According to POSIX, open(".",O_RDONLY) must succeed. And if I'm reading POSIX
correctly, fopen(".","r") must also succeed, since it should have the same
effect as open(".",O_RDONLY). It is only on subsequent attempts to read() from
a directory that POSIX then allows, but not requires, a failure of EISDIR (at
least Linux, Solaris, and cygwin make read() of a directory fail with EISDIR;
OpenBSD allows the read() to succeed but always with 0 bytes [ie. the directory
is indistinguishable from an empty file], and older platforms, such as Elbert
Pol's report for EMX os/2, actually read raw bytes that could then be used to
populate struct dirent).
But on mingw, fopen(".","r") fails with EACCES. Is it worth trying to enhance
the gnulib fopen module to work around this bug, possibly in tandem with
dirfd/fdopendir replacements (fchdir module), such that mingw can be made to
open a FILE stream around a directory, even though such a stream cannot be
directly read from? Adding such a workaround would allow code like this to
work on mingw:
FILE *f = fopen (".", "r");
DIR *d = fdopendir (fileno (f));
readdir (d);
although that seems a bit contrived (why not use opendir() in the first place?).
