Re: sysbus_create_simple Vs qdev_create

[Markus Armbruster <armbru@redhat.com>]

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 28/07/20 09:19, Markus Armbruster wrote:
>>> the composition tree generally mirrors things that are born and die
>>> at the same time, and creating children is generally reserved to the
>>> object itself.
>>
>> Yes.  Notable exceptions: containers /machine/peripheral,
>> /machine/peripheral-anon, /machine/unattached.
>
> And /objects too.  Apart from /machine/unattached, all these dynamic
> objects are created by the monitor or the command line.
>
>>>                 Children are usually embedded directly in a struct, for
>>> example.
>> 
>> We sometimes use object_new() + object_property_add_child() instead.
>> Extra indirection.  I guess we'd be better off without the extra
>> indirection most of the time.  Implementation detail.
>> 
>> We sometimes use object_new() without object_property_add_child(), and
>> have qdev_realize() put the device in the /machine/unattached orphanage.
>> Meh.  I guess the orphanage feature exists to make conversion to QOM
>> slightly easier.  Could we ban its use for new boards at least?
>
> Banning perhaps is too strong, but yes /machine/unattached is an
> anti-pattern.

A ban backed by an automated test will be effective.  Writing "but don't
do that" on the list not so much.

The automated test could have a list of exceptions.  Adding a new
instance of the anti-pattern then isn't impossible (you can update the
list of exceptions), but clearly visible to patch submitter and
reviewers.

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