Re: what is necessary for directory hard links

From: "Horst H. von Brand" <vonbrand@inf.utfsm.cl>
To: "Joshua Hudson" <joshudson@gmail.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: what is necessary for directory hard links
Date: Fri, 21 Jul 2006 14:49:12 -0400	[thread overview]
Message-ID: <200607211849.k6LInCi8011368@laptop13.inf.utfsm.cl> (raw)
In-Reply-To: Your message of "Thu, 20 Jul 2006 18:04:49 MST." <bda6d13a0607201804je89fc3exd0b8f821509a3894@mail.gmail.com>

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. 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.

Besides, the flow "root down through directories" gives a natural order in
which to go locking stuff when needed; if there can be loops, the system
could easily deadlock.
-- 
Dr. Horst H. von Brand                   User #22616 counter.li.org
Departamento de Informatica                     Fono: +56 32 654431
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