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Date: Thu, 4 May 2017 11:52:39 +0200
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Subject: Re: [Qemu-devel] [PATCH v2 23/24] numa: add '-numa cpu,
 ...' option for property based node mapping
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To: Eduardo Habkost <ehabkost@redhat.com>
Cc: Eric Blake <eblake@redhat.com>, qemu-devel@nongnu.org, Peter Maydell <peter.maydell@linaro.org>, Andrew Jones <drjones@redhat.com>, David Gibson <david@gibson.dropbear.id.au>, Paolo Bonzini <pbonzini@redhat.com>, Shannon Zhao <zhaoshenglong@huawei.com>, qemu-arm@nongnu.org, qemu-ppc@nongnu.org, Michael Roth <mdroth@linux.vnet.ibm.com>

On Wed, 3 May 2017 14:58:02 -0300
Eduardo Habkost <ehabkost@redhat.com> wrote:

> On Wed, May 03, 2017 at 02:38:41PM -0300, Eduardo Habkost wrote:
> > On Wed, May 03, 2017 at 11:39:10AM -0500, Eric Blake wrote:  
> > > On 05/03/2017 11:35 AM, Eduardo Habkost wrote:
> > >   
> > > >> +
> > > >> +        memset(&cpu, 0, sizeof(cpu));
> > > >> +        cpu.has_node_id = object->u.cpu.has_node_id;
> > > >> +        cpu.node_id = object->u.cpu.node_id;
> > > >> +        cpu.has_socket_id = object->u.cpu.has_socket_id;
> > > >> +        cpu.socket_id = object->u.cpu.socket_id;
> > > >> +        cpu.has_core_id = object->u.cpu.has_core_id;
> > > >> +        cpu.core_id = object->u.cpu.core_id;
> > > >> +        cpu.has_thread_id = object->u.cpu.has_thread_id;
> > > >> +        cpu.thread_id = object->u.cpu.thread_id;  
> > > > 
> > > > We don't have a way to avoid copying each field individually?
> > > > Some visitor trick, maybe?
> > > > 
> > > > Eric, Markus, Michael, do you have any suggestions?  
> > > 
> > > Markus just added QAPI_CLONE_MEMBERS(), which sounds like what you want:
> > > 
> > > https://lists.gnu.org/archive/html/qemu-devel/2017-04/msg04867.html  
> > 
> > Not sure if it would work in this case. Note that cpu and
> > object->u.cpu have different types. 'cpu' is CpuInstanceProps,
> > but object->u.cpu is NodeCpuOptions.
> > 
> > NodeCpuOptions has { 'base': 'CpuInstanceProps' }, and
> > CpuInstanceProps field declarations are duplicated in struct
> > NodeCpuOptions. Do you know why struct inheritance is implemented
> > by duplicating the fields of the base struct instead of embedding
> > the base struct?  
> 
> Nevermind, I just found out that QAPI generates a
> qapi_NumaCpuOptions_base() upcast helper. So this can be solved
> with no data copying at all:
> 
>  machine_set_cpu_numa_nodes(ms, qapi_NumaCpuOptions_base(&object->u.cpu), &err);
> 

Thanks for finding out, I'll try it this way