bpo-41818: Add os.login_tty() for *nix.

Doc/library/os.rst

@@ -1000,6 +1000,17 @@ as internal buffering of data.
    .. versionadded:: 3.3
 
 
+.. function:: login_tty(fd)
+
+   Prepare the tty of which fd is a file descriptor for a new login session.
+   Make the calling process a session leader; make the tty the controlling tty,
+   the stdin, the stdout, and the stderr of the calling process; close fd.
+
+   .. availability:: Unix.
+
+   .. versionadded:: 3.11
+
+
 .. function:: lseek(fd, pos, how)
 
    Set the current position of file descriptor *fd* to position *pos*, modified

Misc/NEWS.d/next/Library/2022-05-02-03-56-50.gh-issue-85984.RBivvc.rst

@@ -0,0 +1 @@
+New function os.login_tty() for Unix.

Modules/posixmodule.c

@@ -7274,22 +7274,21 @@ os_sched_getaffinity_impl(PyObject *module, pid_t pid)
 #  define DEV_PTY_FILE "/dev/ptmx"
 #endif
 
-#if defined(HAVE_OPENPTY) || defined(HAVE_FORKPTY) || defined(HAVE_DEV_PTMX)
+#if defined(HAVE_OPENPTY) || defined(HAVE_FORKPTY) || defined(HAVE_LOGIN_TTY) || defined(HAVE_DEV_PTMX)
 #ifdef HAVE_PTY_H
 #include <pty.h>
-#else
-#ifdef HAVE_LIBUTIL_H
+#ifdef HAVE_UTMP_H
+#include <utmp.h>
+#endif /* HAVE_UTMP_H */
+#elif defined(HAVE_LIBUTIL_H)
 #include <libutil.h>
-#else
-#ifdef HAVE_UTIL_H
+#elif defined(HAVE_UTIL_H)
 #include <util.h>
-#endif /* HAVE_UTIL_H */
-#endif /* HAVE_LIBUTIL_H */
 #endif /* HAVE_PTY_H */
 #ifdef HAVE_STROPTS_H
 #include <stropts.h>
 #endif
-#endif /* defined(HAVE_OPENPTY) || defined(HAVE_FORKPTY) || defined(HAVE_DEV_PTMX) */
+#endif /* defined(HAVE_OPENPTY) || defined(HAVE_FORKPTY) || defined(HAVE_LOGIN_TTY) || defined(HAVE_DEV_PTMX) */
 
 
 #if defined(HAVE_OPENPTY) || defined(HAVE__GETPTY) || defined(HAVE_DEV_PTMX)
@@ -7392,6 +7391,56 @@ os_openpty_impl(PyObject *module)
 #endif /* defined(HAVE_OPENPTY) || defined(HAVE__GETPTY) || defined(HAVE_DEV_PTMX) */
 
 
+#if defined(HAVE_SETSID) && defined(TIOCSCTTY)
+#define HAVE_FALLBACK_LOGIN_TTY 1
+#endif /* defined(HAVE_SETSID) && defined(TIOCSCTTY) */
+
+#if defined(HAVE_LOGIN_TTY) || defined(HAVE_FALLBACK_LOGIN_TTY)
+/*[clinic input]
+os.login_tty
+
+    fd: fildes
+    /
+
+Prepare the tty of which fd is a file descriptor for a new login session.
+
+Make the calling process a session leader; make the tty the
+controlling tty, the stdin, the stdout, and the stderr of the
+calling process; close fd.
+[clinic start generated code]*/
+
+static PyObject *
+os_login_tty_impl(PyObject *module, int fd)
+/*[clinic end generated code: output=495a79911b4cc1bc input=5f298565099903a2]*/
+{
+#ifdef HAVE_LOGIN_TTY
+    if (login_tty(fd) == -1) {
+        return posix_error();
+    }
+#else /* defined(HAVE_FALLBACK_LOGIN_TTY) */
+    /* Establish a new session. */
+    if (setsid() == -1) {
+        return posix_error();
+    }
+
+    /* The tty becomes the controlling terminal. */
+    if (ioctl(fd, TIOCSCTTY, (char *)NULL) == -1) {
+        return posix_error();
+    }
+
+    /* The tty becomes stdin/stdout/stderr */
+    if (dup2(fd, 0) == -1 || dup2(fd, 1) == -1 || dup2(fd, 2) == -1) {
+        return posix_error();
+    }
+    if (fd > 2) {
+        close(fd);
+    }
+#endif /* HAVE_LOGIN_TTY */
+    Py_RETURN_NONE;
+}
+#endif /* defined(HAVE_LOGIN_TTY) || defined(HAVE_FALLBACK_LOGIN_TTY) */
+
+
 #ifdef HAVE_FORKPTY
 /*[clinic input]
 os.forkpty
@@ -7427,8 +7476,9 @@ os_forkpty_impl(PyObject *module)
         /* parent: release the import lock. */
         PyOS_AfterFork_Parent();
     }
-    if (pid == -1)
+    if (pid == -1) {
         return posix_error();
+    }
     return Py_BuildValue("(Ni)", PyLong_FromPid(pid), master_fd);
 }
 #endif /* HAVE_FORKPTY */
@@ -14797,6 +14847,7 @@ static PyMethodDef posix_methods[] = {
     OS_SCHED_SETAFFINITY_METHODDEF
     OS_SCHED_GETAFFINITY_METHODDEF
     OS_OPENPTY_METHODDEF
+    OS_LOGIN_TTY_METHODDEF
     OS_FORKPTY_METHODDEF
     OS_GETEGID_METHODDEF
     OS_GETEUID_METHODDEF

configure.ac

@@ -2508,7 +2508,7 @@ AC_CHECK_HEADERS([ \
   sys/random.h sys/resource.h sys/select.h sys/sendfile.h sys/socket.h sys/soundcard.h sys/stat.h \
   sys/statvfs.h sys/sys_domain.h sys/syscall.h sys/sysmacros.h sys/termio.h sys/time.h sys/times.h \
   sys/types.h sys/uio.h sys/un.h sys/utsname.h sys/wait.h sys/xattr.h sysexits.h syslog.h \
-  termios.h util.h utime.h \
+  termios.h util.h utime.h utmp.h \
 ])
 AC_HEADER_DIRENT
 AC_HEADER_MAJOR
@@ -4670,14 +4670,17 @@ PY_CHECK_FUNC([setgroups], [
 #endif
 ])
 
-# check for openpty and forkpty
+# check for openpty, login_tty, and forkpty
 
 AC_CHECK_FUNCS(openpty,,
    AC_CHECK_LIB(util,openpty,
      [AC_DEFINE(HAVE_OPENPTY) LIBS="$LIBS -lutil"],
      AC_CHECK_LIB(bsd,openpty, [AC_DEFINE(HAVE_OPENPTY) LIBS="$LIBS -lbsd"])
    )
 )
+AC_SEARCH_LIBS([login_tty], [util],
+ [AC_DEFINE([HAVE_LOGIN_TTY], [1], [Define to 1 if you have the `login_tty' function.])]
+)
 AC_CHECK_FUNCS(forkpty,,
    AC_CHECK_LIB(util,forkpty,
      [AC_DEFINE(HAVE_FORKPTY) LIBS="$LIBS -lutil"],

pyconfig.h.in

@@ -721,6 +721,9 @@
 /* Define to 1 if you have the `log2' function. */
 #undef HAVE_LOG2
 
+/* Define to 1 if you have the `login_tty' function. */
+#undef HAVE_LOGIN_TTY
+
 /* Define to 1 if the system has the type `long double'. */
 #undef HAVE_LONG_DOUBLE
 
@@ -1389,6 +1392,9 @@
 /* Define to 1 if you have the <utime.h> header file. */
 #undef HAVE_UTIME_H
 
+/* Define to 1 if you have the <utmp.h> header file. */
+#undef HAVE_UTMP_H
+
 /* Define to 1 if you have the `uuid_create' function. */
 #undef HAVE_UUID_CREATE