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

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Message-ID: <20071018204703.GQ8181@ftp.linux.org.uk>
Date:	Thu, 18 Oct 2007 21:47:03 +0100
From:	Al Viro <viro@....linux.org.uk>
To:	David Newall <david@...idnewall.com>
Cc:	jaroslav.sykora@...il.com,
	Jan Engelhardt <jengelh@...putergmbh.de>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC PATCH 0/5] Shadow directories

On Fri, Oct 19, 2007 at 06:07:45AM +0930, David Newall wrote:
> >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.

Learn to read.  Linux has never allowed that.  Most of the Unix systems
do not allow that.  Original _did_ allow that, but at the cost of very
easily triggered fs corruption (and it didn't have things like rename(2) -
it _did_ have userland implementation, of course, in suid-root mv(1),
but that sucker had been extremely racy and could be easily used to
screw filesystem to hell and back; adding rename(2) to the set of primitives
combined with multiple links to directories leads to very nasty issues on
_any_ system).
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