From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id B1134CD98F2 for ; Fri, 19 Jun 2026 12:40:23 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1waYW0-0006NB-8j; Fri, 19 Jun 2026 08:40:08 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1waYVx-0006LR-J2 for qemu-devel@nongnu.org; Fri, 19 Jun 2026 08:40:05 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1waYVv-0001qn-10 for qemu-devel@nongnu.org; Fri, 19 Jun 2026 08:40:05 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1781872801; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=bEzSDDFobu00fpA3TkeLk7CbZGsjFtIRYe9S+oe8Mac=; b=Xi8DNAKCp4p3y/SEKL20brbv+20dbARg1LBjkmnCpyDK+U2DA3x5nTTuDFPiDuZHH478oh c26TWNTD0Nh7xzksNV8bPkPct7dH83l5cdHz99ek2HQ7BkgIwq8ObC4ScoF1e1tm/zrp+f 8U9SkRhw6iqa1RR4szqgLOBphKjwVm4= Received: from mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (ec2-35-165-154-97.us-west-2.compute.amazonaws.com [35.165.154.97]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-274--R4G9ZyWPrO97DvQ9C0gQA-1; Fri, 19 Jun 2026 08:39:59 -0400 X-MC-Unique: -R4G9ZyWPrO97DvQ9C0gQA-1 X-Mimecast-MFC-AGG-ID: -R4G9ZyWPrO97DvQ9C0gQA_1781872797 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E5A601845432; Fri, 19 Jun 2026 12:39:56 +0000 (UTC) Received: from redhat.com (unknown [10.44.49.122]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5E94E30001BE; Fri, 19 Jun 2026 12:39:52 +0000 (UTC) Date: Fri, 19 Jun 2026 13:39:49 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: marcandre.lureau@redhat.com Cc: qemu-devel@nongnu.org, devel@lists.libvirt.org, Alex =?utf-8?Q?Benn=C3=A9e?= , Christian Brauner , Markus Armbruster , "Dr. David Alan Gilbert" , Paolo Bonzini , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= Subject: Re: [PATCH v3 32/35] monitor: add support for auto-deleting monitors upon close Message-ID: References: <20260618105836.991609-1-berrange@redhat.com> <20260618105836.991609-33-berrange@redhat.com> <178178367256.2477794.3774306065880935155.b4-review@b4> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <178178367256.2477794.3774306065880935155.b4-review@b4> User-Agent: Mutt/2.3.2 (2026-04-26) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -24 X-Spam_score: -2.5 X-Spam_bar: -- X-Spam_report: (-2.5 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.445, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Thu, Jun 18, 2026 at 03:54:32PM +0400, marcandre.lureau@redhat.com 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 > > Message-ID: <20260618105836.991609-33-berrange@redhat.com> > > > > 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 :|