2 files changed, 85 insertions(+), 22 deletions(-)

M ipn/ipnlocal/local.go
M ipn/ipnlocal/local_test.go

@@ 479,7 479,7 @@ func NewLocalBackend(logf logger.Logf, logID logid.PublicID, sys *tsd.System, lo
 	mConn.SetNetInfoCallback(b.setNetInfo)
 
 	if sys.InitialConfig != nil {
-		if err := b.setConfigLocked(sys.InitialConfig); err != nil {
+		if err := b.initPrefsFromConfig(sys.InitialConfig); err != nil {
 			return nil, err
 		}
 	}


@@ 712,8 712,8 @@ func (b *LocalBackend) SetDirectFileRoot(dir string) {
 // It returns (false, nil) if not running in declarative mode, (true, nil) on
 // success, or (false, error) on failure.
 func (b *LocalBackend) ReloadConfig() (ok bool, err error) {
-	b.mu.Lock()
-	defer b.mu.Unlock()
+	unlock := b.lockAndGetUnlock()
+	defer unlock()
 	if b.conf == nil {
 		return false, nil
 	}


@@ 721,18 721,21 @@ func (b *LocalBackend) ReloadConfig() (ok bool, err error) {
 	if err != nil {
 		return false, err
 	}
-	if err := b.setConfigLocked(conf); err != nil {
+	if err := b.setConfigLockedOnEntry(conf, unlock); err != nil {
 		return false, fmt.Errorf("error setting config: %w", err)
 	}
 
 	return true, nil
 }
 
-func (b *LocalBackend) setConfigLocked(conf *conffile.Config) error {
-
-	// TODO(irbekrm): notify the relevant components to consume any prefs
-	// updates. Currently only initial configfile settings are applied
-	// immediately.
+// initPrefsFromConfig initializes the backend's prefs from the provided config.
+// This should only be called once, at startup. For updates at runtime, use
+// [LocalBackend.setConfigLocked].
+func (b *LocalBackend) initPrefsFromConfig(conf *conffile.Config) error {
+	// TODO(maisem,bradfitz): combine this with setConfigLocked. This is called
+	// before anything is running, so there's no need to lock and we don't
+	// update any subsystems. At runtime, we both need to lock and update
+	// subsystems with the new prefs.
 	p := b.pm.CurrentPrefs().AsStruct()
 	mp, err := conf.Parsed.ToPrefs()
 	if err != nil {


@@ 742,13 745,14 @@ func (b *LocalBackend) setConfigLocked(conf *conffile.Config) error {
 	if err := b.pm.SetPrefs(p.View(), ipn.NetworkProfile{}); err != nil {
 		return err
 	}
+	b.setStaticEndpointsFromConfigLocked(conf)
+	b.conf = conf
+	return nil
+}
 
-	defer func() {
-		b.conf = conf
-	}()
-
+func (b *LocalBackend) setStaticEndpointsFromConfigLocked(conf *conffile.Config) {
 	if conf.Parsed.StaticEndpoints == nil && (b.conf == nil || b.conf.Parsed.StaticEndpoints == nil) {
-		return nil
+		return
 	}
 
 	// Ensure that magicsock conn has the up to date static wireguard


@@ 762,6 766,22 @@ func (b *LocalBackend) setConfigLocked(conf *conffile.Config) error {
 			ms.SetStaticEndpoints(views.SliceOf(conf.Parsed.StaticEndpoints))
 		}
 	}
+}
+
+// setConfigLockedOnEntry uses the provided config to update the backend's prefs
+// and other state.
+func (b *LocalBackend) setConfigLockedOnEntry(conf *conffile.Config, unlock unlockOnce) error {
+	defer unlock()
+	p := b.pm.CurrentPrefs().AsStruct()
+	mp, err := conf.Parsed.ToPrefs()
+	if err != nil {
+		return fmt.Errorf("error parsing config to prefs: %w", err)
+	}
+	p.ApplyEdits(&mp)
+	b.setStaticEndpointsFromConfigLocked(conf)
+	b.setPrefsLockedOnEntry(p, unlock)
+
+	b.conf = conf
 	return nil
 }
 

@@ 13,6 13,7 @@ import (
 	"net/http"
 	"net/netip"
 	"os"
+	"path/filepath"
 	"reflect"
 	"slices"
 	"strings"


@@ 32,6 33,7 @@ import (
 	"tailscale.com/health"
 	"tailscale.com/hostinfo"
 	"tailscale.com/ipn"
+	"tailscale.com/ipn/conffile"
 	"tailscale.com/ipn/ipnauth"
 	"tailscale.com/ipn/store/mem"
 	"tailscale.com/net/netcheck"


@@ 432,16 434,25 @@ func (panicOnUseTransport) RoundTrip(*http.Request) (*http.Response, error) {
 }
 
 func newTestLocalBackend(t testing.TB) *LocalBackend {
+	return newTestLocalBackendWithSys(t, new(tsd.System))
+}
+
+// newTestLocalBackendWithSys creates a new LocalBackend with the given tsd.System.
+// If the state store or engine are not set in sys, they will be set to a new
+// in-memory store and fake userspace engine, respectively.
+func newTestLocalBackendWithSys(t testing.TB, sys *tsd.System) *LocalBackend {
 	var logf logger.Logf = logger.Discard
-	sys := new(tsd.System)
-	store := new(mem.Store)
-	sys.Set(store)
-	eng, err := wgengine.NewFakeUserspaceEngine(logf, sys.Set, sys.HealthTracker(), sys.UserMetricsRegistry())
-	if err != nil {
-		t.Fatalf("NewFakeUserspaceEngine: %v", err)
+	if _, ok := sys.StateStore.GetOK(); !ok {
+		sys.Set(new(mem.Store))
+	}
+	if _, ok := sys.Engine.GetOK(); !ok {
+		eng, err := wgengine.NewFakeUserspaceEngine(logf, sys.Set, sys.HealthTracker(), sys.UserMetricsRegistry())
+		if err != nil {
+			t.Fatalf("NewFakeUserspaceEngine: %v", err)
+		}
+		t.Cleanup(eng.Close)
+		sys.Set(eng)
 	}
-	t.Cleanup(eng.Close)
-	sys.Set(eng)
 	lb, err := NewLocalBackend(logf, logid.PublicID{}, sys, 0)
 	if err != nil {
 		t.Fatalf("NewLocalBackend: %v", err)


@@ 4423,3 4434,35 @@ func TestLoginNotifications(t *testing.T) {
 		})
 	}
 }
+
+// TestConfigFileReload tests that the LocalBackend reloads its configuration
+// when the configuration file changes.
+func TestConfigFileReload(t *testing.T) {
+	cfg1 := `{"Hostname": "foo", "Version": "alpha0"}`
+	f := filepath.Join(t.TempDir(), "cfg")
+	must.Do(os.WriteFile(f, []byte(cfg1), 0600))
+	sys := new(tsd.System)
+	sys.InitialConfig = must.Get(conffile.Load(f))
+	lb := newTestLocalBackendWithSys(t, sys)
+	must.Do(lb.Start(ipn.Options{}))
+
+	lb.mu.Lock()
+	hn := lb.hostinfo.Hostname
+	lb.mu.Unlock()
+	if hn != "foo" {
+		t.Fatalf("got %q; want %q", hn, "foo")
+	}
+
+	cfg2 := `{"Hostname": "bar", "Version": "alpha0"}`
+	must.Do(os.WriteFile(f, []byte(cfg2), 0600))
+	if !must.Get(lb.ReloadConfig()) {
+		t.Fatal("reload failed")
+	}
+
+	lb.mu.Lock()
+	hn = lb.hostinfo.Hostname
+	lb.mu.Unlock()
+	if hn != "bar" {
+		t.Fatalf("got %q; want %q", hn, "bar")
+	}
+}