Re: Examining device state via monitor for debugging (was: [PATCH 0/2] hw/misc/mos6522: Do not open-code hmp_info_human_readable_text())

["Daniel P. Berrangé" <berrange@redhat.com>]

On Tue, Jun 11, 2024 at 07:49:12AM +0200, Markus Armbruster wrote:
> Philippe Mathieu-Daudé <philmd@linaro.org> writes:
> 
> > Officialise the QMP command, use the existing
> > hmp_info_human_readable_text() helper.
> 
> I'm not sure "officialise" is a word :)
> 
> Taking a step back...  "info via" and its new QMP counterpart
> x-query-mos6522-devices dump device state.  I understand why examining
> device state via monitor can be useful for debugging.  However, we have
> more than 2000 devices in the tree.  Clearly, we don't want 2000 device
> state queries.  Not even 100.  Could we have more generic means instead?
> 
> We could use QOM (read-only) properties to expose device state.
> 
> If we use one QOM property per "thing", examining device state becomes
> quite tedious.  Also, you'd have to stop the guest to get a consistent
> view, and adding lots of QOM properties bloats the code.
> 
> If we use a single, object-valued property for the entire state, we get
> to define the objects in QAPI.  Differently tedious, and bloats the
> generated code.
> 
> We could use a single string-valued property.  Too much of an abuse of
> QOM?

Yeah, I'd suggest we just keep it dumb and free form, adding a
callback like this to the QOM base class:

  HumanReadableText (*debug_state)(Error **errp);

With regards,
Daniel
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