doc/cephfs/fs-nfs-export: add note about export update behavior

Signed-off-by: Sage Weil <sage@newdream.net>
(cherry picked from commit fc304f2d56c739633ae4a4f118d48c85a3affee0)

diff --git a/doc/cephfs/fs-nfs-exports.rst b/doc/cephfs/fs-nfs-exports.rst
index b07e4e0f6a3371fb3c34b8b6ed3bbaec0b8e5a4e..06f3b6deadf21e1bd5e5784a49fb46e9f04a1821 100644 (file)
--- a/doc/cephfs/fs-nfs-exports.rst
+++ b/doc/cephfs/fs-nfs-exports.rst
@@ -314,8 +314,14 @@ For example,::
      "clients": []
    }
 
-The exported JSON can be modified and then reapplied.  Here, *pseudo*
-and *access_type* are modified::
+The exported JSON can be modified and then reapplied.  Below, *pseudo*
+and *access_type* are modified.  When modifying an export, the
+provided JSON should fully describe the new state of the export (just
+as when creating a new export), with the exception of the
+authentication credentials, which will be carried over from the
+previous state of the export where possible.
+
+::
 
    $ ceph nfs export apply -i update_cephfs_export.json
    $ cat update_cephfs_export.json