Re: [RFC PATCH 0/5] Shadow directories

[Al Viro <viro@ftp.linux.org.uk>]

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).