Introducción a la portabilidad#

Esta primera sección le introducirá a las características de portar Ubuntu Touch a un dispositivo Android. Tenga en cuenta que está escrita para el público en general en mente, no para el desarrollador en portabilidad experimentado. En las secciones subsiguientes hemos hecho un esfuerzo para diferenciar manteniendo el texto principal más conciso con el fin de satisfacer las necesidades del lector más experimentado, al tiempo que proporcionamos enlaces a lecturas complementarias para los menos experimentados.

La guía en su conjunto está redactada como una secuencia de pasos que describen cómo podría ser una adaptación ideal. Sin embargo, la portabilidad es imprevisible y desordenada. Cada dispositivo es diferente y, en realidad, es probable que se repitan y revisen algunos pasos, que se omitan otros y que se descubran nuevos retos no documentados.

¿Qué es Ubuntu Touch?#

Ubuntu Touch es un sistema operativo de software libre para dispositivos móviles. Puede ser portado a dispositivos que originalmente venían con el sistema operativo Android. Por desgracia, la mayoría de estos dispositivos dependen en cierta medida del software propietario.

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.

Por ello, Ubuntu Touch no puede construirse completamente desde el código fuente para la mayoría de los dispositivos comerciales. En su lugar, la portación del sistema a estos dispositivos implica la integración de los vendor blobs anteriormente mencionados en el resto del sistema, que puede construirse desde el código fuente.

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.

Thus an Ubuntu Touch port is composed of the these components:

The Ubuntu Touch (UT) root filesystem (rootfs)
Halium (contained in the boot and system images)
The vendor blobs

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.

Android version	Halium version	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.

The challenges of the porting process#

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 (Obtener ayuda de la comunidad) 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.

Prior knowledge and skills#

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.

Obtener ayuda de la comunidad#

When you run into trouble, and you will, refer to one or more of the sources below:

General advice#

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.