/qemu_hotplug.c
> index 14654a1..c574f63 100644
> --- a/src/qemu/qemu_hotplug.c
> +++ b/src/qemu/qemu_hotplug.c
> @@ -6168,6 +6168,10 @@ qemuDomainSelectHotplugVcpuEntities(virDomainDefPtr def,
>      } else {
>          *enable = false;
> 
> +        if (nvcpus == curvcpus) {
> +            def->individualvcpus = true;
> +        }

The 'individualvcpus' flag here is deliberately not asserted in this API
so that if only old/legacy vcpu hotplug APIs are used
(qemuDomainSetVcpusFlags, note the plural Vcpus) we don't change the
behaviour or XML. 

With new APIs used (qemuDomainSetVcpu, virsh setvcpu - note singular
vcpu) the flag is asserted always and the output now displays
everything.

The commit message plainly states the facts when the extended cpu state
is displayed, but does not justify why you want to change it, so please
add a justification.

Additionally if you justify the change enough, the correct fix will be
to remove individualvcpus completely from 'def' and always display the
information in the XML rather than adding these hacks.