Function setupConsole

libcontainer/init_linux.go:375–417

setupConsole sets up the console from inside the container, and sends the master pty fd to the config.Pipe (using cmsg). This is done to ensure that consoles are scoped to a container properly (see runc#814 and the many issues related to that). This has to be run *after* we've pivoted to the new roo

(socket *os.File, config *initConfig, mount bool)

// issues related to that). This has to be run *after* we've pivoted to the new
// rootfs (and the users' configuration is entirely set up).
func setupConsole(socket *os.File, config *initConfig, mount bool) error {
	defer socket.Close()
	// At this point, /dev/ptmx points to something that we would expect. We
	// used to change the owner of the slave path, but since the /dev/pts mount
	// can have gid=X set (at the users' option). So touching the owner of the
	// slave PTY is not necessary, as the kernel will handle that for us. Note
	// however, that setupUser (specifically fixStdioPermissions) *will* change
	// the UID owner of the console to be the user the process will run as (so
	// they can actually control their console).

	pty, peerPty, err := safeAllocPty()
	if err != nil {
		return err
	}
	// After we return from here, we don't need the console anymore.
	defer pty.Close()
	defer peerPty.Close()

	if config.ConsoleHeight != 0 && config.ConsoleWidth != 0 {
		err = pty.Resize(console.WinSize{
			Height: config.ConsoleHeight,
			Width:  config.ConsoleWidth,
		})
		if err != nil {
			return err
		}
	}

	// Mount the console inside our rootfs.
	if mount {
		if err := mountConsole(peerPty); err != nil {
			return err
		}
	}
	// While we can access console.master, using the API is a good idea.
	if err := cmsg.SendRawFd(socket, pty.Name(), pty.Fd()); err != nil {
		return err
	}
	runtime.KeepAlive(pty)

	// Now, dup over all the things.
	return dupStdio(peerPty)
}

// syncParentReady sends to the given pipe a JSON payload which indicates that
// the init is ready to Exec the child process. It then waits for the parent to