{"id":2219977,"url":"http://patchwork.ozlabs.org/api/1.2/patches/2219977/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260405-work-qmp-monitor-hotplug-v2-3-ad5bedd2917a@kernel.org/","project":{"id":14,"url":"http://patchwork.ozlabs.org/api/1.2/projects/14/?format=json","name":"QEMU Development","link_name":"qemu-devel","list_id":"qemu-devel.nongnu.org","list_email":"qemu-devel@nongnu.org","web_url":"","scm_url":"","webscm_url":"","list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"<20260405-work-qmp-monitor-hotplug-v2-3-ad5bedd2917a@kernel.org>","list_archive_url":null,"date":"2026-04-05T13:11:19","name":"[v2,3/5] qapi: add monitor-add, monitor-remove, query-monitors commands","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"adce9d03cc62eb698ab326874f547cccacdb2cf5","submitter":{"id":82326,"url":"http://patchwork.ozlabs.org/api/1.2/people/82326/?format=json","name":"Christian Brauner","email":"brauner@kernel.org"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260405-work-qmp-monitor-hotplug-v2-3-ad5bedd2917a@kernel.org/mbox/","series":[{"id":498784,"url":"http://patchwork.ozlabs.org/api/1.2/series/498784/?format=json","web_url":"http://patchwork.ozlabs.org/project/qemu-devel/list/?series=498784","date":"2026-04-05T13:11:16","name":"monitor: add dynamic QMP monitor hotplug support","version":2,"mbox":"http://patchwork.ozlabs.org/series/498784/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2219977/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2219977/checks/","tags":{},"related":[],"headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256\n header.s=k20201202 header.b=WOKgyeyy;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)"],"Received":["from lists.gnu.org (lists.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4fpXtn72Rvz1xy1\n\tfor ; Sun, 05 Apr 2026 23:12:33 +1000 (AEST)","from localhost ([::1] helo=lists1p.gnu.org)\n\tby lists.gnu.org with esmtp (Exim 4.90_1)\n\t(envelope-from )\n\tid 1w9NGV-0006WY-Fp; Sun, 05 Apr 2026 09:11:47 -0400","from eggs.gnu.org ([2001:470:142:3::10])\n by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)\n (Exim 4.90_1) (envelope-from )\n id 1w9NGS-0006W0-Hc\n for qemu-devel@nongnu.org; Sun, 05 Apr 2026 09:11:45 -0400","from sea.source.kernel.org ([172.234.252.31])\n by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)\n (Exim 4.90_1) (envelope-from )\n id 1w9NGQ-0006dZ-EC\n for qemu-devel@nongnu.org; Sun, 05 Apr 2026 09:11:44 -0400","from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58])\n by sea.source.kernel.org (Postfix) with ESMTP id 7B0A840461;\n Sun, 5 Apr 2026 13:11:41 +0000 (UTC)","by smtp.kernel.org (Postfix) with ESMTPSA id 03AB5C2BC9E;\n Sun, 5 Apr 2026 13:11:38 +0000 (UTC)"],"DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org;\n s=k20201202; t=1775394701;\n bh=vUOsnjMPnEut5csZPoZP/V+/ffYrQlfAd/dULVEgPcU=;\n h=From:Date:Subject:References:In-Reply-To:To:Cc:From;\n b=WOKgyeyy3+JV5TY2I2UHfZGudjKdmlmwT4KxeO0HhSNYvzneojpVGw24Yh/j3dZEx\n OdUmEyX93cBevYHhcrsHWTQlBXLBrpHwxz7eEu9ZGTH64UjQyNnr8+cIQqSgT1xFsa\n 0ESijWxoWqgEK8s/YO74KaSE56B+9sqk4o8ur1FWiUJ9i/hmCRComyBIFt6t9xHzjG\n lJ+6evuPhmSwp/LWRy2ga81LXM/oHw/UQE9+X0rCgQc3rR3O/GcnpHPX9hiA4YgBcr\n W9qSPX5yUwLL8tjb0RPFOS1XdMTmHVL7RiCyWJ1GMz7poMTwWahpDhTGR3A/+4FDLr\n ttZgOGMAAxwSw==","From":"Christian Brauner ","Date":"Sun, 05 Apr 2026 15:11:19 +0200","Subject":"[PATCH v2 3/5] qapi: add monitor-add, monitor-remove,\n query-monitors commands","MIME-Version":"1.0","Content-Type":"text/plain; charset=\"utf-8\"","Content-Transfer-Encoding":"7bit","Message-Id":"<20260405-work-qmp-monitor-hotplug-v2-3-ad5bedd2917a@kernel.org>","References":"<20260405-work-qmp-monitor-hotplug-v2-0-ad5bedd2917a@kernel.org>","In-Reply-To":"<20260405-work-qmp-monitor-hotplug-v2-0-ad5bedd2917a@kernel.org>","To":"qemu-devel@nongnu.org","Cc":"Markus Armbruster , Eric Blake ,\n Fabiano Rosas , Laurent Vivier ,\n Paolo Bonzini , Thomas Huth ,\n\t=?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , =?utf-8?q?Dani?=\n\t=?utf-8?q?el_P=2E_Berrang=C3=A9?= ,\n Christian Brauner ","X-Mailer":"b4 0.16-dev","X-Developer-Signature":"v=1; a=openpgp-sha256; l=8601; i=brauner@kernel.org;\n h=from:subject:message-id; bh=vUOsnjMPnEut5csZPoZP/V+/ffYrQlfAd/dULVEgPcU=;\n b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWReim9SENxjv/JytsC6CWKHo7tz05MCPdqXCXQKHi69e\n Caz+rl8RykLgxgXg6yYIotDu0m43HKeis1GmRowc1iZQIYwcHEKwETmTGP4p1tezrV9vmFbBv+O\n utx9QftqjWUVs0zVn/gHXuRfP1ciheE32+sO7W5n6xP/VnXLW0w8Gfoqy+ZfpDbnhz0VSu8F1Xp\n 4AQ==","X-Developer-Key":"i=brauner@kernel.org; a=openpgp;\n fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624","Received-SPF":"pass client-ip=172.234.252.31; envelope-from=brauner@kernel.org;\n helo=sea.source.kernel.org","X-Spam_score_int":"-25","X-Spam_score":"-2.6","X-Spam_bar":"--","X-Spam_report":"(-2.6 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.54,\n DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\n RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001,\n SPF_HELO_NONE=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":",\n ","List-Archive":"","List-Post":"","List-Help":"","List-Subscribe":",\n ","Errors-To":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org","Sender":"qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org"},"content":"Add QMP commands for dynamic monitor lifecycle management:\n\n- monitor-add: Create a QMP monitor on an existing chardev at runtime.\n The chardev must exist and not already have a frontend attached\n (enforced by qemu_chr_fe_init()). The new monitor starts in\n capability negotiation mode.\n\n- monitor-remove: Remove a dynamically-added monitor. CLI-created\n monitors cannot be removed. The removal sequence is:\n\n 1. Mark dead and remove from mon_list under monitor_lock. This\n must happen before disconnecting chardev handlers to prevent\n event broadcast from calling monitor_flush_locked() after the\n gcontext reset, which would create an out_watch on the wrong\n GMainContext (see monitor_cancel_out_watch()).\n 2. Cancel any pending out_watch while gcontext still points to the\n correct context.\n 3. Disconnect chardev handlers. For self-removal, preserve\n gcontext by passing the iothread GMainContext and keep the\n chardev connection open so the command response can be flushed.\n For normal removal, pass context=NULL and close the connection.\n 4. Drain pending requests from any in-flight monitor_qmp_read().\n 5. For self-removal, defer destruction to the dispatcher (the\n response must be flushed first). Otherwise destroy immediately\n via monitor_qmp_destroy().\n\n- query-monitors: Introspect all active monitors with their id, mode,\n chardev name, and whether they were dynamically added.\n\nThe motivating use case is systemd-vmspawn: when an external client\nrequests raw QMP access, vmspawn can create an independent QMP session\non demand rather than pre-allocating spare monitors at launch or\nbuilding an id-rewriting proxy.\n\nSigned-off-by: Christian Brauner (Amutable) \n---\n monitor/qmp-cmds-control.c | 111 +++++++++++++++++++++++++++++++++++++++++++++\n qapi/control.json | 104 ++++++++++++++++++++++++++++++++++++++++++\n 2 files changed, 215 insertions(+)","diff":"diff --git a/monitor/qmp-cmds-control.c b/monitor/qmp-cmds-control.c\nindex 150ca9f5cb..c0a3e03aa5 100644\n--- a/monitor/qmp-cmds-control.c\n+++ b/monitor/qmp-cmds-control.c\n@@ -219,3 +219,114 @@ SchemaInfoList *qmp_query_qmp_schema(Error **errp)\n }\n return schema;\n }\n+\n+void qmp_monitor_add(const char *id, const char *chardev,\n+ bool has_pretty, bool pretty, Error **errp)\n+{\n+ Chardev *chr;\n+\n+ /* Reject duplicate monitor id */\n+ if (monitor_find_by_id(id)) {\n+ error_setg(errp, \"monitor '%s' already exists\", id);\n+ return;\n+ }\n+\n+ chr = qemu_chr_find(chardev);\n+ if (!chr) {\n+ error_setg(errp, \"chardev '%s' not found\", chardev);\n+ return;\n+ }\n+\n+ monitor_init_qmp(chr, has_pretty && pretty, id, true, errp);\n+}\n+\n+void qmp_monitor_remove(const char *id, Error **errp)\n+{\n+ Monitor *mon;\n+ MonitorQMP *qmp_mon;\n+ bool self_remove;\n+\n+ mon = monitor_find_by_id(id);\n+ if (!mon) {\n+ error_setg(errp, \"monitor '%s' not found\", id);\n+ return;\n+ }\n+\n+ if (!mon->is_qmp) {\n+ error_setg(errp, \"monitor '%s' is not a QMP monitor\", id);\n+ return;\n+ }\n+\n+ if (!mon->dynamic) {\n+ error_setg(errp, \"monitor '%s' was not dynamically added\", id);\n+ return;\n+ }\n+\n+ qmp_mon = container_of(mon, MonitorQMP, common);\n+\n+ if (qatomic_read(&qmp_mon->setup_pending)) {\n+ error_setg(errp, \"monitor '%s' is still initializing\", id);\n+ return;\n+ }\n+\n+ self_remove = monitor_qmp_dispatcher_is_servicing(qmp_mon);\n+\n+ /* Remove from mon_list before chardev disconnect. */\n+ WITH_QEMU_LOCK_GUARD(&monitor_lock) {\n+ mon->dead = true;\n+ QTAILQ_REMOVE(&mon_list, mon, entry);\n+ }\n+\n+ /* Cancel out_watch while gcontext still points to the right ctx. */\n+ WITH_QEMU_LOCK_GUARD(&mon->mon_lock) {\n+ monitor_cancel_out_watch(mon);\n+ }\n+\n+ /*\n+ * Clear chardev handlers. Self-removal preserves gcontext so the\n+ * response flush creates out_watch on the correct GMainContext.\n+ */\n+ if (self_remove) {\n+ GMainContext *ctx = mon->use_io_thread\n+ ? iothread_get_g_main_context(mon_iothread) : NULL;\n+\n+ qemu_chr_fe_set_handlers(&mon->chr, NULL, NULL, NULL, NULL,\n+ NULL, ctx, false);\n+ } else {\n+ qemu_chr_fe_set_handlers(&mon->chr, NULL, NULL, NULL, NULL,\n+ NULL, NULL, true);\n+ }\n+\n+ /* Drain requests from any in-flight monitor_qmp_read(). */\n+ monitor_qmp_drain_queue(qmp_mon);\n+\n+ /* Self-removal: defer destruction so the response is flushed first. */\n+ if (self_remove) {\n+ return;\n+ }\n+\n+ monitor_qmp_destroy(qmp_mon);\n+ monitor_fdsets_cleanup();\n+}\n+\n+MonitorInfoList *qmp_query_monitors(Error **errp)\n+{\n+ MonitorInfoList *list = NULL;\n+ Monitor *mon;\n+\n+ WITH_QEMU_LOCK_GUARD(&monitor_lock) {\n+ QTAILQ_FOREACH(mon, &mon_list, entry) {\n+ MonitorInfo *info = g_new0(MonitorInfo, 1);\n+ Chardev *chr = qemu_chr_fe_get_driver(&mon->chr);\n+\n+ info->id = g_strdup(mon->id);\n+ info->mode = mon->is_qmp ? MONITOR_MODE_CONTROL\n+ : MONITOR_MODE_READLINE;\n+ info->chardev = g_strdup(chr ? chr->label : \"unknown\");\n+ info->dynamic = mon->dynamic;\n+ QAPI_LIST_PREPEND(list, info);\n+ }\n+ }\n+\n+ return list;\n+}\ndiff --git a/qapi/control.json b/qapi/control.json\nindex 9a5302193d..fd58b57c31 100644\n--- a/qapi/control.json\n+++ b/qapi/control.json\n@@ -211,3 +211,107 @@\n '*pretty': 'bool',\n 'chardev': 'str'\n } }\n+\n+##\n+# @monitor-add:\n+#\n+# Add a QMP monitor on an existing character device backend.\n+#\n+# The chardev must already exist (created via chardev-add or CLI).\n+# The monitor begins in capability negotiation mode -- the first\n+# client to connect receives the QMP greeting.\n+#\n+# @id: Monitor identifier, must be unique among monitors\n+#\n+# @chardev: Name of the character device backend to attach to\n+#\n+# @pretty: Enable pretty-printing of QMP responses (default: false)\n+#\n+# Errors:\n+# - GenericError if @id is already in use\n+# - GenericError if @chardev does not exist\n+#\n+# Since: 11.0\n+#\n+# .. qmp-example::\n+#\n+# -> { \"execute\": \"monitor-add\",\n+# \"arguments\": { \"id\": \"extra-qmp\",\n+# \"chardev\": \"qmp-extra\" } }\n+# <- { \"return\": {} }\n+##\n+{ 'command': 'monitor-add',\n+ 'data': { 'id': 'str',\n+ 'chardev': 'str',\n+ '*pretty': 'bool' } }\n+\n+##\n+# @monitor-remove:\n+#\n+# Remove a dynamically added QMP monitor.\n+#\n+# The monitor must have been created via monitor-add. Monitors\n+# created via CLI options (-mon, -qmp) cannot be removed. The\n+# underlying chardev is NOT removed -- use chardev-remove separately\n+# if desired.\n+#\n+# If a client is currently connected, the connection is dropped.\n+#\n+# @id: Monitor identifier as passed to monitor-add\n+#\n+# Errors:\n+# - GenericError if @id does not exist\n+# - GenericError if the monitor was not dynamically added\n+#\n+# Since: 11.0\n+#\n+# .. qmp-example::\n+#\n+# -> { \"execute\": \"monitor-remove\",\n+# \"arguments\": { \"id\": \"extra-qmp\" } }\n+# <- { \"return\": {} }\n+##\n+{ 'command': 'monitor-remove',\n+ 'data': { 'id': 'str' } }\n+\n+##\n+# @MonitorInfo:\n+#\n+# Information about a QMP/HMP monitor.\n+#\n+# @id: Monitor identifier (absent for CLI-created monitors without\n+# an explicit id)\n+#\n+# @mode: Monitor mode (readline or control)\n+#\n+# @chardev: Name of the attached character device\n+#\n+# @dynamic: true if created via monitor-add (removable), false if\n+# created via CLI\n+#\n+# Since: 11.0\n+##\n+{ 'struct': 'MonitorInfo',\n+ 'data': { '*id': 'str',\n+ 'mode': 'MonitorMode',\n+ 'chardev': 'str',\n+ 'dynamic': 'bool' } }\n+\n+##\n+# @query-monitors:\n+#\n+# Return information about all active monitors.\n+#\n+# Returns: a list of @MonitorInfo for each active monitor\n+#\n+# Since: 11.0\n+#\n+# .. qmp-example::\n+#\n+# -> { \"execute\": \"query-monitors\" }\n+# <- { \"return\": [ { \"id\": \"mon0\", \"mode\": \"control\",\n+# \"chardev\": \"compat_monitor0\",\n+# \"dynamic\": false } ] }\n+##\n+{ 'command': 'query-monitors',\n+ 'returns': ['MonitorInfo'] }\n","prefixes":["v2","3/5"]}