new INFO filed master_link_down_since_seconds

src/networking.c

@@ -523,6 +523,7 @@ void freeClient(redisClient *c) {
     if (c->flags & REDIS_MASTER) {
         server.master = NULL;
         server.replstate = REDIS_REPL_CONNECT;
+        server.repl_down_since = time(NULL);
         /* Since we lost the connection with the master, we should also
          * close the connection with all our slaves if we have any, so
          * when we'll resync with the master the other slaves will sync again

src/redis.c

@@ -853,6 +853,7 @@ void initServerConfig() {
     server.replstate = REDIS_REPL_NONE;
     server.repl_syncio_timeout = REDIS_REPL_SYNCIO_TIMEOUT;
     server.repl_serve_stale_data = 1;
+    server.repl_down_since = -1;
 
     /* Double constants initialization */
     R_Zero = 0.0;
@@ -1317,7 +1318,14 @@ sds genRedisInfoString(void) {
                 (int)(time(NULL)-server.repl_transfer_lastio)
             );
         }
+
+        if (server.replstate != REDIS_REPL_CONNECTED) {
+            info = sdscatprintf(info,
+                "master_link_down_since_seconds:%ld\r\n",
+                (long)time(NULL)-server.repl_down_since);
+        }
     }
+
     if (server.vm_enabled) {
         lockThreadedIO();
         info = sdscatprintf(info,

src/redis.h

@@ -452,6 +452,7 @@ struct redisServer {
     char *repl_transfer_tmpfile; /* slave-> master SYNC temp file name */
     time_t repl_transfer_lastio; /* unix time of the latest read, for timeout */
     int repl_serve_stale_data; /* Serve stale data when link is down? */
+    time_t repl_down_since; /* unix time at which link with master went down */
     /* Limits */
     unsigned int maxclients;
     unsigned long long maxmemory;