[Qemu-devel] [PATCH v3 19/38] QmpSession: add a return_cb

["Marc-André Lureau" <marcandre.lureau@redhat.com>]

The introduced return_cb will allow to delay finishing the dispatch
and sending the response asynchronously. For now, this is just
modifying qmp_dispatch() to call the callback synchronously, and
return void.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
---
 include/qapi/qmp/dispatch.h |  8 +++-
 monitor.c                   | 52 +++++++++++-----------
 qapi/qmp-dispatch.c         | 19 ++++++--
 qga/main.c                  | 25 ++++++-----
 tests/test-qmp-cmds.c       | 86 ++++++++++++++++++-------------------
 5 files changed, 101 insertions(+), 89 deletions(-)

diff --git a/include/qapi/qmp/dispatch.h b/include/qapi/qmp/dispatch.h
index 10ba0745c7..7bf0b6a437 100644
--- a/include/qapi/qmp/dispatch.h
+++ b/include/qapi/qmp/dispatch.h
@@ -37,8 +37,10 @@ typedef struct QmpCommand
 typedef QTAILQ_HEAD(QmpCommandList, QmpCommand) QmpCommandList;
 
 typedef struct QmpSession QmpSession;
+typedef void (QmpDispatchReturn) (QmpSession *session, QDict *rsp);
 
 struct QmpSession {
+    QmpDispatchReturn *return_cb;
     QmpCommandList *cmds;
 };
 
@@ -46,9 +48,11 @@ void qmp_register_command(QmpCommandList *cmds, const char *name,
                           QmpCommandFunc *fn, QmpCommandOptions options);
 void qmp_unregister_command(QmpCommandList *cmds, const char *name);
 QmpCommand *qmp_find_command(QmpCommandList *cmds, const char *name);
-void qmp_session_init(QmpSession *session, QmpCommandList *cmds);
+void qmp_session_init(QmpSession *session,
+                      QmpCommandList *cmds, QmpDispatchReturn *return_cb);
+
 void qmp_session_destroy(QmpSession *session);
-QDict *qmp_dispatch(QmpSession *session, QDict *request);
+void qmp_dispatch(QmpSession *session, QDict *request);
 void qmp_disable_command(QmpCommandList *cmds, const char *name);
 void qmp_enable_command(QmpCommandList *cmds, const char *name);
 
diff --git a/monitor.c b/monitor.c
index b90f8566c8..93ecb03d04 100644
--- a/monitor.c
+++ b/monitor.c
@@ -3900,23 +3900,6 @@ static int monitor_can_read(void *opaque)
     return !atomic_mb_read(&mon->suspend_cnt);
 }
 
-/* take the ownership of rsp */
-static void monitor_qmp_respond(Monitor *mon, QDict *rsp)
-{
-    if (mon->qmp.session.cmds == &qmp_cap_negotiation_commands) {
-        QDict *qdict = qdict_get_qdict(rsp, "error");
-        if (qdict
-            && !g_strcmp0(qdict_get_try_str(qdict, "class"),
-                          QapiErrorClass_str(ERROR_CLASS_COMMAND_NOT_FOUND))) {
-            /* Provide a more useful error message */
-            qdict_put_str(qdict, "desc", "Expecting capabilities"
-                          " negotiation with 'qmp_capabilities'");
-        }
-    }
-    monitor_json_emitter(mon, QOBJECT(rsp));
-    QDECREF(rsp);
-}
-
 struct QMPRequest {
     /* Owner of the request */
     Monitor *mon;
@@ -3927,6 +3910,24 @@ struct QMPRequest {
 };
 typedef struct QMPRequest QMPRequest;
 
+static void dispatch_return_cb(QmpSession *session, QDict *rsp)
+{
+    Monitor *mon = container_of(session, Monitor, qmp.session);
+
+    if (mon->qmp.session.cmds == &qmp_cap_negotiation_commands) {
+        QDict *qdict = qdict = qdict_get_qdict(rsp, "error");
+        if (qdict
+            && !g_strcmp0(qdict_get_try_str(qdict, "class"),
+                    QapiErrorClass_str(ERROR_CLASS_COMMAND_NOT_FOUND))) {
+            /* Provide a more useful error message */
+            qdict_put_str(qdict, "desc", "Expecting capabilities negotiation"
+                          " with 'qmp_capabilities'");
+        }
+    }
+
+    monitor_json_emitter(mon, QOBJECT(rsp));
+}
+
 /*
  * Dispatch one single QMP request. The function will free the req_obj
  * and objects inside it before return.
@@ -3934,7 +3935,7 @@ typedef struct QMPRequest QMPRequest;
 static void monitor_qmp_dispatch_one(QMPRequest *req_obj)
 {
     Monitor *mon, *old_mon;
-    QDict *req, *rsp = NULL;
+    QDict *req;
 
     req = req_obj->req;
     mon = req_obj->mon;
@@ -3950,16 +3951,9 @@ static void monitor_qmp_dispatch_one(QMPRequest *req_obj)
     old_mon = cur_mon;
     cur_mon = mon;
 
-    rsp = qmp_dispatch(&mon->qmp.session, req);
+    qmp_dispatch(&mon->qmp.session, req);
 
     cur_mon = old_mon;
-
-    /* Respond if necessary */
-    if (rsp) {
-        monitor_qmp_respond(mon, rsp);
-    }
-
-
     QDECREF(req);
 }
 
@@ -4107,7 +4101,8 @@ err:
     qdict = qdict_new();
     qdict_put_obj(qdict, "error", qmp_build_error_object(err));
     error_free(err);
-    monitor_qmp_respond(mon, qdict);
+    monitor_json_emitter(mon, QOBJECT(qdict));
+    QDECREF(qdict);
     qobject_decref(req);
 }
 
@@ -4223,7 +4218,8 @@ static void monitor_qmp_event(void *opaque, int event)
 
     switch (event) {
     case CHR_EVENT_OPENED:
-        qmp_session_init(&mon->qmp.session, &qmp_cap_negotiation_commands);
+        qmp_session_init(&mon->qmp.session,
+                         &qmp_cap_negotiation_commands, dispatch_return_cb);
         monitor_qmp_caps_reset(mon);
         data = get_qmp_greeting(mon);
         monitor_json_emitter(mon, data);
diff --git a/qapi/qmp-dispatch.c b/qapi/qmp-dispatch.c
index 7fd4e41b26..5274aa59cc 100644
--- a/qapi/qmp-dispatch.c
+++ b/qapi/qmp-dispatch.c
@@ -146,17 +146,27 @@ bool qmp_is_oob(const QDict *dict)
     return qbool_get_bool(bool_obj);
 }
 
-void qmp_session_init(QmpSession *session, QmpCommandList *cmds)
+void qmp_session_init(QmpSession *session,
+                      QmpCommandList *cmds, QmpDispatchReturn *return_cb)
 {
+    assert(return_cb);
+    assert(!session->return_cb);
+
     session->cmds = cmds;
+    session->return_cb = return_cb;
 }
 
 void qmp_session_destroy(QmpSession *session)
 {
+    if (!session->return_cb) {
+        return;
+    }
+
     session->cmds = NULL;
+    session->return_cb = NULL;
 }
 
-QDict *qmp_dispatch(QmpSession *session, QDict *req)
+void qmp_dispatch(QmpSession *session, QDict *req)
 {
     Error *err = NULL;
     QObject *ret;
@@ -177,8 +187,9 @@ QDict *qmp_dispatch(QmpSession *session, QDict *req)
         qdict_put_obj(rsp, "return", ret);
     } else {
         QDECREF(rsp);
-        return NULL;
+        return;
     }
 
-    return rsp;
+    session->return_cb(session, rsp);
+    QDECREF(rsp);
 }
diff --git a/qga/main.c b/qga/main.c
index b5d7cc9e8f..46349395ba 100644
--- a/qga/main.c
+++ b/qga/main.c
@@ -580,14 +580,22 @@ static int send_response(GAState *s, QObject *payload)
     return 0;
 }
 
+static void dispatch_return_cb(QmpSession *session, QDict *rsp)
+{
+    GAState *s = container_of(session, GAState, session);
+    int ret = send_response(s, QOBJECT(rsp));
+    if (ret < 0) {
+        g_warning("error sending response: %s", strerror(-ret));
+    }
+}
+
 /* handle requests/control events coming in over the channel */
 static void process_event(JSONMessageParser *parser, GQueue *tokens)
 {
     GAState *s = container_of(parser, GAState, parser);
     QObject *obj;
-    QDict *req, *rsp = NULL;
+    QDict *req;
     Error *err = NULL;
-    int ret;
 
     g_assert(s && parser);
 
@@ -604,19 +612,14 @@ static void process_event(JSONMessageParser *parser, GQueue *tokens)
     }
 
     g_debug("processing command");
-    rsp = qmp_dispatch(&s->session, req);
+    qmp_dispatch(&s->session, req);
 
 end:
     if (err) {
-        rsp = qdict_new();
+        QDict *rsp = qdict_new();
         qdict_put_obj(rsp, "error", qmp_build_error_object(err));
         error_free(err);
-    }
-    if (rsp) {
-        ret = send_response(s, QOBJECT(rsp));
-        if (ret < 0) {
-            g_warning("error sending error response: %s", strerror(-ret));
-        }
+        dispatch_return_cb(&s->session, rsp);
         QDECREF(rsp);
     }
     qobject_decref(obj);
@@ -1305,7 +1308,7 @@ static int run_agent(GAState *s, GAConfig *config, int socket_activation)
     ga_command_state_init(s, s->command_state);
     ga_command_state_init_all(s->command_state);
     json_message_parser_init(&s->parser, process_event);
-    qmp_session_init(&s->session, &ga_commands);
+    qmp_session_init(&s->session, &ga_commands, dispatch_return_cb);
 #ifndef _WIN32
     if (!register_signal_handlers()) {
         g_critical("failed to register signal handlers");
diff --git a/tests/test-qmp-cmds.c b/tests/test-qmp-cmds.c
index 0c1fecb281..5e6e75b133 100644
--- a/tests/test-qmp-cmds.c
+++ b/tests/test-qmp-cmds.c
@@ -93,85 +93,83 @@ __org_qemu_x_Union1 *qmp___org_qemu_x_command(__org_qemu_x_EnumList *a,
     return ret;
 }
 
+static void dispatch_cmd_return(QmpSession *session, QDict *resp)
+{
+    assert(resp != NULL);
+    assert(!qdict_haskey(resp, "error"));
+}
 
 /* test commands with no input and no return value */
 static void test_dispatch_cmd(void)
 {
     QmpSession session = { 0, };
-    QDict *resp, *req = qdict_new();
+    QDict *req = qdict_new();
 
-    qmp_session_init(&session, &qmp_commands);
+    qmp_session_init(&session, &qmp_commands, dispatch_cmd_return);
     qdict_put_str(req, "execute", "user_def_cmd");
-
-    resp = qmp_dispatch(&session, req);
-    assert(resp != NULL);
-    assert(!qdict_haskey(resp, "error"));
-
-    QDECREF(resp);
+    qmp_dispatch(&session, req);
     QDECREF(req);
     qmp_session_destroy(&session);
 }
 
+static void dispatch_cmd_failure_return(QmpSession *session, QDict *resp)
+{
+    assert(resp != NULL);
+    assert(qdict_haskey(resp, "error"));
+}
+
 /* test commands that return an error due to invalid parameters */
 static void test_dispatch_cmd_failure(void)
 {
     QmpSession session = { 0, };
     QDict *req = qdict_new();
-    QDict *resp, *args = qdict_new();
+    QDict *args = qdict_new();
 
-    qmp_session_init(&session, &qmp_commands);
+    qmp_session_init(&session, &qmp_commands, dispatch_cmd_failure_return);
     qdict_put_str(req, "execute", "user_def_cmd2");
-
-    resp = qmp_dispatch(&session, req);
-    assert(resp != NULL);
-    assert(qdict_haskey(resp, "error"));
-
-    QDECREF(resp);
+    qmp_dispatch(&session, req);
     QDECREF(req);
 
     /* check that with extra arguments it throws an error */
     req = qdict_new();
     qdict_put_int(args, "a", 66);
     qdict_put(req, "arguments", args);
-
     qdict_put_str(req, "execute", "user_def_cmd");
-
-    resp = qmp_dispatch(&session, req);
-    assert(resp != NULL);
-    assert(qdict_haskey(resp, "error"));
-
-    QDECREF(resp);
+    qmp_dispatch(&session, req);
     QDECREF(req);
     qmp_session_destroy(&session);
 }
 
+static QObject *dispatch_ret;
+
 static void test_dispatch_cmd_success_response(void)
 {
     QmpSession session = { 0, };
-    QDict *resp, *req = qdict_new();
+    QDict *req = qdict_new();
 
-    qmp_session_init(&session, &qmp_commands);
+    qmp_session_init(&session, &qmp_commands, (QmpDispatchReturn *)abort);
     qdict_put_str(req, "execute", "cmd-success-response");
-    resp = qmp_dispatch(&session, req);
-    assert(resp == NULL);
+    qmp_dispatch(&session, req);
     QDECREF(req);
     qmp_session_destroy(&session);
 }
 
+static void dispatch_return(QmpSession *session, QDict *resp)
+{
+    assert(resp && !qdict_haskey(resp, "error"));
+    dispatch_ret = qdict_get(resp, "return");
+    qobject_incref(dispatch_ret);
+}
 
 static QObject *test_qmp_dispatch(QDict *req)
 {
     QmpSession session = { 0, };
-    QDict *resp;
     QObject *ret;
 
-    qmp_session_init(&session, &qmp_commands);
-    resp = qmp_dispatch(&session, req);
-    assert(resp && !qdict_haskey(resp, "error"));
-    ret = qdict_get(resp, "return");
-    assert(ret);
-    qobject_incref(ret);
-    QDECREF(resp);
+    qmp_session_init(&session, &qmp_commands, dispatch_return);
+    qmp_dispatch(&session, req);
+    ret = dispatch_ret;
+    dispatch_ret = NULL;
     qmp_session_destroy(&session);
     return ret;
 }
@@ -290,21 +288,21 @@ static void test_dealloc_partial(void)
     qapi_free_UserDefTwo(ud2);
 }
 
+static void dispatch_return_id42(QmpSession *session, QDict *resp)
+{
+    assert(!qdict_haskey(resp, "error"));
+    assert(!strcmp(qdict_get_str(resp, "id"), "ID42"));
+}
+
 static void test_dispatch_cmd_id(void)
 {
     QmpSession session = { 0, };
-    QDict *resp, *req = qdict_new();
+    QDict *req = qdict_new();
 
-    qmp_session_init(&session, &qmp_commands);
+    qmp_session_init(&session, &qmp_commands, dispatch_return_id42);
     qdict_put_str(req, "execute", "user_def_cmd");
     qdict_put_str(req, "id", "ID42");
-
-    resp = qmp_dispatch(&session, req);
-    assert(resp != NULL);
-    assert(!qdict_haskey(resp, "error"));
-    assert(!strcmp(qdict_get_str(resp, "id"), "ID42"));
-
-    QDECREF(resp);
+    qmp_dispatch(&session, req);
     QDECREF(req);
     qmp_session_destroy(&session);
 }
-- 
2.17.0.rc1.1.g4c4f2b46a3