In the preceding sections, we talked about Android architecture, AOSP, and third-party open source projects for Android. The software industry has been there for decades. There are so many existing source codes that can be reused and the need to create something from scratch is very rare. The porting and customization for a new platform is basically art of integration.

In this book, we will use the AOSP source code as the foundation and try to build everything on top of it. However, we may not be able to rely on AOSP source code only. In fact, we want to demonstrate how to support a platform that is not supported by AOSP. How are we going to do this? Do we create something from scratch? The answer is no. We will demonstrate how we can integrate all existing projects together to create a new platform. That's the reason why we discuss third-party open source projects.

In our case, VirtualBox is not supported by AOSP and we are going to enable it using AOSP and Android-x86. We need to use projects from both AOSP and Android-x86 to build a system for VirtualBox. However, our goal is to create a new build system for VirtualBox with minimal changes to the AOSP source code tree. This is also the goal of many other projects based on AOSP.

Based on the previous understanding, we have four categories of projects in our integration process:

• The original unmodified AOSP projects: In these kinds of projects, we will use AOSP projects without any changes.
• The third-party projects: In this category, the projects are added by the third-party projects and are not part of AOSP, so there are no changes involved as well.
• Projects modified by both AOSP and one of the third-party projects: This is complicated. We need to review the third-party changes and decide whether we want to include them in our system or not.
• Projects modified by multiple open source projects and AOSP: This is the most complicated case that we should avoid to integrate or change.

It is very easy to understand that we should try to reuse projects in category 1 and 2 as much as possible. The challenges and major work will be in category 3, while we should try to avoid category 4 whenever possible.