The openpty() function finds an available pseudo-tty and returns file
descriptors for the master and slave in amaster and aslave. If
name is not NULL, the filename of the slave is returned in name.
If termp is not NULL, the terminal parameters of the slave will be set
to the values in termp. If winp is not NULL, the window size of
the slave will be set to the values in winp.
The login_tty() function prepares for a login on the tty fd (which
may be a real tty device, or the slave of a pseudo-tty as returned by
openpty()) by creating a new session, making fd the controlling
terminal for the current process, setting fd to be the standard input,
output, and error streams of the current process, and closing fd.
The forkpty() function combines openpty(), fork(), and
login_tty() to create a new process operating in a pseudo-tty. The file
descriptor of the master side of the pseudo-tty is returned in amaster,
and the filename of the slave in name if it is not NULL. The
termp and winp parameters, if not NULL, will determine the
terminal attributes and window size of the slave side of the pseudo-tty.
If a call to openpty(), login_tty(), or forkpty() is not
successful, -1 is returned and errno is set to indicate the error.
Otherwise, openpty(), login_tty(), and the child process of
forkpty() return 0, and the parent process of forkpty() returns
the process ID of the child process.