On Tue, Jun 23, 2026 at 03:54:54PM +0400, Marc-André Lureau wrote:
Hi
On Tue, Jun 23, 2026 at 3:53 PM Daniel P. Berrangé <berrange@redhat.com> wrote:
On Tue, Jun 23, 2026 at 12:38:10PM +0100, Daniel P. Berrangé wrote:
On Tue, Jun 23, 2026 at 01:03:46PM +0200, Peter Krempa wrote:
On Tue, Jun 23, 2026 at 10:55:16 +0100, Daniel P. Berrangé via Devel wrote:
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.
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[1]. So why not give it a go and thus unlock the ability to dynamically create/delete monitors in QMP/HMP.
This series does the conversion in a great many small steps to better understand the implications at each stage.
The high level outcome of this series is
* HMP and QMP monitors are QOM objects, 'monitor-hmp' and 'monitor-qmp' respectively
* Both can be cold plugged and hot plugged. QMP only, can also be hot unplugged.
* '-mon' is obsolete, deprecated and replaced by '-object', but -monitor, -qmp and kept as high level syntax sugar
I was giving this a spin by implementing libvirt support for it. The basic usage seems to work well but I've encoutered a regression in behaviour which happens both when the QMP monitor is instantiated using the new syntax but also the old one ( -mon chardev=charmonitor,id=monitor,mode=control)
When libvirt wants to re-connect to a qemu running with these patches it re-issues a 'qmp_capabilities' command after connecting.
With these patches qemu does not respond to that command even when the old syntax is used. This makes libvirt stuck when re-connecting to VMs.
Oh that's odd, thanks for the warning. I'll investigate this.
/face-palm - a misplaced a line in the auto-delete code, and did not have test coverage of re-opening a monitor. Try testing libvirt with this additional change on top
diff --git a/monitor/qmp.c b/monitor/qmp.c index f6b7fe65bb..10d651ca5c 100644 --- a/monitor/qmp.c +++ b/monitor/qmp.c @@ -613,7 +613,6 @@ static void monitor_qmp_event(void *opaque, QEMUChrEvent event) qobject_unref(data); break; case CHR_EVENT_CLOSED: - mon->delete_pending = true; /* * Note: this is only useful when the output of the chardev * backend is still open. For example, when the backend is @@ -629,6 +628,7 @@ static void monitor_qmp_event(void *opaque, QEMUChrEvent event) case MONITOR_QMP_CLOSE_ACTION_NONE: break; /* nada */ case MONITOR_QMP_CLOSE_ACTION_DELETE: + mon->delete_pending = true; /* * Do NOT run in the AIO context associated with the * monitor. We need to run in the default AIO context
Good, I just asked the same in my review :)
btw, you didn't collect my r-b from v3.
Oh sorry, I will get those. With regards, Daniel -- |: https://berrange.com ~~ https://hachyderm.io/@berrange :| |: https://libvirt.org ~~ https://entangle-photo.org :| |: https://pixelfed.art/berrange ~~ https://fstop138.berrange.com :|