From mboxrd@z Thu Jan  1 00:00:00 1970
From: Valerie Aurora <vaurora@redhat.com>
Subject: Re: Fallthrus as full-length symlinks?
Date: Tue, 17 Nov 2009 14:43:00 -0500
Message-ID: <20091117194300.GD17822@shell>
References: <20091113174631.GD19656@shell> <200911131846.nADIkFR6022038@agora.fsl.cs.sunysb.edu> <20091117191349.GC17822@shell> <1258485506.6132.65.camel@macbook.infradead.org>
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Cc: Erez Zadok <ezk@cs.sunysb.edu>, linux-fsdevel@vger.kernel.org,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Jan Blunck <jblunck@suse.de>,
	Christoph Hellwig <hch@infradead.org>,
	Andy Whitcroft <apw@canonical.com>,
	Scott James Remnant <scott@canonical.com>,
	Sandu Popa Marius <sandupopamarius@gmail.com>,
	Jan Rekorajski <baggins@sith.mimuw.edu.pl>,
	"J. R. Okajima" <hooanon05@yahoo.co.jp>,
	Arnd Bergmann <arnd@arndb.de>,
	Vladimir Dronnikov <dronnikov@gmail.com>,
	Felix Fietkau <nbd@openwrt.org>
To: David Woodhouse <dwmw2@infradead.org>
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On Tue, Nov 17, 2009 at 07:18:26PM +0000, David Woodhouse wrote:
> On Tue, 2009-11-17 at 14:13 -0500, Valerie Aurora wrote:
> > 
> > I can't think of a way to do it without using up namespace - but
> > perhaps there is some part of the symlink target namespace that has no
> > valid meaning that we could use instead, like Arnd's self symlink. 
> 
> I think it's impossible to declare that, since the symlink namespace is
> fair game for userspace do use as it sees fit. 
> 
> Emacs and Mozilla lockfiles being but one example...
> 
> [dwmw2@macbook ~]$ ls -l .#foo.html .mozilla/firefox/b8v9tyu0.default/lock 
> lrwxrwxrwx. 1 dwmw2 dwmw2 44 2009-11-17 19:16 .#foo.html -> dwmw2@macbook.infradead.org.21271:1258450900
> lrwxrwxrwx. 1 dwmw2 dwmw2 19 2009-11-17 09:51 .mozilla/firefox/b8v9tyu0.default/lock -> 90.155.92.212:+3756
> 
> I wouldn't want to bet that no userspace app has ever come up with the
> idea of using a symlink-to-self as a marker for something. I don't think
> it's good practice for us to be trying to play games like that.

That's my feeling too.  I don't see anyway to cleanly implement
fallthrus (or whiteouts) without explicit support from the file system
on the writable layer.  Fortunately it doesn't take much support.

-VAL