all: watch link state on Linux using netlink

So we can detect changed to link and trigger re-bootstrap.

cmd/ctrld/netlink_linux.go

@@ -0,0 +1,27 @@
+package main
+
+import (
+	"github.com/vishvananda/netlink"
+	"golang.org/x/sys/unix"
+)
+
+func (p *prog) watchLinkState() {
+	ch := make(chan netlink.LinkUpdate)
+	done := make(chan struct{})
+	defer close(done)
+	if err := netlink.LinkSubscribe(ch, done); err != nil {
+		mainLog.Warn().Err(err).Msg("could not subscribe link")
+		return
+	}
+	for lu := range ch {
+		if lu.Change == 0xFFFFFFFF {
+			continue
+		}
+		if lu.Change&unix.IFF_UP != 0 {
+			mainLog.Debug().Msgf("link state changed, re-bootstrapping")
+			for _, uc := range p.cfg.Upstream {
+				uc.ReBootstrap()
+			}
+		}
+	}
+}

cmd/ctrld/netlink_others.go

@@ -0,0 +1,5 @@
+//go:build !linux
+
+package main
+
+func (p *prog) watchLinkState() {}

cmd/ctrld/prog.go

@@ -82,6 +82,8 @@ func (p *prog) run() {
 		uc.SetupTransport()
 	}
 
+	go p.watchLinkState()
+
 	for listenerNum := range p.cfg.Listener {
 		p.cfg.Listener[listenerNum].Init()
 		go func(listenerNum string) {