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//go:build linux
package chroot
import (
"fmt"
"os"
"syscall"
"unsafe"
"golang.org/x/sys/unix"
)
// Open a PTY using the /dev/ptmx device. The main advantage of using
// this instead of posix_openpt is that it avoids cgo.
func getPtyDescriptors() (int, int, error) {
// Create a pseudo-terminal -- open a copy of the master side.
controlFd, err := unix.Open("/dev/ptmx", os.O_RDWR, 0o600)
if err != nil {
return -1, -1, fmt.Errorf("opening PTY master using /dev/ptmx: %v", err)
}
// Set the kernel's lock to "unlocked".
locked := 0
if result, _, err := unix.Syscall(unix.SYS_IOCTL, uintptr(controlFd), unix.TIOCSPTLCK, uintptr(unsafe.Pointer(&locked))); int(result) == -1 {
return -1, -1, fmt.Errorf("unlocking PTY descriptor: %v", err)
}
// Get a handle for the other end.
ptyFd, _, err := unix.Syscall(unix.SYS_IOCTL, uintptr(controlFd), unix.TIOCGPTPEER, unix.O_RDWR|unix.O_NOCTTY)
if int(ptyFd) == -1 {
if errno, isErrno := err.(syscall.Errno); !isErrno || (errno != syscall.EINVAL && errno != syscall.ENOTTY) {
return -1, -1, fmt.Errorf("getting PTY descriptor: %v", err)
}
// EINVAL means the kernel's too old to understand TIOCGPTPEER. Try TIOCGPTN.
ptyN, err := unix.IoctlGetInt(controlFd, unix.TIOCGPTN)
if err != nil {
return -1, -1, fmt.Errorf("getting PTY number: %v", err)
}
ptyName := fmt.Sprintf("/dev/pts/%d", ptyN)
fd, err := unix.Open(ptyName, unix.O_RDWR|unix.O_NOCTTY, 0o620)
if err != nil {
return -1, -1, fmt.Errorf("opening PTY %q: %v", ptyName, err)
}
ptyFd = uintptr(fd)
}
return controlFd, int(ptyFd), nil
}
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