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From: Roland McGrath <roland@redhat.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: linasvepstas@gmail.com, Chris Metcalf <cmetcalf@tilera.com>,
	GLIBC Devel <libc-alpha@sourceware.org>,
	linux-kernel@vger.kernel.org, libc-ports@sourceware.org,
	linux-api@vger.kernel.org, Mike Frysinger <vapier@gentoo.org>
Subject: Re: [BUG] Generic syscalls -- chmod vs. fchmodat
Date: Tue, 25 Jan 2011 09:45:15 -0800 (PST)	[thread overview]
Message-ID: <20110125174515.C1DC2183C19@magilla.sf.frob.com> (raw)
In-Reply-To: Arnd Bergmann's message of  Tuesday, 25 January 2011 15:29:24 +0100 <201101251529.24779.arnd@arndb.de>

> My feeling is that it should be in glibc: as Mike mentioned, we don't normally
> change the behavior of existing system calls unless they are obviously
> broken to start with. If we want to keep fchmodat getting the implicit
> "." directory, and at the same time keep fchmod returning an error, the fchmod
> wrapper around fchmodat is the only place that can enforce this.

My point was that it's quite arguable that the *at syscall interfaces were
broken to begin with.  I've never seen anything suggesting their intent was
other than to permit relative pathnames, and the empty string has never
been a valid relative pathname.  To fit the POSIX requirements as I read
them, the *at functions must refuse to resolve the empty string.  So if the
kernel does not change and my interpretation of POSIX stands, then libc
must wrap all the *at syscalls with a function that checks for the empty
string and fails with ENOENT as a special case.

I don't have any strong opinion about this subject, but it makes the most
sense to me for the kernel's behavior to change.  I know of no reason to
think that the current treatment of the empty string was ever intended at
the creation of the *at interfaces.


Thanks,
Roland

WARNING: multiple messages have this Message-ID (diff)
From: Roland McGrath <roland-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
Cc: linasvepstas-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org,
	Chris Metcalf <cmetcalf-kv+TWInifGbQT0dZR+AlfA@public.gmane.org>,
	GLIBC Devel <libc-alpha-9JcytcrH/bA+uJoB2kUjGw@public.gmane.org>,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	libc-ports-9JcytcrH/bA+uJoB2kUjGw@public.gmane.org,
	linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Mike Frysinger <vapier-aBrp7R+bbdUdnm+yROfE0A@public.gmane.org>
Subject: Re: [BUG] Generic syscalls -- chmod vs. fchmodat
Date: Tue, 25 Jan 2011 09:45:15 -0800 (PST)	[thread overview]
Message-ID: <20110125174515.C1DC2183C19@magilla.sf.frob.com> (raw)
In-Reply-To: Arnd Bergmann's message of  Tuesday, 25 January 2011 15:29:24 +0100 <201101251529.24779.arnd-r2nGTMty4D4@public.gmane.org>

> My feeling is that it should be in glibc: as Mike mentioned, we don't normally
> change the behavior of existing system calls unless they are obviously
> broken to start with. If we want to keep fchmodat getting the implicit
> "." directory, and at the same time keep fchmod returning an error, the fchmod
> wrapper around fchmodat is the only place that can enforce this.

My point was that it's quite arguable that the *at syscall interfaces were
broken to begin with.  I've never seen anything suggesting their intent was
other than to permit relative pathnames, and the empty string has never
been a valid relative pathname.  To fit the POSIX requirements as I read
them, the *at functions must refuse to resolve the empty string.  So if the
kernel does not change and my interpretation of POSIX stands, then libc
must wrap all the *at syscalls with a function that checks for the empty
string and fails with ENOENT as a special case.

I don't have any strong opinion about this subject, but it makes the most
sense to me for the kernel's behavior to change.  I know of no reason to
think that the current treatment of the empty string was ever intended at
the creation of the *at interfaces.


Thanks,
Roland

  reply	other threads:[~2011-01-25 17:45 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2011-01-24 19:57 [BUG] Generic syscalls -- chmod vs. fchmodat Linas Vepstas
2011-01-24 21:05 ` Roland McGrath
2011-01-24 21:32   ` Mike Frysinger
2011-01-25 14:29 ` Arnd Bergmann
2011-01-25 14:29   ` Arnd Bergmann
2011-01-25 17:45   ` Roland McGrath [this message]
2011-01-25 17:45     ` Roland McGrath
2011-01-25 18:21     ` Arnd Bergmann
2011-01-25 18:21       ` Arnd Bergmann
2011-01-25 18:34       ` Roland McGrath
2011-01-25 18:34         ` Roland McGrath
2011-01-25 20:04         ` Arnd Bergmann
2011-01-25 20:04           ` Arnd Bergmann
2011-01-25 18:52       ` Mike Frysinger
2011-01-25 18:52         ` Mike Frysinger
2011-01-25 19:56         ` Eric Blake
2011-01-25 19:56           ` Eric Blake
2011-01-25 20:31           ` Eric Blake
2011-01-25 20:31             ` Eric Blake
2011-01-25 21:32             ` Eric Blake
2011-01-25 21:32               ` Eric Blake
2011-01-25 22:10               ` Linas Vepstas
2011-02-10 18:12     ` Andries Brouwer
2011-02-10 18:17       ` Roland McGrath
2011-02-10 18:17         ` Roland McGrath
2011-02-11  9:11       ` Andreas Schwab

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