netmon: Add signals handler

After the signals package has been created and shared with the CLI,
this commit calls into it in order to properly handle the signals
directed to the network monitor process.

Fixes #718

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

netmon/netmon.go

@@ -7,6 +7,7 @@ package main
 
 import (
 	"encoding/json"
+	"errors"
 	"flag"
 	"fmt"
 	"io/ioutil"
@@ -14,10 +15,13 @@ import (
 	"net"
 	"os"
 	"os/exec"
+	"os/signal"
 	"path/filepath"
 	"strings"
+	"syscall"
 	"time"
 
+	"github.com/kata-containers/runtime/pkg/signals"
 	"github.com/sirupsen/logrus"
 	lSyslog "github.com/sirupsen/logrus/hooks/syslog"
 	"github.com/vishvananda/netlink"
@@ -203,6 +207,39 @@ func (n *netmon) cleanup() {
 	close(n.rtDoneCh)
 }
 
+// setupSignalHandler sets up signal handling, starting a go routine to deal
+// with signals as they arrive.
+func (n *netmon) setupSignalHandler() {
+	signals.SetLogger(n.logger())
+
+	sigCh := make(chan os.Signal, 8)
+
+	for _, sig := range signals.HandledSignals() {
+		signal.Notify(sigCh, sig)
+	}
+
+	go func() {
+		for {
+			sig := <-sigCh
+
+			nativeSignal, ok := sig.(syscall.Signal)
+			if !ok {
+				err := errors.New("unknown signal")
+				netmonLog.WithError(err).WithField("signal", sig.String()).Error()
+				continue
+			}
+
+			if signals.FatalSignal(nativeSignal) {
+				netmonLog.WithField("signal", sig).Error("received fatal signal")
+				signals.Die(nil)
+			} else if n.debug && signals.NonFatalSignal(nativeSignal) {
+				netmonLog.WithField("signal", sig).Debug("handling signal")
+				signals.Backtrace()
+			}
+		}
+	}()
+}
+
 func (n *netmon) logger() *logrus.Entry {
 	fields := logrus.Fields{
 		"name":   netmonName,
@@ -641,6 +678,9 @@ func main() {
 		os.Exit(1)
 	}
 
+	// Setup signal handlers
+	n.setupSignalHandler()
+
 	// Scan the current interfaces.
 	if err := n.scanNetwork(); err != nil {
 		n.logger().WithError(err).Fatal("scanNetwork()")