qapi: Add new command to query colo status

Libvirt or other high level software can use this command query colo status.
You can test this command like that:
{'execute':'query-colo-status'}

Signed-off-by: Zhang Chen <zhangckid@gmail.com>
Signed-off-by: Zhang Chen <chen.zhang@intel.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

migration/colo.c

@@ -29,6 +29,7 @@
 #include "net/colo.h"
 #include "block/block.h"
 #include "qapi/qapi-events-migration.h"
+#include "qapi/qmp/qerror.h"
 
 static bool vmstate_loading;
 static Notifier packets_compare_notifier;
@@ -237,6 +238,26 @@ void qmp_xen_colo_do_checkpoint(Error **errp)
 #endif
 }
 
+COLOStatus *qmp_query_colo_status(Error **errp)
+{
+    COLOStatus *s = g_new0(COLOStatus, 1);
+
+    s->mode = get_colo_mode();
+
+    switch (failover_get_state()) {
+    case FAILOVER_STATUS_NONE:
+        s->reason = COLO_EXIT_REASON_NONE;
+        break;
+    case FAILOVER_STATUS_REQUIRE:
+        s->reason = COLO_EXIT_REASON_REQUEST;
+        break;
+    default:
+        s->reason = COLO_EXIT_REASON_ERROR;
+    }
+
+    return s;
+}
+
 static void colo_send_message(QEMUFile *f, COLOMessage msg,
                               Error **errp)
 {

qapi/migration.json

@@ -1307,6 +1307,38 @@
 ##
 { 'command': 'xen-colo-do-checkpoint' }
 
+##
+# @COLOStatus:
+#
+# The result format for 'query-colo-status'.
+#
+# @mode: COLO running mode. If COLO is running, this field will return
+#        'primary' or 'secondary'.
+#
+# @reason: describes the reason for the COLO exit.
+#
+# Since: 3.0
+##
+{ 'struct': 'COLOStatus',
+  'data': { 'mode': 'COLOMode', 'reason': 'COLOExitReason' } }
+
+##
+# @query-colo-status:
+#
+# Query COLO status while the vm is running.
+#
+# Returns: A @COLOStatus object showing the status.
+#
+# Example:
+#
+# -> { "execute": "query-colo-status" }
+# <- { "return": { "mode": "primary", "active": true, "reason": "request" } }
+#
+# Since: 3.0
+##
+{ 'command': 'query-colo-status',
+  'returns': 'COLOStatus' }
+
 ##
 # @migrate-recover:
 #