Re: [Qemu-devel] [PATCH v4 2/5] qmp: distinguish PC-DIMM and NVDIMM in MemoryDeviceInfoList

[Eric Blake]

On 03/07/2018 08:33 PM, Haozhong Zhang wrote:
> It may need to treat PC-DIMM and NVDIMM differently, e.g., when
> deciding the necessity of non-volatile flag bit in SRAT memory
> affinity structures.
>
> NVDIMMDeviceInfo, which inherits from PCDIMMDeviceInfo, is added to
> union type MemoryDeviceInfo to record information of NVDIMM devices.
> The NVDIMM-specific data is currently left empty and will be filled
> when necessary in the future.
>
> It also fixes "info memory-devices"/query-memory-devices which
> currently show nvdimm devices as dimm devices since
> object_dynamic_cast(obj, TYPE_PC_DIMM) happily cast nvdimm to
> TYPE_PC_DIMM which it's been inherited from.
>
> Signed-off-by: Haozhong Zhang <address@hidden>
> ---

> +++ b/qapi/misc.json
> @@ -2830,6 +2830,18 @@
>             }
>   }
>   
> +##
> +# @NVDIMMDeviceInfo:
> +#
> +# NVDIMMDevice state information
> +#
> +# Since: 2.12
> +##
> +{ 'struct': 'NVDIMMDeviceInfo',
> +  'base': 'PCDIMMDeviceInfo',
> +  'data': {}
> +}
> +

As long as you don't have any data members to add, you could omit this 
type...

>   ##
>   # @MemoryDeviceInfo:
>   #
> @@ -2837,7 +2849,11 @@
>   #
>   # Since: 2.1
>   ##
> -{ 'union': 'MemoryDeviceInfo', 'data': {'dimm': 'PCDIMMDeviceInfo'} }
> +{ 'union': 'MemoryDeviceInfo',
> +  'data': { 'dimm': 'PCDIMMDeviceInfo',
> +            'nvdimm': 'NVDIMMDeviceInfo'
> +          }

and just write this as

 'data': { 'dimm': 'PCDIMMDeviceInfo',
           'nvdimm': 'PCDIMMDeviceInfo' }

If, down the road, you want to add data members to one but not both of 
the branches, we can add a new (sub-)type at that time, and it won't 
break backwards compatibility.

--
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org