Re: mingw fopen bug

[Eric Blake]

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According to Bruno Haible on 9/22/2008 6:15 PM:
> But fopen() on a directory? Who does that? If no-one needs that, I would be
> satisfied with mentioning the problem under "Portability problems not fixed by
> Gnulib" in the doc.

The use case where I discovered this bug was with m4 1.4.11.  Compare:

mingw$ m4 .
m4.exe: .: Permission denied
Linux$ m4 .
m4:/:1: Read error
OpenBSD$ m4 . && echo done
done
EMX$ m4 .
<starts trying to interpret struct dirent records as m4 input>

In an effort to unify this behavior, I was considering making m4 1.4.12
pre-reject directories with EISDIR (POSIX allows this, since directories
are not text files, and m4 is only required to operate on text files),
while remembering that doing stat() prior to fopen() is racy.  For most
systems, the inadvertent selection of a directory by fopen (usually with a
name less obvious than '.') can then be detected with fstat(fileno(f)),
but with mingw, the fopen never succeeded in the first place.  So it boils
down to a question of making the m4 test suite accommodate two different
errno values (doable, but not trivial in the current test setup), or work
around the mingw discrepancy so that the fopen always succeeds on a
readable directory (trivial for m4, but more complex in gnulib).  But
either way, the end result is that any attempt to make m4 read a directory
will uniformly result in an error (I really don't like the fact that BSD
treats reads of a directory as an empty file, and gives a 0 exit status,
and the EMX behavior of reading binary contents isn't much better).

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
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