[Qemu-devel] [PATCH v2 15/25] monitor: suspend when running async and client has no async

[Marc-André Lureau]

When the client doesn't support 'async' capability, let's suspend the
monitor until the on-going async command completes. That way, the client
will be able to use -async commands, but will get only in order
reply: (t won't be able to do concurrent commands. In this case, the
'id' field isn't mandatory.

Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com>
---
 monitor.c           | 32 +++++++++++++++++++++++++++++++-
 qapi/qmp-dispatch.c |  3 ++-
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/monitor.c b/monitor.c
index c5c70d7e17..3ff32c000c 100644
--- a/monitor.c
+++ b/monitor.c
@@ -165,6 +165,7 @@ typedef struct {
      * mode.
      */
     bool in_command_mode;       /* are we in command mode? */
+    QObject *suspended;
     QmpClient client;
 } MonitorQMP;
 
@@ -3675,9 +3676,10 @@ static int monitor_can_read(void *opaque)
 {
     Monitor *mon = opaque;
 
-    return (mon->suspend_cnt == 0) ? 1 : 0;
+    return (mon->suspend_cnt == 0 && !mon->qmp.suspended) ? 1 : 0;
 }
 
+
 static bool invalid_qmp_mode(const Monitor *mon, const char *cmd,
                              Error **errp)
 {
@@ -3754,11 +3756,33 @@ static QDict *qmp_check_input_obj(QObject *input_obj, 
Error **errp)
     return input_dict;
 }
 
+static void monitor_qmp_suspend(Monitor *mon, QObject *req)
+{
+    assert(monitor_is_qmp(mon));
+    assert(!mon->qmp.suspended);
+
+    qobject_incref(req);
+    mon->qmp.suspended = req;
+}
+
+static void monitor_qmp_resume(Monitor *mon)
+{
+    assert(monitor_is_qmp(mon));
+    assert(mon->qmp.suspended);
+
+    qobject_decref(mon->qmp.suspended);
+    mon->qmp.suspended = NULL;
+}
+
 static void qmp_dispatch_return(QmpClient *client, QObject *rsp)
 {
     Monitor *mon = container_of(client, Monitor, qmp.client);
 
     monitor_json_emitter(mon, rsp);
+
+    if (mon->qmp.suspended) {
+        monitor_qmp_resume(mon);
+    }
 }
 
 static void handle_qmp_command(JSONMessageParser *parser, GQueue *tokens)
@@ -3797,6 +3821,12 @@ static void handle_qmp_command(JSONMessageParser 
*parser, GQueue *tokens)
     }
 
     qmp_dispatch(&mon->qmp.client, req, rqdict);
+
+    /* suspend if the command is on-going and client doesn't support async */
+    if (!QLIST_EMPTY(&mon->qmp.client.pending) && !mon->qmp.client.has_async) {
+        monitor_qmp_suspend(mon, req);
+    }
+
     qobject_decref(req);
     return;
 
diff --git a/qapi/qmp-dispatch.c b/qapi/qmp-dispatch.c
index 76c7402ac8..5bf4b1b520 100644
--- a/qapi/qmp-dispatch.c
+++ b/qapi/qmp-dispatch.c
@@ -109,7 +109,8 @@ static QObject *do_qmp_dispatch(QObject *request, QmpReturn 
*qret, Error **errp)
         }
         break;
     case QCT_ASYNC:
-        if (!qdict_haskey(qret->rsp, "id")) {
+        if (qret->client->has_async &&
+            !qdict_haskey(qret->rsp, "id")) {
             error_setg(errp, "An async command requires an 'id'");
             break;
         }
-- 
2.11.0.295.gd7dffce1c