introduzione al porting¶
Questa prima sezione ti introdurrà alle specifiche di porting Ubuntu Touch a un dispositivo Android. Si noti che è scritto con il pubblico generale in mente, non principalmente lo sviluppatore porting esperto. Nelle sezioni successive abbiamo fatto uno sforzo per differenziare mantenendo il testo principale più conciso per soddisfare le esigenze del lettore più esperto, fornendo al contempo link alla lettura complementare per i meno esperti.
La guida nel suo insieme è scritta come una sequenza di passi che descrive come un port ideale potrebbe procedere. Tuttavia, il porting è imprevedibile e disordinato. Ogni dispositivo è diverso e in realtà sarà probabile iterare e rivisitare alcuni passaggi, saltare su altri passaggi e scoprire nuove e non documentate sfide.
Cosa è Ubuntu Touch?¶
Ubuntu Touch è un sistema operativo open source per dispositivi mobili. Può essere portato a dispositivi che originariamente erano spediti con Android OS. Ahimè, la maggior parte di questi dispositivi dipende in qualche modo dal software proprietario.
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.
Ecco perché Ubuntu Touch non può essere costruito completamente dal codice sorgente per la maggior parte dei dispositivi commerciali. Invece, portare il sistema a questi dispositivi comporta l’integrazione dei blobs fornitore precedentemente menzionati nel resto del sistema, che può essere costruito dalla fonte.
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 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, Droidian and Ubuntu Touch.
Ubuntu Touch porting builds on top of the Halium GSI. The Halium GSI is discussed further below. 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.
- Pertanto, un trasporto Ubuntu Touch è composto da questi componenti:
L’Ubuntu Touch (UT) root filesystem (rootfs)
Halium (contenuto nelle immagini di avvio e di sistema)
Il fornitore blobs
You, the porter, need to build a Halium kernel, which is installed together with the Ubuntu Touch rootfs and the Halium GSI, 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.
Versione Android |
Versione 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 |
12.0 |
12.0 |
19.1 |
13.0 |
13.0 |
20.0 |
Since 20.04, Ubuntu Touch ports are normally based on Halium 9.0 or later. Older versions of Halium are considered deprecated and are no longer supported for new ports.
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.
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.
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 (Getting community help) 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.
Nota
In the past there used to be different methods for porting. Find the historic details linked in the deprecated porting section.
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.
Getting community help¶
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.