rootfs: replace ISO/squashfs baseline with conf- and seed-driven debootstrap rootfs

[bjordiscollaku]

This change enhances the rootfs build flow by replacing the ISO/squashfs baseline with a deterministic, seed-driven debootstrap baseline. The update spans Baseline rootfs creation, Seed parsing + safety guarantees, Preprocessing refactor, CLI improvements, Config cleanup / removing ISO-era remnants, Package policy changes, and Generalize builder naming + artifacts + GRUB labeling.

What changed (high level)

Baseline rootfs creation

• Replaces the previous Ubuntu ISO → 7z extract → locate *.squashfs → unsquashfs → copy into rootfs/ pipeline with debootstrap.
• Baseline rootfs is now generated from:
    - qcom-product.conf for DISTRO/CODENAME/ARCH (and optional apt settings), and
    - a seed file containing one package per line (supports # comments and blank lines).

Seed parsing + safety guarantees

• Adds seed parsing to produce a debootstrap --include list.
• Enforces “one package token per line” (fails fast on whitespace entries to avoid accidental multi-token installs).
• Ensures a minimal required package set is always included (e.g., lsb-release, apt, sudo, systemd-sysv, etc.) so the existing chroot stages can run unchanged (e.g., apt install, user creation, systemd symlinks, etc.).

Preprocessing refactor

• Consolidates baseline preparation into a single platform/distro agnostic function: image_preprocessing().
• Removes the platform-specific preprocessing entry points (image_preproccessing_iot/compute/server) since baseline generation no longer depends on platform-specific ISO handling.

CLI improvements

• Replaces legacy positional argument modes with explicit named options:
    - --product-conf <qcom-product.conf>
    - --seed <seed_file>
    - --kernel-package <kernel.deb>
    - --firmware <firmware.deb>
    - optional --overlay <package-manifest.json>
• Adds --help usage output and strict validation for required inputs.

Config cleanup / removing ISO-era remnants

• Removes reliance on ISO-era configuration such as BASE_IMAGE_URL / IMG_URL and related defaulting logic, since preprocessing is now strictly debootstrap-based.
• Introduces optional qcom-product.conf knobs for bootstrap control:
    - APT_MIRROR (defaults to an Ubuntu ports mirror)
    - APT_COMPONENTS (defaults to main,universe)

Package policy changes

• Drops implicit desktop-by-default installs:
    - Removes the fixed apt install -y ubuntu-desktop-minimal ... behavior from the chroot stage so package composition is fully defined by the seed and/or overlay manifest.
    - If a desktop image is desired, add ubuntu-desktop-minimal (and any other UI packages) to the seed or overlay manifest explicitly.
• Installs a minimal networking stack in the Step 8 chroot stage:
    - Moves network-manager out of debootstrap --include to avoid observed debootstrap failures during “configure base packages” when using --variant=minbase.
    - Adds a dedicated chroot block that runs apt-get update and installs (with --no-install-recommends):
      - network-manager
      - wpasupplicant
      - iw
      - net-tools

Generalize builder naming + artifacts + GRUB labeling

• Rename the rootfs builder to reflect that it is not Ubuntu-specific:
    - build-ubuntu-rootfs.sh → build-rootfs.sh
    - Header text and usage examples refreshed accordingly.
• Align the default output name with the generic script:
    - ROOTFS_IMG: ubuntu.img → rootfs.img
• Generalize GRUB labeling and remove chroot-side codename detection:
    - Use "${DISTRO} ${CODENAME}" for the GRUB menuentry title (rather than hardcoding “Ubuntu …”).
    - Pass DISTRO/CODENAME into the chroot via environment (from qcom-product.conf) instead of calling lsb_release inside the chroot.

Why this is better

• Deterministic & reproducible: baseline comes from codename + seed rather than ISO contents and squashfs layout variations.
• Less brittle: avoids hunting for minimal.squashfs / ISO layout drift across releases.
• Cleaner interface: explicit flags + seed file makes builds easier to audit and automate.
• Future-ready: preprocessing is no longer tied to a specific target platform and can evolve via product-conf inputs.

Notes / limitations

• This update currently assumes ARCH=arm64 (host/target ARM64) and errors out otherwise.
• User-facing interface change: callers/scripts that reference build-ubuntu-rootfs.sh or ubuntu.img must be updated (or add an out-of-tree compatibility wrapper/symlink if needed).

Example usage

./build-rootfs.sh \
  --product-conf qcom-product.conf \
  --seed seed_file \
  --kernel-package kernel.deb \
  --firmware firmware.deb \
  [--overlay package-manifest.json]

[lool]

Hey –that's pretty cool! Instead of a delta definition and relying on existing images, this actually creates the images from packages.

Could we go one step further and use the same image building tool as the underlying distro? Ubuntu uses livecd-rootfs as a wrapper to the ubuntu-image snap and the live-build deb. If we could call livecd-rootfs directly, that would be neat, or we could call ubuntu-image. Image definitions are nice yaml files which we can easily extend. IMO seeds are a bit cumbersome to maintain for a downstream, but doable; to truly use seeds, we'd want to run germinate somewhere, but perhaps it's overkill and we can stick to standard seeds + extra packages?

For Debian, it's a similar toolset, but the image generation packages are non-trivially patched between Debian and Ubuntu. I've found the Debian Libre Live image building scripts to be quite neat wrappers:
https://gitlab.com/debdistutils/debian-libre/debian-libre-live#debian-libre-live-images