{"id":2219331,"url":"http://patchwork.ozlabs.org/api/1.0/patches/2219331/?format=json","project":{"id":14,"url":"http://patchwork.ozlabs.org/api/1.0/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":""},"msgid":"<20260402-work-qmp-monitor-hotplug-v1-3-6313a5cdd574@kernel.org>","date":"2026-04-02T21:19:18","name":"[3/5] qapi: add monitor-add, monitor-remove, query-monitors commands","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"7f980cf730bd744ff4b49a97162f8bb19a6b4b74","submitter":{"id":82326,"url":"http://patchwork.ozlabs.org/api/1.0/people/82326/?format=json","name":"Christian Brauner","email":"brauner@kernel.org"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/qemu-devel/patch/20260402-work-qmp-monitor-hotplug-v1-3-6313a5cdd574@kernel.org/mbox/","series":[{"id":498554,"url":"http://patchwork.ozlabs.org/api/1.0/series/498554/?format=json","date":"2026-04-02T21:19:15","name":"monitor: add dynamic QMP monitor hotplug support","version":1,"mbox":"http://patchwork.ozlabs.org/series/498554/mbox/"}],"check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2219331/checks/","tags":{},"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=JNssCbUY;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; 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charset=\"utf-8\"","Content-Transfer-Encoding":"7bit","Message-Id":"<20260402-work-qmp-monitor-hotplug-v1-3-6313a5cdd574@kernel.org>","References":"<20260402-work-qmp-monitor-hotplug-v1-0-6313a5cdd574@kernel.org>","In-Reply-To":"<20260402-work-qmp-monitor-hotplug-v1-0-6313a5cdd574@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=7468; i=brauner@kernel.org;\n h=from:subject:message-id; bh=gPO1Pu3xZDZpzDPyynLjlwUEaoGQCjY4ylfy1aTTGVg=;\n b=owGbwMvMwCU28Zj0gdSKO4sYT6slMWSeuxsf1PLUnn0Xf9CM1Wb7Al5qTKgSZEsx/vju/J5rC\n UlGFut2d5SyMIhxMciKKbI4tJuEyy3nqdhslKkBM4eVCWQIAxenAExkfzcjwxXVaFfrHb0vShQe\n 3tomnOxQ19Lc0l1b4dTF333LTJPFgOF/REaslOqPhRwyrCk7D3hs28W/OUtuvvGtJ/5MzRuz76v\n zAAA=","X-Developer-Key":"i=brauner@kernel.org; a=openpgp;\n fpr=4880B8C9BD0E5106FC070F4F7B3C391EFEA93624","Received-SPF":"pass client-ip=2600:3c04:e001:324:0:1991:8:25;\n envelope-from=brauner@kernel.org; helo=tor.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=-0.542,\n DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1,\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 be in use. 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. If the dispatcher is currently servicing\n the target monitor (self-removal), destruction is deferred until the\n in-flight command completes. The underlying chardev is not destroyed.\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 | 94 ++++++++++++++++++++++++++++++++++++++++\n qapi/control.json | 106 +++++++++++++++++++++++++++++++++++++++++++++\n 2 files changed, 200 insertions(+)","diff":"diff --git a/monitor/qmp-cmds-control.c b/monitor/qmp-cmds-control.c\nindex 150ca9f5cb..0998017620 100644\n--- a/monitor/qmp-cmds-control.c\n+++ b/monitor/qmp-cmds-control.c\n@@ -219,3 +219,97 @@ 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+\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->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+ /*\n+ * Step 1: Disconnect chardev handlers so no new data arrives\n+ * and no new requests are enqueued.\n+ */\n+ qemu_chr_fe_set_handlers(&mon->chr, NULL, NULL, NULL, NULL,\n+ NULL, NULL, true);\n+\n+ /* Step 2: Drain pending requests from the queue */\n+ monitor_qmp_cleanup_queue_and_resume(qmp_mon);\n+\n+ /*\n+ * Step 3: Mark dead and remove from mon_list.\n+ * After removal, the dispatcher will never pop new requests from\n+ * this monitor, and event broadcast will skip it.\n+ */\n+ qemu_mutex_lock(&monitor_lock);\n+ mon->dead = true;\n+ QTAILQ_REMOVE(&mon_list, mon, entry);\n+ qemu_mutex_unlock(&monitor_lock);\n+\n+ /*\n+ * Step 4: Check if the dispatcher is currently mid-dispatch on\n+ * this monitor (i.e. monitor-remove was sent from the monitor\n+ * being removed). If so, defer destruction -- the dispatcher\n+ * will call monitor_qmp_destroy() after completing the request.\n+ */\n+ if (monitor_qmp_dispatcher_is_servicing(qmp_mon)) {\n+ return;\n+ }\n+\n+ /* Step 5: Safe to destroy immediately */\n+ monitor_qmp_destroy(qmp_mon);\n+}\n+\n+MonitorInfoList *qmp_query_monitors(Error **errp)\n+{\n+ MonitorInfoList *list = NULL;\n+ Monitor *mon;\n+\n+ qemu_mutex_lock(&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); /* NULL if unnamed */\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+ qemu_mutex_unlock(&monitor_lock);\n+\n+ return list;\n+}\ndiff --git a/qapi/control.json b/qapi/control.json\nindex 9a5302193d..b9f495c08c 100644\n--- a/qapi/control.json\n+++ b/qapi/control.json\n@@ -211,3 +211,109 @@\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) and\n+# must not be in use by another frontend. The monitor begins in\n+# capability negotiation mode -- the first client to connect receives\n+# 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+# - GenericError if @chardev is already in use by another frontend\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":["3/5"]}