[PATCH] migration/dirtyrate: present dirty rate only when querying the rate has completed

[Chuan Zheng <zhengchuan@huawei.com>]

Make dirty_rate field optional, present dirty rate only when querying
the rate has completed.
The qmp results is shown as follow:
@unstarted:
{"return":{"status":"unstarted","start-time":0,"calc-time":0},"id":"libvirt-12"}
@measuring:
{"return":{"status":"measuring","start-time":0,"calc-time":0},"id":"libvirt-14"}
@measured:
{"return":{"status":"measured","dirty-rate":4,"start-time":150146,"calc-time":1},"id":"libvirt-15"}

Signed-off-by: Chuan Zheng <zhengchuan@huawei.com>
---
 migration/dirtyrate.c | 3 +--
 qapi/migration.json   | 9 ++++-----
 2 files changed, 5 insertions(+), 7 deletions(-)

diff --git a/migration/dirtyrate.c b/migration/dirtyrate.c
index 68577ef..9024b0f 100644
--- a/migration/dirtyrate.c
+++ b/migration/dirtyrate.c
@@ -69,9 +69,8 @@ static struct DirtyRateInfo *query_dirty_rate_info(void)
     struct DirtyRateInfo *info = g_malloc0(sizeof(DirtyRateInfo));
 
     if (qatomic_read(&CalculatingState) == DIRTY_RATE_STATUS_MEASURED) {
+        info->has_dirty_rate = true;
         info->dirty_rate = dirty_rate;
-    } else {
-        info->dirty_rate = -1;
     }
 
     info->status = CalculatingState;
diff --git a/qapi/migration.json b/qapi/migration.json
index ce2216c..6e428f7 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -1743,10 +1743,9 @@
 #
 # Information about current dirty page rate of vm.
 #
-# @dirty-rate: @dirtyrate describing the dirty page rate of vm
-#          in units of MB/s.
-#          If this field returns '-1', it means querying has not
-#          yet started or completed.
+# @dirty-rate: dirty-rate describing the dirty page rate of vm
+#              in units of MB/s, present only when querying the
+#              rate has completed.
 #
 # @status: status containing dirtyrate query status includes
 #          'unstarted' or 'measuring' or 'measured'
@@ -1759,7 +1758,7 @@
 #
 ##
 { 'struct': 'DirtyRateInfo',
-  'data': {'dirty-rate': 'int64',
+  'data': {'*dirty-rate': 'int64',
            'status': 'DirtyRateStatus',
            'start-time': 'int64',
            'calc-time': 'int64'} }
-- 
1.8.3.1