[PATCH v4 14/16] qapi: deprecate "device" field of DEVICE_* events

Vladimir Sementsov-Ogievskiy vsementsov at yandex-team.ru
Tue Feb 14 13:51:14 UTC 2023


On 14.02.23 14:57, Markus Armbruster wrote:
> Daniel P. Berrangé <berrange at redhat.com> writes:
> 
>> On Tue, Feb 14, 2023 at 09:54:22AM +0100, Markus Armbruster wrote:
>>> Daniel P. Berrangé <berrange at redhat.com> writes:
>>>
>>>> On Mon, Feb 13, 2023 at 05:01:01PM +0300, Vladimir Sementsov-Ogievskiy wrote:
>>>>> The device field is redundant, because QOM path always include device
>>>>> ID when this ID exist.
>>>>
>>>> The flipside to that view is that applications configuring QEMU are
>>>> specifying the device ID for -device (CLI) / device_add (QMP) and
>>>> not the QOM path. IOW, the device ID is the more interesting field
>>>> than QOM path, so feels like the wrong one to be dropping.
>>>
>>> QOM path is a reliable way to identify a device.  Device ID isn't:
>>> devices need not have one.  Therefore, dropping the QOM path would be
>>> wrong.
>>>
>>>> Is there any real benefit to dropping this ?
>>>
>>> The device ID is a trap for the unwary: relying on it is fine until you
>>> run into a scenario where you have to deal with devices lacking IDs.
>>
>> When a mgmt app is configuring QEMU though, it does it exclusively
>> with device ID values. If I add a device "-device foo,id=dev0",
>> and then later hot-unplug it "device_del dev0", it is pretty
>> reasonable to then expect that the DEVICE_DELETED even will then
>> include the ID value the app has been using elsewhere.
> 
> The management application would be well advised to use QOM paths with
> device_del, because only that works even for devices created by default
> (which have no ID), and devices the user created behind the management
> application's back.
> 
>> If the mgmt app is using IDs everywhere when dealing with a device,
>> then trap effectively doesn't exist for their usage scenario.
> 

What if we go one step further and deprecate "id" in device_add / device_del as well?

So that user will have to use qom path also in device_add. We may return an error if user don't specify "machine/peripheral/" prefix.. Or allow to create device with any QOM path?

-- 
Best regards,
Vladimir



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