Add configurable link-up delay to simulate real NIC carrier negotiation

.github/workflows/ci.yml

@@ -115,6 +115,59 @@ jobs:
           IFACE=$(ls /sys/bus/pci/devices/${DOMAIN}:${BUS}:02.0/net/ 2>/dev/null | head -1)
           [ -n "$IFACE" ] && ethtool -T "$IFACE" || echo "WARN: No interface found"
 
+      - name: Smoke test — link up delay
+        if: steps.load.outputs.load_ok == 'true'
+        run: |
+          set -euo pipefail
+
+          BUS_NR=$(cat /sys/module/netdevsim/parameters/pci_bus_nr 2>/dev/null || echo 31)
+          BUS=$(printf "%02x" "$BUS_NR")
+          FAKE_ROOT=$(ls /sys/bus/pci/devices/ 2>/dev/null | grep ":${BUS}:00\.0" | head -1)
+          DOMAIN="${FAKE_ROOT:+$(echo "$FAKE_ROOT" | cut -d: -f1)}"
+          : "${DOMAIN:=0000}"
+
+          IFACE=$(ls /sys/bus/pci/devices/${DOMAIN}:${BUS}:02.0/net/ 2>/dev/null | head -1)
+          [ -z "$IFACE" ] && { echo "SKIP: no interface found"; exit 0; }
+
+          echo "Interface: $IFACE"
+
+          # Bring down first so we start from a known state
+          sudo ip link set "$IFACE" down
+          sleep 1
+
+          # Set a 3-second link-up delay via debugfs
+          DEBUGFS="/sys/kernel/debug/netdevsim/netdevsim1/ports/0/link_up_delay_ms"
+          echo 3000 | sudo tee "$DEBUGFS"
+          echo "link_up_delay_ms set to $(cat "$DEBUGFS")"
+
+          # Bring interface up — carrier should stay off
+          sudo ip link set "$IFACE" up
+          sleep 0.5
+          CARRIER=$(cat /sys/class/net/"$IFACE"/carrier 2>/dev/null || echo 0)
+          echo "Carrier immediately after up: $CARRIER"
+          [ "$CARRIER" -eq 0 ] || { echo "FAIL: carrier should be 0 during delay"; exit 1; }
+
+          # Wait for the delay to expire
+          sleep 4
+          CARRIER=$(cat /sys/class/net/"$IFACE"/carrier 2>/dev/null || echo 0)
+          echo "Carrier after delay: $CARRIER"
+          [ "$CARRIER" -eq 1 ] || { echo "FAIL: carrier should be 1 after delay"; exit 1; }
+
+          # Verify PTP clock is still readable
+          PHC_IDX=$(ethtool -T "$IFACE" 2>/dev/null | grep -oP 'PTP Hardware Clock: \K[0-9]+' || true)
+          if [ -n "$PHC_IDX" ]; then
+            echo "PHC index: $PHC_IDX"
+            # Read the clock via sysfs — confirms the PTP device works
+            cat /sys/class/nsim_ptp/nsim_ptp${PHC_IDX}/clock 2>/dev/null \
+              && echo "OK: PTP clock readable" \
+              || echo "WARN: could not read PTP clock via sysfs"
+          fi
+
+          # Verify hwtstamp config still works after link-up delay
+          ethtool -T "$IFACE" | grep -E "PTP Hardware Clock|hardware"
+
+          echo "=== LINK UP DELAY TEST PASSED ==="
+
       - name: Cleanup
         if: always()
         run: |

netdevsim/dev.c

@@ -1394,6 +1394,11 @@ static int __nsim_dev_port_add(struct nsim_dev *nsim_dev, enum nsim_dev_port_typ
 		goto err_port_debugfs_exit;
 	}
 
+	if (nsim_dev_port_is_pf(nsim_dev_port))
+		debugfs_create_u32("link_up_delay_ms", 0600,
+				   nsim_dev_port->ddir,
+				   &nsim_dev_port->ns->link_up_delay_ms);
+
 	if (nsim_dev_port_is_vf(nsim_dev_port)) {
 		err = devl_rate_leaf_create(&nsim_dev_port->devlink_port,
 					    nsim_dev_port, NULL);

netdevsim/netdev.c

@@ -400,8 +400,42 @@ static int nsim_set_ts_config(struct net_device *netdev,
 	}
 	return 0;
 }
+static void nsim_link_up_work(struct work_struct *work)
+{
+	struct netdevsim *ns =
+		container_of(work, struct netdevsim, link_up_dwork.work);
+
+	netif_carrier_on(ns->netdev);
+}
+
+static int nsim_open(struct net_device *dev)
+{
+	struct netdevsim *ns = netdev_priv(dev);
+	u32 delay = READ_ONCE(ns->link_up_delay_ms);
+
+	if (delay)
+		schedule_delayed_work(&ns->link_up_dwork,
+				      msecs_to_jiffies(delay));
+	else
+		netif_carrier_on(dev);
+
+	return 0;
+}
+
+static int nsim_stop(struct net_device *dev)
+{
+	struct netdevsim *ns = netdev_priv(dev);
+
+	cancel_delayed_work_sync(&ns->link_up_dwork);
+	netif_carrier_off(dev);
+
+	return 0;
+}
+
 static const struct net_device_ops nsim_netdev_ops = {
 	.ndo_start_xmit = nsim_start_xmit,
+	.ndo_open = nsim_open,
+	.ndo_stop = nsim_stop,
 	.ndo_set_rx_mode = nsim_set_rx_mode,
 	.ndo_set_mac_address = eth_mac_addr,
 	.ndo_validate_addr = eth_validate_addr,
@@ -525,6 +559,8 @@ static int nsim_init_netdevsim(struct netdevsim *ns)
 	ns->phc = phc;
 	ns->netdev->netdev_ops = &nsim_netdev_ops;
 
+	INIT_DELAYED_WORK(&ns->link_up_dwork, nsim_link_up_work);
+
 	err = nsim_udp_tunnels_info_create(ns->nsim_dev, ns->netdev);
 	if (err)
 		goto err_phc_destroy;
@@ -537,6 +573,8 @@ static int nsim_init_netdevsim(struct netdevsim *ns)
 	nsim_macsec_init(ns);
 	nsim_ipsec_init(ns);
 
+	netif_carrier_off(ns->netdev);
+
 	err = register_netdevice(ns->netdev);
 	if (err)
 		goto err_ipsec_teardown;
@@ -624,6 +662,8 @@ void nsim_destroy(struct netdevsim *ns)
 	struct net_device *dev = ns->netdev;
 	struct netdevsim *peer;
 
+	cancel_delayed_work_sync(&ns->link_up_dwork);
+
 	rtnl_lock();
 	peer = rtnl_dereference(ns->peer);
 	if (peer)

netdevsim/netdevsim.h

@@ -157,6 +157,9 @@ struct netdevsim {
 	struct nsim_ethtool ethtool;
 	struct netdevsim __rcu *peer;
 	struct kernel_hwtstamp_config tstamp_config;
+
+	u32 link_up_delay_ms;
+	struct delayed_work link_up_dwork;
 };
 
 struct netdevsim *