diff --git a/Modules/posixmodule.c b/Modules/posixmodule.c
index b3b5572e1cf..6dfe73017ab 100644
--- a/Modules/posixmodule.c
+++ b/Modules/posixmodule.c
@@ -7,6 +7,8 @@
    of the compiler used.  Different compilers define their own feature
    test macro, e.g. '_MSC_VER'. */
 
+// --- Python includes ------------------------------------------------------
+
 #include "Python.h"
 
 #ifdef __VXWORKS__
@@ -26,40 +28,392 @@
 #include "pycore_time.h"          // _PyLong_FromTime_t()
 #include "pycore_typeobject.h"    // _PyType_AddMethod()
 
+#ifndef MS_WINDOWS
+#  include "posixmodule.h"        // _PyLong_FromUid()
+#else
+#  include "pycore_fileutils_windows.h" // _Py_GetFileInformationByName()
+#  include "osdefs.h"             // SEP
+#  include "winreparse.h"         // _Py_REPARSE_DATA_BUFFER
+#endif
+
+
+// --- System includes ------------------------------------------------------
+
+#include <stdio.h>                // ctermid()
+#include <stdlib.h>               // system()
+
 #ifdef HAVE_UNISTD_H
 #  include <unistd.h>             // symlink()
 #endif
 
+#ifdef __APPLE__
+   /* Needed for the implementation of os.statvfs */
+#  include <sys/param.h>
+#  include <sys/mount.h>
+#endif
+
+#ifdef HAVE_SYS_TIME_H
+#  include <sys/time.h>           // futimes()
+#endif
+
+#ifdef HAVE_SYS_PIDFD_H
+#  include <sys/pidfd.h>          // PIDFD_NONBLOCK
+#endif
+
+#ifdef __EMSCRIPTEN__
+#  include "emscripten.h"         // emscripten_debugger()
+#endif
+
+#ifdef HAVE_SYS_UIO_H
+#  include <sys/uio.h>
+#endif
+
+#ifdef HAVE_SYS_TYPES_H
+   /* Should be included before <sys/sysmacros.h> on HP-UX v3 */
+#  include <sys/types.h>
+#endif
+#ifdef HAVE_SYS_SYSMACROS_H
+   /* GNU C Library: major(), minor(), makedev() */
+#  include <sys/sysmacros.h>
+#endif
+
+#ifdef HAVE_SYS_STAT_H
+#  include <sys/stat.h>
+#endif
+
+#ifdef HAVE_SYS_WAIT_H
+#  include <sys/wait.h>           // WNOHANG
+#endif
+
+#ifdef HAVE_LINUX_WAIT_H
+#  include <linux/wait.h>         // P_PIDFD
+#endif
+
+#ifdef HAVE_SIGNAL_H
+#  include <signal.h>
+#endif
+
+#ifdef HAVE_FCNTL_H
+#  include <fcntl.h>              // fcntl()
+#endif
+
+#ifdef HAVE_GRP_H
+#  include <grp.h>                // setgroups()
+#endif
+
+#ifdef HAVE_SYSEXITS_H
+#  include <sysexits.h>           // EX_OK
+#endif
+
+#ifdef HAVE_SYS_LOADAVG_H
+#  include <sys/loadavg.h>        // getloadavg()
+#endif
+
+#ifdef HAVE_SYS_SENDFILE_H
+#  include <sys/sendfile.h>       // sendfile()
+#endif
+
+#if defined(__APPLE__)
+#  include <copyfile.h>           // fcopyfile()
+#endif
+
+#ifdef HAVE_SCHED_H
+#  include <sched.h>              // sched_setscheduler()
+#endif
+#ifdef HAVE_LINUX_SCHED_H
+#  include <linux/sched.h>        // SCHED_IDLE, SCHED_RR
+#endif
+
+#if defined(__FreeBSD__) || defined(__DragonFly__) || defined(__APPLE__)
+#  ifdef HAVE_SYS_SOCKET_H
+#    include <sys/socket.h>
+#  endif
+#endif
+
+#ifdef HAVE_DLFCN_H
+#  include <dlfcn.h>
+#endif
+
+#ifdef __hpux
+#  include <sys/mpctl.h>
+#endif
+
+#if defined(__DragonFly__) || \
+    defined(__OpenBSD__)   || \
+    defined(__FreeBSD__)   || \
+    defined(__NetBSD__)    || \
+    defined(__APPLE__)
+#  include <sys/sysctl.h>
+#endif
+
+#ifdef HAVE_LINUX_RANDOM_H
+#  include <linux/random.h>       // GRND_RANDOM
+#endif
+#ifdef HAVE_GETRANDOM_SYSCALL
+#  include <sys/syscall.h>        // syscall()
+#endif
+
+#ifdef HAVE_POSIX_SPAWN
+#  include <spawn.h>              // posix_spawn()
+#endif
+
+#ifdef HAVE_UTIME_H
+#  include <utime.h>              // utime()
+#endif
+
+#ifdef HAVE_SYS_UTIME_H
+#  include <sys/utime.h>
+#  define HAVE_UTIME_H /* pretend we do for the rest of this file */
+#endif
+
+#ifdef HAVE_SYS_TIMES_H
+#  include <sys/times.h>          // times()
+#endif
+
+#ifdef HAVE_SYS_PARAM_H
+#  include <sys/param.h>
+#endif
+
+#ifdef HAVE_SYS_UTSNAME_H
+#  include <sys/utsname.h>        // uname()
+#endif
+
+/* memfd_create is either defined in sys/mman.h or sys/memfd.h
+ * linux/memfd.h defines additional flags
+ */
+#ifdef HAVE_SYS_MMAN_H
+#  include <sys/mman.h>           // memfd_create()
+#endif
+#ifdef HAVE_SYS_MEMFD_H
+#  include <sys/memfd.h>          // memfd_create()
+#endif
+#ifdef HAVE_LINUX_MEMFD_H
+#  include <linux/memfd.h>        // memfd_create(), MFD_CLOEXEC
+#endif
+
+#ifdef HAVE_SYS_EVENTFD_H
+#  include <sys/eventfd.h>        // eventfd()
+#endif
+
+#ifdef HAVE_SYS_TIMERFD_H
+#  include <sys/timerfd.h>        // timerfd_create()
+#endif
+
+#ifdef _Py_MEMORY_SANITIZER
+#  include <sanitizer/msan_interface.h> // __msan_unpoison()
+#endif
+
+
+// --- More complex system includes -----------------------------------------
+
 #ifdef MS_WINDOWS
 #  include <windows.h>
 #  if !defined(MS_WINDOWS_GAMES) || defined(MS_WINDOWS_DESKTOP)
-#    include <pathcch.h>
+#    include <pathcch.h>          // PathCchSkipRoot()
 #  endif
-#  include <winioctl.h>
-#  include <lmcons.h>             // UNLEN
-#  include "osdefs.h"             // SEP
 #  include <aclapi.h>             // SetEntriesInAcl
+#  include <lmcons.h>             // UNLEN
 #  include <sddl.h>               // SDDL_REVISION_1
+#  include <winioctl.h>           // FSCTL_GET_REPARSE_POINT
 #  if defined(MS_WINDOWS_DESKTOP) || defined(MS_WINDOWS_SYSTEM)
 #    define HAVE_SYMLINK
 #  endif /* MS_WINDOWS_DESKTOP | MS_WINDOWS_SYSTEM */
 #endif
 
-#ifndef MS_WINDOWS
-#  include "posixmodule.h"
-#else
-#  include "pycore_fileutils_windows.h"
-#  include "winreparse.h"
+
+#ifdef _MSC_VER
+#  ifdef HAVE_DIRECT_H
+#    include <direct.h>
+#  endif
+#  ifdef HAVE_IO_H
+#    include <io.h>
+#  endif
+#  ifdef HAVE_PROCESS_H
+#    include <process.h>          // getpid(), _cwait()
+#  endif
+#  include <malloc.h>
+#endif /* _MSC_VER */
+
+
+#ifdef HAVE__GETPTY
+#  include <sys/types.h>          // mode_t
+   // SGI apparently needs this forward declaration
+   extern char * _getpty(int *, int, mode_t, int);
 #endif
 
+
+#if defined(HAVE_SYS_XATTR_H)
+#  if defined(HAVE_LINUX_LIMITS_H) && !defined(__FreeBSD_kernel__) && !defined(__GNU__)
+#    define USE_XATTRS
+#    include <linux/limits.h>  // Needed for XATTR_SIZE_MAX on musl libc.
+#  endif
+#  if defined(__CYGWIN__)
+#    define USE_XATTRS
+#    include <cygwin/limits.h>  // Needed for XATTR_SIZE_MAX and XATTR_LIST_MAX.
+#  endif
+#endif
+#ifdef USE_XATTRS
+#  include <sys/xattr.h>          // fgetxattr()
+#endif
+
+
+#ifdef HAVE_WINDOWS_CONSOLE_IO
+#  define TERMSIZE_USE_CONIO
+#elif defined(HAVE_SYS_IOCTL_H)
+#  include <sys/ioctl.h>          // ioctl(), TIOCGWINSZ
+#  if defined(HAVE_TERMIOS_H)
+#    include <termios.h>
+#  endif
+#  if defined(TIOCGWINSZ)
+#    define TERMSIZE_USE_IOCTL
+#  endif
+#endif
+
+
+/* Various compilers have only certain posix functions */
+/* XXX Gosh I wish these were all moved into pyconfig.h */
+#if defined(__WATCOMC__) && !defined(__QNX__)           /* Watcom compiler */
+#  define HAVE_OPENDIR    1
+#  define HAVE_SYSTEM     1
+#  include <process.h>
+#elif defined( _MSC_VER)
+  /* Microsoft compiler */
+#  if defined(MS_WINDOWS_DESKTOP) || defined(MS_WINDOWS_APP) || defined(MS_WINDOWS_SYSTEM)
+#    define HAVE_GETPPID    1
+#  endif /* MS_WINDOWS_DESKTOP | MS_WINDOWS_APP | MS_WINDOWS_SYSTEM */
+#  if defined(MS_WINDOWS_DESKTOP)
+#    define HAVE_GETLOGIN   1
+#  endif /* MS_WINDOWS_DESKTOP */
+#  if defined(MS_WINDOWS_DESKTOP) || defined(MS_WINDOWS_SYSTEM)
+#    define HAVE_SPAWNV     1
+#    define HAVE_EXECV      1
+#    define HAVE_WSPAWNV    1
+#    define HAVE_WEXECV     1
+#    define HAVE_SYSTEM     1
+#    define HAVE_CWAIT      1
+#  endif /* MS_WINDOWS_DESKTOP | MS_WINDOWS_SYSTEM */
+#  define HAVE_PIPE       1
+#  define HAVE_FSYNC      1
+#  define fsync _commit
+#endif
+
+
+#if !defined(_MSC_VER) && defined(__sgi) && _COMPILER_VERSION>=700
+/* declare ctermid_r if compiling with MIPSPro 7.x in ANSI C mode
+   (default) */
+extern char *ctermid_r(char *);
+#endif
+
+
+#if defined(__VXWORKS__)
+#  include <vxCpuLib.h>
+#  include <rtpLib.h>
+#  include <wait.h>
+#  include <taskLib.h>
+#  ifndef _P_WAIT
+#    define _P_WAIT          0
+#    define _P_NOWAIT        1
+#    define _P_NOWAITO       1
+#  endif
+#endif /* __VXWORKS__ */
+
+
+#ifdef HAVE_DIRENT_H
+#  include <dirent.h>             // opendir()
+#  define NAMLEN(dirent) strlen((dirent)->d_name)
+#else
+#  if defined(__WATCOMC__) && !defined(__QNX__)
+#    include <direct.h>
+#    define NAMLEN(dirent) strlen((dirent)->d_name)
+#  else
+#    define dirent direct
+#    define NAMLEN(dirent) (dirent)->d_namlen
+#  endif
+#  ifdef HAVE_SYS_NDIR_H
+#    include <sys/ndir.h>
+#  endif
+#  ifdef HAVE_SYS_DIR_H
+#    include <sys/dir.h>
+#  endif
+#  ifdef HAVE_NDIR_H
+#    include <ndir.h>
+#  endif
+#endif
+
+
+#if defined(MAJOR_IN_MKDEV)
+#  include <sys/mkdev.h>
+#else
+#  if defined(MAJOR_IN_SYSMACROS)
+#    include <sys/sysmacros.h>
+#  endif
+#  if defined(HAVE_MKNOD) && defined(HAVE_SYS_MKDEV_H)
+#    include <sys/mkdev.h>
+#  endif
+#endif
+
+
+// --- Macros ---------------------------------------------------------------
+
+#ifndef MAXPATHLEN
+#  if defined(PATH_MAX) && PATH_MAX > 1024
+#    define MAXPATHLEN PATH_MAX
+#  else
+#    define MAXPATHLEN 1024
+#  endif
+#endif /* MAXPATHLEN */
+
+
+#ifdef UNION_WAIT
+   /* Emulate some macros on systems that have a union instead of macros */
+#  ifndef WIFEXITED
+#    define WIFEXITED(u_wait) (!(u_wait).w_termsig && !(u_wait).w_coredump)
+#  endif
+#  ifndef WEXITSTATUS
+#    define WEXITSTATUS(u_wait) (WIFEXITED(u_wait)?((u_wait).w_retcode):-1)
+#  endif
+#  ifndef WTERMSIG
+#    define WTERMSIG(u_wait) ((u_wait).w_termsig)
+#  endif
+#  define WAIT_TYPE union wait
+#  define WAIT_STATUS_INT(s) (s.w_status)
+#else
+   /* !UNION_WAIT */
+#  define WAIT_TYPE int
+#  define WAIT_STATUS_INT(s) (s)
+#endif /* UNION_WAIT */
+
+
+/* Don't use the "_r" form if we don't need it (also, won't have a
+   prototype for it, at least on Solaris -- maybe others as well?). */
+#if defined(HAVE_CTERMID_R)
+#  define USE_CTERMID_R
+#endif
+
+
+/* choose the appropriate stat and fstat functions and return structs */
+#undef STAT
+#undef FSTAT
+#undef STRUCT_STAT
+#ifdef MS_WINDOWS
+#  define STAT win32_stat
+#  define LSTAT win32_lstat
+#  define FSTAT _Py_fstat_noraise
+#  define STRUCT_STAT struct _Py_stat_struct
+#else
+#  define STAT stat
+#  define LSTAT lstat
+#  define FSTAT fstat
+#  define STRUCT_STAT struct stat
+#endif
+
+
 #if !defined(EX_OK) && defined(EXIT_SUCCESS)
 #  define EX_OK EXIT_SUCCESS
 #endif
 
-#ifdef __APPLE__
- /* Needed for the implementation of os.statvfs */
-#  include <sys/param.h>
-#  include <sys/mount.h>
+#if !defined(CPU_ALLOC) && defined(HAVE_SCHED_SETAFFINITY)
+#  undef HAVE_SCHED_SETAFFINITY
 #endif
 
 /* On android API level 21, 'AT_EACCESS' is not declared although
@@ -68,25 +422,13 @@
 #  undef HAVE_FACCESSAT
 #endif
 
-#include <stdio.h>                // ctermid()
-#include <stdlib.h>               // system()
-#ifdef HAVE_SYS_TIME_H
-#  include <sys/time.h>           // futimes()
-#endif
-#ifdef HAVE_SYS_PIDFD_H
-#  include <sys/pidfd.h>          // PIDFD_NONBLOCK
+#if defined(__sun)
+/* Something to implement in autoconf, not present in autoconf 2.69 */
+#  define HAVE_STRUCT_STAT_ST_FSTYPE 1
 #endif
 
 
-// SGI apparently needs this forward declaration
-#ifdef HAVE__GETPTY
-#  include <sys/types.h>          // mode_t
-   extern char * _getpty(int *, int, mode_t, int);
-#endif
-
-#ifdef __EMSCRIPTEN__
-#include "emscripten.h" // emscripten_debugger()
-#endif
+// --- Apple __builtin_available() macros -----------------------------------
 
 /*
  * A number of APIs are available on macOS from a certain macOS version.
@@ -247,308 +589,7 @@
 #endif
 
 
-PyDoc_STRVAR(posix__doc__,
-"This module provides access to operating system functionality that is\n\
-standardized by the C Standard and the POSIX standard (a thinly\n\
-disguised Unix interface).  Refer to the library manual and\n\
-corresponding Unix manual entries for more information on calls.");
-
-
-#ifdef HAVE_SYS_UIO_H
-#  include <sys/uio.h>
-#endif
-
-#ifdef HAVE_SYS_TYPES_H
-/* Should be included before <sys/sysmacros.h> on HP-UX v3 */
-#  include <sys/types.h>
-#endif /* HAVE_SYS_TYPES_H */
-
-#ifdef HAVE_SYS_SYSMACROS_H
-/* GNU C Library: major(), minor(), makedev() */
-#  include <sys/sysmacros.h>
-#endif
-
-#ifdef HAVE_SYS_STAT_H
-#  include <sys/stat.h>
-#endif /* HAVE_SYS_STAT_H */
-
-#ifdef HAVE_SYS_WAIT_H
-#  include <sys/wait.h>           // WNOHANG
-#endif
-#ifdef HAVE_LINUX_WAIT_H
-#  include <linux/wait.h>         // P_PIDFD
-#endif
-
-#ifdef HAVE_SIGNAL_H
-#  include <signal.h>
-#endif
-
-#ifdef HAVE_FCNTL_H
-#  include <fcntl.h>
-#endif
-
-#ifdef HAVE_GRP_H
-#  include <grp.h>
-#endif
-
-#ifdef HAVE_SYSEXITS_H
-#  include <sysexits.h>
-#endif
-
-#ifdef HAVE_SYS_LOADAVG_H
-#  include <sys/loadavg.h>
-#endif
-
-#ifdef HAVE_SYS_SENDFILE_H
-#  include <sys/sendfile.h>
-#endif
-
-#if defined(__APPLE__)
-#  include <copyfile.h>
-#endif
-
-#ifdef HAVE_SCHED_H
-#  include <sched.h>
-#endif
-
-#ifdef HAVE_LINUX_SCHED_H
-#  include <linux/sched.h>
-#endif
-
-#if !defined(CPU_ALLOC) && defined(HAVE_SCHED_SETAFFINITY)
-#  undef HAVE_SCHED_SETAFFINITY
-#endif
-
-#if defined(HAVE_SYS_XATTR_H)
-#  if defined(HAVE_LINUX_LIMITS_H) && !defined(__FreeBSD_kernel__) && !defined(__GNU__)
-#    define USE_XATTRS
-#    include <linux/limits.h>  // Needed for XATTR_SIZE_MAX on musl libc.
-#  endif
-#  if defined(__CYGWIN__)
-#    define USE_XATTRS
-#    include <cygwin/limits.h>  // Needed for XATTR_SIZE_MAX and XATTR_LIST_MAX.
-#  endif
-#endif
-
-#ifdef USE_XATTRS
-#  include <sys/xattr.h>
-#endif
-
-#if defined(__FreeBSD__) || defined(__DragonFly__) || defined(__APPLE__)
-#  ifdef HAVE_SYS_SOCKET_H
-#    include <sys/socket.h>
-#  endif
-#endif
-
-#ifdef HAVE_DLFCN_H
-#  include <dlfcn.h>
-#endif
-
-#ifdef __hpux
-#  include <sys/mpctl.h>
-#endif
-
-#if defined(__DragonFly__) || \
-    defined(__OpenBSD__)   || \
-    defined(__FreeBSD__)   || \
-    defined(__NetBSD__)    || \
-    defined(__APPLE__)
-#  include <sys/sysctl.h>
-#endif
-
-#ifdef HAVE_LINUX_RANDOM_H
-#  include <linux/random.h>
-#endif
-#ifdef HAVE_GETRANDOM_SYSCALL
-#  include <sys/syscall.h>
-#endif
-
-#ifdef HAVE_WINDOWS_CONSOLE_IO
-#  define TERMSIZE_USE_CONIO
-#elif defined(HAVE_SYS_IOCTL_H)
-#  include <sys/ioctl.h>
-#  if defined(HAVE_TERMIOS_H)
-#    include <termios.h>
-#  endif
-#  if defined(TIOCGWINSZ)
-#    define TERMSIZE_USE_IOCTL
-#  endif
-#endif /* HAVE_WINDOWS_CONSOLE_IO */
-
-/* Various compilers have only certain posix functions */
-/* XXX Gosh I wish these were all moved into pyconfig.h */
-#if defined(__WATCOMC__) && !defined(__QNX__)           /* Watcom compiler */
-#  define HAVE_OPENDIR    1
-#  define HAVE_SYSTEM     1
-#  include <process.h>
-#elif defined( _MSC_VER)
-  /* Microsoft compiler */
-#  if defined(MS_WINDOWS_DESKTOP) || defined(MS_WINDOWS_APP) || defined(MS_WINDOWS_SYSTEM)
-#    define HAVE_GETPPID    1
-#  endif /* MS_WINDOWS_DESKTOP | MS_WINDOWS_APP | MS_WINDOWS_SYSTEM */
-#  if defined(MS_WINDOWS_DESKTOP)
-#    define HAVE_GETLOGIN   1
-#  endif /* MS_WINDOWS_DESKTOP */
-#  if defined(MS_WINDOWS_DESKTOP) || defined(MS_WINDOWS_SYSTEM)
-#    define HAVE_SPAWNV     1
-#    define HAVE_EXECV      1
-#    define HAVE_WSPAWNV    1
-#    define HAVE_WEXECV     1
-#    define HAVE_SYSTEM     1
-#    define HAVE_CWAIT      1
-#  endif /* MS_WINDOWS_DESKTOP | MS_WINDOWS_SYSTEM */
-#  define HAVE_PIPE       1
-#  define HAVE_FSYNC      1
-#  define fsync _commit
-#endif  /* ! __WATCOMC__ || __QNX__ */
-
-/*[clinic input]
-# one of the few times we lie about this name!
-module os
-[clinic start generated code]*/
-/*[clinic end generated code: output=da39a3ee5e6b4b0d input=94a0f0f978acae17]*/
-
-#ifndef _MSC_VER
-
-#if defined(__sgi)&&_COMPILER_VERSION>=700
-/* declare ctermid_r if compiling with MIPSPro 7.x in ANSI C mode
-   (default) */
-extern char        *ctermid_r(char *);
-#endif
-
-#endif /* !_MSC_VER */
-
-#if defined(__VXWORKS__)
-#  include <vxCpuLib.h>
-#  include <rtpLib.h>
-#  include <wait.h>
-#  include <taskLib.h>
-#  ifndef _P_WAIT
-#    define _P_WAIT          0
-#    define _P_NOWAIT        1
-#    define _P_NOWAITO       1
-#  endif
-#endif /* __VXWORKS__ */
-
-#ifdef HAVE_POSIX_SPAWN
-#  include <spawn.h>
-#endif
-
-#ifdef HAVE_UTIME_H
-#  include <utime.h>
-#endif /* HAVE_UTIME_H */
-
-#ifdef HAVE_SYS_UTIME_H
-#  include <sys/utime.h>
-#  define HAVE_UTIME_H /* pretend we do for the rest of this file */
-#endif /* HAVE_SYS_UTIME_H */
-
-#ifdef HAVE_SYS_TIMES_H
-#  include <sys/times.h>
-#endif /* HAVE_SYS_TIMES_H */
-
-#ifdef HAVE_SYS_PARAM_H
-#  include <sys/param.h>
-#endif /* HAVE_SYS_PARAM_H */
-
-#ifdef HAVE_SYS_UTSNAME_H
-#  include <sys/utsname.h>
-#endif /* HAVE_SYS_UTSNAME_H */
-
-#ifdef HAVE_DIRENT_H
-#  include <dirent.h>
-#  define NAMLEN(dirent) strlen((dirent)->d_name)
-#else
-#  if defined(__WATCOMC__) && !defined(__QNX__)
-#    include <direct.h>
-#    define NAMLEN(dirent) strlen((dirent)->d_name)
-#  else
-#    define dirent direct
-#    define NAMLEN(dirent) (dirent)->d_namlen
-#  endif
-#  ifdef HAVE_SYS_NDIR_H
-#    include <sys/ndir.h>
-#  endif
-#  ifdef HAVE_SYS_DIR_H
-#    include <sys/dir.h>
-#  endif
-#  ifdef HAVE_NDIR_H
-#    include <ndir.h>
-#  endif
-#endif
-
-#ifdef _MSC_VER
-#  ifdef HAVE_DIRECT_H
-#    include <direct.h>
-#  endif
-#  ifdef HAVE_IO_H
-#    include <io.h>
-#  endif
-#  ifdef HAVE_PROCESS_H
-#    include <process.h>
-#  endif
-#  include <malloc.h>
-#endif /* _MSC_VER */
-
-#ifndef MAXPATHLEN
-#  if defined(PATH_MAX) && PATH_MAX > 1024
-#    define MAXPATHLEN PATH_MAX
-#  else
-#    define MAXPATHLEN 1024
-#  endif
-#endif /* MAXPATHLEN */
-
-#ifdef UNION_WAIT
-   /* Emulate some macros on systems that have a union instead of macros */
-#  ifndef WIFEXITED
-#    define WIFEXITED(u_wait) (!(u_wait).w_termsig && !(u_wait).w_coredump)
-#  endif
-#  ifndef WEXITSTATUS
-#    define WEXITSTATUS(u_wait) (WIFEXITED(u_wait)?((u_wait).w_retcode):-1)
-#  endif
-#  ifndef WTERMSIG
-#    define WTERMSIG(u_wait) ((u_wait).w_termsig)
-#  endif
-#  define WAIT_TYPE union wait
-#  define WAIT_STATUS_INT(s) (s.w_status)
-#else
-   /* !UNION_WAIT */
-#  define WAIT_TYPE int
-#  define WAIT_STATUS_INT(s) (s)
-#endif /* UNION_WAIT */
-
-/* Don't use the "_r" form if we don't need it (also, won't have a
-   prototype for it, at least on Solaris -- maybe others as well?). */
-#if defined(HAVE_CTERMID_R)
-#  define USE_CTERMID_R
-#endif
-
-/* choose the appropriate stat and fstat functions and return structs */
-#undef STAT
-#undef FSTAT
-#undef STRUCT_STAT
-#ifdef MS_WINDOWS
-#  define STAT win32_stat
-#  define LSTAT win32_lstat
-#  define FSTAT _Py_fstat_noraise
-#  define STRUCT_STAT struct _Py_stat_struct
-#else
-#  define STAT stat
-#  define LSTAT lstat
-#  define FSTAT fstat
-#  define STRUCT_STAT struct stat
-#endif
-
-#if defined(MAJOR_IN_MKDEV)
-#  include <sys/mkdev.h>
-#else
-#  if defined(MAJOR_IN_SYSMACROS)
-#    include <sys/sysmacros.h>
-#  endif
-#  if defined(HAVE_MKNOD) && defined(HAVE_SYS_MKDEV_H)
-#    include <sys/mkdev.h>
-#  endif
-#endif
+// --- os module ------------------------------------------------------------
 
 #ifdef MS_WINDOWS
 #  define INITFUNC PyInit_nt
@@ -560,37 +601,20 @@ extern char        *ctermid_r(char *);
 #  define MODNAME_OBJ &_Py_ID(posix)
 #endif
 
-#if defined(__sun)
-/* Something to implement in autoconf, not present in autoconf 2.69 */
-#  define HAVE_STRUCT_STAT_ST_FSTYPE 1
-#endif
+/*[clinic input]
+# one of the few times we lie about this name!
+module os
+[clinic start generated code]*/
+/*[clinic end generated code: output=da39a3ee5e6b4b0d input=94a0f0f978acae17]*/
 
-/* memfd_create is either defined in sys/mman.h or sys/memfd.h
- * linux/memfd.h defines additional flags
- */
-#ifdef HAVE_SYS_MMAN_H
-#  include <sys/mman.h>
-#endif
-#ifdef HAVE_SYS_MEMFD_H
-#  include <sys/memfd.h>
-#endif
-#ifdef HAVE_LINUX_MEMFD_H
-#  include <linux/memfd.h>
-#endif
+PyDoc_STRVAR(posix__doc__,
+"This module provides access to operating system functionality that is\n\
+standardized by the C Standard and the POSIX standard (a thinly\n\
+disguised Unix interface).  Refer to the library manual and\n\
+corresponding Unix manual entries for more information on calls.");
 
-/* eventfd() */
-#ifdef HAVE_SYS_EVENTFD_H
-#  include <sys/eventfd.h>
-#endif
 
-/* timerfd_create() */
-#ifdef HAVE_SYS_TIMERFD_H
-#  include <sys/timerfd.h>
-#endif
-
-#ifdef _Py_MEMORY_SANITIZER
-#  include <sanitizer/msan_interface.h>
-#endif
+// --- Functions ------------------------------------------------------------
 
 #ifdef HAVE_FORK
 static void