Simplify namespaces with only nsinit

Docker-DCO-1.1-Signed-off-by: Michael Crosby <michael@crosbymichael.com> (github: crosbymichael)

libcontainer/nsinit/init.go

@@ -0,0 +1,171 @@
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"github.com/dotcloud/docker/pkg/libcontainer"
+	"github.com/dotcloud/docker/pkg/libcontainer/capabilities"
+	"github.com/dotcloud/docker/pkg/system"
+	"log"
+	"os"
+	"path/filepath"
+	"syscall"
+)
+
+func loadContainer() (*libcontainer.Container, error) {
+	f, err := os.Open("container.json")
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+
+	var container *libcontainer.Container
+	if err := json.NewDecoder(f).Decode(&container); err != nil {
+		return nil, err
+	}
+	return container, nil
+}
+
+func main() {
+	container, err := loadContainer()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	if os.Args[1] == "exec" {
+		_, err := execCommand(container)
+		if err != nil {
+			log.Fatal(err)
+		}
+		os.Exit(0)
+	}
+	console := os.Args[1]
+
+	if err := setLogFile(container); err != nil {
+		log.Fatal(err)
+	}
+
+	rootfs, err := resolveRootfs()
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// close pipes so that we can replace it with the pty
+	os.Stdin.Close()
+	os.Stdout.Close()
+	os.Stderr.Close()
+
+	slave, err := openTerminal(console, syscall.O_RDWR)
+	if err != nil {
+		log.Fatalf("open terminal %s", err)
+	}
+	if slave.Fd() != 0 {
+		log.Fatalf("slave fd should be 0")
+	}
+	if err := dupSlave(slave); err != nil {
+		log.Fatalf("dup2 slave %s", err)
+	}
+
+	if _, err := system.Setsid(); err != nil {
+		log.Fatalf("setsid %s", err)
+	}
+	if err := system.Setctty(); err != nil {
+		log.Fatalf("setctty %s", err)
+	}
+	if err := system.ParentDeathSignal(); err != nil {
+		log.Fatalf("parent deth signal %s", err)
+	}
+
+	if err := setupNewMountNamespace(rootfs, console, container.ReadonlyFs); err != nil {
+		log.Fatalf("setup mount namespace %s", err)
+	}
+
+	if container.Network != nil {
+		if err := setupNetworking(container); err != nil {
+			log.Fatalf("setup networking %s", err)
+		}
+	}
+
+	if err := system.Sethostname(container.ID); err != nil {
+		log.Fatalf("sethostname %s", err)
+	}
+	if err := capabilities.DropCapabilities(container); err != nil {
+		log.Fatalf("drop capabilities %s", err)
+	}
+	if err := setupUser(container); err != nil {
+		log.Fatalf("setup user %s", err)
+	}
+	if container.WorkingDir != "" {
+		if err := system.Chdir(container.WorkingDir); err != nil {
+			log.Fatalf("chdir to %s %s", container.WorkingDir, err)
+		}
+	}
+	if err := system.Exec(container.Command.Args[0], container.Command.Args[0:], container.Command.Env); err != nil {
+		log.Fatalf("exec %s", err)
+	}
+	panic("unreachable")
+}
+
+func resolveRootfs() (string, error) {
+	cwd, err := os.Getwd()
+	if err != nil {
+		return "", err
+	}
+	rootfs, err := filepath.Abs(cwd)
+	if err != nil {
+		return "", err
+	}
+	return filepath.EvalSymlinks(rootfs)
+}
+
+func setupUser(container *libcontainer.Container) error {
+	// TODO: honor user passed on container
+	if err := system.Setgroups(nil); err != nil {
+		return err
+	}
+	if err := system.Setresgid(0, 0, 0); err != nil {
+		return err
+	}
+	if err := system.Setresuid(0, 0, 0); err != nil {
+		return err
+	}
+	return nil
+}
+
+func dupSlave(slave *os.File) error {
+	// we close Stdin,etc so our pty slave should have fd 0
+	if slave.Fd() != 0 {
+		return fmt.Errorf("slave fd not 0 %d", slave.Fd())
+	}
+	if err := system.Dup2(slave.Fd(), 1); err != nil {
+		return err
+	}
+	if err := system.Dup2(slave.Fd(), 2); err != nil {
+		return err
+	}
+	return nil
+}
+
+// openTerminal is a clone of os.OpenFile without the O_CLOEXEC addition.
+func openTerminal(name string, flag int) (*os.File, error) {
+	r, e := syscall.Open(name, flag, 0)
+	if e != nil {
+		return nil, &os.PathError{"open", name, e}
+	}
+	return os.NewFile(uintptr(r), name), nil
+}
+
+func setLogFile(container *libcontainer.Container) error {
+	if container.LogFile != "" {
+		f, err := os.OpenFile(container.LogFile, os.O_CREATE|os.O_RDWR|os.O_APPEND, 0655)
+		if err != nil {
+			return err
+		}
+		log.SetOutput(f)
+	}
+	return nil
+}
+
+func setupNetworking(conatiner *libcontainer.Container) error {
+	return nil
+}