replication asynchronous SYNC information in INFO output

src/redis.c

@@ -1183,12 +1183,23 @@ sds genRedisInfoString(void) {
             "master_port:%d\r\n"
             "master_link_status:%s\r\n"
             "master_last_io_seconds_ago:%d\r\n"
+            "master_sync_in_progress:%d\r\n"
             ,server.masterhost,
             server.masterport,
             (server.replstate == REDIS_REPL_CONNECTED) ?
                 "up" : "down",
-            server.master ? ((int)(time(NULL)-server.master->lastinteraction)) : -1
+            server.master ? ((int)(time(NULL)-server.master->lastinteraction)) : -1,
+            server.replstate == REDIS_REPL_TRANSFER
         );
+
+        if (server.replstate == REDIS_REPL_TRANSFER) {
+            info = sdscatprintf(info,
+                "master_sync_left_bytes:%ld\r\n"
+                "master_sync_last_io_seconds_ago:%d\r\n"
+                ,(long)server.repl_transfer_left,
+                (int)(time(NULL)-server.repl_transfer_lastio)
+            );
+        }
     }
     if (server.vm_enabled) {
         lockThreadedIO();