This should be easy ! ● Get the source code ● Build it ● Flash on device ● Enjoy ! 

Or more technically speaking. . . ＄ curl https://storage.googleapis.com/git-repo-downloads/repo > ~/bin/repo ＄ chmod a+x ~/bin/repo ＄ mkdir ~/android ＄ repo init -u https://android.googlesource.com/platform_manifest -b android- 6.0.0_r25 ＄ repo sync ＄ . build/envsetup.sh ＄ lunch full_hammerhead-eng ＄ make ＄ fastboot flash --all 

This should be easy, mostly. ● Get the source code ● Build it ● Make some changes ● Rebuild it ● Flash on device ● Enjoy ! 

This should be easy, mostly, I guess . . . ● Get the source code ● Build it ● Make some changes ● Rebuild it ● Flash on device ● Test it works ● Commit changes ● Enjoy ! 

This should be easy, mostly, I guess. Or is it really??? ● Get the source code ● Build it ● Make some changes ● Rebuild it ● Flash on device ● Test it works ● Commit changes ● Review everyone’s changes ● Release your Android ROM ● Enjoy ! Now fix all the reported bugs. 

Finally I can hack, build, deploy, and test ROMs with a wag of my tail ! Woof Woof ! 

Setting up an Android OS Project Source. Edit. Collaborate. Codereview. Build. Automate. Deploy. - Arnav Gupta 

Before we begin, let me gloat about myself a bit . . . Undergraduate Student, Electrical and Electronics, Delhi Technological University Contributor to CyanogenMod, AOKP and other custom ROM projects. Developer Relations team, YU Televentures. Few contributions to AOSP - in Kitkat and Lollipop. 

The important questions that come to mind ... 

… when we start building ● What architecture can you build on? What architecture can you build for ? ● What packages are needed to build the Android source code ? ● What environmental variables are needed ? ● What are the minimum hardware requirements ? ● How much time does it take to build? How to reduce ? ● Any steps to improve incremental builds ? ● How to build partially, or only some modules ? 

… when we start pushing and pulling ● How to pull updates from upstream ? ● How to collaborate as a team/community ? ● How to make source available over LAN ? ● How to reduce redundant data download when building multiple variant/version ? ● How to contribute to your own project? How to contribute back to Google? ● How to have a transparent, hierarchical, access-controlled code review ? 

… when we start distributing the OS ● How to send updates ? OTA or not ? ● Can OTA updates be delta ? ● How to update system apps over the play store ? ● How to make sure 3rd parties cannot exploit SignatureOrSystem perms ? ● Rooted or not ? Debugging enabled or not ? ● How to handle dirty flashes ? 

… when we use our own ROM 

Managing the source It's 25 GB. So let's not download what we don’t want. Building non AOSP devices means conflicting source trees If you are a company, you’d like to have a local copy of source, instead of each employee downloading it. Contribs & Codereview Github PR’s are great for a single repo. But Android spans across 400+ repos, many interdependent. One single patch might have dependencies on other patches on other projects. Managing rights to merge, make branches, approve. Automated verification that a patch doesn’t break the build. Build and distribute For frequent, multi-device builds, a fairly powerful build machine needed Make builds automatically available over a download server. Generate deltas for updates. Maintain proper versioning of builds. Differentiate between nightlies, betas, stable builds and releases. Keep track of bugs, and fix blames on build numbers correctly. The three problems, and the solutions 

Some numbers, before we begin 

12 GB Checked out size of the inflated source tree 

25 GB Android source code total git history size for Android 6.0 

450 Roughly the number of total repos in the AOSP manifest 

188,000 Patches up for review on android-review.googlesource.com 

197,300 Number of issues opened on code.google.com/p/android 

750,000 Total lines of C/C++ code (without comments) in Android system and bionic 

2,100,000 Total lines of Java code (exculding blanks, comments) in Android frameworks 

50,000,000 Number of people using Cyanogen OS and CyanogenMod ROMs 

42 The answer to life, universe and everything 

The Source There is just way too much of it. 

‘repo’ A tool made by Google to help in managing the source of huge projects like Android, Chromium repo init -u http://url.of/manifest repo sync [-f] [-j 4] repo init -g a,b,-c,-d repo start newbranch . repo upload 

‘repo’ A tool made by Google to help in managing the source of huge projects like Android, Chromium 

manifest An xml file defining all the git repos needed in the project 

The Build Compiled few million LoC, and takes an eternity 

The basic steps . build/envsetup.sh lunch [device-buildtype] lunch aosp_hammerhead-eng make make Contacts.apk cd packages/apps/Contacts && mmm Sets up the build environment. Initialises all env vars. Defines functions to various build tasks. Defines a target device. Generates makefiles and changes env vars accordingly. Well this one’s obvious Two ways to make the Contacts package. First one builds all dependencies. Second one works only for incremental builds. 

What can speed it up ? 

ccache To speed up low level file compilations (drivers, system) ● Set USE_CCACHE=1 and CCACHE_DIR appropriately ● First build will become longer. Subsequent builds will be shorter ● Use separate ccache folders per device if you can afford. ● Set a comfortably large cache max size 

prebuilt chromium * for versions prior to 6.0 (M) Instead of building inline, keep a prebuilt copy of webview.apk and libwebviewchromium.so Webview changes once every 2 months or so. Android 6.0 uses prebuilt Google- signed webview only. 

shared lib cache Cache the dynamic libs review.cyanogenmod.org/92967/ Caches the built up libs, per device. If no changes in source of a lib (or it’s dependencies), it won’t be built. Reduces 30-40% build times for recurring aarch64 builds. 

$$$ money $$$ So that you can ramp up your hardware 03:32:46 - Time taken for clean Nexus 5 build of AOSP 6.0 on Core i5 2.5 Ghz (2-core, hyperthreaded), 8 GB RAM, 5400rpm HDD. 00:24:03 - Time taken for clean Nexus 5 build of AOSP 6.0 on Core i7 3.0 Ghz (4-core hyperthreaded), 16 GB RAM, SSD. 

Code Review Where all the drama happens 

Let’s see some code reviews 

Some things are alarming 

Sometimes there is caution 

Sometimes people don’t want their own patch submitted 

And sometimes . . . well… 

But on a serious note 

Gerrit ● A code-review server written to work on top of Git ● Developed by Google to support large multi-repository projects like Chromium, Android etc. ● Supports comments, voting (+1, +2), approval and verification. ● Has REST API, can be accessed over SSH as well. 

Install Gerrit Download latest from : https://gerrit-releases.storage.googleapis.com/index.html $ wget https://www.gerritcodereview.com/download/gerrit-2.11.5.war Recommended to create separate user gerrit which will run the gerrit daemon. $ sudo adduser gerrit $ sudo su gerrit $ mkdir ~/gerrit_site $ java -jar gerrit-2.11.5.war init -d ~/gerrit_site 

Gerrit Install Wizard Create '/home/gerrit_test/gerrit' [Y/n]? Y Location of Git repositories [git]: Set anywhere, default $GERRIT/git Database server type [h2]: h2/mysql/postgres (default h2) Authentication method [OPENID/?]: OPENID/HTTPS/OAUTH Email Delivery : Use SMTP configs of Gmail/Hotmail etc, or use sendmail Listen on port [29418]: Port for SSH access to gerrit Http Daemon : Set up as per proxies and required port [8080] 

No content

Gerrit OAuth Plugin ● Google makes Gerrit ● Gerrit only supports OpenID ● Google has deprecated OpenID and uses Oauth via Google+ Signin ● Gerrit, by default, has OpenID, but no Oauth. So we need a plugin. 

On a separate note . . 

Google Search and Angular ● Google makes Angular.JS ● Angular is used to make single-page webapps ● Google search cannot index single-page webapps 

. . . but let’s not digress 

Add Oauth login/signup to Gerrit ● https://github.com/davido/gerrit-oauth-provider ● Get latest .jar from releases ● Add to $GERRIT/plugins/ ● Create an app on Google Dev Console. Get an “Other Application” auth token. ● Create an app on Github Dev Console. Get the auth tokens ● Re-run Gerrit init, the wizard will ask for above keys 

The Buildbot First you build the bot, then the bot builds. 

Installing Jenkins ＄ wget -q -O - https://jenkins-ci.org/debian/jenkins-ci.org.key | sudo apt-key add - ＄ sudo sh -c 'echo deb http://pkg.jenkins-ci.org/debian binary/ > /etc/apt/sources.list.d/jenkins.list' ＄ sudo apt-get update ＄ sudo apt-get install jenkins 

Installing Jenkins 

Distributed Jenkins builds ● We can use multiple slaves connected to a master Jenkins bot ● Best way is the use SSH based slaves. All slaved need to be running sshd. ● Add id_rsa.pub from master, and add to authorized_keys of slaves ● Set up the slave using - ○ Manage Jenkins -> Manage Nodes - > New Node 

OTA Updates 

Full size update AOSP ~ 350MB + Gapps ~150MB Enterprise OS can easily be 1 GB Cumbersome for end users to download Should be used only when a delta updates won’t work. OEM’s use full-size updates when updating via PC-suites. Hexdiff partition updates Smallest size updates. 5.0 > 6.0 can be as small as 100MB (for a 1 GB system image). Only safe for controlled environments. Won’t work on devices that are rooted and have a modified system partition. Ideally should check for partition integrity before getting applied. Filewise diff update An unconventional compromise between the two. Smaller than full-size update. Will work with modified system partitions too. http://gerrit.aokp.co/13262/ Different ways to do an OTA Update