daemon-development

name	daemon-development
description	Guide for developing and debugging Nanvix daemons, including guest daemons and host linuxd behavior. Use this when asked about daemon architecture or daemon changes.

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.
linuxd	src/daemons/linuxd/	Host	User VM management.

Guest Daemons (memd, procd)

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.

Host Daemon (linuxd)

• Runs on the host Linux system with full std support.
• Manages User VM deployment and host-side resources.
• Only built for microvm machine.

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.