[PATCH] linkat: avoid OS X 10.10 trailing slash with symlink bug

[Pádraig Brady]

On Darwin 14.3.0 linkat(,"path1",,"dangling_symlink/",)
causes the symlink to be dereferenced, and if it points
to a non existent file, that file will be created as
a hard link to "path1".
This fixes a test failure in test-linkat.c.

* m4/linkat.m4 (gl_FUNC_LINKAT): Augment the test with
this case.  The existing workaround in linkat.c for
trailing slash issues, suffices for this case.
* doc/posix-functions/linkat.texi: Add OS X 10.10 to
the list of platforms with trailing slash issues.
---
 ChangeLog                       | 14 ++++++++++++++
 doc/posix-functions/linkat.texi |  2 +-
 m4/linkat.m4                    | 14 ++++++++++++--
 3 files changed, 27 insertions(+), 3 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 035fb7a..82abe7f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2015-05-29  Pádraig Brady  <address@hidden>
+
+       linkat: avoid OS X 10.10 trailing slash with symlink bug
+       On Darwin 14.3.0 linkat(,"path1",,"dangling_symlink/",)
+       causes the symlink to be dereferenced, and if it points
+       to a non existent file, that file will be created as
+       a hard link to "path1".
+       This fixes a test failure in test-linkat.c.
+       * m4/linkat.m4 (gl_FUNC_LINKAT): Augment the test with
+       this case.  The existing workaround in linkat.c for
+       trailing slash issues, suffices for this case.
+       * doc/posix-functions/linkat.texi: Add OS X 10.10 to
+       the list of platforms with trailing slash issues.
+
 2015-05-28  Pádraig Brady  <address@hidden>
 
        unlinkat: handle ignoring of ".." on Darwin 14
diff --git a/doc/posix-functions/linkat.texi b/doc/posix-functions/linkat.texi
index fadb350..8bdf9d3 100644
--- a/doc/posix-functions/linkat.texi
+++ b/doc/posix-functions/linkat.texi
@@ -19,7 +19,7 @@ Mac OS X 10.10.
 @item
 This function fails to reject trailing slashes on non-directories on
 some platforms:
-AIX 7.1, Solaris 11 2011-11.
+AIX 7.1, Solaris 11 2011-11, Mac OS X 10.10.
 @item
 This functions does not support @code{AT_SYMLINK_FOLLOW} on some platforms:
 Linux kernel 2.6.17.
diff --git a/m4/linkat.m4 b/m4/linkat.m4
index 567cb5d..03cf23a 100644
--- a/m4/linkat.m4
+++ b/m4/linkat.m4
@@ -52,7 +52,7 @@ AC_DEFUN([gl_FUNC_LINKAT],
 
     AC_CACHE_CHECK([whether linkat handles trailing slash correctly],
       [gl_cv_func_linkat_slash],
-      [rm -rf conftest.a conftest.b conftest.c conftest.d
+      [rm -rf conftest.a conftest.b conftest.c conftest.d conftest.e conftest.s
        AC_RUN_IFELSE(
          [AC_LANG_PROGRAM(
             [[#include <unistd.h>
@@ -83,6 +83,16 @@ AC_DEFUN([gl_FUNC_LINKAT],
               if (linkat (AT_FDCWD, "conftest.a", AT_FDCWD, "conftest.d/",
                           AT_SYMLINK_FOLLOW) == 0)
                 result |= 8;
+
+              /* On OS X 10.10 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],
@@ -93,7 +103,7 @@ AC_DEFUN([gl_FUNC_LINKAT],
             *)      gl_cv_func_linkat_slash="guessing no";;
           esac
          ])
-       rm -rf conftest.a conftest.b conftest.c conftest.d])
+       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 ;;
-- 
2.4.1