From c22045bfe6d5ceebd414ff53ff23fff7ad5930d1 Mon Sep 17 00:00:00 2001
From: Maxim Levitsky <mlevitsk@redhat.com>
Date: Tue, 6 Oct 2020 15:38:53 +0300
Subject: [PATCH] qtest: Reintroduce qtest_qmp_receive with QMP event buffering

The new qtest_qmp_receive buffers all the received qmp events, allowing
qtest_qmp_eventwait_ref to return them.

This is intended to solve the race in regard to ordering of qmp events
vs qmp responses, as soon as the callers start using the new interface.

In addition to that, define qtest_qmp_event_ref a function which only scans
the buffer that qtest_qmp_receive stores the events to.  This is intended
for callers that are only interested in events that were received during
the last call to the qtest_qmp_receive.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20201006123904.610658-3-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 tests/qtest/libqos/libqtest.h | 23 ++++++++++++++++
 tests/qtest/libqtest.c        | 49 ++++++++++++++++++++++++++++++++++-
 2 files changed, 71 insertions(+), 1 deletion(-)

diff --git a/tests/qtest/libqos/libqtest.h b/tests/qtest/libqos/libqtest.h
index 9b3f99b322..b7a776068c 100644
--- a/tests/qtest/libqos/libqtest.h
+++ b/tests/qtest/libqos/libqtest.h
@@ -198,6 +198,16 @@ void qtest_qmp_vsend(QTestState *s, const char *fmt, va_list ap)
  */
 QDict *qtest_qmp_receive_dict(QTestState *s);
 
+/**
+ * qtest_qmp_receive:
+ * @s: #QTestState instance to operate on.
+ *
+ * Reads a QMP message from QEMU and returns the response.
+ * Buffers all the events received meanwhile, until a
+ * call to qtest_qmp_eventwait
+ */
+QDict *qtest_qmp_receive(QTestState *s);
+
 /**
  * qtest_qmp_eventwait:
  * @s: #QTestState instance to operate on.
@@ -217,6 +227,19 @@ void qtest_qmp_eventwait(QTestState *s, const char *event);
  */
 QDict *qtest_qmp_eventwait_ref(QTestState *s, const char *event);
 
+/**
+ * qtest_qmp_event_ref:
+ * @s: #QTestState instance to operate on.
+ * @event: event to return.
+ *
+ * Removes non-matching events from the buffer that was set by
+ * qtest_qmp_receive, until an event bearing the given name is found,
+ * and returns it.
+ * If no event matches, clears the buffer and returns NULL.
+ *
+ */
+QDict *qtest_qmp_event_ref(QTestState *s, const char *event);
+
 /**
  * qtest_qmp_receive_success:
  * @s: #QTestState instance to operate on
diff --git a/tests/qtest/libqtest.c b/tests/qtest/libqtest.c
index dadc465825..d4c49a52ff 100644
--- a/tests/qtest/libqtest.c
+++ b/tests/qtest/libqtest.c
@@ -63,6 +63,7 @@ struct QTestState
     bool irq_level[MAX_IRQ];
     GString *rx;
     QTestTransportOps ops;
+    GList *pending_events;
 };
 
 static GHookList abrt_hooks;
@@ -279,6 +280,7 @@ QTestState *qtest_init_without_qmp_handshake(const char *extra_args)
 
     g_test_message("starting QEMU: %s", command);
 
+    s->pending_events = NULL;
     s->wstatus = 0;
     s->expected_status = 0;
     s->qemu_pid = fork();
@@ -386,6 +388,13 @@ void qtest_quit(QTestState *s)
     close(s->fd);
     close(s->qmp_fd);
     g_string_free(s->rx, true);
+
+    for (GList *it = s->pending_events; it != NULL; it = it->next) {
+        qobject_unref((QDict *)it->data);
+    }
+
+    g_list_free(s->pending_events);
+
     g_free(s);
 }
 
@@ -603,6 +612,19 @@ QDict *qmp_fd_receive(int fd)
     return qmp.response;
 }
 
+QDict *qtest_qmp_receive(QTestState *s)
+{
+    while (true) {
+        QDict *response = qtest_qmp_receive_dict(s);
+
+        if (!qdict_get_try_str(response, "event")) {
+            return response;
+        }
+        /* Stash the event for a later consumption */
+        s->pending_events = g_list_prepend(s->pending_events, response);
+    }
+}
+
 QDict *qtest_qmp_receive_dict(QTestState *s)
 {
     return qmp_fd_receive(s->qmp_fd);
@@ -771,9 +793,33 @@ void qtest_qmp_send_raw(QTestState *s, const char *fmt, ...)
     va_end(ap);
 }
 
+QDict *qtest_qmp_event_ref(QTestState *s, const char *event)
+{
+    GList *next = NULL;
+    QDict *response;
+
+    for (GList *it = s->pending_events; it != NULL; it = next) {
+
+        next = it->next;
+        response = (QDict *)it->data;
+
+        s->pending_events = g_list_remove_link(s->pending_events, it);
+
+        if (!strcmp(qdict_get_str(response, "event"), event)) {
+            return response;
+        }
+        qobject_unref(response);
+    }
+    return NULL;
+}
+
 QDict *qtest_qmp_eventwait_ref(QTestState *s, const char *event)
 {
-    QDict *response;
+    QDict *response = qtest_qmp_event_ref(s, event);
+
+    if (response) {
+        return response;
+    }
 
     for (;;) {
         response = qtest_qmp_receive_dict(s);
@@ -1403,6 +1449,7 @@ QTestState *qtest_inproc_init(QTestState **s, bool log, const char* arch,
 {
     QTestState *qts;
     qts = g_new0(QTestState, 1);
+    qts->pending_events = NULL;
     *s = qts; /* Expose qts early on, since the query endianness relies on it */
     qts->wstatus = 0;
     for (int i = 0; i < MAX_IRQ; i++) {