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Date:	Sun, 23 Oct 2016 09:04:52 +0300
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From:	"Eli Zaretskii (eliz AT gnu DOT org) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
To:	djgpp AT delorie DOT com
In-reply-to:	<580BCAA5.2000304@gmx.de> (djgpp@delorie.com)
Subject:	Re: A grep 2.26 test fails because fopen sets errno to EACCES when openning
	an existing directory.
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> Date: Sat, 22 Oct 2016 22:23:01 +0200
> From: "Juan Manuel Guerrero (juan DOT guerrero AT gmx DOT de) [via djgpp AT delorie DOT com]" <djgpp AT delorie DOT com>
> 
> While I was trying to port grep 2.26 I have observed that the implementation of
> open retains errno to values that are generated by intermediary operations even
> if the open operation performs well.
> In this particular case an existing directory shall be open but errno is set to
> EACCES by some DOS call and passed to the calling context that later uses this
> errno to generate an error message.  This is wrong IMHO.

That's what DOS returns when you try to open a directory.

> The calling context
> is the grep code and not the djgpp library code.  The documentation of the open
> function clearly states that is at least possible to use the open function to
> open a directory.

Not on DOS, AFAIK.

> Thus no errno number should be set as consequence of this
> call if the directory exists.  And this is the way linux works.

On Unix, it is indeed possible to open a directory.  But not on DOS.

I see we've made 'open' to be able to do that, but '_open' should
still error out with EACCES, because that's what DOS does.  Not sure
if your patch changes that.

> I have changed fread and fwrite to return with EISDIR if the file pointer
> corresponds to a directory

I don't think EISDIR is right in this case, because Posix doesn't
define that as one of the errno values returned by these functions.  I
think EBADF or ENXIO are better alternatives.

> Of course, after having compiled grep with a changed library, the
> check passes because fopen no longer fails with EACCES but the later
> fread fails with EISDIR as it shall.

Why does the test assume fread will fail with EISDIR?  It doesn't on
Unix, AFAIK.

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