Re: [Qemu-devel] [PATCH RFC] qdev: Let the hotplug_unplug() caller delete the device

[David Hildenbrand <david@redhat.com>]

On 04.12.18 14:33, Igor Mammedov wrote:
> On Wed, 28 Nov 2018 15:54:55 +0100
> David Hildenbrand <david@redhat.com> wrote:
> 
>> When unplugging a device, at one point the device will be destroyed
>> via object_unparent(). This will, one the one hand, unrealize the
>> device hierarchy to be removed, and on the other hand, destroy/free the
>> device hierarchy.
>>
>> When chaining interrupt handlers, we want to overwrite a bus hotplug
>> handler by the machine hotplug handler, to be able to perform
>> some part of the plug/unplug and to forward the calls to the bus hotplug
>> handler.
>>
>> For now, the bus hotplug handler would trigger an object_unparent(), not
>> allowing us to perform some unplug action on a device after we forwarded
>> the call to the bus hotplug handler. The device would be gone at that
>> point.
>>
>> hotplug_handler_unplug(dev) -> calls machine_unplug_handler()
>>     machine_unplug_handler(dev) {
>>         /* eventually do unplug stuff */
>>         bus_unplug_handler(dev) -> calls object_unparent(dev)
>>         /* dev is gone, we can't do more unplug stuff */
>>     }
>>
>> So move the object_unparent() to the original caller of the unplug. For
>> now, keep the unrealize() at the original places of the
>> object_unparent().
>>
>> hotplug_handler_unplug(dev) -> calls machine_unplug_handler()
>>     machine_unplug_handler(dev) {
>>         /* eventually do unplug stuff */
>>         bus_unplug_handler(dev) -> calls unrealize(dev)
>>         /* we can do more unplug stuff but device already unrealized */
>>     }
>> object_unparent(dev)
>>
>> In the long run, every unplug action should be factored out of the
>> unrealize() function into the unplug handler (especially for PCI). Then
>> we can get rid of the additonal unrealize() calls and object_unparent()
>> will properly unrealize the device hierarchy after the device has been
>> unplugged.
>>
>> hotplug_handler_unplug(dev) -> calls machine_unplug_handler()
>>     machine_unplug_handler(dev) {
>>         /* eventually do unplug stuff */
>>         bus_unplug_handler(dev) -> only unplugs, does not unrealize
>>         /* we can do more unplug stuff */
>>     }
>> object_unparent(dev) -> will unrealize
>>
>>
>> The original approach was suggested by Igor Mammedov for the PCI
>> part, but I extended it to all hotplug handlers. I consider this one
>> step into the right direction.
>>
>> Signed-off-by: David Hildenbrand <david@redhat.com>
> Sorry but I've lost track of all hotplug patches that where
> reviewed and pending form merge.
> Lets revisit this patch once those are merged to have a coherent
> view on how things stand.

At least from my side, there is only
 [PATCH v3 00/11] pci: hotplug handler reworks​

-- 

Thanks,

David / dhildenb