http://bugs.gentoo.org/250342

 http://sources.redhat.com/bugzilla/show_bug.cgi?id=9685

 we cant assume sock_cloexec and pipe2 are bound together as the former defines

 are found in glibc only while the latter are a combo of kernel headers and

 glibc.  so if we do a runtime detection of SOCK_CLOEXEC, but pipe2() is a stub

 inside of glibc, we hit a problem.  for example:

 #include <grp.h>

 #include <stdio.h>

 main()

 {

 	getgrnam("portage");

 	if (!popen("ls", "r"))

 		perror("popen()");

 }

 getgrnam() will detect that the kernel supports SOCK_CLOEXEC and then set both

 __have_sock_cloexec and __have_pipe2 to true.  but if glibc was built against

 older kernel headers where __NR_pipe2 does not exist, glibc will have a ENOSYS

 stub for it.  so popen() will always fail as glibc assumes pipe2() works.

 diff -durN glibc-2.10.1.orig/include/unistd.h glibc-2.10.1/include/unistd.h

 --- glibc-2.10.1.orig/include/unistd.h	2008-07-27 20:23:17.000000000 +0200

 +++ glibc-2.10.1/include/unistd.h	2009-11-13 00:50:15.000000000 +0100

 @@ -167,9 +167,6 @@

  extern int __pause_nocancel (void) attribute_hidden;

  extern int __have_sock_cloexec;

 -/* At lot of other functionality became available at the same time as

 -   SOCK_CLOEXEC.  Avoid defining separate variables for all of them

 -   unless it is really necessary.  */

 -#define __have_pipe2 __have_sock_cloexec

 +extern int __have_pipe2;

  #endif

 diff -durN glibc-2.10.1.orig/socket/have_sock_cloexec.c glibc-2.10.1/socket/have_sock_cloexec.c

 --- glibc-2.10.1.orig/socket/have_sock_cloexec.c	2008-07-25 18:46:23.000000000 +0200

 +++ glibc-2.10.1/socket/have_sock_cloexec.c	2009-11-13 00:50:15.000000000 +0100

 @@ -16,9 +16,14 @@

     Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA

     02111-1307 USA.  */

 +#include <fcntl.h>

  #include <sys/socket.h>

  #include <kernel-features.h>

  #if defined SOCK_CLOEXEC && !defined __ASSUME_SOCK_CLOEXEC

  int __have_sock_cloexec;

  #endif

 +

 +#if defined O_CLOEXEC && !defined __ASSUME_PIPE2

 +int __have_pipe2;

 +#endif