From mboxrd@z Thu Jan  1 00:00:00 1970
From: Carsten Schoenert <c.schoenert@gmail.com>
Date: Thu, 11 Jul 2013 09:42:28 +0200
Subject: [Buildroot] [PATCH] Raspberry Pi - WiringPi Library Package
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To: buildroot@busybox.net

Hello Guillermo,

Am 11.07.2013 08:38, schrieb Guillermo A. Amaral:
> I searched around for alternative ways around the issue when I first
> encountered it, it seemed no-oping it would be most portable/safest approach.

The O_CLOEXEC variable was introduced in 2.6.23.

>        O_CLOEXEC (Since Linux 2.6.23)
>               Enable the close-on-exec flag for the new file descriptor.
>               Specifying this flag permits a program to avoid additional
>               fcntl(2) F_SETFD operations to set the FD_CLOEXEC flag.
>               Additionally, use of this flag is essential in some
>               multithreaded programs since using a separate fcntl(2) F_SETFD
>               operation to set the FD_CLOEXEC flag does not suffice to avoid
>               race conditions where one thread opens a file descriptor at
>               the same time as another thread does a fork(2) plus execve(2).

So if you use a kernel less then 2.6.23 it make no sense to define
O_CLOEXEC to whatever you want, the kernel doesn't know this. And in the
opposite you can't defined it to some different then already defined for
O_CLOEXEC.

The function 'open' can also used without the 3rd parameter.

So I think you have to check which kernel version is used and build a
patch which does something like

#ifdef KERNEL_VER < 2_6_23
  if ((fd = open ("/dev/mem", O_RDWR | O_SYNC) ) < 0)
#else
  if ((fd = open ("/dev/mem", O_RDWR | O_SYNC | O_CLOEXEC) ) < 0)
#endif

The guys from linux-wireless do a lot of this to get the wireless
package working om different kernel versions.

Regards
Carsten