Function get_network_manager 

pub fn get_network_manager() -> &'static NetworkManager

Network layer manager

Global registry for protocol layer instances, following the VFS pattern. Each layer (Ethernet, IP, TCP) is registered once and shared across all sockets.

Design Philosophy

• Singleton layers: Each protocol layer is instantiated once and shared
• Global registry: Similar to VfsManager, provides centralized layer management
• Namespace isolation: Future support for per-task network namespaces

Example Usage

// During system initialization
let net_manager = NetworkManager::new();

// Register shared protocol layers
let ethernet = Arc::new(EthernetLayer::new());
let ip = Arc::new(IpLayer::new());
let tcp = Arc::new(TcpLayer::new());

net_manager.register_layer("ethernet", ethernet.clone());
net_manager.register_layer("ip", ip.clone());
net_manager.register_layer("tcp", tcp.clone());

// Setup protocol hierarchy - ONE WAY ONLY (lower -> upper)
ethernet.register_protocol(0x0800, ip.clone()); // Ethernet knows about IP
ip.register_protocol(6, tcp.clone());           // IP knows about TCP
// ❌ DON'T: tcp.register_protocol(X, ip.clone()) - creates circular reference!

// Socket creation retrieves shared layers
let tcp_layer = net_manager.get_layer("tcp")?;
let ip_layer = net_manager.get_layer("ip")?;
let eth_layer = net_manager.get_layer("ethernet")?;

// Create socket with references to shared layers (temporary, no cycle)
let socket = TcpSocket::new(tcp_layer, ip_layer, eth_layer);

Avoiding Circular References

Protocol registration creates permanent Arc references for receive routing. To avoid cycles:

1. Registration: Only lower layers register upper layers (one-way)
   • Ethernet → IP → TCP (receive path)
2. Sending: Upper layers pass lower layers as temporary parameters
   • send(packet, context, &[next_layer]) (no permanent storage)
3. Sockets: Hold references to all layers they need (temporary per-socket)