# 命名空间Go实现 - Mount

func PivotRoot(newroot string, putold string) (err error)

# Git repo: https://github.com/teddyking/ns-process
# Git tag: 4.0
$ mkdir -p /tmp/ns-process/rootfs
$ tar -C /tmp/ns-process/rootfs -xf assets/busybox.tar

# Git repo: https://github.com/teddyking/ns-process
# Git tag: 4.0
# Filename: rootfs.go
func pivotRoot(newroot string) error {
	putold := filepath.Join(newroot, "/.pivot_root")

	// bind mount newroot to itself - this is a slight hack
	// needed to work around a pivot_root requirement
	if err := syscall.Mount(
		newroot,
		newroot,
		"",
		syscall.MS_BIND|syscall.MS_REC,
		"",
	); err != nil {
		return err
	}

	// create putold directory
	if err := os.MkdirAll(putold, 0700); err != nil {
		return err
	}

	// call pivot_root
	if err := syscall.PivotRoot(newroot, putold); err != nil {
		return err
	}

	// ensure current working directory is set to new root
	if err := os.Chdir("/"); err != nil {
		return err
	}

	// umount putold, which now lives at /.pivot_root
	putold = "/.pivot_root"
	if err := syscall.Unmount(
		putold,
		syscall.MNT_DETACH,
	); err != nil {
		return err
	}

	// remove putold
	if err := os.RemoveAll(putold); err != nil {
		return err
	}

	return nil
}

# Git repo: https://github.com/teddyking/ns-process
# Git tag: 4.0
# Filename: ns_process.go
func nsInitialisation() {
	newrootPath := os.Args[1]

	if err := pivotRoot(newrootPath); err != nil {
		fmt.Printf("Error running pivot_root - %s\n", err)
		os.Exit(1)
	}

	nsRun()
}

func main() {
	var rootfsPath string
	// ...
	cmd := reexec.Command("nsInitialisation", rootfsPath)
}

# Git repo: https://github.com/teddyking/ns-process
# Git tag: 4.1
# Filename: rootfs.go
func mountProc(newroot string) error {
	source := "proc"
	target := filepath.Join(newroot, "/proc")
	fstype := "proc"
	flags := 0
	data := ""

	os.MkdirAll(target, 0755)
	if err := syscall.Mount(
		source,
		target,
		fstype,
		uintptr(flags),
		data,
	); err != nil {
		return err
	}

	return nil
}

# Git repo: https://github.com/teddyking/ns-process
# Git tag: 4.1
# Filename: ns_process.go
func nsInitialisation() {
	newrootPath := os.Args[1]

	if err := mountProc(newrootPath); err != nil {
		fmt.Printf("Error mounting /proc - %s\n", err)
		os.Exit(1)
	}

	if err := pivotRoot(newrootPath); err != nil {
		fmt.Printf("Error running pivot_root - %s\n", err)
		os.Exit(1)
	}

	nsRun()
}

# Git repo: https://github.com/bingbig/container
# Git tag: 4.0
# Filename: container.go
# ...
func nsInitialisation() {
	fmt.Printf("\n>> namespace setup code goes here <<\n\n")

	setMount("/root/containerFS")

	nsRun()
}

func setMount(root string) error {
	if err := syscall.Chroot(root); err != nil {
		return err
	}
	// 设置容器里面的当前工作目录
	if err := syscall.Chdir("/"); err != nil {
		return err
	}

	return nil
}

# Git repo: https://github.com/bingbig/container
# Git tag: 4.0
# Filename: container.go
# ...
func setMount(root string) error {
	if err := syscall.Chroot(root); err != nil {
		return err
	}
	// 设置容器里面的当前工作目录
	if err := syscall.Chdir("/"); err != nil {
		return err
	}

	if err := syscall.Mount("proc", "proc", "proc", 0, ""); err != nil {
		return err
	}

	return nil
}

func nsRun() {
	cmd := exec.Command(os.Args[1], os.Args[2:]...)

	cmd.Stdin = os.Stdin
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr

	cmd.Env = []string{"PS1=-[container]- # "}

	if err := cmd.Run(); err != nil {
		fmt.Printf("Error running the %s command - %s\n", os.Args[1], err)
		os.Exit(1)
	}

	syscall.Unmount("/proc", 0)
}

# Git repo: https://github.com/bingbig/container
# Git tag: 4.0
# Filename: container.go
# ...
cmd.SysProcAttr = &syscall.SysProcAttr{
		Cloneflags: syscall.CLONE_NEWNS |
			syscall.CLONE_NEWUTS |
			syscall.CLONE_NEWIPC |
			syscall.CLONE_NEWPID |
			syscall.CLONE_NEWNET |
			syscall.CLONE_NEWUSER,
		Unshareflags: syscall.CLONE_NEWNS,
		UidMappings: []syscall.SysProcIDMap{
			{
				ContainerID: 0,
				HostID:      os.Getuid(),
				Size:        1,
			},
		},
		GidMappings: []syscall.SysProcIDMap{
			{
				ContainerID: 0,
				HostID:      os.Getgid(),
				Size:        1,
			},
		},
	}