skip setup signal notifier for detached container

For detached container, we don't need to setup signal notifier, because
there is no customer to consume the signals in `forward()`.
This commit also moves notifySocket out of signalHandler to make the
code more clear.

Signed-off-by: lifubang <[email protected]>

Author: lifubang

notify_socket.go

@@ -150,6 +150,22 @@ func (n *notifySocket) run(pid1 int) error {
 	}
 }
 
+// forward reads systemd notifications from the container and forwards them
+// to notifySocketHost.
+func (s *notifySocket) forward(process *libcontainer.Process, detach bool) error {
+	if detach {
+		pid, err := process.Pid()
+		if err != nil {
+			return err
+		}
+		_ = s.run(pid)
+	} else {
+		_ = s.run(os.Getpid())
+		go func() { _ = s.run(0) }()
+	}
+	return nil
+}
+
 // notifyHost tells the host (usually systemd) that the container reported READY.
 // Also sends MAINPID and BARRIER.
 func notifyHost(client *net.UnixConn, ready []byte, pid1 int) error {

signals.go

@@ -5,7 +5,6 @@ import (
 	"os/signal"
 
 	"github.com/opencontainers/runc/libcontainer"
-	"github.com/opencontainers/runc/libcontainer/system"
 	"github.com/opencontainers/runc/libcontainer/utils"
 
 	"github.com/sirupsen/logrus"
@@ -16,15 +15,7 @@ const signalBufferSize = 2048
 
 // newSignalHandler returns a signal handler for processing SIGCHLD and SIGWINCH signals
 // while still forwarding all other signals to the process.
-// If notifySocket is present, use it to read systemd notifications from the container and
-// forward them to notifySocketHost.
-func newSignalHandler(enableSubreaper bool, notifySocket *notifySocket) chan *signalHandler {
-	if enableSubreaper {
-		// set us as the subreaper before registering the signal handler for the container
-		if err := system.SetSubreaper(1); err != nil {
-			logrus.Warn(err)
-		}
-	}
+func newSignalHandler() chan *signalHandler {
 	handler := make(chan *signalHandler)
 	// signal.Notify is actually quite expensive, as it has to configure the
 	// signal mask and add signal handlers for all signals (all ~65 of them).
@@ -37,8 +28,7 @@ func newSignalHandler(enableSubreaper bool, notifySocket *notifySocket) chan *si
 		// handle all signals for the process.
 		signal.Notify(s)
 		handler <- &signalHandler{
-			signals:      s,
-			notifySocket: notifySocket,
+			signals: s,
 		}
 	}()
 	return handler
@@ -52,33 +42,19 @@ type exit struct {
 }
 
 type signalHandler struct {
-	signals      chan os.Signal
-	notifySocket *notifySocket
+	signals chan os.Signal
 }
 
 // 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, detach bool) (int, error) {
+func (h *signalHandler) forward(process *libcontainer.Process, tty *tty) (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 {
-		if detach {
-			_ = h.notifySocket.run(pid1)
-			return 0, nil
-		}
-		_ = h.notifySocket.run(os.Getpid())
-		go func() { _ = h.notifySocket.run(0) }()
-	}
-
 	// Perform the initial tty resize. Always ignore errors resizing because
 	// stdout might have disappeared (due to races with when SIGHUP is sent).
 	_ = tty.resize()

utils_linux.go

@@ -18,6 +18,7 @@ import (
 	"github.com/opencontainers/runc/libcontainer"
 	"github.com/opencontainers/runc/libcontainer/configs"
 	"github.com/opencontainers/runc/libcontainer/specconv"
+	"github.com/opencontainers/runc/libcontainer/system"
 	"github.com/opencontainers/runc/libcontainer/system/kernelversion"
 	"github.com/opencontainers/runc/libcontainer/utils"
 )
@@ -217,7 +218,10 @@ type runner struct {
 }
 
 func (r *runner) run(config *specs.Process) (int, error) {
-	var err error
+	var (
+		err       error
+		handlerCh chan *signalHandler
+	)
 	defer func() {
 		if err != nil {
 			r.destroy()
@@ -249,10 +253,18 @@ func (r *runner) run(config *specs.Process) (int, error) {
 		process.ExtraFiles = append(process.ExtraFiles, os.NewFile(uintptr(i), "PreserveFD:"+strconv.Itoa(i)))
 	}
 	detach := r.detach || (r.action == CT_ACT_CREATE)
+	if r.enableSubreaper {
+		// set us as the subreaper before registering the signal handler for the container
+		if err := system.SetSubreaper(1); err != nil {
+			logrus.Warn(err)
+		}
+	}
+	if !detach {
+		handlerCh = newSignalHandler()
+	}
 	// Setting up IO is a two stage process. We need to modify process to deal
 	// with detaching containers, and then we get a tty after the container has
 	// started.
-	handlerCh := newSignalHandler(r.enableSubreaper, r.notifySocket)
 	tty, err := setupIO(process, r.container, config.Terminal, detach, r.consoleSocket)
 	if err != nil {
 		return -1, err
@@ -291,14 +303,20 @@ func (r *runner) run(config *specs.Process) (int, error) {
 			return -1, err
 		}
 	}
-	handler := <-handlerCh
-	status, err := handler.forward(process, tty, detach)
-	if err != nil {
-		r.terminate(process)
+	if r.notifySocket != nil {
+		if err := r.notifySocket.forward(process, detach); err != nil {
+			r.terminate(process)
+			return -1, err
+		}
 	}
 	if detach {
 		return 0, nil
 	}
+	handler := <-handlerCh
+	status, err := handler.forward(process, tty)
+	if err != nil {
+		r.terminate(process)
+	}
 	if err == nil {
 		r.destroy()
 	}