doc/mgr: Add limitations section to plugin guide

Signed-off-by: Tim Serong <tserong@suse.com>

diff --git a/doc/mgr/plugins.rst b/doc/mgr/plugins.rst
index 9e73b7a58cdf20991fe3cb74e703329b73168686..ecf2943d39f604b920001eea7d2aeb3320e72957 100644 (file)
--- a/doc/mgr/plugins.rst
+++ b/doc/mgr/plugins.rst
@@ -193,6 +193,15 @@ If a module implements the ``serve()`` method, it should also implement
 the ``shutdown()`` method to shutdown cleanly: misbehaving modules
 may otherwise prevent clean shutdown of ceph-mgr.
 
+Limitations
+-----------
+
+It is not possible to call back into C++ code from a module's
+``__init__()`` method.  For example calling ``self.get_config()`` at
+this point will result in an assertion failure in ceph-mgr.  For modules
+that implement the ``serve()`` method, it usually makes sense to do most
+initialization inside that method instead.
+
 Is something missing?
 ---------------------