[Qemu-devel] What's our ABI promise for externally visible QOM?

[Markus Armbruster <armbru@redhat.com>]

QOM types and the QOM graph are externally visible:

* qom-list-types returns QOM type names and parents.

  Fine print: the result is limited to concrete types by default.
  Aside: that's the only way to figure out whether a type is abstract.
  Interface design fail.  The result can optionally be limited to
  sub-types of a certain type.

* qom-list-properties returns a named type's static properties.

* qom-list returns an object's properties.  This lets clients traverse
  the QOM graph.

* qom-get returns a property's value.

* qom-set changes a property's value.

* -object and object-add create a QOM object of a certain type with
  certain property values.  The type must be a sub-type of
  "user-creatable".

* Types are identified by name.

* Objects and properties are identified by QOM path.  An absolute QOM
  paths is the path within the composition tree starting at the root.
  Partial paths are a convenience you don't want to understand.

What promises do we make regarding the stability  / backward
compatibility of these externally visible entities?

The QMP command documentation is silent on it.  A user could reasonably
assume that the general QMP stability promise extends to all of QOM.
Does it?

Was that the intent when we created qom-list, qom-set, qom-get?
Andreas, do you remember?

Is it practical given the current state of affairs?

Is it a good idea?