os-build-system/doc/sdk-03-technical.md

The Devuan SDK more in-depth

The following parts will explain the Devuan SDK more technically. It will show its configuration, important functions, and show how it all glues together.

Configuration

Much of the libdevuansdk configuration is done in libdevuansdk/config. Here you can edit the defaults if you wish to do something your needs are expressing. However, overriding these through upper levels is recommended.

config file

vars and arrs are global arrays for holding other global variables and arrays, respectively. This is required for zuper and helps a lot with debugging. If you declare new variables or arrays, add them to the aforementioned variables.

• os holds the name of the distribution being worked on.

• release holds the release codename of the distribution. Used for apt repositories mostly.

• version is the version of the distribution being worked on.

• mirror is a mirror holding the required packages for debootstrap.

• section are the sections of the repository. For adding in /etc/apt/sources.list. Separate them with whitespaces.

• image_name is the output name of the raw image. If you declare a blend or a device name (arm-sdk), they will be appended to this name.

• rootcredentials and usercredentials are currently placeholders.

• core_packages is an array holding the core packages that will be installed in the bootstrap process.

• base_packages is an array holding the base packages that will be installed at a later point in the bootstrap process.

• purge_packages is an array of packages that will get purged at the end of the bootstrap process.

Helper functions

You can find useful helper functions in libdevuansdk/zlibs/helpers. They are intended to help when it comes to writing wrappers, as well as making the developers' jobs easier for developing libdevuansdk. Some of these functions are required for libdevuansdk to work properly as well.

build_image_dist()

This function is a kind of a wrapper function. It's used in arm-sdk to build a complete dd-able image from start to end. To run, it requires $arch, $size, $parted_type, $workdir, $strapdir, and $image_name to be declared. See the section dedicated to "Creating wrappers" for insight on these variables.

The workflow of this function is bootstrapping a complete rootfs, creating a raw image, installing/compiling a kernel, rsyncing everything to the raw image, and finally compressing the raw image.

This same workflow is applied in the next two functions in this file, which are build_iso_dist and build_vagrant_dist. To get a better understanding of libdevuansdk, it's recommended to go through one of these functions and following it deeper to find and figure out the other functions and how they work together.

devprocsys()

This function is a simple helper function that takes two arguments. It mounts or unmounts /dev, /proc, and /sys filesystems to or from wherever you tell it to. For example:

$ devprocsys mount $strapdir
$ devprocsys umount $strapdir

It is very necessary to use this if one wants to do anything requiring access to hardware or the system's resources, i.e. cryptography.

dpkgdivert()

This function, like devprocsys takes two arguments and will create or remove a dpkg diversion in the place you tell it to and remove invoke-rc.d so that apt does not autostart daemons when they are installed.

chroot-script()

This very useful functions allows you to chroot into $strapdir and execute the script/binary that's passed as a parameter to this function. It also takes an optional argument -d that will call dpkgdivert on and off before and after execution.

The chroot-script is also an example on its own that shows how to use the chroot-script function.

Mandatory variables

• $R is the root directory of a wrapper. It's defined already in all the existing ones. In almost evert situation it can be $PWD.

• $workdir is the working directory of the current build. A sane default is $R/tmp/workdir

• $strapdir is the bootstrap directory of the build. It holds the rootfs when you debootstrap it, and customize it further on. Default is $workdir/rootfs.

• $arch is the CPU architecture of the build. I.e. amd64, armhf, etc.