all: implement reload command

This commit adds reload command to ctrld for re-fetch new config from
ContorlD API or re-read the current config on disk.

cmd/cli/netlink_linux.go

@@ -1,11 +1,13 @@
 package cli
 
 import (
+	"context"
+
 	"github.com/vishvananda/netlink"
 	"golang.org/x/sys/unix"
 )
 
-func (p *prog) watchLinkState() {
+func (p *prog) watchLinkState(ctx context.Context) {
 	ch := make(chan netlink.LinkUpdate)
 	done := make(chan struct{})
 	defer close(done)
@@ -13,14 +15,19 @@ func (p *prog) watchLinkState() {
 		mainLog.Load().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.Load().Debug().Msgf("link state changed, re-bootstrapping")
-			for _, uc := range p.cfg.Upstream {
-				uc.ReBootstrap()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case lu := <-ch:
+			if lu.Change == 0xFFFFFFFF {
+				continue
+			}
+			if lu.Change&unix.IFF_UP != 0 {
+				mainLog.Load().Debug().Msgf("link state changed, re-bootstrapping")
+				for _, uc := range p.cfg.Upstream {
+					uc.ReBootstrap()
+				}
 			}
 		}
 	}