1 files changed, 95 insertions, 0 deletions
diff --git a/m4/linkat.m4 b/m4/linkat.m4
new file mode 100644
index 00000000..b0b7d7bd
--- /dev/null
+++ b/m4/linkat.m4
@@ -0,0 +1,95 @@
+# serial 6
+# See if we need to provide linkat replacement.
+
+dnl Copyright (C) 2009-2012 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])
+  AC_CHECK_HEADERS_ONCE([sys/param.h])
+  if test $ac_cv_func_linkat = no; then
+    HAVE_LINKAT=0
+  else
+    AC_CACHE_CHECK([whether linkat(,AT_SYMLINK_FOLLOW) works],
+      [gl_cv_func_linkat_follow],
+      [rm -rf conftest.f1 conftest.f2
+       touch conftest.f1
+       AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
+#include <fcntl.h>
+#include <unistd.h>
+#ifdef __linux__
+/* Linux added linkat in 2.6.16, but did not add AT_SYMLINK_FOLLOW
+   until 2.6.18.  Always replace linkat to support older kernels.  */
+choke me
+#endif
+]], [return linkat (AT_FDCWD, "conftest.f1", AT_FDCWD, "conftest.f2",
+                    AT_SYMLINK_FOLLOW);])],
+         [gl_cv_func_linkat_follow=yes],
+         [gl_cv_func_linkat_follow="need runtime check"])
+       rm -rf conftest.f1 conftest.f2])
+    AC_CACHE_CHECK([whether linkat handles trailing slash correctly],
+      [gl_cv_func_linkat_slash],
+      [rm -rf conftest.a conftest.b conftest.c conftest.d
+       AC_RUN_IFELSE(
+         [AC_LANG_PROGRAM(
+            [[#include <unistd.h>
+              #include <fcntl.h>
+              #include <errno.h>
+              #include <stdio.h>
+            ]],
+            [[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;
+              return result;
+            ]])],
+         [gl_cv_func_linkat_slash=yes],
+         [gl_cv_func_linkat_slash=no],
+         [# Guess yes on glibc systems, no otherwise.
+          case "$host_os" in
+            *-gnu*) gl_cv_func_linkat_slash="guessing yes";;
+            *)      gl_cv_func_linkat_slash="guessing no";;
+          esac
+         ])
+       rm -rf conftest.a conftest.b conftest.c conftest.d])
+    case "$gl_cv_func_linkat_slash" in
+      *yes) gl_linkat_slash_bug=0 ;;
+      *)    gl_linkat_slash_bug=1 ;;
+    esac
+    if test "$gl_cv_func_linkat_follow" != 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.])
+    fi
+  fi
+])