Date: Thu, 29 Dec 2005 05:20:07 GMT From: Dmitrij Tejblum <tejblum@yandex-team.ru> To: freebsd-threads@FreeBSD.org Subject: Re: threads/79887: [patch] freopen() isn't thread-safe Message-ID: <200512290520.jBT5K74e070718@freefall.freebsd.org>
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The following reply was made to PR threads/79887; it has been noted by GNATS.
From: Dmitrij Tejblum <tejblum@yandex-team.ru>
To: David Xu <davidxu@freebsd.org>
Cc: bug-followup@freebsd.org
Subject: Re: threads/79887: [patch] freopen() isn't thread-safe
Date: Thu, 29 Dec 2005 08:12:58 +0300
David Xu wrote:
> Indeed, this a bug, but the patch you provided breaks the samentic the
> FILE structure was designed for, here you conditionally call
> fp->_close(), this is incorrect, because the hook may be an external
> function, it should always be called to notify external code.
I only assume that
1) _file and _close fields are internal to stdio, i.e. only stdio code
manipulate with them directly
2) If _file != -1, then the FILE is associated with the file descriptor,
fp->_close == __sclose (because the only code that can set fp_close to
something different is funopen, and it set _file to -1) and __sclose
just close the _fp->_file
If so, we know that dup2() will close the descriptor too, dup2() is
required to do it.
> I think the right fix is to fix those code which is still using
> STDERR_FILENO, or don't do following hack in freopen.c:
> if (wantfd >= 0 && f != wantfd) {
> if (_dup2(f, wantfd) >= 0) {
> (void)_close(f);
> f = wantfd;
> }
> }
> This is not required by standard.
Well, I tried to keep existing behaviour, and I think that the hack is
indeed a good idea even though it is not required.
>
>
> David Xu
>
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