[PATCH V13 06/15] monitor: track IOThread users with QOM paths

[Zhang Chen <zhangckid@gmail.com>]

Monitors that require an IOThread share the internal mon_iothread.
Account for each monitor explicitly in IOThread holder tracking, using
the monitor's canonical QOM path to distinguish holders.

Acquire the shared monitor IOThread AioContext once, using the monitor
QOM path as the holder, and reuse the stored context for later
operations.

Release the holder from the Monitor ObjectClass::unparent callback,
while the canonical QOM path is still available. This covers every
object_unparent() path and avoids duplicating the cleanup in
monitor_cleanup() and monitor_qmp_prepare_delete().

The internal mon_iothread remains hidden from query-iothreads, as before.

Signed-off-by: Zhang Chen <zhangckid@gmail.com>
---
 monitor/monitor-internal.h |  3 +++
 monitor/monitor.c          | 33 ++++++++++++++++++++++++++++-----
 monitor/qmp.c              |  5 +++--
 3 files changed, 34 insertions(+), 7 deletions(-)

diff --git a/monitor/monitor-internal.h b/monitor/monitor-internal.h
index 23829f32f9..caecceec93 100644
--- a/monitor/monitor-internal.h
+++ b/monitor/monitor-internal.h
@@ -153,6 +153,9 @@ struct Monitor {
     guint out_watch;
     int mux_out;
     int reset_seen;
+
+    /* iothread context */
+    AioContext *ctx;
 };
 
 struct MonitorHMPClass {
diff --git a/monitor/monitor.c b/monitor/monitor.c
index ed195fd97b..da6d18f475 100644
--- a/monitor/monitor.c
+++ b/monitor/monitor.c
@@ -79,6 +79,22 @@ int monitor_device_index;
 OBJECT_DEFINE_TYPE_EXTENDED(Monitor, monitor, MONITOR, OBJECT, true,
                             { TYPE_USER_CREATABLE }, {});
 
+static void monitor_unparent(Object *obj)
+{
+    Monitor *mon = MONITOR(obj);
+
+    if (mon->ctx && monitor_requires_iothread(mon)) {
+        g_autofree char *path = object_get_canonical_path(obj);
+        const IOThreadHolder io_holder = {
+            .type = IO_THREAD_HOLDER_KIND_QOM_OBJECT,
+            .u.qom_object.qom_path = path,
+        };
+
+        iothread_unref_and_put_aio_context(mon_iothread, &io_holder);
+        mon->ctx = NULL;
+    }
+}
+
 static void monitor_finalize(Object *obj)
 {
     Monitor *mon = MONITOR(obj);
@@ -114,6 +130,8 @@ static void monitor_class_init(ObjectClass *cls, const void *data)
 {
     UserCreatableClass *ucc = USER_CREATABLE_CLASS(cls);
 
+    cls->unparent = monitor_unparent;
+
     object_class_property_add_str(cls, "chardev",
                                   monitor_get_chardev_id,
                                   monitor_set_chardev_id);
@@ -573,7 +591,7 @@ void monitor_suspend(Monitor *mon)
          * Kick I/O thread to make sure this takes effect.  It'll be
          * evaluated again in prepare() of the watch object.
          */
-        aio_notify(iothread_get_aio_context(mon_iothread));
+        aio_notify(mon->ctx);
     }
 
     trace_monitor_suspend(mon, 1);
@@ -713,7 +731,6 @@ char *monitor_compat_id(void)
 static void monitor_complete(UserCreatable *uc, Error **errp)
 {
     Monitor *mon = MONITOR(uc);
-    AioContext *ctx;
 
     if (mon->chardev_id) {
         Chardev *chr = qemu_chr_find(mon->chardev_id);
@@ -732,11 +749,17 @@ static void monitor_complete(UserCreatable *uc, Error **errp)
             mon_iothread = iothread_create("mon_iothread", &error_abort);
         }
 
-        ctx = iothread_get_aio_context(mon_iothread);
+        g_autofree char *path = object_get_canonical_path(OBJECT(mon));
+        const IOThreadHolder io_holder = {
+            .type = IO_THREAD_HOLDER_KIND_QOM_OBJECT,
+            .u.qom_object.qom_path = path,
+        };
+
+        mon->ctx = iothread_ref_and_get_aio_context(mon_iothread, &io_holder);
     } else {
-        ctx = qemu_get_aio_context();
+        mon->ctx = qemu_get_aio_context();
     }
-    mon->accept_input_bh = aio_bh_new(ctx, monitor_accept_input, mon);
+    mon->accept_input_bh = aio_bh_new(mon->ctx, monitor_accept_input, mon);
 }
 
 int monitor_new(MonitorOptions *opts, bool allow_hmp, Error **errp)
diff --git a/monitor/qmp.c b/monitor/qmp.c
index 338d37cb7e..cf1c8644cd 100644
--- a/monitor/qmp.c
+++ b/monitor/qmp.c
@@ -733,7 +733,8 @@ static void monitor_qmp_complete(UserCreatable *uc, Error **errp)
          * thread.  Schedule a bottom half.
          */
         mon->setup_pending = true;
-        aio_bh_schedule_oneshot(iothread_get_aio_context(mon_iothread),
+
+        aio_bh_schedule_oneshot(MONITOR(mon)->ctx,
                                 monitor_qmp_setup_handlers_bh, mon);
         /* The bottom half will add @mon to @mon_list */
     } else {
@@ -788,7 +789,7 @@ static bool monitor_qmp_prepare_delete(UserCreatable *uc, Error **errp)
 
     /* Synchronize with in-flight iothread callbacks. */
     if (monitor_requires_iothread(mon)) {
-        aio_wait_bh_oneshot(iothread_get_aio_context(mon_iothread),
+        aio_wait_bh_oneshot(MONITOR(mon)->ctx,
                             monitor_qmp_iothread_quiesce, NULL);
     }
 
-- 
2.55.0