Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757416AbYBNPUj (ORCPT ); Thu, 14 Feb 2008 10:20:39 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752289AbYBNPUD (ORCPT ); Thu, 14 Feb 2008 10:20:03 -0500 Received: from www.tglx.de ([62.245.132.106]:47017 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756215AbYBNPT7 (ORCPT ); Thu, 14 Feb 2008 10:19:59 -0500 Date: Thu, 14 Feb 2008 16:19:42 +0100 From: =?UTF-8?B?SGFucy1Kw7xyZ2Vu?= Koch To: Jan Engelhardt Cc: Andi Kleen , Jasper Bryant-Greene , rzryyvzy , linux-kernel@vger.kernel.org Subject: Re: Is there a "blackhole" /dev/null directory? Message-ID: <20080214161942.55ce5089@dilbert.local> In-Reply-To: References: <20080214093051.7240852AB0E31@trashmail.net> <1202981957.10928.17.camel@phobos.jasper.bg> Organization: Linutronix X-Mailer: Claws Mail 3.2.0 (GTK+ 2.12.2; i486-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1686 Lines: 42 Am Thu, 14 Feb 2008 16:00:06 +0100 (CET) schrieb Jan Engelhardt : > > On Feb 14 2008 10:46, Andi Kleen wrote: > >Jasper Bryant-Greene writes: > >> > >> This could be done fairly trivially with FUSE, and IMHO is a good > >> use for FUSE because since you're just throwing most data away, > >> performance is not a concern. > > There is a much more interesting 'problem' with a "/dev/null > directory". > > Q: Why would you need such a directory? > A: To temporarily fool a program into believing it wrote something. > > Q: Should all files disappear? (e.g. "unlink after open") > A: Maybe not, programs may stat() the file right afterwards and > get confused by the "inexistence". > > Q: What if a program attempts to mkdir /dev/nullmnt/foo to just > create a file /dev/nullmnt/foo/barfile? > A: /dev/nullmnt/foo must continue to exist or be accepted for a while, > or perhaps for eternity. Well, the problem seems to be that a "directory" is not just data but also contains metadata. While it's easy to write data to /dev/null, you cannot simply discard metadata associated with a directory. So, such a "/dev/null-directory" would have to remember metadata (at least all created filenames including subdirectories) in the same way as other filesystems do. Only file _content_ can be discarded. To be honest, I still cannot see many sensible usecases for that... Thanks, Hans -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/