From 8eb20d1fb0eb3a3b96d5e80e2e2617f893ef6986 Mon Sep 17 00:00:00 2001
From: Siri Hansen <siri@erlang.org>
Date: Thu, 20 Feb 2014 16:45:28 +0100
Subject: Add info about upgrade of core applications

In ref man for appup and in system documentation, design prinsiples,
add a warning related to upgrade when version of erts, kernel, stdlib
or sasl is changed. This will cause an emulator restart where new
version of emulator and core applications will startup together with
old versions of other applications. Care must be taken to avoid
problems due to backwards incompatibility.
---
 lib/sasl/doc/src/appup.xml                        | 23 ++++++++++++++++++++---
 system/doc/design_principles/release_handling.xml | 17 +++++++++++++++--
 2 files changed, 35 insertions(+), 5 deletions(-)

diff --git a/lib/sasl/doc/src/appup.xml b/lib/sasl/doc/src/appup.xml
index 85fcbed3ba..95f315d269 100644
--- a/lib/sasl/doc/src/appup.xml
+++ b/lib/sasl/doc/src/appup.xml
@@ -4,7 +4,7 @@
 <fileref>
   <header>
     <copyright>
-      <year>1997</year><year>2013</year>
+      <year>1997</year><year>2014</year>
       <holder>Ericsson AB. All Rights Reserved.</holder>
     </copyright>
     <legalnotice>
@@ -84,6 +84,9 @@
     version identifier must be specified as a binary, e.g.</p>
     <code type="none">&lt;&lt;"2\\.1\\.[0-9]+">></code>
     <p>will match all versions <c>2.1.x</c>, where x is any number.</p>
+    <p>Note that the regular expression must match the complete
+    version string, so the above example will work for for
+    e.g. <c>2.1.1</c>, but not for <c>2.1.1.1</c></p>
   </section>
 
   <section>
@@ -339,7 +342,7 @@ restart_new_emulator
       version of erts, kernel, stdlib and sasl are used when the
       emulator restarts. Only one <c>restart_new_emulator</c>
       instruction is allowed in the relup, and it shall be placed
-      first. <seealso marker="systools#make_relup/3">systools:make_relup3,4</seealso>
+      first. <seealso marker="systools#make_relup/3">systools:make_relup/3,4</seealso>
       will ensure this when the relup is generated. The rest of the
       relup script is executed after the restart as a part of the boot
       script.</p>
@@ -347,11 +350,25 @@ restart_new_emulator
       completed. To programatically find out if the upgrade is
       complete,
       call <seealso marker="release_handler#which_releases/0">
-      release_handler:which_releases</seealso> and check if the
+      release_handler:which_releases/0,1</seealso> and check if the
       expected release has status <c>current</c>.</p>
     <p>The new release must still be made permanent after the upgrade
       is completed. Otherwise, the old emulator is started in case of
       an emulator restart.</p>
+    <warning>
+      <p>As stated above, the <c>restart_new_emulator</c>
+	instruction causes the emulator to be restarted with new
+	versions of <c>erts</c>, <c>kernel</c>, <c>stdlib</c> and
+	<c>sasl</c>. All other applications, however, will at startup
+	be running their old versions in this new emulator. In most
+	cases this is no problem, but every now and then there will be
+	incompatible changes to the core applications which may cause
+	trouble in this setting. Such incompatible changes (when
+	functions are removed) are normally preceded by a deprecation
+	over two major releases. To make sure your application is not
+	crashed by an incompatible change, always remove any call to
+	deprecated functions as soon as possible.</p>
+    </warning>
     <pre>
 restart_emulator
     </pre>
diff --git a/system/doc/design_principles/release_handling.xml b/system/doc/design_principles/release_handling.xml
index 2a5831b89f..ba8a88d1c2 100644
--- a/system/doc/design_principles/release_handling.xml
+++ b/system/doc/design_principles/release_handling.xml
@@ -4,7 +4,7 @@
 <chapter>
   <header>
     <copyright>
-      <year>2003</year><year>2013</year>
+      <year>2003</year><year>2014</year>
       <holder>Ericsson AB. All Rights Reserved.</holder>
     </copyright>
     <legalnotice>
@@ -329,13 +329,26 @@
         automatically ensured.</p>
       <p>When the release handler encounters the instruction, it first
         generates a temporary boot file, which starts the new versions
-        of the emulator and the core applications. Then it shuts down
+        of the emulator and the core applications, and the old version
+        of all other applications. Then it shuts down
         the current emulator by calling <c>init:reboot()</c>, see
         <c>init(3)</c>. All processes are terminated gracefully and
         the system is rebooted by the heart program, using the
         temporary boot file. After the reboot, the rest of the relup
         instructions are executed. This is done as a part of the
         temporary boot script.</p>
+      <warning>
+	<p>Since this mechanism causes the new versions of the
+	emulator and core applications to run with the old version of
+	other applications during startup, extra care must be taken to
+	avoid incompatibility. Incompatible changes in the core
+	applications may in some situations be necessary. If possible,
+	such changes are preceded by deprecation over two major
+	releases before the actual change. To make sure your
+	application is not crashed by an incompatible change, always
+	remove any call to deprecated functions as soon as
+	possible.</p>
+      </warning>
       <p>An info report is written when the upgrade is completed. To
         programatically find out if the upgrade is complete,
         call <c>release_handler:which_releases(current)</c> and check
-- 
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