Interprocess Communication and Middleware Interaction

UBUS: Message Bus Internals and Protocol

Internals:

• ubusd daemon manages the bus, handling client connections.
• Uses Unix sockets for communication.
• Supports JSON-formatted messages for method calls and events.
• Provides namespaces for organizing objects (e.g., network, system).

Protocol:

• Clients connect to ubusd via /var/run/ubus.sock.
• Messages include method calls, responses, and event notifications.
• Lightweight and optimized for low-resource devices.

UBUS Objects and Methods

Objects:

• Represent system components (e.g., network.interface, uci).
• Registered by services like netifd or rpcd. Methods:
• Expose functions (e.g., network.interface.status to check interface state).
• Called via UBUS CLI (ubus call) or programmatically. Examples:
• ubus call network.interface status retrieves network status.
• ubus call uci get '{"config":"network"}' reads UCI settings.

Client and Server Implementations in C

Client:

• Uses libubus to connect to ubusd and call methods.
• Example: Querying network status via ubus_call(). Server:
• Registers objects and methods with ubusd.
• Example: A custom service exposing status via UBUS. Libraries:
• libubus for client/server communication.
• libubox for utilities like JSON parsing.

UCI + UBUS Integration Flow

Integration:

• UCI stores configurations in /etc/config/.
• uci command or libuci interacts with UBUS to apply changes.
• netifd and LuCI use UBUS to read/write UCI settings.
• Example: Changing Wi-Fi SSID via LuCI triggers UBUS call to uci, which updates /etc/config/wireless.

Event Notification and Subscription Mechanism

Mechanism:

• ubus supports event broadcasting (e.g., interface up/down).
• Clients subscribe to events using ubus subscribe.
• Example: netifd notifies subscribers of link status changes.
• Events are lightweight and sent via Unix sockets.

RPCD and Remote Procedure Calls (via JSON-RPC)

Mechanism:

• rpcd exposes UBUS methods via JSON-RPC 2.0 over HTTP.
• Used by LuCI and external clients for remote management.
• Supports authentication via tokens or credentials.
• Example: POST /ubus with JSON payload to query system status.