Introduction au portage#

Cette première section vous présentera les spécificités du portage d’Ubuntu Touch sur un appareil Android. Veuillez noter qu’elle a été rédigée à l’intention du grand public et non du développeur de portage expérimenté. Dans les sections suivantes, nous avons fait un effort de différenciation en gardant le texte principal plus concis afin de répondre aux besoins du lecteur plus expérimenté, tout en fournissant des liens vers des lectures complémentaires pour les moins expérimentés.

L’ensemble du guide est rédigé sous forme d’une séquence d’étapes décrivant comment pourrait se passer un portage idéal. Cependant, le portage est imprévisible et compliqué. Chaque appareil est différent et, en réalité, vous allez probablement itérer sur certaines étapes, en sauter d’autres et découvrir des défis nouveaux et non documentés.

Qu’est-ce qu’Ubuntu Touch ?#

Ubuntu Touch est un système d’exploitation libre pour les appareils mobiles. Il peut être porté sur des appareils qui, à l’origine, étaient équipés d’un système d’exploitation Android. Hélas, la majorité de ces appareils dépendent dans une certaine mesure de logiciels propriétaires.

To be specific, device vendors tend to keep the code that speaks directly to the device hardware (the low level device drivers) proprietary. These components are commonly called the vendor “blobs” (Binary Large OBjects). The vendor blobs need to be incorporated into an Ubuntu Touch port. Note that these components are specific not only to each device, but also to each Android version. It is therefore necessary to secure the correct version of these components when building a port.

C’est pourquoi Ubuntu Touch ne peut pas être entièrement créé à partir du code source de la plupart des appareils commerciaux. Au lieu de cela, le portage du système sur ces appareils implique l’intégration des blobs mentionnés précédemment dans le reste du système, qui peut être construit à partir du code source.

The next component of Ubuntu Touch is a pre-compiled root filesystem which needs to be installed on the device. This component does not communicate directly with the device hardware. Instead, this communication is mediated by a Hardware Abstraction Layer (HAL) which needs to be built for each specific device, because each device has its specific hardware architecture. This component is called Halium and is available in different versions (5.1 which is largely obsolete, 7.1, 9, 10 and 11 as of writing) corresponding to different Android versions.

The Halium project enables Linux systems to run on Android hardware. It is a joint effort by multiple mobile operating systems, notably Lune OS and UBports.

UBports porting builds on top of Halium porting. Consequently, you will be using both the Halium porting guide and the UBports porting guide. At times it may also be helpful to test with one of the other operating systems to debug a problem from different angles.

Halium is an indispensible part of an Ubuntu Touch port and is available in the form of open source software. Developing a new version of Halium is a very considerable task which is why only a few versions of Halium are available. Each port of Ubuntu Touch has to be based on one of the available Halium versions and vendor blobs from the corresponding Android version. See the first two columns of the table below for details.

Ainsi, un portage d’Ubuntu Touch est composé de ces composants :

Le système de fichiers racine (rootfs) d’Ubuntu Touch (UT)
Halium (contenu dans les images de démarrage et du système)
Les blobs des fabricants

You, the porter, need to build Halium (in part or in whole, depending on porting method) and install this together with the Ubuntu Touch rootfs in order to create a functioning Ubuntu Touch port.

Android and Halium versions#

Halium is built using source code for a modified version of the Android operating system called LineageOS (see the LineageOS website and wiki). The required source code is available online and needs to be downloaded and configured to build the correct Halium version for each individual device port. The table below shows which versions are required for the different Halium versions.

Version d’Android	Version d’Halium	Lineage OS (LOS)
7.1	7.1	14.1
9.0	9.0	16.0
10.0	10.0	17.1
11.0	11.0	18.1

Generic System Image#

Starting with Android version 9.0, a significant change of architecture was introduced. The device-specific vendor blobs now reside on a separate partition instead of sharing a partition with the rest of the system image. This separation of device-specific code from generic code made possible what is known as the Generic System Image (GSI).

A GSI is a system image that is built to be able to function with a wide range of devices. Android devices, as of version 9.0, use a GSI. For more information, see the Android Developer pages

The development of the Android GSI architecture also cleared the way for the now available generic Halium 9.0 arm64 system image (hereafter referred to as the Halium GSI, or simply the GSI) which is used for Ubuntu Touch. This, however, is somewhat different from the Android GSI. For a more detailed explanation of the Halium GSI, please refer to the wiki page on Gitlab CI builds of the generic Halium system image.

What does this mean for the porting process?#

Since the GSI is a prebuilt, device-independent component, it effectively simplifies the task of building a viable port by removing much of the meticulous and time consuming task of getting the hardware-specific vendor blobs compiled into the system image and configured to function properly.

Porting methods#

This guide documents three different porting methods, which we call: Full system image method, Halium-boot method, and Standalone kernel method. When porting based on Halium 7.1 the Full system image method is the only available method to follow. For Halium 9.0 all three methods are possible.

Full system image method#

This porting method requires building both the boot image (halium-boot.img) and the full device specific system image (system.img) from source and installing these together with the UBports root file system (rootfs). For Halium 7.1 ports this is the only possible method (Consequently, this method is sometimes referred to as the Halium 7.1 method). For Halium 9.0 it is also possible to use this method, however for Halium 9.0 the other two methods below are probably easier.

Halium-boot method#

For this porting method it is sufficent to build the halium-boot.img and install this together with the Halium GSI and the UBports rootfs. This method can be used for Halium 9.0 ports.

Standalone kernel method#

This porting method only requires building the kernel and installing this together with the Halium ramdisk, the Halium GSI and the UBports rootfs. This method can be used for Halium 9.0 ports.

All methods share some common steps. However, there are also significant differences that must not be missed. Therefore, the methods will be treated separately in the subsequent sections where needed.

The remainder of this section gives some words of advice to new porters. If you already have porting experience or ROM building experience, you can likely skip straight to Preparations.

Les défis du processus de portage#

Building the necessary components and getting them to work together properly always involves an amount of code modifications, configuring and testing, but considerably moreso when doing full system image builds, compared to builds using the GSI (see porting methods).

Luckily, there is a community of porters out there who are eager to see Ubuntu Touch ported to new devices. When you run into trouble, you should search the sources below (Obtenir de l’aide de la communauté) to see if others before you have solved the issue. There are online Telegram chat groups you can join to ask for help, but please bear in mind that those participating are doing so in their spare time.

Connaissances et compétences préalables#

Porters come in all sizes and shapes, so to speak. Therefore, this guide does not presuppose extensive knowledge or skills in any particular field. You should, however, as a bare minimum be familiar with some common shell commands and be comfortable working from the terminal on you host PC. Furthermore, the guide is based on a host PC running Linux. If you have some knowledge of programming, this will come in handy at some point, especially if you are familiar with C / C++. Also, you should familiarize yourself with git and set up a Github or Gitlab account to keep track of your code changes. It is wise to start documenting your steps from the very beginning.

We have attempted to give a certain amount of explanation along the way. However, this guide is not an in-depth reference into the architecture and inner workings of Ubuntu Touch, and gaining a deeper understanding will consequently require an amount of research on your part.

Obtenir de l’aide de la communauté#

Si vous avez des problèmes, et vous en aurez, consultez une ou plusieurs des sources ci-dessous :

Conseils généraux#

The more rigorous you are at making notes and documenting your steps, the less time you will spend backtracking your steps and guessing your way along. When dealing with issues that arise along the way, it is wise to work on them one at a time. If you try to correct several things at once, you risk ending up trying to guess which changes solved a given issue, which easily leads to breaking the functionality in question once more at some later stage.

If you are not discouraged after reading this, we welcome your efforts and wish you the best of luck!

The next section presents a key to the rest of this guide.