[Buildroot] [PATCH] Raspberry Pi - WiringPi Library Package
Carsten Schoenert
c.schoenert at gmail.com
Thu Jul 11 07:42:28 UTC 2013
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
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