[PATCH 1/5] migration: Store downtime timestamps in an array

[Joao Martins <joao.m.martins@oracle.com>]

Right now downtime_start is stored in MigrationState.

In preparation to having more downtime timestamps during
switchover, move downtime_start to an array namely, @timestamp.

Add a setter/getter surrounding which timestamps to record,
to make it easier to spread to various migration functions.

Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
---
 qapi/migration.json   | 14 ++++++++++++++
 migration/migration.h |  7 +++++--
 migration/migration.c | 24 ++++++++++++++++++++----
 3 files changed, 39 insertions(+), 6 deletions(-)

diff --git a/qapi/migration.json b/qapi/migration.json
index 8843e74b59c7..b836cc881d33 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -190,6 +190,20 @@
 { 'struct': 'VfioStats',
   'data': {'transferred': 'int' } }
 
+##
+# @MigrationDowntime:
+#
+# An enumeration of downtime timestamps for all
+# steps of the switchover.
+#
+# @start:Timestamp taken at the start of the switchover right before
+#        we stop the VM.
+#
+# Since: 8.2
+##
+{ 'enum': 'MigrationDowntime',
+  'data': [ 'start' ] }
+
 ##
 # @MigrationInfo:
 #
diff --git a/migration/migration.h b/migration/migration.h
index c390500604b6..180dc31c5306 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -319,8 +319,8 @@ struct MigrationState {
     int64_t start_time;
     /* Total time used by latest migration (ms) */
     int64_t total_time;
-    /* Timestamp when VM is down (ms) to migrate the last stuff */
-    int64_t downtime_start;
+    /* Timestamps e.g. when VM is down (ms) to migrate the last stuff */
+    int64_t timestamp[MIGRATION_DOWNTIME__MAX];
     int64_t downtime;
     int64_t expected_downtime;
     bool capabilities[MIGRATION_CAPABILITY__MAX];
@@ -516,4 +516,7 @@ void migration_populate_vfio_info(MigrationInfo *info);
 void migration_reset_vfio_bytes_transferred(void);
 void postcopy_temp_page_reset(PostcopyTmpPage *tmp_page);
 
+void migration_set_timestamp(MigrationDowntime tm);
+int64_t migration_get_timestamp(MigrationDowntime tm);
+
 #endif
diff --git a/migration/migration.c b/migration/migration.c
index d61e5727429a..dd955c61acc7 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -2312,6 +2312,21 @@ static int migration_maybe_pause(MigrationState *s,
     return s->state == new_state ? 0 : -EINVAL;
 }
 
+void migration_set_timestamp(MigrationDowntime type)
+{
+    MigrationState *s = migrate_get_current();
+
+    s->timestamp[type] = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+}
+
+int64_t migration_get_timestamp(MigrationDowntime type)
+{
+    MigrationState *s = migrate_get_current();
+
+    return s->timestamp[type];
+}
+
+
 /**
  * migration_completion: Used by migration_thread when there's not much left.
  *   The caller 'breaks' the loop when this returns.
@@ -2325,7 +2340,7 @@ static void migration_completion(MigrationState *s)
 
     if (s->state == MIGRATION_STATUS_ACTIVE) {
         qemu_mutex_lock_iothread();
-        s->downtime_start = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+        migration_set_timestamp(MIGRATION_DOWNTIME_START);
         qemu_system_wakeup_request(QEMU_WAKEUP_REASON_OTHER, NULL);
 
         s->vm_old_state = runstate_get();
@@ -2670,7 +2685,7 @@ static void migration_calculate_complete(MigrationState *s)
          * It's still not set, so we are precopy migration.  For
          * postcopy, downtime is calculated during postcopy_start().
          */
-        s->downtime = end_time - s->downtime_start;
+        s->downtime = end_time - migration_get_timestamp(MIGRATION_DOWNTIME_START);
     }
 
     transfer_time = s->total_time - s->setup_time;
@@ -3069,7 +3084,8 @@ static void bg_migration_vm_start_bh(void *opaque)
     s->vm_start_bh = NULL;
 
     vm_start();
-    s->downtime = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) - s->downtime_start;
+    s->downtime = qemu_clock_get_ms(QEMU_CLOCK_REALTIME) -
+             migration_get_timestamp(MIGRATION_DOWNTIME_START);
 }
 
 /**
@@ -3134,7 +3150,7 @@ static void *bg_migration_thread(void *opaque)
     s->setup_time = qemu_clock_get_ms(QEMU_CLOCK_HOST) - setup_start;
 
     trace_migration_thread_setup_complete();
-    s->downtime_start = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+    migration_set_timestamp(MIGRATION_DOWNTIME_START);
 
     qemu_mutex_lock_iothread();
 
-- 
2.39.3