O_CLOEXEC not always available...

[antijn]

O_CLOEXEC is relatively new (for some definition of new), it was included in POSIX 2008. It was available earlier on Linux, but only if _GNU_SOURCE was defined.

This leads to libugpio failing to compile for some environments, my Debian Squeeze box for example:
/bin/sh ../libtool --tag=CC --mode=compile gcc -DHAVE_CONFIG_H -I. -I.. -g -O2 -MT gpio.lo -MD -MP -MF .deps/gpio.Tpo -c -o gpio.lo gpio.c
libtool: compile: gcc -DHAVE_CONFIG_H -I. -I.. -g -O2 -MT gpio.lo -MD -MP -MF .deps/gpio.Tpo -c gpio.c -fPIC -DPIC -o .libs/gpio.o
gpio.c: In function ‘gpio_check’:
gpio.c:71: error: ‘O_CLOEXEC’ undeclared (first use in this function)
gpio.c:71: error: (Each undeclared identifier is reported only once
gpio.c:71: error: for each function it appears in.)
make[2]: *** [gpio.lo] Error 1

I can see three possible solutions:

1. Add a simple

   define _GNU_SOURCE

   before including fcntl.h
   This will only work on Linux (but hey, I don't think any other OS uses sysfs gpio... :-)

2. Add a:

   ifndef O_CLOEXEC

   define O_CLOEXEC 0

   endif

Will eliminate the compile error, but may disable O_CLOEXEC where it actually could work.

1. Do some autoconf magic (which I am not a master of)