Re: Fallthrus as full-length symlinks?

[Valerie Aurora <vaurora@redhat.com>]

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