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]>
---
monitor/monitor-internal.h | 3 +
monitor/qmp.c | 59 +++++++++++++++++++
qapi/qom.json | 21 ++++++-
qemu-options.hx | 10 +++-
.../generic/test_monitor_hotplug.py | 53 +++++++++++++++--
5 files changed, 140 insertions(+), 6 deletions(-)
diff --git a/monitor/monitor-internal.h b/monitor/monitor-internal.h
index 2e8e5ec721..165002f535 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"
@@ -179,7 +180,9 @@ 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 d471428488..905f924ea6 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;
+ 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);
+ break;
+ default:
+ g_assert_not_reached();
+ }
break;
case CHR_EVENT_BREAK:
case CHR_EVENT_MUX_IN:
diff --git a/qapi/qom.json b/qapi/qom.json
index 6ed510858e..63335b8fd0 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/qemu-options.hx b/qemu-options.hx
index 031417b79d..848a53ea34 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -5730,7 +5730,7 @@ SRST
controls whether the monitor provides interactive
prompts
- ``-object monitor-qmp,id=id,chardev=chardev_id,pretty=on|off``
+ ``-object
monitor-qmp,id=id,chardev=chardev_id,pretty=on|off,close-action=none|delete``
Set up a monitor running the QEMU Monitor Protocol,
connected to the chardev ``chrid``.
@@ -5747,6 +5747,14 @@ SRST
constrained to a single line without extraneous
whitespace.
+ The ``close-action`` parameter, which defaults to ``none``,
+ controls what happens when the connection to the monitor
+ is terminated by the user. If set to ``delete``, then the
+ ``monitor-qmp`` object and its associated character
+ device are both immediately deleted. This can be useful
+ if an extra monitor was hotplugged for a specific task
+ and should be unplugged when completed.
+
``-object
memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align,offset=offset,readonly=on|off,rom=on|off|auto``
Creates a memory file backend object, which can be used to back
the guest RAM with huge pages.
diff --git a/tests/functional/generic/test_monitor_hotplug.py
b/tests/functional/generic/test_monitor_hotplug.py
index 03087faafc..f7d72a77c2 100755
--- a/tests/functional/generic/test_monitor_hotplug.py
+++ b/tests/functional/generic/test_monitor_hotplug.py
@@ -25,7 +25,7 @@ def setUp(self):
sock_dir = self.socket_dir()
self._sock_path = os.path.join(sock_dir.name, 'hotplug.sock')
- def _add_monitor(self):
+ def _add_monitor(self, autodelete=False):
"""Create a chardev + monitor and return the socket path."""
sock = self._sock_path
self.vm.cmd('chardev-add', id='hotplug-chr', backend={
@@ -39,9 +39,15 @@ def _add_monitor(self):
'wait': False,
}
})
- self.vm.cmd('object-add', id='hotplug-mon',
- qom_type='monitor-qmp',
- chardev='hotplug-chr')
+ if autodelete:
+ self.vm.cmd('object-add', id='hotplug-mon',
+ qom_type='monitor-qmp',
+ chardev='hotplug-chr',
+ close_action='delete')
+ else:
+ self.vm.cmd('object-add', id='hotplug-mon',
+ qom_type='monitor-qmp',
+ chardev='hotplug-chr')
return sock
def _remove_monitor(self):
@@ -118,6 +124,45 @@ def test_self_removal(self):
# Clean up the chardev
self.vm.cmd('chardev-remove', id='hotplug-chr')
+ def test_auto_delete(self):
+ """
+ A dynamically-added monitor is configured with 'close-action=delete'
+ should see itself deleted when the client is closed.
+ """
+ self.set_machine('none')
+ self.vm.add_args('-nodefaults')
+ self.vm.launch()
+
+ sock = self._add_monitor(autodelete=True)
+
+ cdevs = [c["label"] for c in self.vm.cmd('query-chardev')]
+ objs = [o["name"] for o in self.vm.cmd('qom-list', path='/objects')]
+ assert ('hotplug-chr' in cdevs)
+ assert ('hotplug-mon' in objs)
+
+ qmp = QEMUMonitorProtocol(sock)
+ greeting = qmp.connect(negotiate=True)
+ self.assertIn('QMP', greeting)
+
+ cdevs = [c["label"] for c in self.vm.cmd('query-chardev')]
+ objs = [o["name"] for o in self.vm.cmd('qom-list', path='/objects')]
+ assert ('hotplug-chr' in cdevs)
+ assert ('hotplug-mon' in objs)
+
+ qmp.close()
+
+ for i in range(10):
+ cdevs = [c["label"] for c in self.vm.cmd('query-chardev')]
+ if 'hotplug-chr' not in cdevs:
+ break
+ # Sleep upto 1/2 second to vary the races
+ time.sleep(random.random() / 0.5)
+
+ cdevs = [c["label"] for c in self.vm.cmd('query-chardev')]
+ objs = [o["name"] for o in self.vm.cmd('qom-list', path='/objects')]
+ assert ('hotplug-chr' not in cdevs)
+ assert ('hotplug-mon' not in objs)
+
def test_large_response(self):
"""
Send a command with a large response (query-qmp-schema) on a
--
2.54.0
