doc: Mention VSL changes

doc/sphinx/whats-new/changes-trunk.rst

@@ -47,7 +47,13 @@ VMODs
 varnishlog
 ==========
 
-**XXX changes concerning varnishlog(1) and/or vsl(7)**
+The ``BackendReuse`` log record has been retired. It was inconsistently named
+compared to other places like stat counters where we use the words reuse and
+recycle (it should have been named ``BackendRecycle`` if anything).
+
+The ``BackendOpen`` record can now tell whether the connection to the backend
+was opened or reused from the pool, and the ``BackendClose`` record will tell
+whether the connection was effectively closed or recycled into the pool.
 
 varnishadm
 ==========

doc/sphinx/whats-new/upgrading-trunk.rst

@@ -61,4 +61,16 @@ After::
     }
   }
 
+VSL
+===
+
+If you need to build VSL queries that depend on ``BackendReuse`` you can
+now rely on ``BackendClose``, for example::
+
+    varnishlog -q 'BackendReuse[2] ~ www'
+
+The new query would be::
+
+    varnishlog -q 'BackendClose[2] ~ www and BackendClose[3] eq recycle'
+
 *eof*