Re: [PATCH v3 0/5] monitor: add dynamic QMP monitor hotplug support

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

On Tue, Apr 07, 2026 at 09:32:44AM +0200, Christian Brauner wrote:
> QEMU supports runtime hotplug for chardevs, devices, block backends,
> and netdevs. Monitors are the only major subsystem that lacks this --
> all QMP monitors must be configured at launch via -mon or -qmp CLI
> options.
> 
> This series adds monitor-add, monitor-remove, and query-monitors QMP
> commands so that management tools can create independent QMP sessions
> on demand at runtime.
> 
> I've implemented a QMP-to-Varlink bridge in systemd. This allows
> systemd-vmspawn to control virtual machines and containers through a
> unified Varlink interface. Varlink allows protocol upgrades. For
> example, it is possible to switch from Varlink to say http. I'm
> allowing Varlink clients to upgrade from the Varlink interface to the
> native QMP interface. Such clients get a new monitor assigned that
> allows them to manage the virtual machine directly via QMP. The main
> monitor remains unaffected and tied to the generic Varlink interface. We
> can't pre-allocate monitors as we have no control over how many protocol
> upgrades we actually get but it won't just be one. And having unused
> monitors around really isn't ideal either.
> 
> Having the ability to hotplug monitors would really be helpful. I'm not
> yet super well-versed in qemu internals so this might be done wrong but
> testing works so far.

Can you say if AI agents/LLMs were used in creating these patches ? 

> 
> My systemd patch that triggered this is at
> https://github.com/systemd/systemd/pull/41449.
> 
> The usage pattern mirrors chardev hotplug:
> 
>   -> chardev-add id=qmp-extra backend=socket,...
>   -> monitor-add id=extra-qmp chardev=qmp-extra
>   [client connects to socket, gets QMP greeting, negotiates, sends commands]
>   -> monitor-remove id=extra-qmp
>   -> chardev-remove id=qmp-extra

With regards,
Daniel
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