Add 'query-events' command to QMP to query async events

Sometimes it is neccessary for an application to determine
whether a particular QMP event is available, so they can
decide whether to use compatibility code instead. This
introduces a new 'query-events' command to QMP to do just
that

 { "execute": "query-events" }
 {"return": [{"name": "WAKEUP"},
             {"name": "SUSPEND"},
             {"name": "DEVICE_TRAY_MOVED"},
             {"name": "BLOCK_JOB_CANCELLED"},
             {"name": "BLOCK_JOB_COMPLETED"},
             ...snip...
             {"name": "SHUTDOWN"}]}

* monitor.c: Turn MonitorEvent -> string conversion
  into a lookup from a static table of constant strings.
  Add impl of qmp_query_events monitor command handler
* qapi-schema.json, qmp-commands.hx: Define contract of
  query-events command

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

4 files changed, 108 insertions, 62 deletions

diff --git a/monitor.c b/monitor.c
index f956c24e3..c21a76eed 100644
--- a/monitor.c
+++ b/monitor.c
@@ -422,6 +422,30 @@ static void timestamp_put(QDict *qdict)
     qdict_put_obj(qdict, "timestamp", obj);
 }
 
+
+static const char *monitor_event_names[] = {
+    [QEVENT_SHUTDOWN] = "SHUTDOWN",
+    [QEVENT_RESET] = "RESET",
+    [QEVENT_POWERDOWN] = "POWERDOWN",
+    [QEVENT_STOP] = "STOP",
+    [QEVENT_RESUME] = "RESUME",
+    [QEVENT_VNC_CONNECTED] = "VNC_CONNECTED",
+    [QEVENT_VNC_INITIALIZED] = "VNC_INITIALIZED",
+    [QEVENT_VNC_DISCONNECTED] = "VNC_DISCONNECTED",
+    [QEVENT_BLOCK_IO_ERROR] = "BLOCK_IO_ERROR",
+    [QEVENT_RTC_CHANGE] = "RTC_CHANGE",
+    [QEVENT_WATCHDOG] = "WATCHDOG",
+    [QEVENT_SPICE_CONNECTED] = "SPICE_CONNECTED",
+    [QEVENT_SPICE_INITIALIZED] = "SPICE_INITIALIZED",
+    [QEVENT_SPICE_DISCONNECTED] = "SPICE_DISCONNECTED",
+    [QEVENT_BLOCK_JOB_COMPLETED] = "BLOCK_JOB_COMPLETED",
+    [QEVENT_BLOCK_JOB_CANCELLED] = "BLOCK_JOB_CANCELLED",
+    [QEVENT_DEVICE_TRAY_MOVED] = "DEVICE_TRAY_MOVED",
+    [QEVENT_SUSPEND] = "SUSPEND",
+    [QEVENT_WAKEUP] = "WAKEUP",
+};
+QEMU_BUILD_BUG_ON(ARRAY_SIZE(monitor_event_names) != QEVENT_MAX)
+
 /**
  * monitor_protocol_event(): Generate a Monitor event
  *
@@ -435,68 +459,8 @@ void monitor_protocol_event(MonitorEvent event, QObject *data)
 
     assert(event < QEVENT_MAX);
 
-    switch (event) {
-        case QEVENT_SHUTDOWN:
-            event_name = "SHUTDOWN";
-            break;
-        case QEVENT_RESET:
-            event_name = "RESET";
-            break;
-        case QEVENT_POWERDOWN:
-            event_name = "POWERDOWN";
-            break;
-        case QEVENT_STOP:
-            event_name = "STOP";
-            break;
-        case QEVENT_RESUME:
-            event_name = "RESUME";
-            break;
-        case QEVENT_VNC_CONNECTED:
-            event_name = "VNC_CONNECTED";
-            break;
-        case QEVENT_VNC_INITIALIZED:
-            event_name = "VNC_INITIALIZED";
-            break;
-        case QEVENT_VNC_DISCONNECTED:
-            event_name = "VNC_DISCONNECTED";
-            break;
-        case QEVENT_BLOCK_IO_ERROR:
-            event_name = "BLOCK_IO_ERROR";
-            break;
-        case QEVENT_RTC_CHANGE:
-            event_name = "RTC_CHANGE";
-            break;
-        case QEVENT_WATCHDOG:
-            event_name = "WATCHDOG";
-            break;
-        case QEVENT_SPICE_CONNECTED:
-            event_name = "SPICE_CONNECTED";
-            break;
-        case QEVENT_SPICE_INITIALIZED:
-            event_name = "SPICE_INITIALIZED";
-            break;
-        case QEVENT_SPICE_DISCONNECTED:
-            event_name = "SPICE_DISCONNECTED";
-            break;
-        case QEVENT_BLOCK_JOB_COMPLETED:
-            event_name = "BLOCK_JOB_COMPLETED";
-            break;
-        case QEVENT_BLOCK_JOB_CANCELLED:
-            event_name = "BLOCK_JOB_CANCELLED";
-            break;
-        case QEVENT_DEVICE_TRAY_MOVED:
-             event_name = "DEVICE_TRAY_MOVED";
-            break;
-        case QEVENT_SUSPEND:
-            event_name = "SUSPEND";
-            break;
-        case QEVENT_WAKEUP:
-            event_name = "WAKEUP";
-            break;
-        default:
-            abort();
-            break;
-    }
+    event_name = monitor_event_names[event];
+    assert(event_name != NULL);
 
     qmp = qdict_new();
     timestamp_put(qmp);
@@ -738,6 +702,25 @@ CommandInfoList *qmp_query_commands(Error **errp)
     return cmd_list;
 }
 
+EventInfoList *qmp_query_events(Error **errp)
+{
+    EventInfoList *info, *ev_list = NULL;
+    MonitorEvent e;
+
+    for (e = 0 ; e < QEVENT_MAX ; e++) {
+        const char *event_name = monitor_event_names[e];
+        assert(event_name != NULL);
+        info = g_malloc0(sizeof(*info));
+        info->value = g_malloc0(sizeof(*info->value));
+        info->value->name = g_strdup(event_name);
+
+        info->next = ev_list;
+        ev_list = info;
+    }
+
+    return ev_list;
+}
+
 /* set the current CPU defined by the user */
 int monitor_set_cpu(int cpu_index)
 {
diff --git a/monitor.h b/monitor.h
index 0d498006f..cd1d8786d 100644
--- a/monitor.h
+++ b/monitor.h
@@ -41,6 +41,10 @@ typedef enum MonitorEvent {
     QEVENT_DEVICE_TRAY_MOVED,
     QEVENT_SUSPEND,
     QEVENT_WAKEUP,
+
+    /* Add to 'monitor_event_names' array in monitor.c when
+     * defining new events here */
+
     QEVENT_MAX,
 } MonitorEvent;
 
diff --git a/qapi-schema.json b/qapi-schema.json
index 2ca7195d2..94aa0ae4d 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -228,6 +228,28 @@
 { 'command': 'query-commands', 'returns': ['CommandInfo'] }
 
 ##
+# @EventInfo:
+#
+# Information about a QMP event
+#
+# @name: The event name
+#
+# Since: 1.2.0
+##
+{ 'type': 'EventInfo', 'data': {'name': 'str'} }
+
+##
+# @query-events:
+#
+# Return a list of supported QMP events by this server
+#
+# Returns: A list of @EventInfo for all supported events
+#
+# Since: 1.2.0
+##
+{ 'command': 'query-events', 'returns': ['EventInfo'] }
+
+##
 # @MigrationStats
 #
 # Detailed migration status.
diff --git a/qmp-commands.hx b/qmp-commands.hx
index db980fa81..9c15d3cbd 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -1179,6 +1179,43 @@ EQMP
     },
 
 SQMP
+query-events
+--------------
+
+List QMP available events.
+
+Each event is represented by a json-object, the returned value is a json-array
+of all events.
+
+Each json-object contains:
+
+- "name": event's name (json-string)
+
+Example:
+
+-> { "execute": "query-events" }
+<- {
+      "return":[
+         {
+            "name":"SHUTDOWN"
+         },
+         {
+            "name":"RESET"
+         }
+      ]
+   }
+
+Note: This example has been shortened as the real response is too long.
+
+EQMP
+
+    {
+        .name       = "query-events",
+        .args_type  = "",
+        .mhandler.cmd_new = qmp_marshal_input_query_events,
+    },
+
+SQMP
 query-chardev
 -------------