client: check for luminous MDS before sending FLUSH_MDLOG

This is needed to make it safe to run newer clients
on pre-luminous MDS.

Signed-off-by: John Spray <john.spray@redhat.com>

diff --git a/src/client/Client.cc b/src/client/Client.cc
index 15019d11e13b44624ae2d9da644fc68723ff6766..c5813ed88e5ac8e4a16a31ca43e4a7ce2c028258 100644 (file)
--- a/src/client/Client.cc
+++ b/src/client/Client.cc
@@ -5812,8 +5812,13 @@ void Client::flush_mdlog_sync()
 
 void Client::flush_mdlog(MetaSession *session)
 {
-  MClientSession *m = new MClientSession(CEPH_SESSION_REQUEST_FLUSH_MDLOG);
-  session->con->send_message(m);
+  // Only send this to Luminous or newer MDS daemons, older daemons
+  // will crash if they see an unknown CEPH_SESSION_* value in this msg.
+  const uint64_t features = session->con->get_features();
+  if (HAVE_FEATURE(features, SERVER_LUMINOUS)) {
+    MClientSession *m = new MClientSession(CEPH_SESSION_REQUEST_FLUSH_MDLOG);
+    session->con->send_message(m);
+  }
 }