monitor: implement support for deleting QMP objects
The removal sequence is: 1. Remove from mon_list under monitor_lock. This must happen before disconnecting chardev handlers to prevent event broadcast from calling monitor_flush_locked() after the gcontext reset, which would create an out_watch on the wrong GMainContext (see monitor_cancel_out_watch()). 2. Cancel any pending out_watch while gcontext still points to the correct context. 3. Disconnect chardev handlers, passing context=NULL and close the connection. 4. Drain pending requests from any in-flight monitor_qmp_read(). 5. Destroy the monitor object Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org> [DB: extracted from a larger commit and refactored to apply to the new monitor class structure. Remove 'self delete' feature which requires complex special-case code] Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com> Tested-by: Peter Krempa <pkrempa@redhat.com> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com> Message-ID: <20260706135824.2623960-28-berrange@redhat.com> Signed-off-by: Markus Armbruster <armbru@redhat.com>
Christian Brauner committed
Jul 6, 2026 at 14:58 UTC
a5df506e1293e6901a3ff38927a4d562fa042806
3 files changed
+76
-2
monitor/monitor-internal.h
+2
@@ -178,6 +178,7 @@ struct MonitorQMP {
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Monitor parent_obj;
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JSONMessageParser parser;
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bool pretty;
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+ bool setup_pending; /* iothread BH has not yet set up chardev handlers */
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/*
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* When a client connects, we're in capabilities negotiation mode.
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* @commands is &qmp_cap_negotiation_commands then. When command
@@ -206,6 +207,7 @@ extern MonitorList mon_list;
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bool monitor_requires_iothread(const Monitor *mon);
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int monitor_can_read(void *opaque);
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+void monitor_cancel_out_watch(Monitor *mon);
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void monitor_list_append(Monitor *mon);
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void monitor_fdsets_cleanup(void);
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int monitor_set_cpu(Monitor *mon, int cpu_index);
monitor/monitor.c
+22
@@ -179,6 +179,28 @@ static gboolean monitor_unblocked(void *do_not_use, GIOCondition cond,
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return G_SOURCE_REMOVE;
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}
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+/* Cancel a pending out_watch GSource. Caller must hold mon_lock. */
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+void monitor_cancel_out_watch(Monitor *mon)
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+{
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+ if (mon->out_watch) {
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+ GMainContext *ctx = NULL;
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+ GSource *src;
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+
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+ if (monitor_requires_iothread(mon)) {
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+ ctx = iothread_get_g_main_context(mon_iothread);
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+ }
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+ src = g_main_context_find_source_by_id(ctx, mon->out_watch);
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+ if (!src && ctx) {
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+ /* Handler disconnect may have reset gcontext to NULL. */
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+ src = g_main_context_find_source_by_id(NULL, mon->out_watch);
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+ }
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+ if (src) {
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+ g_source_destroy(src);
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+ }
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+ mon->out_watch = 0;
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+ }
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+}
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+
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/* Caller must hold mon->mon_lock */
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void monitor_flush_locked(Monitor *mon)
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{
monitor/qmp.c
+52
-2
@@ -184,6 +184,12 @@ static void monitor_qmp_cleanup_req_queue_locked(MonitorQMP *mon)
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}
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}
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+static void monitor_qmp_drain_queue(MonitorQMP *mon)
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+{
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+ QEMU_LOCK_GUARD(&mon->qmp_queue_lock);
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+ monitor_qmp_cleanup_req_queue_locked(mon);
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+}
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+
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static void monitor_qmp_cleanup_queue_and_resume(MonitorQMP *mon)
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{
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QEMU_LOCK_GUARD(&mon->qmp_queue_lock);
@@ -597,6 +603,7 @@ static void monitor_qmp_setup_handlers_bh(void *opaque)
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monitor_qmp_read, monitor_qmp_event,
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NULL, &mon->parent_obj, context, true);
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monitor_list_append(&mon->parent_obj);
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+ qatomic_set(&mon->setup_pending, false);
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}
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void monitor_new_qmp(const char *id, const char *chardev_id,
@@ -644,6 +651,7 @@ static void monitor_qmp_complete(UserCreatable *uc, Error **errp)
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* since chardev might be running in the monitor I/O
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* thread. Schedule a bottom half.
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*/
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+ mon->setup_pending = true;
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aio_bh_schedule_oneshot(iothread_get_aio_context(mon_iothread),
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monitor_qmp_setup_handlers_bh, mon);
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/* The bottom half will add @mon to @mon_list */
@@ -655,8 +663,14 @@ static void monitor_qmp_complete(UserCreatable *uc, Error **errp)
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}
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}
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+static void monitor_qmp_iothread_quiesce(void *opaque)
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+{
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+ /* No-op: synchronization point only */
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+}
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+
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static bool monitor_qmp_prepare_delete(UserCreatable *uc, Error **errp)
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{
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+ Monitor *mon = MONITOR(uc);
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MonitorQMP *qmp = MONITOR_QMP(uc);
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if (monitor_qmp_dispatcher_is_servicing(qmp)) {
@@ -664,8 +678,44 @@ static bool monitor_qmp_prepare_delete(UserCreatable *uc, Error **errp)
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return false;
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}
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- error_setg(errp, "Deleting QMP monitors is not supported");
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- return false;
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+ if (qatomic_read(&qmp->setup_pending)) {
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+ error_setg(errp, "monitor is still initializing");
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+ return false;
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+ }
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+
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+ /* Remove from mon_list before chardev disconnect. */
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+ WITH_QEMU_LOCK_GUARD(&monitor_lock) {
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+ QTAILQ_REMOVE(&mon_list, mon, entry);
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+ }
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+
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+ /* Cancel out_watch while gcontext still points to the right ctx. */
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+ WITH_QEMU_LOCK_GUARD(&mon->mon_lock) {
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+ monitor_cancel_out_watch(mon);
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+ }
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+
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+ qemu_chr_fe_set_handlers(&mon->chr, NULL, NULL, NULL, NULL,
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+ NULL, NULL, true);
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+
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+ /* Drain requests from any in-flight monitor_qmp_read(). */
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+ monitor_qmp_drain_queue(qmp);
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+
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+ WITH_QEMU_LOCK_GUARD(&mon->mon_lock) {
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+ /* Disable flushes before cancel -- gcontext is already wrong. */
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+ qemu_chr_fe_set_open(&mon->chr, false);
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+ monitor_cancel_out_watch(mon);
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+ }
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+
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+ /* Synchronize with in-flight iothread callbacks. */
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+ if (monitor_requires_iothread(mon)) {
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+ aio_wait_bh_oneshot(iothread_get_aio_context(mon_iothread),
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+ monitor_qmp_iothread_quiesce, NULL);
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+ }
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+
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+ /* Catch requests from a racing monitor_qmp_read(). */
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+ monitor_qmp_drain_queue(qmp);
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+ monitor_fdsets_cleanup();
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+
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+ return true;
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}
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static void monitor_qmp_accept_input(Monitor *mon)