Re: [PATCH 00/18] qapi/qom: QAPIfy object-add

[Paolo Bonzini]

On 30/11/20 13:25, Kevin Wolf wrote:
> This series adds a QAPI type for the properties of all user creatable
> QOM types and finally makes QMP object-add use the new ObjectOptions
> union so that QAPI introspection can be used for user creatable objects.
>
> After this series, there is least one obvious next step that needs to be
> done: Change HMP and all of the command line parser to use
> ObjectOptions, too, so that the QAPI schema is consistently enforced in
> all external interfaces. I am planning to send another series to address
> this.
>
> In a third step, we can try to start deduplicating and integrating things
> better between QAPI and the QOM implementation, e.g. by generating parts
> of the QOM boilerplate from the QAPI schema.

With this series it's basically pointless to have QOM properties at all. 
 Instead, you are basically having half of QEMU's backend data model 
into a single struct.

So the question is, are we okay with shoveling half of QEMU's backend 
data model into a single struct?  If so, there are important consequences.

1) QOM basically does not need properties anymore except for devices and 
machines (accelerators could be converted to QAPI as well). All 
user-creatable objects can be changed to something like chardev's "get a 
struct and use it fill in the fields", and only leave properties to 
devices and machines.

2) User-creatable objects can have a much more flexible schema.  This 
means there's no reason to have block device creation as its own command 
and struct for example.

The problem with this series is that you are fine with deduplicating 
things as a third step, but you cannot be sure that such deduplication 
is possible at all.  So while I don't have any problems in principle 
with the ObjectOptions concept, I don't think it should be committed 
without a clear idea of how to do the third step.

In the meanwhile, of course I have no problem with deprecating the 
opened and loaded properties.

Paolo