Re: fdopendir incompatibility with POSIX, with proposed patch

[Eric Blake]

On 09/12/2010 04:18 PM, Paul Eggert wrote:
> While coding up recent changes to GNU tar, I discovered a
> POSIX-emulation problem in gnulib's implementation of fdopendir.
> I had written code like this:
>
>
>         DIR *dp = fdopendir (fd);
>         int fd1 = openat (fd, "subdir", O_RDONLY);
>
> This works with POSIX fdopendir,

Technically, our previous implementation _is_ POSIX-compliant - POSIX 
does not require that dirfd(fdopendir(fd))==fd.  But I can see how it is 
confusing, and how wrapping DIR around the desired fd makes coding much 
easier.

> How about the following patch to help ameliorate this problem?  It
> would have fixed the bug for GNU tar, anyway.  (I have reworked GNU
> tar to use a different approach, so this patch is not needed for GNU
> tar, but still it should help avoid future gotchas like this.)  This
> patch won't work in general (multithreaded apps, signal handers) but
> it should work for single-threaded apps whose signal handers don't open
> or close files.

Looks good to me!

--
Eric Blake   address@hidden    +1-801-349-2682
Libvirt virtualization library http://libvirt.org