qapi: Add HV_BALLOON_STATUS_REPORT event and its QMP query command

Used by the hv-balloon driver for (optional) guest memory status reports.

Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>

hw/hyperv/hv-balloon-stub.c

@@ -0,0 +1,19 @@
+/*
+ * QEMU Hyper-V Dynamic Memory Protocol driver
+ *
+ * Copyright (C) 2023 Oracle and/or its affiliates.
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "qapi/qapi-commands-machine.h"
+#include "qapi/qapi-types-machine.h"
+
+HvBalloonInfo *qmp_query_hv_balloon_status_report(Error **errp)
+{
+    error_setg(errp, "hv-balloon device not enabled in this build");
+    return NULL;
+}

hw/hyperv/hv-balloon.c

@@ -1102,7 +1102,35 @@ static void hv_balloon_handle_status_report(HvBalloon *balloon,
     balloon->status_report.available *= HV_BALLOON_PAGE_SIZE;
     balloon->status_report.received = true;
 
-    /* report event */
+    qapi_event_send_hv_balloon_status_report(balloon->status_report.committed,
+                                             balloon->status_report.available);
+}
+
+HvBalloonInfo *qmp_query_hv_balloon_status_report(Error **errp)
+{
+    HvBalloon *balloon;
+    HvBalloonInfo *info;
+
+    balloon = HV_BALLOON(object_resolve_path_type("", TYPE_HV_BALLOON, NULL));
+    if (!balloon) {
+        error_setg(errp, "no %s device present", TYPE_HV_BALLOON);
+        return NULL;
+    }
+
+    if (!balloon->status_report.enabled) {
+        error_setg(errp, "guest memory status reporting not enabled");
+        return NULL;
+    }
+
+    if (!balloon->status_report.received) {
+        error_setg(errp, "no guest memory status report received yet");
+        return NULL;
+    }
+
+    info = g_malloc0(sizeof(*info));
+    info->committed = balloon->status_report.committed;
+    info->available = balloon->status_report.available;
+    return info;
 }
 
 static void hv_balloon_handle_unballoon_response(HvBalloon *balloon,

hw/hyperv/meson.build

@@ -2,4 +2,4 @@ specific_ss.add(when: 'CONFIG_HYPERV', if_true: files('hyperv.c'))
 specific_ss.add(when: 'CONFIG_HYPERV_TESTDEV', if_true: files('hyperv_testdev.c'))
 specific_ss.add(when: 'CONFIG_VMBUS', if_true: files('vmbus.c'))
 specific_ss.add(when: 'CONFIG_SYNDBG', if_true: files('syndbg.c'))
-specific_ss.add(when: 'CONFIG_HV_BALLOON', if_true: files('hv-balloon.c', 'hv-balloon-page_range_tree.c', 'hv-balloon-our_range_memslots.c'))
+specific_ss.add(when: 'CONFIG_HV_BALLOON', if_true: files('hv-balloon.c', 'hv-balloon-page_range_tree.c', 'hv-balloon-our_range_memslots.c'), if_false: files('hv-balloon-stub.c'))

monitor/monitor.c

@@ -315,6 +315,7 @@ static MonitorQAPIEventConf monitor_qapi_event_conf[QAPI_EVENT__MAX] = {
     [QAPI_EVENT_QUORUM_FAILURE]    = { 1000 * SCALE_MS },
     [QAPI_EVENT_VSERPORT_CHANGE]   = { 1000 * SCALE_MS },
     [QAPI_EVENT_MEMORY_DEVICE_SIZE_CHANGE] = { 1000 * SCALE_MS },
+    [QAPI_EVENT_HV_BALLOON_STATUS_REPORT] = { 1000 * SCALE_MS },
 };
 
 /*

qapi/machine.json

@@ -1137,6 +1137,68 @@
 { 'event': 'BALLOON_CHANGE',
   'data': { 'actual': 'int' } }
 
+##
+# @HvBalloonInfo:
+#
+# hv-balloon guest-provided memory status information.
+#
+# @committed: the amount of memory in use inside the guest plus the
+#     amount of the memory unusable inside the guest (ballooned out,
+#     offline, etc.)
+#
+# @available: the amount of the memory inside the guest available for
+#     new allocations ("free")
+#
+# Since: 8.2
+##
+{ 'struct': 'HvBalloonInfo',
+  'data': { 'committed': 'size', 'available': 'size' } }
+
+##
+# @query-hv-balloon-status-report:
+#
+# Returns the hv-balloon driver data contained in the last received "STATUS"
+# message from the guest.
+#
+# Returns:
+# - @HvBalloonInfo on success
+# - If no hv-balloon device is present, guest memory status reporting
+#   is not enabled or no guest memory status report received yet,
+#   GenericError
+#
+# Since: 8.2
+#
+# Example:
+#
+# -> { "execute": "query-hv-balloon-status-report" }
+# <- { "return": {
+#          "committed": 816640000,
+#          "available": 3333054464
+#       }
+#    }
+##
+{ 'command': 'query-hv-balloon-status-report', 'returns': 'HvBalloonInfo' }
+
+##
+# @HV_BALLOON_STATUS_REPORT:
+#
+# Emitted when the hv-balloon driver receives a "STATUS" message from
+# the guest.
+#
+# Note: this event is rate-limited.
+#
+# Since: 8.2
+#
+# Example:
+#
+# <- { "event": "HV_BALLOON_STATUS_REPORT",
+#      "data": { "committed": 816640000, "available": 3333054464 },
+#      "timestamp": { "seconds": 1600295492, "microseconds": 661044 } }
+#
+##
+{ 'event': 'HV_BALLOON_STATUS_REPORT',
+  'data': 'HvBalloonInfo' }
+
 ##
 # @MemoryInfo:
 #

tests/qtest/qmp-cmd-test.c

@@ -45,6 +45,7 @@ static int query_error_class(const char *cmd)
         { "query-acpi-ospm-status", ERROR_CLASS_GENERIC_ERROR },
         { "query-balloon", ERROR_CLASS_DEVICE_NOT_ACTIVE },
         { "query-hotpluggable-cpus", ERROR_CLASS_GENERIC_ERROR },
+        { "query-hv-balloon-status-report", ERROR_CLASS_GENERIC_ERROR },
         { "query-vm-generation-id", ERROR_CLASS_GENERIC_ERROR },
         /* Only valid with a USB bus added */
         { "x-query-usb", ERROR_CLASS_GENERIC_ERROR },