File 2865-Add-fix-comments.patch of Package erlang

From b47e36d305f463fb7b3c27dad79086b38a283480 Mon Sep 17 00:00:00 2001
From: Anders Svensson <anders@erlang.org>
Date: Sun, 9 Feb 2020 19:39:33 +0100
Subject: [PATCH 5/7] Add/fix comments

The former in diameter_dist, on the role of its gen_server the; latter
in diameter_traffic, on how a request on a remote node is processed.
---
 lib/diameter/src/base/diameter_dist.erl    | 17 ++++++++++++++++-
 lib/diameter/src/base/diameter_traffic.erl | 18 ++++++++++++------
 2 files changed, 28 insertions(+), 7 deletions(-)

diff --git a/lib/diameter/src/base/diameter_dist.erl b/lib/diameter/src/base/diameter_dist.erl
index ed23152b8b..1edca58eb9 100644
--- a/lib/diameter/src/base/diameter_dist.erl
+++ b/lib/diameter/src/base/diameter_dist.erl
@@ -1,7 +1,7 @@
 %%
 %% %CopyrightBegin%
 %%
-%% Copyright Ericsson AB 2019. All Rights Reserved.
+%% Copyright Ericsson AB 2019-2020. All Rights Reserved.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -27,6 +27,21 @@
 %% transport configuration, to be able to distribute incoming Diameter
 %% requests to handler processes (local or remote) in various ways.
 %%
+%% The gen_server implemented here must be started on each node on
+%% which {diameter_dist, route_session, _} is configured as a
+%% spawn_opt MFA, as well as each node that wants to receive requests.
+%% This happens as a consequence of diameter application start, but a
+%% minimal solution could start only this server on nodes that should
+%% handle requests but not configure transport. (Although the typical
+%% case is probably that diameter should be started in any case; for
+%% example, to be able to originate requests.)
+%%
+%% Moreover, attach/1 must be called to communicate the list of
+%% services for which the local node is willing to handle requests.
+%% The servers on different nodes communicate so that each server
+%% knows which nodes are prepared to handle requests for which
+%% services.
+%%
 
 %% spawn_opt callbacks
 -export([spawn_local/2,
diff --git a/lib/diameter/src/base/diameter_traffic.erl b/lib/diameter/src/base/diameter_traffic.erl
index cdcb113170..3a85b7c4d7 100644
--- a/lib/diameter/src/base/diameter_traffic.erl
+++ b/lib/diameter/src/base/diameter_traffic.erl
@@ -284,12 +284,18 @@ recv(false, false, TPid, Pkt, _, _) ->
 spawn_request(false, _, _, _, _, _, _) ->  %% no transport
     discard;
 
-%% An MFA should return the pid() of a process in which the argument
-%% fun in applied, or the atom 'discard' if the fun is not applied.
-%% The latter results in an acknowledgment back to the transport
-%% process when appropriate, to ensure that send/recv callbacks can
-%% count outstanding requests. Acknowledgement is implicit if the
-%% handler process dies (in a handle_request callback for example).
+%% An MFA should return the pid() of a process that invokes
+%% diameter_traffic:request(ReqT), or the atom 'discard' if the
+%% function is not called. The latter results in an acknowledgment
+%% back to the transport process when appropriate, to ensure that
+%% send/recv callbacks can count outstanding requests. Acknowledgement
+%% is implicit if the handler process dies (in a handle_request
+%% callback for example).
+%%
+%% There is no requirement that diameter be started on nodes on which
+%% handler processes are spawned, just that diameter and application
+%% callbacks are on the code path. (Although the MFA itself may have
+%% requirements, as in the case of diameter_dist.)
 spawn_request(AppT, {M,F,A}, Ack, TPid, Pkt, Dict0, RecvData) ->
     %% Term to pass to request/1 in an appropriate process. Module
     %% diameter_dist implements callbacks.
-- 
2.16.4