mds: include session uptime when diplaying session list

Fixes: http://tracker.ceph.com/issues/35937
Signed-off-by: Venky Shankar <vshankar@redhat.com>
(cherry picked from commit b23a204)

src/mds/MDSRank.cc

@@ -2144,6 +2144,7 @@ void MDSRankDispatcher::dump_sessions(const SessionFilter &filter, Formatter *f)
     if (s->is_open() || s->is_stale()) {
       f->dump_unsigned("request_load_avg", s->get_load_avg());
     }
+    f->dump_float("uptime", s->get_session_uptime());
     f->dump_int("replay_requests", is_clientreplay() ? s->get_request_count() : 0);
     f->dump_unsigned("completed_requests", s->get_num_completed_requests());
     f->dump_bool("reconnecting", server->waiting_for_reconnect(p->first.num()));

src/mds/SessionMap.h

@@ -228,6 +228,11 @@ class Session : public RefCountedObject {
     load_avg.hit(ceph_clock_now(), load_avg_rate);
   }
 
+  double get_session_uptime() const {
+    chrono::duration<double> uptime = clock::now() - birth_time;
+    return uptime.count();
+  }
+
   time get_birth_time() const {
     return birth_time;
   }