wgengine/monitor: ignore OS-specific uninteresting interfaces

Currently we ignore these interfaces in the darwin osMon but then would consider it
interesting when checking if anything had changed.

Signed-off-by: Maisem Ali <maisem@tailscale.com>

wgengine/monitor/monitor.go

@@ -42,6 +42,10 @@ type osMon interface {
 	// until the osMon is closed. After a Close, the returned
 	// error is ignored.
 	Receive() (message, error)
+
+	// IsInterestingInterface reports whether the provided interface should
+	// be considered for network change events.
+	IsInterestingInterface(iface string) bool
 }
 
 // ChangeFunc is a callback function that's called when the network
@@ -282,6 +286,13 @@ func (m *Mon) notifyRuleDeleted(rdm ipRuleDeletedMessage) {
 	}
 }
 
+// isInterestingInterface reports whether the provided interface should be
+// considered when checking for network state changes.
+// The ips parameter should be the IPs of the provided interface.
+func (m *Mon) isInterestingInterface(i interfaces.Interface, ips []netaddr.IPPrefix) bool {
+	return m.om.IsInterestingInterface(i.Name) && interfaces.UseInterestingInterfaces(i, ips)
+}
+
 // debounce calls the callback function with a delay between events
 // and exits when a stop is issued.
 func (m *Mon) debounce() {
@@ -299,7 +310,7 @@ func (m *Mon) debounce() {
 			m.mu.Lock()
 
 			oldState := m.ifState
-			changed := !curState.EqualFiltered(oldState, interfaces.UseInterestingInterfaces, interfaces.UseInterestingIPs)
+			changed := !curState.EqualFiltered(oldState, m.isInterestingInterface, interfaces.UseInterestingIPs)
 			if changed {
 				m.gwValid = false
 				m.ifState = curState

wgengine/monitor/monitor_darwin.go

@@ -112,11 +112,18 @@ func addrType(addrs []route.Addr, rtaxType int) route.Addr {
 	return nil
 }
 
+func (m *darwinRouteMon) IsInterestingInterface(iface string) bool {
+	baseName := strings.TrimRight(iface, "0123456789")
+	switch baseName {
+	case "llw", "awdl", "pdp_ip", "ipsec":
+		return false
+	}
+	return true
+}
+
 func (m *darwinRouteMon) skipInterfaceAddrMessage(msg *route.InterfaceAddrMessage) bool {
 	if la, ok := addrType(msg.Addrs, unix.RTAX_IFP).(*route.LinkAddr); ok {
-		baseName := strings.TrimRight(la.Name, "0123456789")
-		switch baseName {
-		case "llw", "awdl", "pdp_ip", "ipsec":
+		if !m.IsInterestingInterface(la.Name) {
 			return true
 		}
 	}

wgengine/monitor/monitor_freebsd.go

@@ -34,6 +34,8 @@ func newOSMon(logf logger.Logf, m *Mon) (osMon, error) {
 	return &devdConn{conn}, nil
 }
 
+func (c *devdConn) IsInterestingInterface(iface string) bool { return true }
+
 func (c *devdConn) Close() error {
 	return c.conn.Close()
 }

wgengine/monitor/monitor_linux.go

@@ -64,6 +64,8 @@ func newOSMon(logf logger.Logf, m *Mon) (osMon, error) {
 	return &nlConn{logf: logf, conn: conn, addrCache: make(map[uint32]map[netaddr.IP]bool)}, nil
 }
 
+func (c *nlConn) IsInterestingInterface(iface string) bool { return true }
+
 func (c *nlConn) Close() error { return c.conn.Close() }
 
 func (c *nlConn) Receive() (message, error) {

wgengine/monitor/monitor_windows.go

@@ -72,6 +72,8 @@ func newOSMon(logf logger.Logf, _ *Mon) (osMon, error) {
 	return m, nil
 }
 
+func (m *winMon) IsInterestingInterface(iface string) bool { return true }
+
 func (m *winMon) Close() (ret error) {
 	m.cancel()
 	m.noDeadlockTicker.Stop()

wgengine/monitor/polling.go

@@ -38,6 +38,10 @@ type pollingMon struct {
 	stop      chan struct{}
 }
 
+func (pm *pollingMon) IsInterestingInterface(iface string) bool {
+	return true
+}
+
 func (pm *pollingMon) Close() error {
 	pm.closeOnce.Do(func() {
 		close(pm.stop)