Golang syscall.Chdir函數代碼示例

func switchRoot(rootfs, subdir string, rmUsr bool) error {
	if err := syscall.Unmount(config.OEM, 0); err != nil {
		log.Debugf("Not umounting OEM: %v", err)
	}

	if subdir != "" {
		fullRootfs := path.Join(rootfs, subdir)
		if _, err := os.Stat(fullRootfs); os.IsNotExist(err) {
			if err := os.MkdirAll(fullRootfs, 0755); err != nil {
				log.Errorf("Failed to create directory %s: %v", fullRootfs, err)
				return err
			}
		}

		log.Debugf("Bind mounting mount %s to %s", fullRootfs, rootfs)
		if err := syscall.Mount(fullRootfs, rootfs, "", syscall.MS_BIND, ""); err != nil {
			log.Errorf("Failed to bind mount subdir for %s: %v", fullRootfs, err)
			return err
		}
	}

	for _, i := range []string{"/dev", "/sys", "/proc", "/run"} {
		log.Debugf("Moving mount %s to %s", i, path.Join(rootfs, i))
		if err := os.MkdirAll(path.Join(rootfs, i), 0755); err != nil {
			return err
		}
		if err := syscall.Mount(i, path.Join(rootfs, i), "", syscall.MS_MOVE, ""); err != nil {
			return err
		}
	}

	if err := copyMoveRoot(rootfs, rmUsr); err != nil {
		return err
	}

	log.Debugf("chdir %s", rootfs)
	if err := syscall.Chdir(rootfs); err != nil {
		return err
	}

	log.Debugf("mount MS_MOVE %s", rootfs)
	if err := syscall.Mount(rootfs, "/", "", syscall.MS_MOVE, ""); err != nil {
		return err
	}

	log.Debug("chroot .")
	if err := syscall.Chroot("."); err != nil {
		return err
	}

	log.Debug("chdir /")
	if err := syscall.Chdir("/"); err != nil {
		return err
	}

	log.Debugf("Successfully moved to new root at %s", path.Join(rootfs, subdir))
	os.Unsetenv("DOCKER_RAMDISK")

	return nil
}

// EnterChroot changes the current directory to the path specified,
// and then calls chroot(2) with the same path.  This must be called
// while the process has CAP_SYS_CHROOT.
func EnterChroot(path string) (err error) {
	if err = syscall.Chdir(path); err != nil {
		return
	}
	if err = syscall.Chroot(path); err != nil {
		return
	}
	if err = syscall.Chdir("/"); err != nil {
		return
	}
	return
}

func main() {
	cwd1 := make([]byte, BUF_SZ)

	fmt.Print("This is where I am now: ")
	if _, err := syscall.Getcwd(cwd1); err != nil {
		log.Fatal("Error: syscall.Getcwd(2): ", err)
	}
	fmt.Println(string(cwd1))

	fmt.Println("chroot(2)ing back to /home/christos")
	// Commented out doesn't work for some reason. TODO: Why not?
	//cwd_s := string(cwd[:])
	//if err := syscall.Chroot(cwd_s); err != nil {
	if err := syscall.Chroot("/home/christos"); err != nil {
		log.Fatal("Error: syscall.Chroot(2): ", err)
	}

	fmt.Print("This is where I am now: ")
	cwd2 := make([]byte, BUF_SZ)
	if _, err := syscall.Getcwd(cwd2); err != nil {
		log.Fatal("Error: syscall.Getcwd(2): ", err)
	}
	fmt.Println(string(cwd2))

	fmt.Println("chdir(2)ing to parent")
	if err := syscall.Chdir(".."); err != nil {
		log.Fatal("Error: syscall.Chdir(2): ", err)
	}

	fmt.Print("This is where I am now: ")
	cwd3 := make([]byte, BUF_SZ)
	if _, err := syscall.Getcwd(cwd3); err != nil {
		log.Fatal("Error: syscall.Getcwd(2): ", err)
	}
	fmt.Println(string(cwd3))

	fmt.Println("Again, chdir(2)ing to parent")
	if err := syscall.Chdir(".."); err != nil {
		log.Fatal("Error: syscall.Chdir(2): ", err)
	}

	fmt.Print("This is where I am now: ")
	cwd4 := make([]byte, BUF_SZ)
	if _, err := syscall.Getcwd(cwd4); err != nil {
		log.Fatal("Error: syscall.Getcwd(2): ", err)
	}
	fmt.Println(string(cwd4))

	return
}

func afterDaemonize(err error) {
	// Ignore SIGCHLD signal
	signal.Ignore(syscall.SIGCHLD)

	// Close STDOUT, STDIN, STDERR
	syscall.Close(0)
	syscall.Close(1)
	syscall.Close(2)

	// Become the process group leader
	syscall.Setsid()

	// // Clear umask
	syscall.Umask(022)

	// // chdir for root directory
	syscall.Chdir("/")

	// Notify that the child process started successfuly
	pipe := os.NewFile(uintptr(3), "pipe")
	if pipe != nil {
		defer pipe.Close()
		if err == nil {
			pipe.Write([]byte{DAEMONIZE_SUCCESS})
		} else {
			pipe.Write([]byte{DAEMONIZE_FAIL})
		}
	}
}

// InitializeMountNamespace sets up the devices, mount points, and filesystems for use inside a
// new mount namespace.
func InitializeMountNamespace(rootfs, console string, sysReadonly bool, mountConfig *MountConfig) error {
	var (
		err  error
		flag = syscall.MS_PRIVATE
	)
	if mountConfig.NoPivotRoot {
		flag = syscall.MS_SLAVE
	}
	if err := syscall.Mount("", "/", "", uintptr(flag|syscall.MS_REC), ""); err != nil {
		return fmt.Errorf("mounting / with flags %X %s", (flag | syscall.MS_REC), err)
	}
	if err := syscall.Mount(rootfs, rootfs, "bind", syscall.MS_BIND|syscall.MS_REC, ""); err != nil {
		return fmt.Errorf("mouting %s as bind %s", rootfs, err)
	}
	if err := mountSystem(rootfs, sysReadonly, mountConfig); err != nil {
		return fmt.Errorf("mount system %s", err)
	}
	if err := setupBindmounts(rootfs, mountConfig); err != nil {
		return fmt.Errorf("bind mounts %s", err)
	}
	if err := nodes.CreateDeviceNodes(rootfs, mountConfig.DeviceNodes); err != nil {
		return fmt.Errorf("create device nodes %s", err)
	}
	if err := SetupPtmx(rootfs, console, mountConfig.MountLabel); err != nil {
		return err
	}

	// stdin, stdout and stderr could be pointing to /dev/null from parent namespace.
	// Re-open them inside this namespace.
	if err := reOpenDevNull(rootfs); err != nil {
		return fmt.Errorf("Failed to reopen /dev/null %s", err)
	}

	if err := setupDevSymlinks(rootfs); err != nil {
		return fmt.Errorf("dev symlinks %s", err)
	}

	if err := syscall.Chdir(rootfs); err != nil {
		return fmt.Errorf("chdir into %s %s", rootfs, err)
	}

	if mountConfig.NoPivotRoot {
		err = MsMoveRoot(rootfs)
	} else {
		err = PivotRoot(rootfs)
	}
	if err != nil {
		return err
	}

	if mountConfig.ReadonlyFs {
		if err := SetReadonly(); err != nil {
			return fmt.Errorf("set readonly %s", err)
		}
	}

	syscall.Umask(0022)

	return nil
}

func main() {
	flag.Usage = usage
	flag.Parse()
	if flag.NArg() < 1 {
		usage()
	}
	args := flag.Args()

	ck(syscall.Chroot(args[0]))
	ck(syscall.Chdir("/"))

	var cmd *exec.Cmd
	if len(args) == 1 {
		shell := os.Getenv("SHELL")
		if shell == "" {
			shell = "/bin/sh"
		}
		cmd = exec.Command(shell, "-i")
	} else {
		cmd = exec.Command(args[1], args[2:]...)
	}
	cmd.Stdin = os.Stdin
	cmd.Stderr = os.Stderr
	cmd.Stdout = os.Stdout
	ck(cmd.Run())
}

func pivotRoot(rootfs, pivotBaseDir string) error {
	if pivotBaseDir == "" {
		pivotBaseDir = "/"
	}
	tmpDir := filepath.Join(rootfs, pivotBaseDir)
	if err := os.MkdirAll(tmpDir, 0755); err != nil {
		return fmt.Errorf("can't create tmp dir %s, error %v", tmpDir, err)
	}
	pivotDir, err := ioutil.TempDir(tmpDir, ".pivot_root")
	if err != nil {
		return fmt.Errorf("can't create pivot_root dir %s, error %v", pivotDir, err)
	}
	if err := syscall.PivotRoot(rootfs, pivotDir); err != nil {
		return fmt.Errorf("pivot_root %s", err)
	}
	if err := syscall.Chdir("/"); err != nil {
		return fmt.Errorf("chdir / %s", err)
	}
	// path to pivot dir now changed, update
	pivotDir = filepath.Join(pivotBaseDir, filepath.Base(pivotDir))

	// Make pivotDir rprivate to make sure any of the unmounts don't
	// propagate to parent.
	if err := syscall.Mount("", pivotDir, "", syscall.MS_PRIVATE|syscall.MS_REC, ""); err != nil {
		return err
	}

	if err := syscall.Unmount(pivotDir, syscall.MNT_DETACH); err != nil {
		return fmt.Errorf("unmount pivot_root dir %s", err)
	}
	return os.Remove(pivotDir)
}

func pivotRoot(root string) error {
	// we need this to satisfy restriction:
	// "new_root and put_old must not be on the same filesystem as the current root"
	if err := syscall.Mount(root, root, "bind", syscall.MS_BIND|syscall.MS_REC, ""); err != nil {
		return fmt.Errorf("Mount rootfs to itself error: %v", err)
	}
	// create rootfs/.pivot_root as path for old_root
	pivotDir := filepath.Join(root, ".pivot_root")
	if err := os.Mkdir(pivotDir, 0777); err != nil {
		return err
	}
	logrus.Debugf("Pivot root dir: %s", pivotDir)
	logrus.Debugf("Pivot root to %s", root)
	// pivot_root to rootfs, now old_root is mounted in rootfs/.pivot_root
	// mounts from it still can be seen in `mount`
	if err := syscall.PivotRoot(root, pivotDir); err != nil {
		return fmt.Errorf("pivot_root %v", err)
	}
	// change working directory to /
	// it is recommendation from man-page
	if err := syscall.Chdir("/"); err != nil {
		return fmt.Errorf("chdir / %v", err)
	}
	// path to pivot root now changed, update
	pivotDir = filepath.Join("/", ".pivot_root")
	// umount rootfs/.pivot_root(which is now /.pivot_root) with all submounts
	// now we have only mounts that we mounted ourself in `mount`
	if err := syscall.Unmount(pivotDir, syscall.MNT_DETACH); err != nil {
		return fmt.Errorf("unmount pivot_root dir %v", err)
	}
	// remove temporary directory
	return os.Remove(pivotDir)
}

func pivotRoot(rootfs, pivotBaseDir string) error {
	if pivotBaseDir == "" {
		pivotBaseDir = "/"
	}
	tmpDir := filepath.Join(rootfs, pivotBaseDir)
	if err := os.MkdirAll(tmpDir, 0755); err != nil {
		return fmt.Errorf("can't create tmp dir %s, error %v", tmpDir, err)
	}
	pivotDir, err := ioutil.TempDir(tmpDir, ".pivot_root")
	if err != nil {
		return fmt.Errorf("can't create pivot_root dir %s, error %v", pivotDir, err)
	}
	if err := syscall.PivotRoot(rootfs, pivotDir); err != nil {
		return fmt.Errorf("pivot_root %s", err)
	}
	if err := syscall.Chdir("/"); err != nil {
		return fmt.Errorf("chdir / %s", err)
	}
	// path to pivot dir now changed, update
	pivotDir = filepath.Join(pivotBaseDir, filepath.Base(pivotDir))
	if err := syscall.Unmount(pivotDir, syscall.MNT_DETACH); err != nil {
		return fmt.Errorf("unmount pivot_root dir %s", err)
	}
	return os.Remove(pivotDir)
}

// Setup working directory
func setupWorkingDirectory(workdir string) {
	if workdir == "" {
		return
	}
	if err := syscall.Chdir(workdir); err != nil {
		log.Fatalf("Unable to change dir to %v: %v", workdir, err)
	}
}

// Setup working directory
func setupWorkingDirectory(args *DockerInitArgs) error {
	if args.workDir == "" {
		return nil
	}
	if err := syscall.Chdir(args.workDir); err != nil {
		return fmt.Errorf("Unable to change dir to %v: %v", args.workDir, err)
	}
	return nil
}

func realChroot(path string) error {
	if err := syscall.Chroot(path); err != nil {
		return fmt.Errorf("Error after fallback to chroot: %v", err)
	}
	if err := syscall.Chdir("/"); err != nil {
		return fmt.Errorf("Error changing to new root after chroot: %v", err)
	}
	return nil
}

// setupRootfs sets up the devices, mount points, and filesystems for use inside a
// new mount namespace.
func setupRootfs(config *configs.Config, console *linuxConsole) (err error) {
	if err := prepareRoot(config); err != nil {
		return newSystemError(err)
	}

	setupDev := len(config.Devices) == 0
	for _, m := range config.Mounts {
		for _, precmd := range m.PremountCmds {
			if err := mountCmd(precmd); err != nil {
				return newSystemError(err)
			}
		}
		if err := mountToRootfs(m, config.Rootfs, config.MountLabel); err != nil {
			return newSystemError(err)
		}

		for _, postcmd := range m.PostmountCmds {
			if err := mountCmd(postcmd); err != nil {
				return newSystemError(err)
			}
		}
	}
	if !setupDev {
		if err := createDevices(config); err != nil {
			return newSystemError(err)
		}
		if err := setupPtmx(config, console); err != nil {
			return newSystemError(err)
		}
		if err := setupDevSymlinks(config.Rootfs); err != nil {
			return newSystemError(err)
		}
	}
	if err := syscall.Chdir(config.Rootfs); err != nil {
		return newSystemError(err)
	}
	if config.NoPivotRoot {
		err = msMoveRoot(config.Rootfs)
	} else {
		err = pivotRoot(config.Rootfs, config.PivotDir)
	}
	if err != nil {
		return newSystemError(err)
	}
	if !setupDev {
		if err := reOpenDevNull(); err != nil {
			return newSystemError(err)
		}
	}
	if config.Readonlyfs {
		if err := setReadonly(); err != nil {
			return newSystemError(err)
		}
	}
	syscall.Umask(0022)
	return nil
}

func msMoveRoot(rootfs string) error {
	if err := syscall.Mount(rootfs, "/", "", syscall.MS_MOVE, ""); err != nil {
		return err
	}
	if err := syscall.Chroot("."); err != nil {
		return err
	}
	return syscall.Chdir("/")
}

// Initialises a daemon with recommended values. Called by Daemonize.
//
// Currently, this only calls umask(0) and chdir("/").
func Init() error {
	syscall.Umask(0)

	err := syscall.Chdir("/")
	if err != nil {
		return err
	}

	// setrlimit RLIMIT_CORE
	return nil
}