From c5547e10f8274eb894e5871f6a84cc389e2270c6 Mon Sep 17 00:00:00 2001
From: Daniel Micay <danielmicay@gmail.com>
Date: Tue, 8 Oct 2019 09:15:37 -0400
Subject: [PATCH] document delta generation

---
 static/build.html | 44 +++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 43 insertions(+), 1 deletion(-)

diff --git a/static/build.html b/static/build.html
index 9201587f..549e60af 100644
--- a/static/build.html
+++ b/static/build.html
@@ -67,7 +67,12 @@
                         <li><a href="#upgrading-to-android-10">Upgrading to Android 10</a></li>
                     </ul>
                 </li>
-                <li><a href="#generating-signed-factory-images-and-full-update-packages">Generating signed factory images and full update packages</a></li>
+                <li>
+                    <a href="#generating-signed-factory-images-and-full-update-packages">Generating signed factory images and full update packages</a>
+                    <ul>
+                        <li><a href="#generating-delta-updates">Generating delta updates</a></li>
+                    </ul>
+                </li>
                 <li>
                     <a href="#prebuilt-code">Prebuilt code</a>
                     <ul>
@@ -546,6 +551,43 @@ cd ../..</pre>
             incremental updates from those to the most recent signed <code>target_files</code>
             zip.</p>
 
+            <h3 id="generating-delta-updates">
+                <a href="#generating-delta-updates">Generating delta updates</a>
+            </h3>
+
+            <p>Incremental updates shipping only the changes between two versions can be generated
+            as a much more efficient way of shipping updates than a full update package containing
+            the entire operating system. The GrapheneOS Updater app will automatically use a delta
+            update if one exists for going directly from the currently installed version to the
+            latest release. In order to generate a delta update, the original signed target files
+            package for both the source version and target version are needed. The
+            <code>script/generate_delta.sh</code> script provides a wrapper script for generating
+            delta updates by passing the device, source version build number and target version
+            build number. For example:</p>
+
+            <pre>script/generate_delta.sh crosshatch 2019.09.25.00 2019.10.07.21</pre>
+
+            <p>The script assumes that the releases are organized in the following directory
+            structure:</p>
+
+<pre>releases
+├── 2019.09.25.00
+│   └── release-crosshatch-2019.09.25.00
+│       ├── crosshatch-factory-2019.09.25.00.zip
+│       ├── crosshatch-factory-2019.09.25.00.zip.sig
+│       ├── crosshatch-img-2019.09.25.00.zip
+│       ├── crosshatch-ota_update-2019.09.25.00.zip
+│       ├── crosshatch-target_files-2019.09.25.00.zip
+│       └── crosshatch-testing
+└── 2019.10.07.21
+    └── release-crosshatch-2019.10.07.21
+        ├── crosshatch-factory-2019.10.07.21.zip
+        ├── crosshatch-factory-2019.10.07.21.zip.sig
+        ├── crosshatch-img-2019.10.07.21.zip
+        ├── crosshatch-ota_update-2019.10.07.21.zip
+        ├── crosshatch-target_files-2019.10.07.21.zip
+        └── crosshatch-testing</pre>
+
             <h2 id="prebuilt-code">
                 <a href="#prebuilt-code">Prebuilt code</a>
             </h2>