On Thu, Jun 18, 2026 at 03:54:32PM +0400, [email protected] wrote: > > The default monitor is usually a long lived object that will exist for > > the entire lifetime of the VM. A monitor can only service a single > > client at a time though, and so it might be desirable to hotplug > > additional monitors at runtime for specific tasks. If doing that, > > however, there is a need to remove the monitor when it is no longer > > needed. > > > > Allowing a client to run "object-del" against its own monitor adds > > complex edge cases, as it would be desirable to send the QMP response > > despite the monitor sending it being deleted. Doing "object-del" alone > > will also result in orphaning a character device backend instance, as > > there is no opportunity to run the companion "chardev-del" command. > > > > A simpler way to ensure cleanup is to add the concept of auto-deleting > > monitor objects. Specifically when the "CHR_EVENT_CLOSED" event is > > emitted, the equivalent of "object-del" + "chardev-del" can be run > > internally. Since the transient client has already droppped its > > monitor connection, there is no synchronization to be concerned about. > > > > This is implemented via a new "close-action=none|delete" property on > > the 'monitor-qmp' object. This concept could be extended with further > > actions in future, for example: > > > > * close-action=shutdown - graceful guest shutdown > > * close-action=terminate - immediate guest poweroff > > * close-action=stop - pause guest CPUs while the monitor is not > > connected to any client > > > > This is left as an exercise for future interested contributors. > > > > Signed-off-by: Daniel P. Berrangé <[email protected]> > > Message-ID: <[email protected]> > > > > diff --git a/qapi/qom.json b/qapi/qom.json > > index 6ed510858e1..63335b8fd09 100644 > > --- a/qapi/qom.json > > +++ b/qapi/qom.json > > @@ -1213,18 +1213,37 @@ > > 'base': 'MonitorProperties', > > 'data': { '*readline': 'bool' } } > > > > + > > +## > > +# @MonitorQMPCloseAction: > > +# > > +# Action to take when the character device backend is > > +# closed. > > +# > > +# @none: take no action (the default) > > +# @delete: delete both the 'monitor-qmp' object and its associated > > +# character device backend object > > +# > > +# Since 11.1 > > +## > > +{ 'enum' : 'MonitorQMPCloseAction', > > + 'data': ['none', 'delete'] } > > + > > ## > > # @MonitorQMPProperties: > > # > > # Properties for the QMP monitor > > # > > # @pretty: whether to pretty print JSON responses (default: disabled) > > +# @close-action: action to take when the character device backend > > +# is closed (default: none) > > # > > # Since: 11.1 > > ## > > { 'struct': 'MonitorQMPProperties', > > 'base': 'MonitorProperties', > > - 'data': { '*pretty': 'bool' } } > > + 'data': { '*pretty': 'bool', > > + '*close-action': 'MonitorQMPCloseAction' } } > > > > ## > > # @ObjectType: > > diff --git a/monitor/monitor-internal.h b/monitor/monitor-internal.h > > index 5522e05464b..23829f32f9a 100644 > > --- a/monitor/monitor-internal.h > > +++ b/monitor/monitor-internal.h > > @@ -28,6 +28,7 @@ > > #include "chardev/char-fe.h" > > #include "monitor/monitor.h" > > #include "qapi/qapi-types-control.h" > > +#include "qapi/qapi-types-qom.h" > > #include "qapi/qmp-registry.h" > > #include "qobject/json-parser.h" > > #include "qemu/readline.h" > > @@ -178,7 +179,9 @@ struct MonitorQMP { > > Monitor parent_obj; > > JSONMessageParser parser; > > bool pretty; > > + MonitorQMPCloseAction close_action; > > bool setup_pending; /* iothread BH has not yet set up chardev handlers > > */ > > + bool delete_pending; /* close_action has started 'delete' process */ > > /* > > * When a client connects, we're in capabilities negotiation mode. > > * @commands is &qmp_cap_negotiation_commands then. When command > > diff --git a/monitor/qmp.c b/monitor/qmp.c > > index 5301927f09f..7257edc19d2 100644 > > --- a/monitor/qmp.c > > +++ b/monitor/qmp.c > > @@ -28,6 +28,7 @@ > > #include "monitor-internal.h" > > #include "qapi/error.h" > > #include "qapi/qapi-commands-control.h" > > +#include "qapi/qapi-commands-char.h" > > #include "qobject/qdict.h" > > #include "qobject/qjson.h" > > #include "qobject/qlist.h" > > @@ -103,6 +104,20 @@ static void monitor_qmp_set_pretty(Object *obj, bool > > val, Error **errp) > > mon->pretty = val; > > } > > > > +static int monitor_qmp_get_close_action(Object *obj, Error **errp) > > +{ > > + MonitorQMP *mon = MONITOR_QMP(obj); > > + > > + return mon->close_action; > > +} > > + > > +static void monitor_qmp_set_close_action(Object *obj, int val, Error > > **errp) > > +{ > > + MonitorQMP *mon = MONITOR_QMP(obj); > > + > > + mon->close_action = val; > > +} > > + > > static void monitor_qmp_emit_event(Monitor *mon, QAPIEvent event, QDict > > *qdict); > > static bool monitor_qmp_requires_iothread(const Monitor *mon); > > static void monitor_qmp_complete(UserCreatable *uc, Error **errp); > > @@ -117,6 +132,11 @@ static void monitor_qmp_class_init(ObjectClass *cls, > > const void *data) > > object_class_property_add_bool(cls, "pretty", > > monitor_qmp_get_pretty, > > monitor_qmp_set_pretty); > > + object_class_property_add_enum(cls, "close-action", > > + "MonitorQMPCloseAction", > > + &MonitorQMPCloseAction_lookup, > > + monitor_qmp_get_close_action, > > + monitor_qmp_set_close_action); > > > > moncls->emit_event = monitor_qmp_emit_event; > > moncls->requires_iothread = monitor_qmp_requires_iothread; > > @@ -550,11 +570,33 @@ static QDict *qmp_greeting(MonitorQMP *mon) > > ver, cap_list); > > } > > > > +static void monitor_qmp_self_delete_bh(void *opaque) > > +{ > > + MonitorQMP *mon = opaque; > > There is a potential race if object-del is called on the same MonitorQMP > before the BH fires. > > > + g_autofree char *mon_id = object_property_get_child_name( > > + object_get_objects_root(), OBJECT(mon)); > > + g_autofree char *chardev_id = g_strdup(mon->parent_obj.chardev_id); > > + Error *local_error = NULL; > > + > > + g_assert(mon_id); > > + > > + user_creatable_del(mon_id, &local_error); > > + if (local_error != NULL) { > > + error_report_err(local_error); > > + } else { > > + qmp_chardev_remove(chardev_id, NULL); > > + } > > +} > > + > > static void monitor_qmp_event(void *opaque, QEMUChrEvent event) > > { > > QDict *data; > > MonitorQMP *mon = opaque; > > > > + if (mon->delete_pending) { > > + return; > > + } > > + > > switch (event) { > > case CHR_EVENT_OPENED: > > WITH_QEMU_LOCK_GUARD(&mon->parent_obj.mon_lock) { > > @@ -577,6 +619,23 @@ static void monitor_qmp_event(void *opaque, > > QEMUChrEvent event) > > json_message_parser_init(&mon->parser, handle_qmp_command, > > mon, NULL); > > monitor_fdsets_cleanup(); > > + switch (mon->close_action) { > > + 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 > > + * which is the same context in which 'qmp_object_del' > > + * will execute > > + */ > > + aio_bh_schedule_oneshot(qemu_get_aio_context(), > > + monitor_qmp_self_delete_bh, mon); > > ref it?
We should have checked the "delete_pending" flag in the prepare_delete callback too, to block this situation. 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 :|
