add docs

README.md

@@ -26,7 +26,7 @@ By default, the Builder uses `podman` as the container engine. If you prefer usi
 
 A config directory serves as the input for the Builder and is used to create a Linux system image. It consists of the following components:
 
-- **`features` directory**: Contains sub-directories for each feature. You can create your own features by referring to the example in [gardenlinux/features/example](https://github.com/gardenlinux/gardenlinux/tree/main/features/example).
+- **`features` directory**: Contains sub-directories for each feature. You can create your own features by referring to [features.md](docs/features.md).
 
 - **`cert` directory** (optional): If you plan to use secure boot, include a `cert` directory.
 
@@ -38,6 +38,8 @@ In addition to the above components, your configuration directory must include t
 - `get_version`: This script should output the version of the package repository to use. For example, use `bookworm` for Debian or `today` for Garden Linux.
 - `keyring.gpg`: The PGP key used to validate the package repository. For Debian, you can obtain this key from the [debian-archive-keyring](https://packages.debian.org/bookworm/debian-archive-keyring) package.
 
+For a quick start guide on setting up your own config directory with your own features checkout [getting_started.md](docs/getting_started.md).
+
 ### Example Config Directory
 
 If you're new to configuring the Builder, you can find a minimal example config directory at [gardenlinux/builder_example](https://github.com/gardenlinux/builder_example). For a more comprehensive example, refer to the main [gardenlinux](https://github.com/gardenlinux/gardenlinux) repository.

docs/features.md

@@ -0,0 +1,77 @@
+# Features
+
+Each feature must at least contain an `info.yaml` file
+
+The `info.yaml` file has the following structure fields:
+
+- `description`: (*optional*) a string explaining what this feature does / what it is used for.
+- `type`: can be any of `platform`, `element`, or `flag`. The builder does not make any technical distinction between each type of feature, however it is strongly encouraged that each image uses exactly one platform and flags should only perform minor changes and not include any other features.
+- `features`: (*optional*) sub-structure containing related features
+	- `include`: (*optional*) list of features that will automatically be included as well if this feature gets included
+	- `exclude`: (*optional*) list of features that are incompatible with this feature. If any of these features were included implicitly from another they will be removed from the feature set. If they were explicitly provided as part of the target the build will fail.
+
+An example `info.yaml` looks as follows:
+
+```yaml
+description: example platform feature
+type: platform
+features:
+  include:
+    - A
+    - B
+  exclude:
+    - C
+```
+
+Additionally a feature may contain any of the following:
+
+## `pkg.include`
+
+A list of packages to be installed into the image.
+
+## `pkg.exclude`
+
+A list of packages to be ignored if provided by another features `pkg.include`
+
+## `file.include`
+
+A directory containing files to copy into the target rootfs.
+This directory is copied recursively into the root directory.
+By default only the executable bit of the files permission will be preserved when copying.
+The other permissions will be set to read write for owner and read for group and other.
+The owner of all copied files will be root by default.
+
+To overwrite these defaults see `file.stat` below
+
+## `file.stat`
+
+A file to assign owner and permissions to files copied by `file.include`.
+Each line should contain an entry of the form:
+
+```
+user group permissions file
+```
+
+## `file.exclude`
+
+A list of files / directories to remove from the rootfs at the end of the configure stage.
+Wildcard in file paths are allowed.
+
+## `exec.config` `exec.early` `exec.late` `exec.post`
+
+Scripts to be executed to configure the image.
+All scripts except `exec.post` are executed inside the rootfs of the system being build without any parameters.
+`exec.post` is executed inside the builder container with the path of the rootfs provided as `argv[1]`.
+
+The order of exectution is as follows:
+
+- bootstrap (outside chroot)
+- `exec.early`
+- package install (from `pkg.include`)
+- copy files from `file.include` and set permissions according to `file.stat`
+- `exec.config`
+- `exec.late`
+- remove files according to `file.exclude`
+- `exec.post` (outside chroot)
+
+When building with multiple features the execution steps of each feature are interleaved; so for example the `exec.config` step will run for all features before any features `exec.late` runs.

docs/getting_started.md

@@ -0,0 +1,86 @@
+# Getting started
+
+These instructions will guide you through how to create a custom linux image using the builder.
+We will start from the builder example repo, and build our own feature on top to add an `nginx` http server.
+
+First clone the builder example repo:
+
+```shell
+git clone https://github.com/gardenlinux/builder_example
+cd builder_example
+```
+
+At this point you can test, that your local podman install works by running `./build base`.
+This should create a bootable debian bookworm disk image at `.build/base-amd64-bookworm-6f72b564.raw` (the commit may have changed since the time of writing).
+You can test run the image with
+
+```shell
+qemu-system-x86_64 -m 2048 -nodefaults -display none -serial mon:stdio -drive if=pflash,unit=0,readonly=on,format=raw,file=/usr/share/OVMF/OVMF_CODE.fd -drive if=virtio,format=raw,file=.build/base-amd64-bookworm-6f72b564.raw
+```
+
+Now that we know all local tooling works, let's start building our own feature.
+
+1. Create a feature directory called `nginx`.
+
+```shell
+mkdir features/nginx
+```
+
+2. create a file `features/nginx/info.yaml` and edit it using the editor of your choice to have the following content:
+
+```yaml
+description: http server using nginx
+type: element
+```
+
+3. create a file `features/nginx/pkg.include` with the following content:
+
+```
+nginx
+```
+
+4. create a file `features/nginx/exec.config` with the following content:
+
+```shell
+#!/usr/bin/env bash
+
+set -eufo pipefail
+
+systemctl enable nginx
+```
+
+5. make this executable `chmod +x features/nginx/exec.config`
+
+6. create a `/var/www/html` directory inside the nginx `file.include` directory
+
+```shell
+mkdir -p features/nginx/file.include/var/www/html
+```
+
+7. create a dummy `index.html` file inside `features/nginx/file.include/var/www/html` with content like the following or whatever you like:
+
+```html
+<!DOCTYPE html>
+<html>
+	<body>
+		<p>Hello World!</p>
+	</body>
+</html>
+```
+
+With this we have created our own first feature for the builder.
+Test it by building with
+
+```shell
+./build base-nginx
+```
+
+and running with
+
+```shell
+qemu-system-x86_64 -m 2048 -nodefaults -display none -serial mon:stdio -drive if=pflash,unit=0,readonly=on,format=raw,file=/usr/share/OVMF/OVMF_CODE.fd -drive if=virtio,format=raw,file=.build/base-nginx-amd64-bookworm-local.raw -netdev user,id=net0,hostfwd=tcp::8080-:80 -device virtio-net-pci,netdev=net0
+```
+
+if everything worked as intended you should see the system boot up and once booted opening http://localhost:8080 in a browser should display the hello world message.
+
+Congrats, you have just successfully created a feature for the builder :tada: