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

[Peter Maydell <peter.maydell@linaro.org>]

On Tue, 11 Jun 2024 at 06:50, Markus Armbruster <armbru@redhat.com> 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 already have a machine readable mandatory-for-every-device
representation of its entire state -- it's the vmstate struct.
Admittedly this is sometimes a bit different from the guest-facing
view of a device and we don't machine-record the field names...

-- PMM