Re: [Qemu-devel] [PATCH v4 04/14] pc: prepare for multi stage hotplug handlers

[David Hildenbrand]

On 08.06.2018 14:55, Michael S. Tsirkin wrote:
> On Fri, Jun 08, 2018 at 02:32:09PM +0200, David Hildenbrand wrote:
>>
>>>>> if (TYPE_PC_DIMM) {
>>>>>     pc_dimm_plug()
>>>>>     /* do here additional concrete machine specific things */
>>>>> } else if (TYPE_VIRTIO_MEM) {
>>>>>     virtio_mem_plug() <- do forwarding in there
>>>>>     /* and do here additional concrete machine specific things */
>>>>> } else if (TYPE_CPU) {
>>>>>     cpu_plug()
>>>>>     /* do here additional concrete machine specific things */
>>>>> }  
>>>>
>>>> That will result in a lot of duplicate code - for every machine we
>>>> support (dimm/virtio-mem/virtio-pmem/*add more memory devices here*) -
>>>> virtio-mem and virtio-pmem could most probably share the code.
>>> maybe or maybe not, depending on if pmem endups as memory device or
>>> separate controller. And even with duplication, machine code would
>>> be easy to follow just down one explicit call chain.
>>
>> Not 100% convinced but I am now going into that direction.
> 
> Can this go into DeviceClass? Failover has the same need to
> allocate/free resources for vfio without a full realize/unrealize.
> 

Conceptually, I would have called here something like

virtio_mem_plug() ...

Which would end up calling memory_device_plug() and triggering the
target hotplug handler.

I assume this can also be done from a device class callback.

So we would need a total of 3 callbacks for

a) pre_plug
b) plug
c) unplug

In addition, unplug requests might be necessary, so

d) unplug_request

>> -- 
>>
>> Thanks,
>>
>> David / dhildenb


-- 

Thanks,

David / dhildenb