gh-85984: Add POSIX pseudo-terminal functions. (GH-102413)

Signed-off-by: Soumendra Ganguly <soumendraganguly@gmail.com>
Co-authored-by: Gregory P. Smith <greg@krypto.org>
Co-authored-by: Petr Viktorin <encukou@gmail.com>

Modules/posixmodule.c

@@ -8358,6 +8358,149 @@ error:
 #endif /* HAVE_SCHED_H */
 
 
+#ifdef HAVE_POSIX_OPENPT
+/*[clinic input]
+os.posix_openpt -> int
+
+    oflag: int
+    /
+
+Open and return a file descriptor for a master pseudo-terminal device.
+
+Performs a posix_openpt() C function call. The oflag argument is used to
+set file status flags and file access modes as specified in the manual page
+of posix_openpt() of your system.
+[clinic start generated code]*/
+
+static int
+os_posix_openpt_impl(PyObject *module, int oflag)
+/*[clinic end generated code: output=ee0bc2624305fc79 input=0de33d0e29693caa]*/
+{
+    int fd;
+
+#if defined(O_CLOEXEC)
+    oflag |= O_CLOEXEC;
+#endif
+
+    fd = posix_openpt(oflag);
+    if (fd == -1) {
+        posix_error();
+        return -1;
+    }
+
+    // Just in case, likely a no-op given O_CLOEXEC above.
+    if (_Py_set_inheritable(fd, 0, NULL) < 0) {
+        close(fd);
+        return -1;
+    }
+
+    return fd;
+}
+#endif /* HAVE_POSIX_OPENPT */
+
+#ifdef HAVE_GRANTPT
+/*[clinic input]
+os.grantpt
+
+    fd: fildes
+        File descriptor of a master pseudo-terminal device.
+    /
+
+Grant access to the slave pseudo-terminal device.
+
+Performs a grantpt() C function call.
+[clinic start generated code]*/
+
+static PyObject *
+os_grantpt_impl(PyObject *module, int fd)
+/*[clinic end generated code: output=dfd580015cf548ab input=0668e3b96760e849]*/
+{
+    int ret;
+    int saved_errno;
+    PyOS_sighandler_t sig_saved;
+
+    sig_saved = PyOS_setsig(SIGCHLD, SIG_DFL);
+
+    ret = grantpt(fd);
+    if (ret == -1)
+        saved_errno = errno;
+
+    PyOS_setsig(SIGCHLD, sig_saved);
+
+    if (ret == -1) {
+        errno = saved_errno;
+        return posix_error();
+    }
+
+    Py_RETURN_NONE;
+}
+#endif /* HAVE_GRANTPT */
+
+#ifdef HAVE_UNLOCKPT
+/*[clinic input]
+os.unlockpt
+
+    fd: fildes
+        File descriptor of a master pseudo-terminal device.
+    /
+
+Unlock a pseudo-terminal master/slave pair.
+
+Performs an unlockpt() C function call.
+[clinic start generated code]*/
+
+static PyObject *
+os_unlockpt_impl(PyObject *module, int fd)
+/*[clinic end generated code: output=e08d354dec12d30c input=de7ab1f59f69a2b4]*/
+{
+    if (unlockpt(fd) == -1)
+        return posix_error();
+
+    Py_RETURN_NONE;
+}
+#endif /* HAVE_UNLOCKPT */
+
+#if defined(HAVE_PTSNAME) || defined(HAVE_PTSNAME_R)
+/*[clinic input]
+os.ptsname
+
+    fd: fildes
+        File descriptor of a master pseudo-terminal device.
+    /
+
+Return the name of the slave pseudo-terminal device.
+
+If the ptsname_r() C function is available, it is called;
+otherwise, performs a ptsname() C function call.
+[clinic start generated code]*/
+
+static PyObject *
+os_ptsname_impl(PyObject *module, int fd)
+/*[clinic end generated code: output=ef300fadc5675872 input=1369ccc0546f3130]*/
+{
+#ifdef HAVE_PTSNAME_R
+    int ret;
+    char name[MAXPATHLEN+1];
+
+    ret = ptsname_r(fd, name, sizeof(name));
+    if (ret != 0) {
+        errno = ret;
+        return posix_error();
+    }
+#else
+    char *name;
+
+    name = ptsname(fd);
+    /* POSIX manpage: Upon failure, ptsname() shall return a null pointer and may set errno.
+       *MAY* set errno? Hmm... */
+    if (name == NULL)
+        return posix_error();
+#endif /* HAVE_PTSNAME_R */
+
+    return PyUnicode_DecodeFSDefault(name);
+}
+#endif /* defined(HAVE_PTSNAME) || defined(HAVE_PTSNAME_R) */
+
 /* AIX uses /dev/ptc but is otherwise the same as /dev/ptmx */
 #if defined(HAVE_DEV_PTC) && !defined(HAVE_DEV_PTMX)
 #  define DEV_PTY_FILE "/dev/ptc"
@@ -16275,6 +16418,10 @@ static PyMethodDef posix_methods[] = {
     OS_SCHED_YIELD_METHODDEF
     OS_SCHED_SETAFFINITY_METHODDEF
     OS_SCHED_GETAFFINITY_METHODDEF
+    OS_POSIX_OPENPT_METHODDEF
+    OS_GRANTPT_METHODDEF
+    OS_UNLOCKPT_METHODDEF
+    OS_PTSNAME_METHODDEF
     OS_OPENPTY_METHODDEF
     OS_LOGIN_TTY_METHODDEF
     OS_FORKPTY_METHODDEF