signals: support detach and notify socket together

let runc run until READY= is received and then proceed with
detaching the process.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

notify_socket.go

@@ -63,7 +63,9 @@ func (s *notifySocket) setupSocket() error {
 	return nil
 }
 
-func (notifySocket *notifySocket) run() {
+// pid1 must be set only with -d, as it is used to set the new process as the main process
+// for the service in systemd
+func (notifySocket *notifySocket) run(pid1 int) {
 	buf := make([]byte, 512)
 	notifySocketHostAddr := net.UnixAddr{Name: notifySocket.host, Net: "unixgram"}
 	client, err := net.DialUnix("unixgram", nil, &notifySocketHostAddr)
@@ -93,6 +95,12 @@ func (notifySocket *notifySocket) run() {
 				if err != nil {
 					return
 				}
+
+				// now we can inform systemd to use pid1 as the pid to monitor
+				if pid1 > 0 {
+					newPid := fmt.Sprintf("MAINPID=%d\n", pid1)
+					client.Write([]byte(newPid))
+				}
 				return
 			}
 		}

restore.go

@@ -188,10 +188,7 @@ func restoreContainer(context *cli.Context, spec *specs.Spec, config *configs.Co
 			return -1, err
 		}
 	}
-	if detach {
-		return 0, nil
-	}
-	return handler.forward(process, tty)
+	return handler.forward(process, tty, detach)
 }
 
 func criuOptions(context *cli.Context) *libcontainer.CriuOpts {

signals.go

@@ -51,16 +51,25 @@ type signalHandler struct {
 
 // forward handles the main signal event loop forwarding, resizing, or reaping depending
 // on the signal received.
-func (h *signalHandler) forward(process *libcontainer.Process, tty *tty) (int, error) {
+func (h *signalHandler) forward(process *libcontainer.Process, tty *tty, detach bool) (int, error) {
 	// make sure we know the pid of our main process so that we can return
 	// after it dies.
+	if detach && h.notifySocket == nil {
+		return 0, nil
+	}
+
 	pid1, err := process.Pid()
 	if err != nil {
 		return -1, err
 	}
 
 	if h.notifySocket != nil {
-		go h.notifySocket.run()
+		if detach {
+			h.notifySocket.run(pid1)
+			return 0, nil
+		} else {
+			go h.notifySocket.run(0)
+		}
 	}
 
 	// perform the initial tty resize.

utils_linux.go

@@ -219,10 +219,6 @@ func (r *runner) run(config *specs.Process) (int, error) {
 		r.destroy()
 		return -1, fmt.Errorf("cannot use console socket if runc will not detach or allocate tty")
 	}
-	if detach && r.notifySocket != nil {
-		r.destroy()
-		return -1, fmt.Errorf("cannot detach when using NOTIFY_SOCKET")
-	}
 
 	startFn := r.container.Start
 	if !r.create {
@@ -294,13 +290,13 @@ func (r *runner) run(config *specs.Process) (int, error) {
 			return -1, err
 		}
 	}
-	if detach {
-		return 0, nil
-	}
-	status, err := handler.forward(process, tty)
+	status, err := handler.forward(process, tty, detach)
 	if err != nil {
 		r.terminate(process)
 	}
+	if detach {
+		return 0, nil
+	}
 	r.destroy()
 	return status, err
 }