Launch and monitor ulogd daemon

Exec the ulogd daemon on weave-npc startup, copying any log output to
our own logs. Exit if the ulogd process terminates for any reason.

cmd/weave-npc/main.go

@@ -19,6 +19,7 @@ import (
 	"k8s.io/kubernetes/pkg/util/wait"
 
 	weavenpc "github.com/weaveworks/weave-npc/pkg/controller"
+	"github.com/weaveworks/weave-npc/pkg/ulogd"
 	"github.com/weaveworks/weave-npc/pkg/util/ipset"
 )
 
@@ -101,6 +102,10 @@ func resetIPSets(ips ipset.Interface) error {
 func main() {
 	log.Infof("Starting Weaveworks NPC %s", version)
 
+	if err := ulogd.Start(); err != nil {
+		log.Fatalf("Failed to start ulogd: %v", err)
+	}
+
 	client, err := unversioned.NewInCluster()
 	if err != nil {
 		log.Fatal(err)

pkg/ulogd/ulogd.go

@@ -0,0 +1,29 @@
+package ulogd
+
+import (
+	log "github.com/Sirupsen/logrus"
+	"io"
+	"os"
+	"os/exec"
+)
+
+func waitForExit(cmd *exec.Cmd) {
+	if err := cmd.Wait(); err != nil {
+		log.Fatalf("ulogd terminated: %v", err)
+	}
+	log.Fatal("ulogd terminated normally")
+}
+
+func Start() error {
+	cmd := exec.Command("/usr/sbin/ulogd", "-v")
+	stdout, err := cmd.StderrPipe()
+	if err != nil {
+		return err
+	}
+	if err := cmd.Start(); err != nil {
+		return err
+	}
+	go io.Copy(os.Stdout, stdout)
+	go waitForExit(cmd)
+	return nil
+}