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Merged
thedevbirb merged 3 commits into from
Feb 26, 2026
Merged

fix: unique device names #203

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82df428
chore(linkem): bridge id based on simulation id
thedevbirb Feb 24, 2026
637efb8
chore(linkem): test multiple networks
thedevbirb Feb 24, 2026
c48de0d
Merge branch 'main' into lore/chore/hub-id
Karrq Feb 26, 2026
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8 changes: 6 additions & 2 deletions linkem/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -11,20 +11,24 @@ traffic control.
Each peer runs in an isolated network namespace, connected through a central hub:

```text
Hub Namespace (linkem-hub)
Hub Namespace (lem-{id}-hub)
┌─────────────────────────────────────────────────────────────┐
│ Bridge (linkem-br0) │
│ Bridge (lem-br{id}) │
└─────────┬───────────────────┬───────────────────┬───────────┘
│ │ │
veth pair veth pair veth pair
│ │ │
┌─────────┴─────────┐ ┌───────┴──────────┐ ┌──────┴───────────┐
│ Peer 1 Namespace │ │ Peer 2 Namespace │ │ Peer 3 Namespace │
│ (lem-{id}-1) │ │ (lem-{id}-2) │ │ (lem-{id}-3) │
│ IP: 10.0.0.1 │ │ IP: 10.0.0.2 │ │ IP: 10.0.0.3 │
│ TC: per-dest │ │ TC: per-dest │ │ TC: per-dest │
└───────────────────┘ └──────────────────┘ └──────────────────┘
```

Where `{id}` is a 4-digit hex identifier derived from the process ID, ensuring
multiple concurrent simulations don't clash.

See [`src/network.rs`](src/network.rs) for detailed architecture documentation.

## Features
Expand Down
108 changes: 90 additions & 18 deletions linkem/src/network.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -13,20 +13,20 @@
//! │ Hub Namespace (lem-{id}-hub) │
//! │ │
//! │ ┌─────────────────────────────────────────────────────────────────────┐ │
//! │ │ Bridge (linkem-br0) │ │
//! │ │ Bridge (lem-br{id}) │ │
//! │ │ │ │
//! │ │ Acts as a virtual switch connecting all peer veth endpoints │ │
//! │ └─────────────────────────────────────────────────────────────────────┘ │
//! │ │ │ │ │
//! │ msg-veth1-br msg-veth2-br msg-veth3-br │
//! │ lv{id}-1-br lv{id}-2-br lv{id}-3-br │
//! └──────────┼────────────────────┼────────────────────┼────────────────────────┘
//! │ │ │
//! ═══════════════ ═══════════════ ═══════════════
//! veth pair veth pair veth pair
//! ═══════════════ ═══════════════ ═══════════════
//! │ │ │
//! ┌──────────┼─────────┐ ┌────────┼─────────┐ ┌────────┼─────────┐
//! │ msg-veth1 │ │ msg-veth2 │ │ msg-veth3 │
//! │ lv{id}-1 │ │ lv{id}-2 │ │ lv{id}-3 │
//! │ │ │ │ │ │
//! │ Peer 1 Namespace │ │ Peer 2 Namespace │ │ Peer 3 Namespace │
//! │ (lem-{id}-1) │ │ (lem-{id}-2) │ │ (lem-{id}-3) │
Expand Down Expand Up @@ -108,21 +108,29 @@ pub type PeerId = usize;
pub const NAMESPACE_PREFIX: &str = "lem";

/// Prefix for all virtual ethernet device names created by this crate.
pub const LINK_PREFIX: &str = "msg-veth";
///
/// Kept short because Linux interface names are limited to 15 characters (IFNAMSIZ - 1),
/// and the full name is `{LINK_PREFIX}{sim_id:04x}-{peer_id}` with a `-br` suffix
/// for the bridge endpoint.
pub const LINK_PREFIX: &str = "lv";

/// Extension trait for peer IDs providing namespace and device naming utilities.
pub trait PeerIdExt: Display + Copy {
/// Compute the IP address for this peer's veth device within the given subnet.
fn veth_address(self, subnet: Subnet) -> IpAddr;

/// Get the name of the veth device inside the peer's namespace.
fn veth_name(self) -> String {
format!("{LINK_PREFIX}{self}")
///
/// Format: `lv{sim_id:04x}-{peer_id}` (e.g. `lva3f1-1`).
fn veth_name(self, sim_id: u16) -> String {
format!("{LINK_PREFIX}{sim_id:04x}-{self}")
}

/// Get the name of the veth device endpoint attached to the hub bridge.
fn veth_br_name(self) -> String {
format!("{}-br", self.veth_name())
///
/// Format: `lv{sim_id:04x}-{peer_id}-br` (e.g. `lva3f1-1-br`).
fn veth_br_name(self, sim_id: u16) -> String {
format!("{}-br", self.veth_name(sim_id))
}
}

Expand Down Expand Up @@ -246,6 +254,11 @@ pub fn default_runtime_factory() -> RuntimeFactory {
})
}

/// Return the name to use for a bridge device based on the simulation id.
fn bridge_name(sim_id: u16) -> String {
format!("lem-br{sim_id:04x}")
}

/// Common context provided to all namespaces.
///
/// This context gives access to rtnetlink for network configuration.
Expand Down Expand Up @@ -420,14 +433,11 @@ pub struct Network {
}

impl Network {
/// Name of the bridge device in the hub namespace.
const BRIDGE_NAME: &str = "linkem-br0";

/// Create a new simulated network with the given IP subnet.
///
/// This creates:
/// 1. A hub network namespace (e.g. `lem-{sim_id}-hub`)
/// 2. A bridge device (`linkem-br0`) in the hub namespace
/// 1. A hub network namespace (e.g. `lem-a3f1-hub`)
/// 2. A bridge device (e.g. `lem-bra3f1`) in the hub namespace
///
/// Peers can then be added with [`add_peer`](Self::add_peer).
pub async fn new(subnet: Subnet) -> Result<Self> {
Expand Down Expand Up @@ -472,7 +482,7 @@ impl Network {
network
.rtnetlink_handle
.link()
.add(LinkBridge::new(Self::BRIDGE_NAME).up().setns_by_fd(fd).build())
.add(LinkBridge::new(&bridge_name(sim_id)).up().setns_by_fd(fd).build())
.execute()
.await?;

Expand All @@ -498,8 +508,8 @@ impl Network {
pub async fn add_peer_with_options(&mut self, options: PeerOptions) -> Result<PeerId> {
let peer_id = PEER_ID_NEXT.load(Ordering::Relaxed);
let namespace_name = self.peer_namespace_name(peer_id);
let veth_name = Arc::new(peer_id.veth_name());
let veth_br_name = Arc::new(peer_id.veth_br_name());
let veth_name = Arc::new(peer_id.veth_name(self.sim_id));
let veth_br_name = Arc::new(peer_id.veth_br_name(self.sim_id));

let _span =
tracing::debug_span!("add_peer", ?peer_id, %namespace_name, %veth_name, %veth_br_name)
Expand Down Expand Up @@ -584,13 +594,15 @@ impl Network {
.receive()
.await??;

let bridge_name = bridge_name(self.sim_id);

// Step 4: Attach the bridge endpoint to the hub's bridge device.
self.network_hub_namespace
.task_sender
.submit(|ctx| {
Box::pin(async move {
let index =
wrappers::if_nametoindex(Self::BRIDGE_NAME).expect("to find bridge").get();
wrappers::if_nametoindex(&bridge_name).expect("to find bridge").get();

// Set the bridge as the controller for this veth endpoint
ctx.handle
Expand Down Expand Up @@ -762,6 +774,7 @@ impl Network {
let subnet = self.subnet;

// Execute the TC configuration in the source peer's namespace.
let sim_id = self.sim_id;
src_peer
.namespace
.task_sender
Expand All @@ -776,7 +789,7 @@ impl Network {
Box::pin(
async move {
// Get the interface index for the peer's veth device.
let if_index = wrappers::if_nametoindex(&ctx.peer_id.veth_name())
let if_index = wrappers::if_nametoindex(&ctx.peer_id.veth_name(sim_id))
.expect("to find dev")
.get() as i32;

Expand Down Expand Up @@ -1460,4 +1473,63 @@ mod linkem_network {
received_count
);
}

/// Test that two processes can create networks concurrently without name conflicts.
///
/// Uses `fork()` so each child has a different PID (and therefore a different `sim_id`).
/// Both children create a network with peers; the parent waits for both to exit
/// successfully.
#[test]
fn concurrent_simulations_no_conflicts() {
use nix::sys::wait::{WaitStatus, waitpid};
use nix::unistd::{ForkResult, fork};

let _ = tracing_subscriber::fmt::try_init();

/// Spawn a child process that creates a network with 3 peers.
/// Returns the child PID.
fn spawn_simulation() -> nix::unistd::Pid {
// SAFETY: we are single-threaded at this point in the test (no tokio
// runtime yet), so fork is safe.
match unsafe { fork() }.expect("fork failed") {
ForkResult::Child => {
let rt =
tokio::runtime::Builder::new_multi_thread().enable_all().build().unwrap();

let code = rt.block_on(async {
let subnet = Subnet::new(Ipv4Addr::new(10, 0, 0, 0).into(), 16);
let mut network = match Network::new(subnet).await {
Ok(n) => n,
Err(e) => {
eprintln!("Network::new failed: {e}");
return 1;
}
};

for _ in 0..3 {
if let Err(e) = network.add_peer().await {
eprintln!("add_peer failed: {e}");
return 1;
}
}

0
});

std::process::exit(code);
}
ForkResult::Parent { child } => child,
}
}

let child_a = spawn_simulation();
let child_b = spawn_simulation();

for (label, pid) in [("A", child_a), ("B", child_b)] {
match waitpid(pid, None).expect("waitpid failed") {
WaitStatus::Exited(_, 0) => {}
status => panic!("child {label} (pid {pid}) failed: {status:?}"),
}
}
}
}
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