(jm_AC_FUNC_LINK_FOLLOWS_SYMLINK): New file/macro.

diff --git a/m4/link-follow.m4 b/m4/link-follow.m4
new file mode 100644 (file)
index 0000000..a57ab88
--- /dev/null
+++ b/m4/link-follow.m4
@@ -0,0 +1,55 @@
+#serial 1
+dnl Run a program to determine whether whether link(2) follows symlinks.
+dnl Set LINK_FOLLOWS_SYMLINKS accordingly.
+
+AC_DEFUN(jm_AC_FUNC_LINK_FOLLOWS_SYMLINK,
+[dnl
+  AC_CACHE_CHECK([whether link(2) follows symlinks],
+                jm_ac_cv_func_link_follows_symlink,
+  [
+    # Create a regular file, `conftest.file'.
+    echo > conftest.file
+    AC_TRY_RUN(
+      [
+#       include <sys/types.h>
+#       include <sys/stat.h>
+#       ifdef HAVE_UNISTD_H
+#        include <unistd.h>
+#       endif
+
+#       define SAME_INODE(Stat_buf_1, Stat_buf_2) \
+         ((Stat_buf_1).st_ino == (Stat_buf_2).st_ino \
+          && (Stat_buf_1).st_dev == (Stat_buf_2).st_dev)
+
+       int
+       main ()
+       {
+         const char *file = "conftest.file";
+         const char *sym = "conftest.sym";
+         const char *hard = "conftest.hard";
+         struct stat sb_file, sb_hard;
+
+         /* Create a symlink `conftest.sym' to it. */
+         if (symlink (file, sym))
+           abort ();
+
+         /* Create a hard link `conftest.hard' to that symlink.  */
+         if (link (sym, hard))
+           abort ();
+
+         if (lstat (hard, &sb_hard))
+           abort ();
+         if (lstat (file, &sb_file))
+           abort ();
+
+         /* If the dev/inode of hard and file are the same, then
+            the link call followed the symlink.  */
+         return SAME_INODE (sb_hard, sb_file) ? 0 : 1;
+       }
+      ],
+      jm_ac_cv_func_link_follows_symlink=yes,
+      jm_ac_cv_func_link_follows_symlink=no,
+      jm_ac_cv_func_link_follows_symlink=yes, We're cross compiling.
+    )
+  ])
+])