Start kernel router and vertex executable

kernel/main.go

@@ -1,5 +1,98 @@
 package main
 
+import (
+	"flag"
+	"os"
+	"os/exec"
+	"os/user"
+	"strconv"
+	"syscall"
+
+	"github.com/vertex-center/vertex/pkg/log"
+	"github.com/vertex-center/vertex/router"
+	"github.com/vertex-center/vlog"
+)
+
 func main() {
-	return
+	ensureRoot()
+
+	r := router.NewKernelRouter()
+
+	go func() {
+		err := r.Start()
+		defer r.Stop()
+
+		if err != nil {
+			log.Error(err)
+			os.Exit(1)
+		}
+	}()
+
+	u := getUnprivilegedUser()
+
+	go func() {
+		vertex, err := runVertex(u)
+		defer vertex.Process.Kill()
+
+		if err != nil {
+			log.Error(err)
+			os.Exit(1)
+		}
+
+		err = vertex.Wait()
+		if err != nil {
+			log.Error(err)
+			os.Exit(1)
+		}
+	}()
+
+	select {}
+}
+
+func ensureRoot() {
+	if os.Getuid() != 0 {
+		log.Warn("vertex-kernel must be run as root to work properly")
+	}
+}
+
+func getUnprivilegedUser() *user.User {
+	flagUnprivilegedUsername := flag.String("u", "vertex", "unprivileged username")
+	flag.Parse()
+	username := *flagUnprivilegedUsername
+	return getUser(username)
+}
+
+func getUser(username string) *user.User {
+	u, err := user.Lookup(username)
+	if err != nil {
+		log.Error(err)
+		os.Exit(1)
+	}
+	return u
+}
+
+func runVertex(user *user.User) (*exec.Cmd, error) {
+	uid, err := strconv.Atoi(user.Uid)
+	if err != nil {
+		return nil, err
+	}
+
+	gid, err := strconv.Atoi(user.Gid)
+	if err != nil {
+		return nil, err
+	}
+
+	log.Info("Running vertex",
+		vlog.String("username", user.Username),
+		vlog.Int("uid", uid),
+		vlog.Int("gid", gid),
+	)
+
+	cmd := exec.Command("./vertex")
+	cmd.SysProcAttr = &syscall.SysProcAttr{}
+	cmd.SysProcAttr.Credential = &syscall.Credential{Uid: uint32(uid), Gid: uint32(gid)}
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+
+	return cmd, cmd.Start()
 }