Don't log "p9.channel.service: flipcall connection shutdown".

This gets quite spammy, especially in tests.

PiperOrigin-RevId: 277970468

pkg/flipcall/ctrl_futex.go

@@ -113,7 +113,7 @@ func (ep *Endpoint) enterFutexWait() error {
 		return nil
 	case epsBlocked | epsShutdown:
 		atomic.AddInt32(&ep.ctrl.state, -epsBlocked)
-		return shutdownError{}
+		return ShutdownError{}
 	default:
 		// Most likely due to ep.enterFutexWait() being called concurrently
 		// from multiple goroutines.

pkg/flipcall/flipcall.go

@@ -136,8 +136,8 @@ func (ep *Endpoint) unmapPacket() {
 
 // Shutdown causes concurrent and future calls to ep.Connect(), ep.SendRecv(),
 // ep.RecvFirst(), and ep.SendLast(), as well as the same calls in the peer
-// Endpoint, to unblock and return errors. It does not wait for concurrent
-// calls to return. Successive calls to Shutdown have no effect.
+// Endpoint, to unblock and return ShutdownErrors. It does not wait for
+// concurrent calls to return. Successive calls to Shutdown have no effect.
 //
 // Shutdown is the only Endpoint method that may be called concurrently with
 // other methods on the same Endpoint.
@@ -154,10 +154,12 @@ func (ep *Endpoint) isShutdownLocally() bool {
 	return atomic.LoadUint32(&ep.shutdown) != 0
 }
 
-type shutdownError struct{}
+// ShutdownError is returned by most Endpoint methods after Endpoint.Shutdown()
+// has been called.
+type ShutdownError struct{}
 
 // Error implements error.Error.
-func (shutdownError) Error() string {
+func (ShutdownError) Error() string {
 	return "flipcall connection shutdown"
 }
 

pkg/flipcall/futex_linux.go

@@ -61,7 +61,7 @@ func (ep *Endpoint) futexSwitchToPeer() error {
 	if !atomic.CompareAndSwapUint32(ep.connState(), ep.activeState, ep.inactiveState) {
 		switch cs := atomic.LoadUint32(ep.connState()); cs {
 		case csShutdown:
-			return shutdownError{}
+			return ShutdownError{}
 		default:
 			return fmt.Errorf("unexpected connection state before FUTEX_WAKE: %v", cs)
 		}
@@ -81,14 +81,14 @@ func (ep *Endpoint) futexSwitchFromPeer() error {
 			return nil
 		case ep.inactiveState:
 			if ep.isShutdownLocally() {
-				return shutdownError{}
+				return ShutdownError{}
 			}
 			if err := ep.futexWaitConnState(ep.inactiveState); err != nil {
 				return fmt.Errorf("failed to FUTEX_WAIT for peer Endpoint: %v", err)
 			}
 			continue
 		case csShutdown:
-			return shutdownError{}
+			return ShutdownError{}
 		default:
 			return fmt.Errorf("unexpected connection state before FUTEX_WAIT: %v", cs)
 		}

pkg/p9/server.go

@@ -453,7 +453,11 @@ func (cs *connState) initializeChannels() (err error) {
 		go func() { // S/R-SAFE: Server side.
 			defer cs.channelWg.Done()
 			if err := res.service(cs); err != nil {
-				log.Warningf("p9.channel.service: %v", err)
+				// Don't log flipcall.ShutdownErrors, which we expect to be
+				// returned during server shutdown.
+				if _, ok := err.(flipcall.ShutdownError); !ok {
+					log.Warningf("p9.channel.service: %v", err)
+				}
 			}
 		}()
 	}