[PATCH 4/5] migration: Provide QMP access to downtime stats

[Joao Martins]

Deliver the downtime breakdown also via `query-migrate`
to allow users to understand what their downtime value
represents.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
---
 qapi/migration.json   | 22 ++++++++++++++++++++++
 migration/migration.c | 14 ++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/qapi/migration.json b/qapi/migration.json
index 2d91fbcb22ff..088e1b2bf440 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -217,6 +217,27 @@
   'data': [ 'start', 'stop', 'precopy-iterable', 'precopy-noniterable',
             'resume-return-path' ] }
 
+##
+# @DowntimeStats:
+#
+# Detailed migration downtime statistics.
+#
+# @stop: Time taken to stop the VM during switchover.
+#
+# @precopy: Time taken to save all precopy state during switchover.
+#
+# @precopy-iterable: Time taken to save all precopy iterable state.
+#
+# @precopy-noniterable: Time taken to save all precopy non iterable state.
+#
+# @resume-return-path: Time taken to resume if return path is enabled,
+#                      otherwise zero.
+#
+# Since: 8.2
+##
+{ 'struct': 'DowntimeStats',
+  'data': {'stop': 'int64', 'precopy': 'int64', 'precopy-iterable': 'int64',
+           'precopy-noniterable': 'int64', 'resume-return-path': 'int64' } }
 
 ##
 # @MigrationInfo:
@@ -308,6 +329,7 @@
            '*total-time': 'int',
            '*expected-downtime': 'int',
            '*downtime': 'int',
+           '*downtime-stats': 'DowntimeStats',
            '*setup-time': 'int',
            '*cpu-throttle-percentage': 'int',
            '*error-desc': 'str',
diff --git a/migration/migration.c b/migration/migration.c
index 4b5bed3eb09b..dec6c88fbff9 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -921,6 +921,19 @@ static int64_t 
migrate_get_downtime_resume_rp(MigrationState *s)
     return 0;
 }
 
+static void populate_downtime_info(MigrationInfo *info, MigrationState *s)
+{
+    DowntimeStats *stats;
+
+    info->downtime_stats = g_malloc0(sizeof(*info->downtime_stats));
+    stats = info->downtime_stats;
+    stats->stop = migrate_get_downtime_stop(s);
+    stats->precopy_iterable = migrate_get_downtime_precopy_iterable(s);
+    stats->precopy_noniterable = migrate_get_downtime_precopy_noniterable(s);
+    stats->precopy = stats->precopy_iterable + stats->precopy_noniterable;
+    stats->resume_return_path = migrate_get_downtime_resume_rp(s);
+}
+
 static void populate_time_info(MigrationInfo *info, MigrationState *s)
 {
     info->has_status = true;
@@ -939,6 +952,7 @@ static void populate_time_info(MigrationInfo *info, 
MigrationState *s)
     if (migrate_show_downtime(s)) {
         info->has_downtime = true;
         info->downtime = s->downtime;
+        populate_downtime_info(info, s);
     } else {
         info->has_expected_downtime = true;
         info->expected_downtime = s->expected_downtime;
-- 
2.39.3