Signal Handling

Overview

Signal handling in Morinaga OS allows processes to communicate with the kernel to perform specific tasks, such as updating process priorities or reverting the file system to a previous state. This is integrated with Watson to provide seamless system control.

Implementing Signal Handlers

Custom Kernel Signals

Create custom signals or use existing ones (e.g., SIGUSR1, SIGUSR2) for inter-process communication:

// In the kernel module
static int signal_handler(struct notifier_block *nb, unsigned long code, void *_param) {
    // Handle signal
    if(code == SIGUSR1) {
        // Perform action, e.g., revert file system
    }
    return NOTIFY_OK;
}

static struct notifier_block nb = {
    .notifier_call = signal_handler,
};

int init_module(void) {
    // Register signal handler
    register_signal_notifier(&nb);
    return 0;
}

User-Space Signal Sending

Watson or other user-space processes can send signals to the kernel:

kill(getpid(), SIGUSR1); // Send signal to self

Reverting the File System

Upon receiving a specific signal, the kernel can trigger a file system rollback using Btrfs snapshots:

# Create a snapshot
btrfs subvolume snapshot /path/to/subvolume /path/to/snapshot

# Rollback to snapshot
btrfs subvolume delete /path/to/subvolume
btrfs subvolume snapshot /path/to/snapshot /path/to/subvolume

Automate this process within the signal handler for immediate effect.

Security Considerations

• Ensure that only authorized processes can send critical signals.
• Implement proper permission checks and authentication mechanisms.