linux-kernel - Re: [RFC PATCH 0/5] Shadow directories

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Message-ID: <4717C419.8060602@davidnewall.com>
Date:	Fri, 19 Oct 2007 06:07:45 +0930
From:	David Newall <david@...idnewall.com>
To:	jaroslav.sykora@...il.com
CC:	Jan Engelhardt <jengelh@...putergmbh.de>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH 0/5] Shadow directories

Jaroslav Sykora wrote:
> If anybody can think of any other solution of the "redirector problem", possibly
> even non-kernel based one, let me know and I'd be glad :-)

If I understand your problem, you wish to treat an archive file as if it 
was a directory.  Thus, in the ideal situation, you could do the following:

	cat hello.zip/hello.c
	gcc hello.zip/hello.c -o hello
	etc..

Rather than complicate matters with a second tree, use FUSE with an 
explicit directory.  For example, ~/expand could be your shadow, thus to 
compile hello.c from ~/hello.zip:

	gcc ~/expand/hello.zip^/hello.c -o hello

I think no kernel change would be required.

I'm not keen on the caret.  One of the early claims made in 
http://lwn.net/Articles/100148/ is:
> Another branch, led by Al Viro, worries about the locking 
> considerations of this whole scheme. Linux, like most Unix systems, 
> has never allowed hard links to directories for a number of reasons;

The claim is wrong.  UNIX systems have traditionally allowed the 
superuser to create hard links to directories.  See link(2) for 2.10BSD 
<http://www.freebsd.org/cgi/man.cgi?query=link&sektion=2&manpath=2.10+BSD>.  
Having got that wrong throws doubt on the argument; perhaps a path can 
simultaneously be a file and a directory.
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