Date: Thu, 29 Dec 2005 05:30:08 GMT From: David Xu <davidxu@freebsd.org> To: freebsd-threads@FreeBSD.org Subject: Re: threads/79887: [patch] freopen() isn't thread-safe Message-ID: <200512290530.jBT5U8qX071114@freefall.freebsd.org>
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The following reply was made to PR threads/79887; it has been noted by GNATS.
From: David Xu <davidxu@freebsd.org>
To: Dmitrij Tejblum <tejblum@yandex-team.ru>
Cc: bug-followup@freebsd.org
Subject: Re: threads/79887: [patch] freopen() isn't thread-safe
Date: Thu, 29 Dec 2005 13:26:03 +0800
Dmitrij Tejblum wrote:
>
> 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 we allow _close and others to be changed by user code unless
someone can clarify that this is not allowed now, otherwise your
assumption is false.
>> 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.
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