Re: [Qemu-devel] [RFC 0/3] qmp: Return extra information on qom-list-types

[Markus Armbruster]

Eduardo Habkost <address@hidden> writes:

> This series adds 'abstract' and 'parent-types' fields to the
> output of qom-list-types.

Peeking at PATCH 3, it looks like 'parent-types' is the transitive
closure of the single direct parent type (TypeImpl member parent_type).
Do we need information on interfaces as well?

> For reference, below are the sizes of the output of
> "qom-list-types abstract=true" on qemu-system-x86_64, before and
> after applying the patches:
>
> * before: 11724 bytes
> * with 'abstract' field: 20119 bytes
> * with 'abstract' and 'parent-types': 44383 bytes

Obvious ways to save space:

* Make 'abstract' optional, default to false, present only when
  necessary (79 out of 456 times right now)

* Pare down 'parent-types' to *direct* parent types.  The indirect ones
  are redundant.

A less obvious way:

* 'parent-types' defines a relation with adjacency lists.  If the
  relation is tree-shaped, we can send the tree instead, i.e. a tree of
  device names rather than list of (device name, adjacency list).  New
  command unless we're willing to break qom-list-types.

> I'm not sure if extending qom-list-types with this info is the
> right way to go, or if we should keep qom-list-types as-is and
> add a new "query-qom-type" QMP command to query info on one QOM
> type at a time.

Might lead to more traffic rather than less.  Depends on what
information the client needs to query.