Buildroot recipe — what is in the appliance OS?

Buildroot cross-compiles a tiny Linux userspace and kernel from a locked version of the Buildroot tree. This project does not ship a general-purpose distro (no apt, no desktop). The image is optimized for:

  1. running one BACnet router daemon with predictable serial timing
  2. a small management web UI on the LAN
  3. SSH for host networking and config files

Pins

Item Where
Buildroot version / commit config/buildroot-lock.toml (currently 2026.05.2)
rusty-bacnet git SHA config/upstream-lock.toml (baked into routerd)
Project Rust toolchain (CI) rust-toolchain.toml (1.93.0)

CI workflow: build-os → scripts/build-image.sh.

Layers (mental model) 

┌─────────────────────────────────────────┐
│  React static UI  (/usr/share/.../web)  │
├─────────────────────────────────────────┤
│  diy-bacnet-router (routerd)            │  Rust — BACnet + Axum management
├─────────────────────────────────────────┤
│  Dropbear SSH · eudev · CA certs · tzdata│  minimal services
├─────────────────────────────────────────┤
│  Linux kernel (+ USB-serial fragment)   │  FTDI / CH34x for RS-485 dongles
├─────────────────────────────────────────┤
│  rootfs.ext2 / rootfs.iso / sdcard.img  │  board packaging
└─────────────────────────────────────────┘

Userspace packages (common fragment)

From buildroot-external/fragments/common.config:

Package / setting Why it is there
diy-bacnet-router The appliance binary + config + web assets + init script
Dropbear SSH so you set IP/routes with normal Linux tools
eudev Runs udev rules (serial by-id helpers, FTDI latency)
CA certificates / tzdata TLS trust store basics and correct timestamps
ext2/4 rootfs Simple durable root for QEMU and lab

Device creation is forced to eudev (not mdev-only) so rules under /etc/udev/rules.d/ actually run.

Kernel USB-serial fragment

buildroot-external/fragments/linux-usb-serial.fragment enables USB serial support aimed at lab RS-485 dongles (FTDI and WCH CH341/CH343). Unknown Kconfig symbols are dropped by olddefconfig — confirm with udevadm on hardware.

Init and privilege

  • SysV script S80diy-bacnet-router starts the daemon with start-stop-daemon as user dbr (not root).
  • Config lives at /etc/diy-bacnet-router/router.toml.
  • Web UI is static files under /usr/share/diy-bacnet-router/web.
  • FTDI latency helper: /usr/sbin/set-ftdi-latency.sh + /etc/udev/rules.d/99-ftdi-latency.rules.

What is intentionally missing

  • No BBMD / foreign-device product claims until evidenced
  • No browser config writes until auth gates pass
  • No full desktop, docker, or package manager
  • No claim that QEMU smoke equals a live MS/TP trunk

Download story (TODO — milestone M8)

Today you download workflow artifacts from Actions (short retention). The product goal is:

  1. build-os publishes a GitHub Release per version tag
  2. this docs site links straight to https://github.com/bbartling/diy-bacnet-router/releases/download/vX/...
  3. you flash sdcard.img / boot rootfs.iso without rebuilding Buildroot locally

Until then, treat local VMware Buildroot loops as optional debug, not the install path. See Build images.