bug in freopen

[Eric Blake]

POSIX requires that freopen(NULL, mode, f) reopen f in the new
mode, and allows implementations the option of not even closing
f in the first place.  But in cygwin, it is failing with EFAULT, which is
not even one of the errors allowed by POSIX.

http://www.opengroup.org/susv3xsh/freopen.html

#include <stdio.h>
#include <errno.h>
int main(void)
{
   FILE* f = freopen (NULL, "rb", stdin); /* Ensure that stdin is binary */
   printf ("file is %s, errno %d:%s\n", f ? "good" : "null", errno,
           strerror(errno));
   return 0;
}

CVS coreutils recently switched to this idiom, replacing its former
use of the nonstandard <io.h> and setmode() with something
that is required by the standards.  But until this bug is fixed, CVS
coreutils will not work with cygwin.  The strace in cygwin shows
that newlib tried to perform open(NULL), which is the cause of
the EFAULT.

--
Eric Blake

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