doc: Add null:// manpage

src/channel/meson.build

@@ -37,6 +37,7 @@ endif
 
 mansources = [
 	'common.rst',
+	'null.rst',
 	'tcp.rst',
 	'udp.rst',
 	'zero.rst',

src/channel/null.rst

@@ -0,0 +1,46 @@
+tll-channel-zero
+================
+
+:Manual Section: 7
+:Manual Group: TLL
+:Subtitle: No-op blackhole channel
+
+Synopsis
+--------
+
+``null://``
+
+Description
+-----------
+
+Channel implements object that is never ready to provide message but always ready to consume them,
+like ``/dev/null`` special device. Post to does nothing and can never fail.
+
+This channel can be used to disable input or output stream - replace normal object with ``null://``
+without changing other configuration, output will be silently discarded and no input generated.
+
+Also it can be used in benchmarking - post overhead is several nanoseconds (due to single pointer
+call) and does small effect on overall time.
+
+Init parameters
+~~~~~~~~~~~~~~~
+
+This channel has no specific parameters other then common ones described in
+``tll-channel-common(7)``.
+
+Examples
+--------
+
+Create channel that consumes everything and generates nothing:
+
+::
+
+    null://
+
+See also
+--------
+
+``tll-channel-common(7)``
+
+..
+    vim: sts=4 sw=4 et tw=100