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Architecture

We have two direcotry in this repository, system and overlay. Top level Makefile will run $(MAKE) -C system and $(MAKE) -C overlay to make sub target.

system

System directory whill generate a ready for use root file system in ./build/rootfs directory, waiting for next step process. This root file system may be Ubuntu, Debian, ArchLinux or buildroot etc. You can read the source code in ./system directory to find more information.

overlay

The root file system generate from system directory is very primary, and we doing some modification in ./overlay directory. We summarize three types of change, for each type, we have corresponding directory to handle different situations.

1. (execution) - Need compiled package like button driver
2. (file) - Some files need be copied into the root file system like network configuration files
3. (tuning) - Install package using apt within root file system (works with Debian/Ubuntu only)

execution

Default CC is aarch64-linux-gnu-gcc, for other type of language like Go, you can add your own compiler by edit Makefile in execution directory.

Note: execution directory will make before file directory.

file

Any user file can added into this directory, and Makefile will move all files in ./overlay/file directory to target root file system.

Note: file directory will make before tuning directory.

tuning

Some package may not be easy to install to target root file system, like install an openssh-server. For situation like this, we use chroot command to tuning the target root file system directly. We asume user are using x86 host to build this repository, so you may need qemu-aarch64-static copied into target root file system to emulate aarch64 on x86 machine.

You can run sudo apt install qemu-user-static to get the binary.

After change to target root file system (which will be done by repository's build system, you don't have to care about it), the build system will run install.sh in any sub directory in ./overlay/tuning/ directory. The running priority is arranged according to alphabetical order. ./overlay/tuning/abc/install.sh will run before ./overlay/tuning/def/install.sh.

You can add packages into ./overlay/tuning/ directory, and remenber, if you have pre-package foo need to install before package bar, you have to make sure foo is running before bar by add number to the package name like this:

./overlay/tuning/01-foo/install.sh
./overlay/tuning/02-bar/install.sh

Install.sh should exit 0 when install success, 1 when error happened.