mgr: initialize PyModuleRegistry sooner

This was waiting on MgrMap to init, so that it would know whether
modules should be enabled.  However, you don't really need to know
that until someone calls standby_start or active_start, so we
can initialize during MgrStandby::init, and fill out the enabled
flags later.

This prevents the mgr from prematurely emitting a MMgrBeacon
that claims no modules are found.

http://tracker.ceph.com/issues/22918
Signed-off-by: John Spray <john.spray@redhat.com>

src/mgr/MgrStandby.cc

@@ -141,6 +141,8 @@ int MgrStandby::init()
   client.init();
   timer.init();
 
+  py_module_registry.init();
+
   tick();
 
   dout(4) << "Complete." << dendl;
@@ -327,6 +329,8 @@ void MgrStandby::handle_mgr_map(MMgrMap* mmap)
   dout(4) << "active in map: " << active_in_map
           << " active is " << map.active_gid << dendl;
 
+  // We initialize py_module_registry on the first MgrMap, because earlier
+  // we did not know which modules should be enabled.
   if (!py_module_registry.is_initialized()) {
     int r = py_module_registry.init(map);
 

src/mgr/PyModuleRegistry.cc

@@ -37,7 +37,7 @@ std::string PyModuleRegistry::config_prefix;
 
 
 
-int PyModuleRegistry::init(const MgrMap &map)
+int PyModuleRegistry::init()
 {
   Mutex::Locker locker(lock);
 
@@ -79,6 +79,8 @@ int PyModuleRegistry::init(const MgrMap &map)
 
     bool enabled = (mgr_map.modules.count(module_name) > 0);
 
+    // Everything starts disabled, set enabled flag on module
+    // when we see first MgrMap
     auto mod = std::make_shared<PyModule>(module_name, enabled);
     int r = mod->load(pMainThreadState);
     if (r != 0) {
@@ -109,6 +111,10 @@ void PyModuleRegistry::standby_start(MonClient *monc)
   assert(standby_modules == nullptr);
   assert(is_initialized());
 
+  // Must have seen a MgrMap by this point, in order to know
+  // which modules should be enabled
+  assert(mgr_map.epoch > 0);
+
   dout(4) << "Starting modules in standby mode" << dendl;
 
   standby_modules.reset(new StandbyPyModules(monc, mgr_map, clog));

src/mgr/PyModuleRegistry.h

@@ -85,6 +85,11 @@ class PyModuleRegistry
   {
     Mutex::Locker l(lock);
 
+    if (mgr_map.epoch == 0) {
+      // First time we see MgrMap, set the enabled flags on modules
+      xyz todo
+    }
+
     bool modules_changed = mgr_map_.modules != mgr_map.modules;
     mgr_map = mgr_map_;
 
@@ -100,7 +105,7 @@ class PyModuleRegistry
     return mgr_map.epoch > 0;
   }
 
-  int init(const MgrMap &map);
+  int init();
 
   void active_start(
                 PyModuleConfig &config_,