Date: Thu, 26 Dec 1996 14:40:15 -0500 (EST) From: Charles Owens <owensc@enc.edu> To: J Wunsch <j@uriah.heep.sax.de> Cc: FreeBSD hackers <freebsd-hackers@freebsd.org>, ben@narcissus.ml.org Subject: Re: multi-group file access techniques / directory hardlinks Message-ID: <Pine.FBS.3.93.961226140036.24466D-100000@dingo.its.enc.edu> In-Reply-To: <199612261629.RAA08400@uriah.heep.sax.de>
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On Thu, 26 Dec 1996, J Wunsch wrote:
> As Charles Owens wrote:
>
> > >From what I've gleaned from these postings, one of the biggest problems
> > with them is the potential for creating loops in the file tree, which fsck
> > is generally very unhappy about. If one is very careful not to create
>
> Our fsck were always very unhappy about additional hardlinks to
> directories.
>
> > such loops _is_ it possible to safely employ hard-linked directories (and
> > keep fsck happy) ? I can certainly see that they're very dangerous, but
> > can they be used safely with FreeBSD? Anyone?
>
> Directory hardlinks are impossible in FreeBSD. They have been
> discontinued quite some time ago.
Uhhh... well, sort of. At least as of 2.1.6 it is still possible to use
ln(1) to create directory hardlinks using an undocumented flag. This,
along with some other observations suggests to me the following:
1. The file system does in fact support directory hardlinks. (This is
true at least to some extent, since the '.' and '..' entries are,
in fact, directory hardlinks.)
2. Certain key tools do _not_ understand directory hardlinks. The ones
that I know of are fsck, rm, and rmdir.
3. The official FreeBSD stance (that I seem to be hearing) that
directory hardlinks are unsupported is based on:
a. the insufficient status of the tool support (previous point)
- and/or -
b. the fact that directory hardlinks are dangerous in the
hands of the uncareful.
Am I correct here? Would someone in the know provide clarification?
As I stated in my original posting (on Dec 18), my goal is to come up with
an optimum technique for allowing multiple groups controlled access to a
file tree. (To my surprise, I had very little response to this posting,
which deals with what I think is a rather interesting challenge. If you'd
like me to repost, please holler). Essentially I'm trying to achieve a
subset of the functionality offered by Access Control Lists as implemented
in AIX et al.
A recent *article in 'Sys Admin' deals with this problem. One of the two
techniques suggested relies on the use of directory hardlinks, which is
why I'm currently interested in the topic. Although they more or less do
what I want I'm not thrilled with either of the techniques and was hoping
that someone here had some other suggestions. Please see my original
posting for more details.
Thanks
* Morris, Doug. "Techniques for Simulating Multiple Group Access,"
_Sys_Admin_. October 1996, page 71.
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Charles Owens Email: owensc@enc.edu
"I read somewhere to learn is to
Information Technology Services remember... and I've learned that
Eastern Nazarene College we've all forgot..." - King's X
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