Re: [PATCH RFC 00/17] monitor: turn QMP and HMP into QOM objects

[Markus Armbruster <armbru@redhat.com>]

Daniel P. Berrangé <berrange@redhat.com> writes:

> Conceptually -object and object_add/object_del should be sufficient
> for essentially all QEMU configuration....if only we ported all our
> internal custom backends/devices/etc to QOM. That is of course a big
> job which is why it hasn't happened.

In addition, we'd need a more unified object life cycle.  See "Problem
5: QOM lacks a clear life cycle" in

    Subject: Dynamic & heterogeneous machines, initial configuration: problems
    Date: Wed, 31 Jan 2024 21:14:21 +0100
    Message-ID: <87o7d1i7ky.fsf@pond.sub.org>
    https://lore.kernel.org/qemu-devel/87o7d1i7ky.fsf@pond.sub.org/

> This series started with the premise that the monitor is one of the
> easier areas to convert since we have no more than three classes,
> a common base, and QMP and HMP subclasses. So why not give it a go
> and thus unlock the ability to dynamically create/delete monitors
> in QMP/HMP.

Makes sense.

> This series does the conversion in as many small steps as I could
> achieve. At the end it is possible to create HMP and QMP monitors
> with -object and object_add.

I'll try to squeeze in review.

> In theory object_del is possible but is unsafe since there's no
> synchronization wrt "in use" monitors. Christian Brauner sent
> a proposal for monitor_add/monitor_del commands that address the
> safety/synchronization issues, but I've not yet integrated the
> relevent bits of that series with this proposal:
>
>   https://lists.nongnu.org/archive/html/qemu-devel/2026-04/msg01349.html
>
> My overall feeling is that we're better off turning monitors
> into QOM classes, rather than inventing more type specific
> QMP commands.

I agree!

> What's missing:
>
>  - Integration of code for safe deletion of monitors
>  - The existing -mon/-qmp/-monitor args should be turned
>    into syntax sugar around -object & -chardev

Yes.  A step we sometimes neglect.

>  - The new approach must be documented
>  - Functional tests are needed for the hot add/remove of
>    monitors and new -object syntax. (The pre-existing
>    test suites cover the static config with the traditional
>    args).