Use fdopendir, fstatat and readlinkat, for efficiency.

On my host, this speeds up directory-files-and-attributes by a
factor of 3, when applied to Emacs's src directory.
These functions are standardized by POSIX and are common these
days; fall back on a (slower) gnulib implementation if the host
is too old to supply them.
* .bzrignore: Add lib/dirent.h.
* lib/Makefile.am (libgnu_a_SOURCES): Add openat-die.c, save-cwd.c.
* lib/careadlinkat.c, lib/careadlinkat.h: Merge from gnulib,
incorporating: 2013-01-29 careadlinkat: do not provide careadlinkatcwd.
* lib/gnulib.mk, m4/gnulib-comp.m4: Regenerate.
* lib/dirent.in.h, lib/fdopendir.c, lib/fstatat.c, lib/openat-priv.h:
* lib/openat-proc.c, lib/openat.h, m4/dirent_h.m4, m4/fdopendir.m4:
* m4/fstatat.m4: New files, from gnulib.
* lib/openat-die.c, lib/save-cwd.c, lib/save-cwd.h: New files.
These last three are specific to Emacs and are not copied from gnulib.
They are simpler than the gnulib versions and are tuned for Emacs.
* admin/merge-gnulib (GNULIB_MODULES): Add fdopendir, fstatat, readlinkat.
(GNULIB_TOOL_FLAGS): Do not avoid at-internal, openat-h.
Avoid dup, open, opendir.
* nt/inc/sys/stat.h (fstatat):
* nt/inc/unistd.h (readlinkat): New decls.
* src/conf_post.h (GNULIB_SUPPORT_ONLY_AT_FDCWD): Remove.
* src/dired.c: Include <fcntl.h>.
(open_directory): New function, which uses open and fdopendir
rather than opendir.  DOS_NT platforms still use opendir, though.
(directory_files_internal, file_name_completion): Use it.
(file_attributes): New function, with most of the old Ffile_attributes.
(directory_files_internal, Ffile_attributes): Use it.
(file_attributes, file_name_completion_stat): First arg is now fd,
not dir name.  All uses changed.  Use fstatat rather than lstat +
stat.
(file_attributes): Use emacs_readlinkat rather than Ffile_symlink_p.
* src/fileio.c: Include <allocator.h>, <careadlinkat.h>.
(emacs_readlinkat): New function, with much of the old
Ffile_symlink_p, but with an fd argument for speed.
It uses readlinkat rather than careadlinkatcwd, so that it
need not assume the working directory.
(Ffile_symlink_p): Use it.
* src/filelock.c (current_lock_owner): Use emacs_readlinkat
rather than emacs_readlink.
* src/lisp.h (emacs_readlinkat): New decl.
(READLINK_BUFSIZE, emacs_readlink): Remove.
* src/sysdep.c: Do not include <allocator.h>, <careadlinkat.h>.
(emacs_norealloc_allocator, emacs_readlink): Remove.
This stuff is moved to fileio.c.
* src/w32.c (fstatat, readlinkat): New functions.
(careadlinkat): Don't check that fd == AT_FDCWD.
(careadlinkatcwd): Remove; no longer needed.

Fixes: debbugs:13539

5 files changed, 282 insertions, 0 deletions

diff --git a/m4/dirent_h.m4 b/m4/dirent_h.m4
new file mode 100644
index 00000000000..54c16634314
--- /dev/null
+++ b/m4/dirent_h.m4
@@ -0,0 +1,64 @@
+# dirent_h.m4 serial 16
+dnl Copyright (C) 2008-2013 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+dnl Written by Bruno Haible.
+
+AC_DEFUN([gl_DIRENT_H],
+[
+  dnl Use AC_REQUIRE here, so that the default behavior below is expanded
+  dnl once only, before all statements that occur in other macros.
+  AC_REQUIRE([gl_DIRENT_H_DEFAULTS])
+
+  dnl <dirent.h> is always overridden, because of GNULIB_POSIXCHECK.
+  gl_CHECK_NEXT_HEADERS([dirent.h])
+  if test $ac_cv_header_dirent_h = yes; then
+    HAVE_DIRENT_H=1
+  else
+    HAVE_DIRENT_H=0
+  fi
+  AC_SUBST([HAVE_DIRENT_H])
+
+  dnl Check for declarations of anything we want to poison if the
+  dnl corresponding gnulib module is not in use.
+  gl_WARN_ON_USE_PREPARE([[#include <dirent.h>
+    ]], [alphasort closedir dirfd fdopendir opendir readdir rewinddir scandir])
+])
+
+AC_DEFUN([gl_DIRENT_MODULE_INDICATOR],
+[
+  dnl Use AC_REQUIRE here, so that the default settings are expanded once only.
+  AC_REQUIRE([gl_DIRENT_H_DEFAULTS])
+  gl_MODULE_INDICATOR_SET_VARIABLE([$1])
+  dnl Define it also as a C macro, for the benefit of the unit tests.
+  gl_MODULE_INDICATOR_FOR_TESTS([$1])
+])
+
+AC_DEFUN([gl_DIRENT_H_DEFAULTS],
+[
+  AC_REQUIRE([gl_UNISTD_H_DEFAULTS]) dnl for REPLACE_FCHDIR
+  GNULIB_OPENDIR=0;     AC_SUBST([GNULIB_OPENDIR])
+  GNULIB_READDIR=0;     AC_SUBST([GNULIB_READDIR])
+  GNULIB_REWINDDIR=0;   AC_SUBST([GNULIB_REWINDDIR])
+  GNULIB_CLOSEDIR=0;    AC_SUBST([GNULIB_CLOSEDIR])
+  GNULIB_DIRFD=0;       AC_SUBST([GNULIB_DIRFD])
+  GNULIB_FDOPENDIR=0;   AC_SUBST([GNULIB_FDOPENDIR])
+  GNULIB_SCANDIR=0;     AC_SUBST([GNULIB_SCANDIR])
+  GNULIB_ALPHASORT=0;   AC_SUBST([GNULIB_ALPHASORT])
+  dnl Assume proper GNU behavior unless another module says otherwise.
+  HAVE_OPENDIR=1;       AC_SUBST([HAVE_OPENDIR])
+  HAVE_READDIR=1;       AC_SUBST([HAVE_READDIR])
+  HAVE_REWINDDIR=1;     AC_SUBST([HAVE_REWINDDIR])
+  HAVE_CLOSEDIR=1;      AC_SUBST([HAVE_CLOSEDIR])
+  HAVE_DECL_DIRFD=1;    AC_SUBST([HAVE_DECL_DIRFD])
+  HAVE_DECL_FDOPENDIR=1;AC_SUBST([HAVE_DECL_FDOPENDIR])
+  HAVE_FDOPENDIR=1;     AC_SUBST([HAVE_FDOPENDIR])
+  HAVE_SCANDIR=1;       AC_SUBST([HAVE_SCANDIR])
+  HAVE_ALPHASORT=1;     AC_SUBST([HAVE_ALPHASORT])
+  REPLACE_OPENDIR=0;    AC_SUBST([REPLACE_OPENDIR])
+  REPLACE_CLOSEDIR=0;   AC_SUBST([REPLACE_CLOSEDIR])
+  REPLACE_DIRFD=0;      AC_SUBST([REPLACE_DIRFD])
+  REPLACE_FDOPENDIR=0;  AC_SUBST([REPLACE_FDOPENDIR])
+])
diff --git a/m4/fdopendir.m4 b/m4/fdopendir.m4
new file mode 100644
index 00000000000..b7be78324dc
--- /dev/null
+++ b/m4/fdopendir.m4
@@ -0,0 +1,61 @@
+# serial 10
+# See if we need to provide fdopendir.
+
+dnl Copyright (C) 2009-2013 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+# Written by Eric Blake.
+
+AC_DEFUN([gl_FUNC_FDOPENDIR],
+[
+  AC_REQUIRE([gl_DIRENT_H_DEFAULTS])
+  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+
+  dnl FreeBSD 7.3 has the function, but failed to declare it.
+  AC_CHECK_DECLS([fdopendir], [], [HAVE_DECL_FDOPENDIR=0], [[
+#include <dirent.h>
+    ]])
+  AC_CHECK_FUNCS_ONCE([fdopendir])
+  if test $ac_cv_func_fdopendir = no; then
+    HAVE_FDOPENDIR=0
+  else
+    AC_CACHE_CHECK([whether fdopendir works],
+      [gl_cv_func_fdopendir_works],
+      [AC_RUN_IFELSE([AC_LANG_PROGRAM([[
+#include <dirent.h>
+#include <fcntl.h>
+#include <unistd.h>
+#if !HAVE_DECL_FDOPENDIR
+extern
+# ifdef __cplusplus
+"C"
+# endif
+DIR *fdopendir (int);
+#endif
+]], [int result = 0;
+     int fd = open ("conftest.c", O_RDONLY);
+     if (fd < 0) result |= 1;
+     if (fdopendir (fd)) result |= 2;
+     if (close (fd)) result |= 4;
+     return result;])],
+         [gl_cv_func_fdopendir_works=yes],
+         [gl_cv_func_fdopendir_works=no],
+         [case "$host_os" in
+                    # Guess yes on glibc systems.
+            *-gnu*) gl_cv_func_fdopendir_works="guessing yes" ;;
+                    # If we don't know, assume the worst.
+            *)      gl_cv_func_fdopendir_works="guessing no" ;;
+          esac
+         ])])
+    case "$gl_cv_func_fdopendir_works" in
+      *yes) ;;
+      *)
+        REPLACE_FDOPENDIR=1
+        ;;
+    esac
+  fi
+])
diff --git a/m4/fstatat.m4 b/m4/fstatat.m4
new file mode 100644
index 00000000000..adbc7e57f51
--- /dev/null
+++ b/m4/fstatat.m4
@@ -0,0 +1,60 @@
+# fstatat.m4 serial 3
+dnl Copyright (C) 2004-2013 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+# Written by Jim Meyering.
+
+# If we have the fstatat function, and it has the bug (in AIX 7.1)
+# that it does not fill in st_size correctly, use the replacement function.
+AC_DEFUN([gl_FUNC_FSTATAT],
+[
+  AC_REQUIRE([gl_SYS_STAT_H_DEFAULTS])
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+  AC_REQUIRE([gl_FUNC_LSTAT_FOLLOWS_SLASHED_SYMLINK])
+  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+  AC_CHECK_FUNCS_ONCE([fstatat])
+
+  if test $ac_cv_func_fstatat = no; then
+    HAVE_FSTATAT=0
+  else
+    dnl Test for an AIX 7.1 bug; see
+    dnl <http://lists.gnu.org/archive/html/bug-tar/2011-09/msg00015.html>.
+    AC_CACHE_CHECK([whether fstatat (..., 0) works],
+      [gl_cv_func_fstatat_zero_flag],
+      [AC_RUN_IFELSE(
+         [AC_LANG_SOURCE(
+            [[
+              #include <fcntl.h>
+              #include <sys/stat.h>
+              int
+              main (void)
+              {
+                struct stat a;
+                return fstatat (AT_FDCWD, ".", &a, 0) != 0;
+              }
+            ]])],
+         [gl_cv_func_fstatat_zero_flag=yes],
+         [gl_cv_func_fstatat_zero_flag=no],
+         [case "$host_os" in
+            aix*) gl_cv_func_fstatat_zero_flag="guessing no";;
+            *)    gl_cv_func_fstatat_zero_flag="guessing yes";;
+          esac
+         ])
+      ])
+
+    case $gl_cv_func_fstatat_zero_flag+$gl_cv_func_lstat_dereferences_slashed_symlink in
+    *yes+*yes) ;;
+    *) REPLACE_FSTATAT=1
+       case $gl_cv_func_fstatat_zero_flag in
+       *yes)
+         AC_DEFINE([HAVE_WORKING_FSTATAT_ZERO_FLAG], [1],
+           [Define to 1 if fstatat (..., 0) works.
+            For example, it does not work in AIX 7.1.])
+         ;;
+       esac
+       ;;
+    esac
+  fi
+])
diff --git a/m4/gnulib-comp.m4 b/m4/gnulib-comp.m4
index b7109c5f87f..8098a52e501 100644
--- a/m4/gnulib-comp.m4
+++ b/m4/gnulib-comp.m4
@@ -40,6 +40,7 @@ AC_DEFUN([gl_EARLY],
   AC_REQUIRE([gl_PROG_AR_RANLIB])
   # Code from module alloca-opt:
   # Code from module allocator:
+  # Code from module at-internal:
   # Code from module c-ctype:
   # Code from module c-strcase:
   # Code from module careadlinkat:
@@ -49,6 +50,7 @@ AC_DEFUN([gl_EARLY],
   # Code from module crypto/sha1:
   # Code from module crypto/sha256:
   # Code from module crypto/sha512:
+  # Code from module dirent:
   # Code from module dosname:
   # Code from module dtoastr:
   # Code from module dtotimespec:
@@ -61,8 +63,10 @@ AC_DEFUN([gl_EARLY],
   # Code from module extern-inline:
   # Code from module faccessat:
   # Code from module fcntl-h:
+  # Code from module fdopendir:
   # Code from module filemode:
   # Code from module fpending:
+  # Code from module fstatat:
   # Code from module getgroups:
   # Code from module getloadavg:
   # Code from module getopt-gnu:
@@ -82,11 +86,13 @@ AC_DEFUN([gl_EARLY],
   # Code from module mktime:
   # Code from module multiarch:
   # Code from module nocrash:
+  # Code from module openat-h:
   # Code from module pathmax:
   # Code from module pselect:
   # Code from module pthread_sigmask:
   # Code from module putenv:
   # Code from module readlink:
+  # Code from module readlinkat:
   # Code from module root-uid:
   # Code from module sig2str:
   # Code from module signal-h:
@@ -159,6 +165,7 @@ AC_DEFUN([gl_INIT],
   gl_SHA1
   gl_SHA256
   gl_SHA512
+  gl_DIRENT_H
   AC_REQUIRE([gl_C99_STRTOLD])
   gl_FUNC_DUP2
   if test $HAVE_DUP2 = 0 || test $REPLACE_DUP2 = 1; then
@@ -178,12 +185,23 @@ AC_DEFUN([gl_INIT],
   gl_MODULE_INDICATOR([faccessat])
   gl_UNISTD_MODULE_INDICATOR([faccessat])
   gl_FCNTL_H
+  gl_FUNC_FDOPENDIR
+  if test $HAVE_FDOPENDIR = 0 || test $REPLACE_FDOPENDIR = 1; then
+    AC_LIBOBJ([fdopendir])
+  fi
+  gl_DIRENT_MODULE_INDICATOR([fdopendir])
+  gl_MODULE_INDICATOR([fdopendir])
   gl_FILEMODE
   gl_FUNC_FPENDING
   if test $ac_cv_func___fpending = no; then
     AC_LIBOBJ([fpending])
     gl_PREREQ_FPENDING
   fi
+  gl_FUNC_FSTATAT
+  if test $HAVE_FSTATAT = 0 || test $REPLACE_FSTATAT = 1; then
+    AC_LIBOBJ([fstatat])
+  fi
+  gl_SYS_STAT_MODULE_INDICATOR([fstatat])
   gl_GETLOADAVG
   if test $HAVE_GETLOADAVG = 0; then
     AC_LIBOBJ([getloadavg])
@@ -253,6 +271,11 @@ AC_DEFUN([gl_INIT],
     gl_PREREQ_READLINK
   fi
   gl_UNISTD_MODULE_INDICATOR([readlink])
+  gl_FUNC_READLINKAT
+  if test $HAVE_READLINKAT = 0; then
+    AC_LIBOBJ([readlinkat])
+  fi
+  gl_UNISTD_MODULE_INDICATOR([readlinkat])
   gl_FUNC_SIG2STR
   if test $ac_cv_func_sig2str = no; then
     AC_LIBOBJ([sig2str])
@@ -311,11 +334,13 @@ AC_DEFUN([gl_INIT],
   fi
   gl_STDLIB_MODULE_INDICATOR([unsetenv])
   gl_UTIMENS
+  gl_gnulib_enabled_260941c0e5dc67ec9e87d1fb321c300b=false
   gl_gnulib_enabled_dosname=false
   gl_gnulib_enabled_euidaccess=false
   gl_gnulib_enabled_getgroups=false
   gl_gnulib_enabled_be453cec5eecf5731a274f2de7f2db36=false
   gl_gnulib_enabled_a9786850e999ae65a836a6041e8e5ed1=false
+  gl_gnulib_enabled_03e0aaad4cb89ca757653bd367a6ccb7=false
   gl_gnulib_enabled_pathmax=false
   gl_gnulib_enabled_6099e9737f757db36c47fa9d9f02e88c=false
   gl_gnulib_enabled_stat=false
@@ -323,6 +348,13 @@ AC_DEFUN([gl_INIT],
   gl_gnulib_enabled_strtoull=false
   gl_gnulib_enabled_verify=false
   gl_gnulib_enabled_682e609604ccaac6be382e4ee3a4eaec=false
+  func_gl_gnulib_m4code_260941c0e5dc67ec9e87d1fb321c300b ()
+  {
+    if ! $gl_gnulib_enabled_260941c0e5dc67ec9e87d1fb321c300b; then
+      AC_LIBOBJ([openat-proc])
+      gl_gnulib_enabled_260941c0e5dc67ec9e87d1fb321c300b=true
+    fi
+  }
   func_gl_gnulib_m4code_dosname ()
   {
     if ! $gl_gnulib_enabled_dosname; then
@@ -385,6 +417,12 @@ AC_DEFUN([gl_INIT],
       fi
     fi
   }
+  func_gl_gnulib_m4code_03e0aaad4cb89ca757653bd367a6ccb7 ()
+  {
+    if ! $gl_gnulib_enabled_03e0aaad4cb89ca757653bd367a6ccb7; then
+      gl_gnulib_enabled_03e0aaad4cb89ca757653bd367a6ccb7=true
+    fi
+  }
   func_gl_gnulib_m4code_pathmax ()
   {
     if ! $gl_gnulib_enabled_pathmax; then
@@ -456,11 +494,29 @@ AC_DEFUN([gl_INIT],
     fi
   }
   if test $HAVE_FACCESSAT = 0; then
+    func_gl_gnulib_m4code_260941c0e5dc67ec9e87d1fb321c300b
+  fi
+  if test $HAVE_FACCESSAT = 0; then
     func_gl_gnulib_m4code_dosname
   fi
   if test $HAVE_FACCESSAT = 0; then
     func_gl_gnulib_m4code_euidaccess
   fi
+  if test $HAVE_FACCESSAT = 0; then
+    func_gl_gnulib_m4code_03e0aaad4cb89ca757653bd367a6ccb7
+  fi
+  if test $HAVE_FDOPENDIR = 0; then
+    func_gl_gnulib_m4code_260941c0e5dc67ec9e87d1fb321c300b
+  fi
+  if test $HAVE_FSTATAT = 0 || test $REPLACE_FSTATAT = 1; then
+    func_gl_gnulib_m4code_260941c0e5dc67ec9e87d1fb321c300b
+  fi
+  if test $HAVE_FSTATAT = 0 || test $REPLACE_FSTATAT = 1; then
+    func_gl_gnulib_m4code_dosname
+  fi
+  if test $HAVE_FSTATAT = 0 || test $REPLACE_FSTATAT = 1; then
+    func_gl_gnulib_m4code_03e0aaad4cb89ca757653bd367a6ccb7
+  fi
   if test $REPLACE_GETOPT = 1; then
     func_gl_gnulib_m4code_be453cec5eecf5731a274f2de7f2db36
   fi
@@ -473,6 +529,15 @@ AC_DEFUN([gl_INIT],
   if test $HAVE_READLINK = 0 || test $REPLACE_READLINK = 1; then
     func_gl_gnulib_m4code_stat
   fi
+  if test $HAVE_READLINKAT = 0; then
+    func_gl_gnulib_m4code_260941c0e5dc67ec9e87d1fb321c300b
+  fi
+  if test $HAVE_READLINKAT = 0; then
+    func_gl_gnulib_m4code_dosname
+  fi
+  if test $HAVE_READLINKAT = 0; then
+    func_gl_gnulib_m4code_03e0aaad4cb89ca757653bd367a6ccb7
+  fi
   if { test $HAVE_STRTOIMAX = 0 || test $REPLACE_STRTOIMAX = 1; } && test $ac_cv_type_long_long_int = yes; then
     func_gl_gnulib_m4code_strtoll
   fi
@@ -486,11 +551,13 @@ AC_DEFUN([gl_INIT],
     func_gl_gnulib_m4code_verify
   fi
   m4_pattern_allow([^gl_GNULIB_ENABLED_])
+  AM_CONDITIONAL([gl_GNULIB_ENABLED_260941c0e5dc67ec9e87d1fb321c300b], [$gl_gnulib_enabled_260941c0e5dc67ec9e87d1fb321c300b])
   AM_CONDITIONAL([gl_GNULIB_ENABLED_dosname], [$gl_gnulib_enabled_dosname])
   AM_CONDITIONAL([gl_GNULIB_ENABLED_euidaccess], [$gl_gnulib_enabled_euidaccess])
   AM_CONDITIONAL([gl_GNULIB_ENABLED_getgroups], [$gl_gnulib_enabled_getgroups])
   AM_CONDITIONAL([gl_GNULIB_ENABLED_be453cec5eecf5731a274f2de7f2db36], [$gl_gnulib_enabled_be453cec5eecf5731a274f2de7f2db36])
   AM_CONDITIONAL([gl_GNULIB_ENABLED_a9786850e999ae65a836a6041e8e5ed1], [$gl_gnulib_enabled_a9786850e999ae65a836a6041e8e5ed1])
+  AM_CONDITIONAL([gl_GNULIB_ENABLED_03e0aaad4cb89ca757653bd367a6ccb7], [$gl_gnulib_enabled_03e0aaad4cb89ca757653bd367a6ccb7])
   AM_CONDITIONAL([gl_GNULIB_ENABLED_pathmax], [$gl_gnulib_enabled_pathmax])
   AM_CONDITIONAL([gl_GNULIB_ENABLED_6099e9737f757db36c47fa9d9f02e88c], [$gl_gnulib_enabled_6099e9737f757db36c47fa9d9f02e88c])
   AM_CONDITIONAL([gl_GNULIB_ENABLED_stat], [$gl_gnulib_enabled_stat])
@@ -656,6 +723,7 @@ AC_DEFUN([gl_FILE_LIST], [
   lib/careadlinkat.h
   lib/close-stream.c
   lib/close-stream.h
+  lib/dirent.in.h
   lib/dosname.h
   lib/dtoastr.c
   lib/dtotimespec.c
@@ -665,10 +733,12 @@ AC_DEFUN([gl_FILE_LIST], [
   lib/execinfo.in.h
   lib/faccessat.c
   lib/fcntl.in.h
+  lib/fdopendir.c
   lib/filemode.c
   lib/filemode.h
   lib/fpending.c
   lib/fpending.h
+  lib/fstatat.c
   lib/ftoastr.c
   lib/ftoastr.h
   lib/getgroups.c
@@ -689,11 +759,15 @@ AC_DEFUN([gl_FILE_LIST], [
   lib/md5.h
   lib/mktime-internal.h
   lib/mktime.c
+  lib/openat-priv.h
+  lib/openat-proc.c
+  lib/openat.h
   lib/pathmax.h
   lib/pselect.c
   lib/pthread_sigmask.c
   lib/putenv.c
   lib/readlink.c
+  lib/readlinkat.c
   lib/root-uid.h
   lib/sha1.c
   lib/sha1.h
@@ -746,6 +820,7 @@ AC_DEFUN([gl_FILE_LIST], [
   m4/c-strtod.m4
   m4/clock_time.m4
   m4/close-stream.m4
+  m4/dirent_h.m4
   m4/dup2.m4
   m4/environ.m4
   m4/euidaccess.m4
@@ -755,8 +830,10 @@ AC_DEFUN([gl_FILE_LIST], [
   m4/faccessat.m4
   m4/fcntl-o.m4
   m4/fcntl_h.m4
+  m4/fdopendir.m4
   m4/filemode.m4
   m4/fpending.m4
+  m4/fstatat.m4
   m4/getgroups.m4
   m4/getloadavg.m4
   m4/getopt.m4
@@ -780,6 +857,7 @@ AC_DEFUN([gl_FILE_LIST], [
   m4/pthread_sigmask.m4
   m4/putenv.m4
   m4/readlink.m4
+  m4/readlinkat.m4
   m4/setenv.m4
   m4/sha1.m4
   m4/sha256.m4
diff --git a/m4/readlinkat.m4 b/m4/readlinkat.m4
new file mode 100644
index 00000000000..b2ff40dcb02
--- /dev/null
+++ b/m4/readlinkat.m4
@@ -0,0 +1,19 @@
+# serial 3
+# See if we need to provide readlinkat replacement.
+
+dnl Copyright (C) 2009-2013 Free Software Foundation, Inc.
+dnl This file is free software; the Free Software Foundation
+dnl gives unlimited permission to copy and/or distribute it,
+dnl with or without modifications, as long as this notice is preserved.
+
+# Written by Eric Blake.
+
+AC_DEFUN([gl_FUNC_READLINKAT],
+[
+  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+  AC_CHECK_FUNCS_ONCE([readlinkat])
+  if test $ac_cv_func_readlinkat = no; then
+    HAVE_READLINKAT=0
+  fi
+])