83 lines
2.5 KiB
Go
83 lines
2.5 KiB
Go
// +build !solaris
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package main
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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(uid, gid int) (*os.File, string, 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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if err := os.Chmod(console, 0600); err != nil {
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return nil, "", err
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}
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if err := os.Chown(console, uid, gid); err != nil {
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return nil, "", err
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}
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return master, console, 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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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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