1 files changed, 128 insertions, 0 deletions
diff --git a/m4/linkat.m4 b/m4/linkat.m4
new file mode 100644
index 0000000..2a6f83b
--- /dev/null
+++ b/m4/linkat.m4
@@ -0,0 +1,128 @@
+# serial 14
+# See if we need to provide linkat replacement.
+
+dnl Copyright (C) 2009-2022 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_LINKAT],
+[
+  AC_REQUIRE([gl_FUNC_OPENAT])
+  AC_REQUIRE([gl_FUNC_LINK_FOLLOWS_SYMLINK])
+  AC_REQUIRE([gl_UNISTD_H_DEFAULTS])
+  AC_REQUIRE([gl_USE_SYSTEM_EXTENSIONS])
+  AC_REQUIRE([AC_CANONICAL_HOST]) dnl for cross-compiles
+  AC_CHECK_FUNCS_ONCE([linkat symlink])
+  if test $ac_cv_func_linkat = no; then
+    HAVE_LINKAT=0
+  else
+    dnl OS X Yosemite has linkat() but it's not sufficient
+    dnl to our needs since it doesn't support creating
+    dnl hardlinks to symlinks.  Therefore check for that
+    dnl capability before considering using the system version.
+    AC_CACHE_CHECK([whether linkat() can link symlinks],
+      [gl_cv_func_linkat_nofollow],
+      [rm -rf conftest.l1 conftest.l2
+       ln -s target conftest.l1
+       AC_RUN_IFELSE([AC_LANG_PROGRAM(
+                        [[#include <fcntl.h>
+                          #include <unistd.h>
+                        ]],
+                        [[return linkat (AT_FDCWD, "conftest.l1", AT_FDCWD,
+                                         "conftest.l2", 0);
+                        ]])],
+         [gl_cv_func_linkat_nofollow=yes],
+         [gl_cv_func_linkat_nofollow=no],
+         [case "$host_os" in
+           darwin*) gl_cv_func_linkat_nofollow="guessing no" ;;
+           *)       gl_cv_func_linkat_nofollow="guessing yes" ;;
+          esac])
+
+       rm -rf conftest.l1 conftest.l2])
+
+    case $gl_cv_func_linkat_nofollow in
+      *no) LINKAT_SYMLINK_NOTSUP=1 ;;
+      *yes) LINKAT_SYMLINK_NOTSUP=0 ;;
+    esac
+
+    AC_CACHE_CHECK([whether linkat handles trailing slash correctly],
+      [gl_cv_func_linkat_slash],
+      [rm -rf conftest.a conftest.b conftest.c conftest.d conftest.e conftest.s
+       AC_RUN_IFELSE(
+         [AC_LANG_PROGRAM(
+            [[#include <unistd.h>
+              #include <fcntl.h>
+              #include <errno.h>
+              #include <stdio.h>
+            ]GL_MDA_DEFINES],
+            [[int result;
+              int fd;
+              /* Create a regular file.  */
+              fd = open ("conftest.a", O_CREAT | O_EXCL | O_WRONLY, 0600);
+              if (fd < 0)
+                return 1;
+              if (write (fd, "hello", 5) < 5)
+                return 2;
+              if (close (fd) < 0)
+                return 3;
+              /* Test whether hard links are supported on the current
+                 device.  */
+              if (linkat (AT_FDCWD, "conftest.a", AT_FDCWD, "conftest.b",
+                          AT_SYMLINK_FOLLOW) < 0)
+                return 0;
+              result = 0;
+              /* Test whether a trailing "/" is treated like "/.".  */
+              if (linkat (AT_FDCWD, "conftest.a/", AT_FDCWD, "conftest.c",
+                          AT_SYMLINK_FOLLOW) == 0)
+                result |= 4;
+              if (linkat (AT_FDCWD, "conftest.a", AT_FDCWD, "conftest.d/",
+                          AT_SYMLINK_FOLLOW) == 0)
+                result |= 8;
+
+              /* On Mac OS X 10.13 a trailing "/" will cause the second path to be
+                 dereferenced, and thus will succeed on a dangling symlink.  */
+              if (symlink ("conftest.e", "conftest.s") == 0)
+                {
+                  if (linkat (AT_FDCWD, "conftest.a", AT_FDCWD, "conftest.s/",
+                      AT_SYMLINK_FOLLOW) == 0)
+                    result |= 16;
+                }
+
+              return result;
+            ]])],
+         [gl_cv_func_linkat_slash=yes],
+         [gl_cv_func_linkat_slash=no],
+         [
+          case "$host_os" in
+                             # Guess yes on Linux systems.
+            linux-* | linux) gl_cv_func_linkat_slash="guessing yes";;
+                             # Guess yes on glibc systems.
+            *-gnu* | gnu*)   gl_cv_func_linkat_slash="guessing yes";;
+                             # If we don't know, obey --enable-cross-guesses.
+            *)               gl_cv_func_linkat_slash="$gl_cross_guess_normal";;
+          esac
+         ])
+       rm -rf conftest.a conftest.b conftest.c conftest.d conftest.e conftest.s])
+    case "$gl_cv_func_linkat_slash" in
+      *yes) gl_linkat_slash_bug=0 ;;
+      *)    gl_linkat_slash_bug=1 ;;
+    esac
+
+    case "$gl_cv_func_linkat_nofollow" in
+      *yes) linkat_nofollow=yes ;;
+      *) linkat_nofollow=no ;;
+    esac
+
+    if test "$linkat_nofollow" != yes \
+       || test $gl_linkat_slash_bug = 1; then
+      REPLACE_LINKAT=1
+      AC_DEFINE_UNQUOTED([LINKAT_TRAILING_SLASH_BUG], [$gl_linkat_slash_bug],
+        [Define to 1 if linkat fails to recognize a trailing slash.])
+      AC_DEFINE_UNQUOTED([LINKAT_SYMLINK_NOTSUP], [$LINKAT_SYMLINK_NOTSUP],
+        [Define to 1 if linkat can create hardlinks to symlinks])
+    fi
+  fi
+])