Add QMP commands for dynamic monitor lifecycle management:
- monitor-add: Create a QMP monitor on an existing chardev at runtime.
The chardev must exist and not be in use. The new monitor starts in
capability negotiation mode.
- monitor-remove: Remove a dynamically-added monitor. CLI-created
monitors cannot be removed. If the dispatcher is currently servicing
the target monitor (self-removal), destruction is deferred until the
in-flight command completes. The underlying chardev is not destroyed.
- query-monitors: Introspect all active monitors with their id, mode,
chardev name, and whether they were dynamically added.
The motivating use case is systemd-vmspawn: when an external client
requests raw QMP access, vmspawn can create an independent QMP session
on demand rather than pre-allocating spare monitors at launch or
building an id-rewriting proxy.
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
monitor/qmp-cmds-control.c | 94 ++++++++++++++++++++++++++++++++++++++++
qapi/control.json | 106 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 200 insertions(+)
diff --git a/monitor/qmp-cmds-control.c b/monitor/qmp-cmds-control.c
index 150ca9f5cb..0998017620 100644
--- a/monitor/qmp-cmds-control.c
+++ b/monitor/qmp-cmds-control.c
@@ -219,3 +219,97 @@ SchemaInfoList *qmp_query_qmp_schema(Error **errp)
}
return schema;
}
+
+void qmp_monitor_add(const char *id, const char *chardev,
+ bool has_pretty, bool pretty, Error **errp)
+{
+ Chardev *chr;
+
+ /* Reject duplicate monitor id */
+ if (monitor_find_by_id(id)) {
+ error_setg(errp, "monitor '%s' already exists", id);
+ return;
+ }
+
+ chr = qemu_chr_find(chardev);
+ if (!chr) {
+ error_setg(errp, "chardev '%s' not found", chardev);
+ return;
+ }
+
+ monitor_init_qmp(chr, has_pretty && pretty, id, true, errp);
+}
+
+void qmp_monitor_remove(const char *id, Error **errp)
+{
+ Monitor *mon;
+ MonitorQMP *qmp_mon;
+
+ mon = monitor_find_by_id(id);
+ if (!mon) {
+ error_setg(errp, "monitor '%s' not found", id);
+ return;
+ }
+
+ if (!mon->dynamic) {
+ error_setg(errp, "monitor '%s' was not dynamically added", id);
+ return;
+ }
+
+ qmp_mon = container_of(mon, MonitorQMP, common);
+
+ /*
+ * Step 1: Disconnect chardev handlers so no new data arrives
+ * and no new requests are enqueued.
+ */
+ qemu_chr_fe_set_handlers(&mon->chr, NULL, NULL, NULL, NULL,
+ NULL, NULL, true);
+
+ /* Step 2: Drain pending requests from the queue */
+ monitor_qmp_cleanup_queue_and_resume(qmp_mon);
+
+ /*
+ * Step 3: Mark dead and remove from mon_list.
+ * After removal, the dispatcher will never pop new requests from
+ * this monitor, and event broadcast will skip it.
+ */
+ qemu_mutex_lock(&monitor_lock);
+ mon->dead = true;
+ QTAILQ_REMOVE(&mon_list, mon, entry);
+ qemu_mutex_unlock(&monitor_lock);
+
+ /*
+ * Step 4: Check if the dispatcher is currently mid-dispatch on
+ * this monitor (i.e. monitor-remove was sent from the monitor
+ * being removed). If so, defer destruction -- the dispatcher
+ * will call monitor_qmp_destroy() after completing the request.
+ */
+ if (monitor_qmp_dispatcher_is_servicing(qmp_mon)) {
+ return;
+ }
+
+ /* Step 5: Safe to destroy immediately */
+ monitor_qmp_destroy(qmp_mon);
+}
+
+MonitorInfoList *qmp_query_monitors(Error **errp)
+{
+ MonitorInfoList *list = NULL;
+ Monitor *mon;
+
+ qemu_mutex_lock(&monitor_lock);
+ QTAILQ_FOREACH(mon, &mon_list, entry) {
+ MonitorInfo *info = g_new0(MonitorInfo, 1);
+ Chardev *chr = qemu_chr_fe_get_driver(&mon->chr);
+
+ info->id = g_strdup(mon->id); /* NULL if unnamed */
+ info->mode = mon->is_qmp ? MONITOR_MODE_CONTROL
+ : MONITOR_MODE_READLINE;
+ info->chardev = g_strdup(chr ? chr->label : "unknown");
+ info->dynamic = mon->dynamic;
+ QAPI_LIST_PREPEND(list, info);
+ }
+ qemu_mutex_unlock(&monitor_lock);
+
+ return list;
+}
diff --git a/qapi/control.json b/qapi/control.json
index 9a5302193d..b9f495c08c 100644
--- a/qapi/control.json
+++ b/qapi/control.json
@@ -211,3 +211,109 @@
'*pretty': 'bool',
'chardev': 'str'
} }
+
+##
+# @monitor-add:
+#
+# Add a QMP monitor on an existing character device backend.
+#
+# The chardev must already exist (created via chardev-add or CLI) and
+# must not be in use by another frontend. The monitor begins in
+# capability negotiation mode -- the first client to connect receives
+# the QMP greeting.
+#
+# @id: Monitor identifier, must be unique among monitors
+#
+# @chardev: Name of the character device backend to attach to
+#
+# @pretty: Enable pretty-printing of QMP responses (default: false)
+#
+# Errors:
+# - GenericError if @id is already in use
+# - GenericError if @chardev does not exist
+# - GenericError if @chardev is already in use by another frontend
+#
+# Since: 11.0
+#
+# .. qmp-example::
+#
+# -> { "execute": "monitor-add",
+# "arguments": { "id": "extra-qmp",
+# "chardev": "qmp-extra" } }
+# <- { "return": {} }
+##
+{ 'command': 'monitor-add',
+ 'data': { 'id': 'str',
+ 'chardev': 'str',
+ '*pretty': 'bool' } }
+
+##
+# @monitor-remove:
+#
+# Remove a dynamically added QMP monitor.
+#
+# The monitor must have been created via monitor-add. Monitors
+# created via CLI options (-mon, -qmp) cannot be removed. The
+# underlying chardev is NOT removed -- use chardev-remove separately
+# if desired.
+#
+# If a client is currently connected, the connection is dropped.
+#
+# @id: Monitor identifier as passed to monitor-add
+#
+# Errors:
+# - GenericError if @id does not exist
+# - GenericError if the monitor was not dynamically added
+#
+# Since: 11.0
+#
+# .. qmp-example::
+#
+# -> { "execute": "monitor-remove",
+# "arguments": { "id": "extra-qmp" } }
+# <- { "return": {} }
+##
+{ 'command': 'monitor-remove',
+ 'data': { 'id': 'str' } }
+
+##
+# @MonitorInfo:
+#
+# Information about a QMP/HMP monitor.
+#
+# @id: Monitor identifier (absent for CLI-created monitors without
+# an explicit id)
+#
+# @mode: Monitor mode (readline or control)
+#
+# @chardev: Name of the attached character device
+#
+# @dynamic: true if created via monitor-add (removable), false if
+# created via CLI
+#
+# Since: 11.0
+##
+{ 'struct': 'MonitorInfo',
+ 'data': { '*id': 'str',
+ 'mode': 'MonitorMode',
+ 'chardev': 'str',
+ 'dynamic': 'bool' } }
+
+##
+# @query-monitors:
+#
+# Return information about all active monitors.
+#
+# Returns: a list of @MonitorInfo for each active monitor
+#
+# Since: 11.0
+#
+# .. qmp-example::
+#
+# -> { "execute": "query-monitors" }
+# <- { "return": [ { "id": "mon0", "mode": "control",
+# "chardev": "compat_monitor0",
+# "dynamic": false } ] }
+##
+{ 'command': 'query-monitors',
+ 'returns': ['MonitorInfo'] }
--
2.47.3