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Date: Fri, 08 Apr 2016 00:48:57 +0200
From: "Juan Manuel Guerrero (juan DOT guerrero AT gmx DOT de) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
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To: djgpp AT delorie DOT com
Subject: Re: Different dup2 behaviour between DOS/DJGPP and posix.
References: <5706CAFA DOT 1060201 AT gmx DOT de>
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Reply-To: djgpp AT delorie DOT com

Am 07.04.2016 23:02, schrieb Juan Manuel Guerrero (juan DOT guerrero AT gmx DOT de) [via djgpp AT delorie DOT com]:
[snip]
> The question is why DOS/DJGPP allows to close STDIN and reopen it with FD 0
> meanwhile posix seems not to allow this. Is this behaviour expected?
> I have inspected the code of dup2 and the implementation seems OK.
>
> The consequence of this check is that Autoconf assumes that DJGPP's dup2
> implementaion does not work.


OK I think I have got it.  It is a bug in the DJGPP implementation of dup2.
According to http://pubs.opengroup.org/onlinepubs/009695399/functions/dup.html
The dup2() function shall fail if:

[EBADF]
     The fildes argument is not a valid open file descriptor or the argument fildes2 is negative or greater than or equal to {OPEN_MAX}.


The current implementation checks first if fd == newfd and if this is the case
it returns inmediatly with newfd.  Here some fix will be required because no one
of the 3 conditions are checked.  May be these error conditions were not in effect
in those days when dup2 was implemented.


Regards,
Juan M. Guerrero