Migration: Emit event at start of pass

Emit an event each time we sync the dirty bitmap on the source;
this helps libvirt use postcopy by giving it a kick when it
might be a good idea to start the postcopy.
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: NJuan Quintela <quintela@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NAmit Shah <amit.shah@redhat.com>
Message-Id: <1450266458-3178-5-git-send-email-dgilbert@redhat.com>
Signed-off-by: NAmit Shah <amit.shah@redhat.com>

docs/qmp-events.txt

@@ -496,6 +496,20 @@ Example:
 {"timestamp": {"seconds": 1432121972, "microseconds": 744001},
  "event": "MIGRATION", "data": {"status": "completed"}}
 
+MIGRATION_PASS
+--------------
+
+Emitted from the source side of a migration at the start of each pass
+(when it syncs the dirty bitmap)
+
+Data: None.
+
+  - "pass": An incrementing count (starting at 1 on the first pass)
+
+Example:
+{"timestamp": {"seconds": 1449669631, "microseconds": 239225},
+ "event": "MIGRATION_PASS", "data": {"pass": 2}}
+
 STOP
 ----
 

migration/ram.c

@@ -27,6 +27,7 @@
  */
 #include <stdint.h>
 #include <zlib.h>
+#include "qapi-event.h"
 #include "qemu/bitops.h"
 #include "qemu/bitmap.h"
 #include "qemu/timer.h"
@@ -682,6 +683,9 @@ static void migration_bitmap_sync(void)
         num_dirty_pages_period = 0;
     }
     s->dirty_sync_count = bitmap_sync_count;
+    if (migrate_use_events()) {
+        qapi_event_send_migration_pass(bitmap_sync_count, NULL);
+    }
 }
 
 /**

qapi/event.json

@@ -254,6 +254,19 @@
 { 'event': 'MIGRATION',
   'data': {'status': 'MigrationStatus'}}
 
+##
+# @MIGRATION_PASS
+#
+# Emitted from the source side of a migration at the start of each pass
+# (when it syncs the dirty bitmap)
+#
+# @pass: An incrementing count (starting at 1 on the first pass)
+#
+# Since: 2.6
+##
+{ 'event': 'MIGRATION_PASS',
+  'data': { 'pass': 'int' } }
+
 ##
 # @ACPI_DEVICE_OST
 #