Provisioner

Overview

Provisioner is a developer-focused provisioning sidekick for single-board computers (SBCs), particularly U-Boot-based platforms.

It provides a self-contained environment to:

• Remotely access boards
• Automate bring-up workflows
• Provision kernels and root filesystems
• Execute flashing operations
• Share lab hardware safely

The operational model is intentionally simple:

One board => One provisioner instance

Provisioner runs close to the hardware and exposes controlled remote access to developers through a secure, multiplexed interface.

System Components

The project is composed of two primary elements:

Provisioner orchestrates workflows; goinit executes them locally on the board.

Architecture Overview

Provisioner bridges three operational planes:

1. User Access Plane: SSH monitor & tunnels
2. Provisioning Plane: TFTP & HTTP artifact delivery
3. Board Control Plane: Serial console & goinit APIs

This allows continuous control from bootloader to runtime provisioning.

Core Subsystems

Serial Engine

Owns the physical console connection and provides:

• Console multiplexing
• Interactive monitor
• Script automation
• File transfer
• Logging

Serial remains the ultimate fallback control path.

Provisioning Services

Embedded services provide boot artifacts:

TFTP

• Kernel delivery
• HTTP proxy fetch via encoded filenames

HTTP

• Rootfs images
• Device trees
• Kernel artifacts
• Generic binaries

Control Plane via SSH

Provisioner exposes a unified SSH endpoint acting as both access and control layer.

All remote interactions are multiplexed over a single SSH connection and governed via public key authentication.

Multiplexed channels include:

• Monitor shell
• Serial console tunnels
• Control CLI
• File transfers

Access governance:

• Public key identity
• Tunnel enable/disable per user
• Centralized permission enforcement

SSH therefore carries both:

• Management plane traffic
• Serial data plane streams

Internal Router

At the heart of Provisioner's I/O model sits the router, a pluggable software artifact that brokers terminal streams between producers and consumers.

All console traffic flows through this component rather than directly between subsystems.

Producer / Consumer Model

Router clients may:

• Produce terminal data
• Consume terminal data
• Operate bidirectionally

Examples:

• SSH monitor sessions
• Serial tunnels
• Automation scripts
• Logging agents
• Transfer utilities

Human vs Machine Clients

The router distinguishes between two client variants:

This allows tailored stream handling for usability vs determinism.

Routing Strategies

Unicast

• Single recipient
• Used for exclusive control sessions or transfers

Multicast

• Broadcast delivery
• Used for monitoring, logging, observers

Multiple engineers can watch the same console without interference.

ANSI Watcher

A dedicated pluggable watcher mitigates ANSI terminal nuances:

• Observes control sequences
• Normalizes rendering artifacts
• Prevents automation breakage

Implemented as a plugin rather than hardcoded logic.

Monitor CLI

The monitor shell provides interactive board control.

> ?  
 ? : this text  
 board_stat : report last goinit board stat; board must have printed PROVISIONER_MGMT_*  
 echo : echoes back the argument  
 enuser : enable user for tunnel  
 exec_assm : Load and executes the specified assm script  
 exec_scr : Load and executes the specified script  
 exec_state : returns the state of the specified script  
 exit : exit this shell  
 filter : Filter commands: type 'filter help' for more info  
 help : this text  
 log_serial : copies in a file ser.log all sent and received from the serial. Note: overwrites previous.  
 log_serial_stop : Requires serila log subsystem to stop.  
 send_serial : send file over serial: send_serial <file> <plain|gzip|xmodem_unix|xmodem_uboot> [dest_path]  
 send_serial_deps : check remote deps for send_serial plain/gzip: stty, dd, base64, gzip, rm (or busybox).  
 toff : command PDU using snmp to turn off the board  
 ton : command PDU using snmp to turn on the board  
 tterm : terminate serial tunnel connection  
 ulist : list user state for tunnel  
>

Filter Subsystem

filter help
available: enable, disable, default, show, add, remove, help

Rules may be defined in ASCII or HEX:

filter add ascii Hello Hello World 
filter add hex 48656c6c6f 48656c6c6f 576f726c64

Filters can:

• Intercept received data
• Forward or suppress streams
• Inject responses

This is useful for boot automation and console normalization.

Serial File Transfer

Provisioner supports direct serial file transfer:

send_serial <file> <mode> [dest_path]

Modes:

Dependencies checked via:

send_serial_deps

Required utilities:

• stty
• dd
• base64
• gzip
• rm / busybox

send_console-ng Integration

The transfer engine derives from the standalone utility send_console-ng, adapted into Provisioner. It enables file transfer when:

• No network exists
• Only a shell prompt is available
• Recovery tooling must be pushed manually

Capabilities:

• Remote terminal configuration
• Compression & encoding
• Buffered streaming
• Dependency probing

Compared to the original utility:

• stdbuf and cat dependencies removed
• dd introduced for portability
• XMODEM support added where receivers exist

This allows Provisioner to operate even in severely degraded board states.

Automation & Scripting

assm: Native Scripts

Assembly-like expect engine:

• Prompt matching
• Deterministic responses
• Byte-oriented execution

Best suited for login and boot flows.

exec_scr: External Scripts

Executes external programs bound to the serial stream.

Modes:

Optional Integrations

Google Calendar (Optional)

Lightweight reservation integration exists but is not a primary project focus. Used only for:

• Time-based access
• Shared lab booking

Provisioner does not aim to become a full lab scheduler.

Build & Portability

Provisioner is written in Go and cross-compiles easily.

Native build

make

Cross-compile examples

GOARCH=arm64 make

No external toolchains required.

Deployable on:

• Servers
• Edge hosts
• Raspberry Pi class systems
• Lab gateways