nanvix/daemon-development

Daemon Development

Use this skill when the user asks about developing, modifying, or debugging system daemons in Nanvix. Daemons are long-running system services that run in user-space and provide core OS functionality.

Daemon Overview

| Daemon | Path | Target | Purpose | |----------|-----------------------|--------|----------------------| | memd | src/daemons/memd/ | Guest | Memory management. | | procd | src/daemons/procd/ | Guest | Process management. | | wasmd | src/daemons/wasmd/ | Guest | WebAssembly runtime. | | linuxd | src/daemons/linuxd/ | Host | L2 VM management. |

Guest Daemons (memd, procd, wasmd)

Guest daemons are #![no_std], #![no_main] Rust binaries that run inside the Nanvix microkernel environment. They communicate with the kernel through kernel calls (sys::kcall) and handle system events/messages.

Memory Daemon (memd)

• Handles page faults by terminating faulting processes and resuming exception events.
• Processes IPC requests for memory management.
• Uses sys::kcall::pm::terminate() and sys::kcall::event::resume().

Process Daemon (procd)

• Manages process lifecycle (creation, termination, scheduling).
• Handles IPC-based process management requests.

WebAssembly Daemon (wasmd)

• Runs WASM modules using the wasmi interpreter.
• Configured via WASM_BINARY and WASMD_SOCKADDR.
• Socket address defaults to 127.0.0.1:8585.

Host Daemon (linuxd)

• Runs on the host Linux system with full std support.
• Manages L2 VM deployment and host-side resources.
• Configuration in build/linuxd_config.toml.
• Only built for microvm and hyperlight machines.

Building Daemons

# Build all daemons as part of the full build.
./z build -- all

# Guest daemons: GUEST_CARGO_BUILD_CMD.
# Host daemons (linuxd): HOST_CARGO_BUILD_CMD.

Creating a New Guest Daemon

1. Create directory at src/daemons/<name>/.

2. Add Cargo.toml:

   [package]
   name = "<name>"
   version.workspace = true
   license-file.workspace = true
   authors.workspace = true
   edition.workspace = true
   
   [[bin]]
   name = "<name>"
   path = "src/main.rs"
   
   [dependencies]
   sys = { workspace = true }
   syslog = { workspace = true }
   # Additional dependencies as needed.
   

3. Create src/main.rs with:

   // Copyright(c) The Maintainers of Nanvix.
   // Licensed under the MIT License.
   
   #![no_std]
   #![no_main]
   
   extern crate alloc;
   
   // Daemon implementation.
   

4. Add the crate to the workspace members in root Cargo.toml.

5. Add the daemon name to ALL_GUEST_DAEMONS in the Makefile.

Coding Rules (Daemon-Specific)

• Guest daemons must be #![no_std] and #![no_main].
• Use kernel calls (sys::kcall::*) for system interactions.
• Handle IPC messages by parsing SystemMessage structures.
• Always handle errors gracefully — daemons must not crash.
• Log all errors with error! before returning.
• Use the syslog crate for logging within guest daemons.