linux-kernel - Re: [BUG] Generic syscalls -- chmod vs. fchmodat

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Message-Id: <201101252104.58011.arnd@arndb.de>
Date:	Tue, 25 Jan 2011 21:04:57 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Roland McGrath <roland@...hat.com>
Cc:	linasvepstas@...il.com, Chris Metcalf <cmetcalf@...era.com>,
	GLIBC Devel <libc-alpha@...rceware.org>,
	linux-kernel@...r.kernel.org, libc-ports@...rceware.org,
	linux-api@...r.kernel.org, Mike Frysinger <vapier@...too.org>
Subject: Re: [BUG] Generic syscalls -- chmod vs. fchmodat

On Tuesday 25 January 2011 19:34:37 Roland McGrath wrote:
> I don't think this was part of the original intent when the calls were
> added, but I suppose it makes sense.

More importantly, even if it was never meant this way, anyone could have
assumed that it was and started using the system call in this way.

> > Treating the empty string special for AT_FDCWD is rather pointless, but
> > at least consistent.
> 
> I agree about the consistency point.  However, one could also call it
> consistent if the empty string fails to resolve when operating on either a
> directory file descriptor or AT_FDCWD but works on a non-directory file
> descriptor. 

Yes.

> POSIX does not mandate that *at calls fail with ENOTDIR when
> passed a non-directory file descriptor (it's a "may fail" error, not a
> "shall fail" error).  So that behavior would be consistent both with the
> POSIX requirements as I read them, and with the desire you mentioned to let
> the fblahat system call serve to implement fblah as well as blah.  Then
> libc would not have to wrap the *at calls with any special check to conform
> to POSIX.

Makes sense.

	Arnd
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