init/GEMINI.md

GEMINI.md - Project Context

Project Overview

This project is an init system (currently incomplete). It manages the execution of system services in a dependency-aware order. The system consists of two main components:

1. Solver (bin/solver): Analyzes service scripts for a given "runlevel," resolves their dependencies using a topological sort, and generates an execution plan.
2. Main Runner (bin/main): Executes the generated plan for a specific runlevel using the interpreter specified by the SHELL macro in src/config.h.

The individual service scripts are interpreted by the configured SHELL (default: /bin/sh). Consequently, all scripts must be compatible with this interpreter.

Core Components

• src/main.c: The entry point for the runner. It sets up the environment (adding the script directory to PATH) and invokes the SHELL to execute the generated runlevel plan.
• src/solver.c: The dependency solver logic. It parses script headers for dependencies and outputs an ordered list of generic script names to a runlevel file.
• src/config.h: Contains configuration constants such as INIT_DIRECTORY, SHELL, and DEPENDENCY_PREFIX.
• examples/: Directory containing both the individual service scripts and the generated runlevel plans.

Building and Running

Prerequisites

• GCC or another C compiler.
• The interpreter specified in src/config.h (e.g., /bin/sh).

Building

Compile the components manually:

gcc src/main.c -o bin/main
gcc src/solver.c -o bin/solver

Running

1. Solve Dependencies: Generate the execution plan for a runlevel (e.g., runlevel 1):

   bin/solver 1
   

   This creates a file named 1 in the examples/ directory.

2. Execute Runlevel: Start the services in the correct order:

   bin/main 1
   

Development Conventions

Service Scripts

• Location: Place scripts in the directory defined by INIT_DIRECTORY (default: examples/).
• Naming:
  • Runlevel-specific: <runlevel>.<generic_name> (e.g., 1.logging.sh). These are typically symlinks to the generic scripts.
  • Generic: <generic_name> (e.g., logging.sh). This is the file actually executed by the runner.
• No Shebangs: Do not use shebangs (e.g., #!/bin/sh). The first line of every runlevel-specific script is reserved for dependency declarations. Including a shebang will break the dependency solver.
• Language: Scripts are interpreted by the language defined in src/config.h via the SHELL macro.

Declaring Dependencies

• Dependencies MUST be declared on the first line of the runlevel-specific script.
• Use the prefix defined by DEPENDENCY_PREFIX (default: #).
• List the generic names of the dependencies, separated by spaces.
• Example (examples/3.app.sh):

  # db.sh network.sh
  echo "Application service started"
  

  In this example, app.sh depends on db.sh and network.sh.

Coding Style

• The codebase uses standard C with POSIX system calls (fork, execl, waitpid, etc.).
• Error handling is performed via perror and exit.