> 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]>
> Message-ID: <[email protected]>
>
> 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?
--
Marc-André Lureau <[email protected]>
