Re: [PATCH] fcntl-h: default O_SEARCH, O_EXEC to O_PATH if available

[Paul Eggert]

On 11/07/2012 11:34 PM, Jim Meyering wrote:
>     + mkdir -mu=rwx,g=rx,o=w,-s,+t t
>     mkdir: cannot change permissions of 't': Bad file descriptor

Thanks for mentioning that.  Yes, the O_PATH was the culprit.
I backed out most of it, as follows.  Arguably this is a
Linux kernel bug with fchmod.

>From f859fdddb8e8c7535fbba06b5c5729ee0e96db1b Mon Sep 17 00:00:00 2001
From: Paul Eggert <address@hidden>
Date: Thu, 8 Nov 2012 01:23:20 -0800
Subject: [PATCH] fcntl-h: default O_SEARCH, O_EXEC back to O_RDONLY

O_PATH doesn't work with Linux kernel 3.6.5, as fchmod (fd, ...)
fails with errno == EBADF when fd is opened with O_PATH.
Reported by Jim Meyering in
<http://lists.gnu.org/archive/html/bug-gnulib/2012-11/msg00026.html>.
* doc/posix-headers/fcntl.texi (fcntl.h): Document this.
* lib/fcntl.in.h (O_EXEC, O_SEARCH) [O_PATH]: Default back to O_RDONLY.
---
 ChangeLog                    | 10 ++++++++++
 doc/posix-headers/fcntl.texi |  7 ++++---
 lib/fcntl.in.h               | 12 ++----------
 3 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index bd05f3c..9817769 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,13 @@
+2012-11-08  Paul Eggert  <address@hidden>
+
+       fcntl-h: default O_SEARCH, O_EXEC back to O_RDONLY
+       O_PATH doesn't work with Linux kernel 3.6.5, as fchmod (fd, ...)
+       fails with errno == EBADF when fd is opened with O_PATH.
+       Reported by Jim Meyering in
+       <http://lists.gnu.org/archive/html/bug-gnulib/2012-11/msg00026.html>.
+       * doc/posix-headers/fcntl.texi (fcntl.h): Document this.
+       * lib/fcntl.in.h (O_EXEC, O_SEARCH) [O_PATH]: Default back to O_RDONLY.
+
 2012-11-07  Paul Eggert  <address@hidden>
 
        test-utimens: speed up by taking shorter naps
diff --git a/doc/posix-headers/fcntl.texi b/doc/posix-headers/fcntl.texi
index 4a75a54..7366513 100644
--- a/doc/posix-headers/fcntl.texi
+++ b/doc/posix-headers/fcntl.texi
@@ -28,9 +28,10 @@ non-zero value; otherwise, the gnulib replacement is 0.
 
 @item
 @samp{O_EXEC} and @samp{O_SEARCH} are not defined on some platforms.
-On platforms such as GNU/Linux 2.6.39 and later that have @samp{O_PATH},
-Gnulib defines these macros to @samp{O_PATH}.
-On other platforms, it defines them to @samp{O_RDONLY}, which is typically 0.
+Gnulib defines these macros to @samp{O_RDONLY}, which is typically 0.
+The @samp{O_PATH} macro of GNU/Linux is not a suitable substitute, as
+fchmod fails with @samp{errno==EBADF} when invoked on a file
+descriptor that was opened with @samp{O_PATH}.
 
 @item
 @samp{O_ACCMODE} is not defined on some platforms:
diff --git a/lib/fcntl.in.h b/lib/fcntl.in.h
index fb402ee..604c31b 100644
--- a/lib/fcntl.in.h
+++ b/lib/fcntl.in.h
@@ -213,11 +213,7 @@ _GL_WARN_ON_USE (openat, "openat is not portable - "
 #endif
 
 #ifndef O_EXEC
-# ifdef O_PATH
-#  define O_EXEC O_PATH
-# else
-#  define O_EXEC O_RDONLY /* This is often close enough in older systems.  */
-# endif
+# define O_EXEC O_RDONLY /* This is often close enough in older systems.  */
 #endif
 
 #ifndef O_IGNORE_CTTY
@@ -274,11 +270,7 @@ _GL_WARN_ON_USE (openat, "openat is not portable - "
 #endif
 
 #ifndef O_SEARCH
-# ifdef O_PATH
-#  define O_SEARCH O_PATH
-# else
-#  define O_SEARCH O_RDONLY /* This is often close enough in older systems.  */
-# endif
+# define O_SEARCH O_RDONLY /* This is often close enough in older systems.  */
 #endif
 
 #ifndef O_SYNC
-- 
1.7.11.7