github.com/runcom/containerd@v0.0.0-20160708090337-9bff9f934c0d/containerd-shim/console.go (about)

     1  // +build !solaris
     2  
     3  package main
     4  
     5  import (
     6  	"fmt"
     7  	"os"
     8  	"syscall"
     9  	"unsafe"
    10  )
    11  
    12  // NewConsole returns an initialized console that can be used within a container by copying bytes
    13  // from the master side to the slave that is attached as the tty for the container's init process.
    14  func newConsole(uid, gid int) (*os.File, string, error) {
    15  	master, err := os.OpenFile("/dev/ptmx", syscall.O_RDWR|syscall.O_NOCTTY|syscall.O_CLOEXEC, 0)
    16  	if err != nil {
    17  		return nil, "", err
    18  	}
    19  	console, err := ptsname(master)
    20  	if err != nil {
    21  		return nil, "", err
    22  	}
    23  	if err := unlockpt(master); err != nil {
    24  		return nil, "", err
    25  	}
    26  	if err := os.Chmod(console, 0600); err != nil {
    27  		return nil, "", err
    28  	}
    29  	if err := os.Chown(console, uid, gid); err != nil {
    30  		return nil, "", err
    31  	}
    32  	return master, console, nil
    33  }
    34  
    35  func ioctl(fd uintptr, flag, data uintptr) error {
    36  	if _, _, err := syscall.Syscall(syscall.SYS_IOCTL, fd, flag, data); err != 0 {
    37  		return err
    38  	}
    39  	return nil
    40  }
    41  
    42  // unlockpt unlocks the slave pseudoterminal device corresponding to the master pseudoterminal referred to by f.
    43  // unlockpt should be called before opening the slave side of a pty.
    44  func unlockpt(f *os.File) error {
    45  	var u int32
    46  	return ioctl(f.Fd(), syscall.TIOCSPTLCK, uintptr(unsafe.Pointer(&u)))
    47  }
    48  
    49  // ptsname retrieves the name of the first available pts for the given master.
    50  func ptsname(f *os.File) (string, error) {
    51  	var n int32
    52  	if err := ioctl(f.Fd(), syscall.TIOCGPTN, uintptr(unsafe.Pointer(&n))); err != nil {
    53  		return "", err
    54  	}
    55  	return fmt.Sprintf("/dev/pts/%d", n), nil
    56  }