151 lines
4.0 KiB
Go
151 lines
4.0 KiB
Go
package libcontainer
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import (
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"fmt"
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"os"
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"syscall"
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"unsafe"
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)
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// newConsole returns an initialized console that can be used within a container by copying bytes
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// from the master side to the slave that is attached as the tty for the container's init process.
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func newConsole() (Console, error) {
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master, err := os.OpenFile("/dev/ptmx", syscall.O_RDWR|syscall.O_NOCTTY|syscall.O_CLOEXEC, 0)
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if err != nil {
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return nil, err
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}
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if err := saneTerminal(master); err != nil {
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return nil, err
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}
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console, err := ptsname(master)
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if err != nil {
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return nil, err
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}
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if err := unlockpt(master); err != nil {
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return nil, err
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}
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return &linuxConsole{
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slavePath: console,
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master: master,
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}, nil
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}
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// linuxConsole is a linux pseudo TTY for use within a container.
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type linuxConsole struct {
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master *os.File
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slavePath string
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}
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func (c *linuxConsole) File() *os.File {
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return c.master
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}
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func (c *linuxConsole) Path() string {
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return c.slavePath
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}
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func (c *linuxConsole) Read(b []byte) (int, error) {
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return c.master.Read(b)
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}
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func (c *linuxConsole) Write(b []byte) (int, error) {
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return c.master.Write(b)
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}
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func (c *linuxConsole) Close() error {
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if m := c.master; m != nil {
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return m.Close()
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}
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return nil
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}
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// mount initializes the console inside the rootfs mounting with the specified mount label
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// and applying the correct ownership of the console.
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func (c *linuxConsole) mount() error {
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oldMask := syscall.Umask(0000)
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defer syscall.Umask(oldMask)
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f, err := os.Create("/dev/console")
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if err != nil && !os.IsExist(err) {
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return err
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}
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if f != nil {
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f.Close()
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}
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return syscall.Mount(c.slavePath, "/dev/console", "bind", syscall.MS_BIND, "")
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}
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// dupStdio opens the slavePath for the console and dups the fds to the current
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// processes stdio, fd 0,1,2.
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func (c *linuxConsole) dupStdio() error {
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slave, err := c.open(syscall.O_RDWR)
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if err != nil {
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return err
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}
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fd := int(slave.Fd())
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for _, i := range []int{0, 1, 2} {
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if err := syscall.Dup3(fd, i, 0); err != nil {
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return err
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}
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}
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return nil
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}
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// open is a clone of os.OpenFile without the O_CLOEXEC used to open the pty slave.
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func (c *linuxConsole) open(flag int) (*os.File, error) {
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r, e := syscall.Open(c.slavePath, flag, 0)
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if e != nil {
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return nil, &os.PathError{
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Op: "open",
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Path: c.slavePath,
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Err: e,
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}
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}
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return os.NewFile(uintptr(r), c.slavePath), nil
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}
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func ioctl(fd uintptr, flag, data uintptr) error {
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if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, fd, flag, data); err != 0 {
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return err
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}
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return nil
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}
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// unlockpt unlocks the slave pseudoterminal device corresponding to the master pseudoterminal referred to by f.
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// unlockpt should be called before opening the slave side of a pty.
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func unlockpt(f *os.File) error {
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var u int32
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return ioctl(f.Fd(), syscall.TIOCSPTLCK, uintptr(unsafe.Pointer(&u)))
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}
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// ptsname retrieves the name of the first available pts for the given master.
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func ptsname(f *os.File) (string, error) {
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var n int32
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if err := ioctl(f.Fd(), syscall.TIOCGPTN, uintptr(unsafe.Pointer(&n))); err != nil {
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return "", err
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}
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return fmt.Sprintf("/dev/pts/%d", n), nil
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}
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// saneTerminal sets the necessary tty_ioctl(4)s to ensure that a pty pair
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// created by us acts normally. In particular, a not-very-well-known default of
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// Linux unix98 ptys is that they have +onlcr by default. While this isn't a
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// problem for terminal emulators, because we relay data from the terminal we
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// also relay that funky line discipline.
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func saneTerminal(terminal *os.File) error {
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// Go doesn't have a wrapper for any of the termios ioctls.
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var termios syscall.Termios
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if err := ioctl(terminal.Fd(), syscall.TCGETS, uintptr(unsafe.Pointer(&termios))); err != nil {
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return fmt.Errorf("ioctl(tty, tcgets): %s", err.Error())
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}
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// Set -onlcr so we don't have to deal with \r.
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termios.Oflag &^= syscall.ONLCR
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if err := ioctl(terminal.Fd(), syscall.TCSETS, uintptr(unsafe.Pointer(&termios))); err != nil {
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return fmt.Errorf("ioctl(tty, tcsets): %s", err.Error())
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}
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return nil
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}
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