From: Vernon Mauery <vernux@us.ibm.com>
To: "Horst H. von Brand" <vonbrand@inf.utfsm.cl>,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: what is necessary for directory hard links
Date: Sun, 23 Jul 2006 15:27:23 -0700 [thread overview]
Message-ID: <200607231527.23484.vernux@us.ibm.com> (raw)
In-Reply-To: <200607230219.k6N2JMHI021999@laptop13.inf.utfsm.cl>
On Saturday 22 July 2006 19:19, you wrote:
> Bodo Eggert <7eggert@elstempel.de> wrote:
> > Horst H. von Brand <vonbrand@inf.utfsm.cl> wrote:
> > > Joshua Hudson <joshudson@gmail.com> wrote:
> > >> This patch is the sum total of all that I had to change in the kernel
> > >> VFS layer to support hard links to directories
> > >
> > > Can't be done, as it creates the possibility of loops.
> >
> > Don't do that then?
>
> Stop /everything/ to make sure no concurrent activity creates a loop, while
> checking the current mkdir(2) doesn't create one?
This doesn't seem that big of an issue for people to be up in arms about. You
wouldn't have to stop /everything/, would you, just have an in kernel mutex
in vfs_mkdir. It's not the most commonly used system call in the book --
meaning serializing the checking/creating of new directories would not really
hamper your system /that/ much.
Personally, I don't think hard linked directories are necessary or even that
interesting, but they certainly aren't impossible to do. I suppose there
might be some specialty filesystem that might like to do hardlinked
directories and I don't think the vfs core should make it difficult.
--Vernon
> > > The "only files can
> > > be hardlinked" idea makes garbage collection (== deleting of
> > > unreachable objects) simple: Just check the number of references.
> > >
> > > Detecting unconnected subgraphs uses a /lot/ of memory; and much worse,
> > > you have to stop (almost) all filesystem activity while doing it.
> >
> > In order to disconnect a directory, you'd have to empty it first, and
> > after emptying a directory, it won't be part of a loop. Maybe emtying is
> > the problem ...
>
> What does "emptying a directory" mean if there might be loops?
>
> > This feature was implemented,
>
> Never in my memory of any Unix (and lookalike) system in real use (I've
> seen a few).
>
> > and I asume it was removed for a reason.
> > Can somebody remember?
>
> See my objections.
next prev parent reply other threads:[~2006-07-23 22:27 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <6ARGK-19L-5@gated-at.bofh.it>
[not found] ` <6B8og-1iB-17@gated-at.bofh.it>
2006-07-22 16:59 ` what is necessary for directory hard links Bodo Eggert
2006-07-22 18:13 ` Joshua Hudson
2006-07-24 6:45 ` Nikita Danilov
2006-07-24 7:25 ` Valdis.Kletnieks
2006-07-24 16:21 ` Joshua Hudson
2006-07-24 17:55 ` Horst H. von Brand
2006-07-24 18:22 ` Valdis.Kletnieks
2006-07-25 4:49 ` Joshua Hudson
2006-07-25 12:43 ` Valdis.Kletnieks
2006-07-25 14:47 ` Horst H. von Brand
2006-07-23 2:19 ` Horst H. von Brand
2006-07-23 22:27 ` Vernon Mauery [this message]
2006-07-25 23:43 ` Peter Chubb
[not found] <6CcT1-1lH-39@gated-at.bofh.it>
[not found] ` <6Cwov-5xl-5@gated-at.bofh.it>
2006-07-25 21:28 ` Bodo Eggert
2006-07-26 1:00 ` Horst H. von Brand
2006-07-26 9:13 ` Bodo Eggert
2006-07-21 1:04 Joshua Hudson
2006-07-21 18:49 ` Horst H. von Brand
2006-07-21 20:28 ` Rob Sims
2006-07-21 21:57 ` Joshua Hudson
2006-07-24 6:42 ` Nikita Danilov
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