Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762609AbXFTGDT (ORCPT ); Wed, 20 Jun 2007 02:03:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757616AbXFTGDM (ORCPT ); Wed, 20 Jun 2007 02:03:12 -0400 Received: from pentafluge.infradead.org ([213.146.154.40]:48278 "EHLO pentafluge.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757380AbXFTGDM (ORCPT ); Wed, 20 Jun 2007 02:03:12 -0400 Subject: Re: [RFC PATCH 1/4] Union mount documentation. From: Arjan van de Ven To: bharata@linux.vnet.ibm.com Cc: linux-kernel@vger.kernel.org In-Reply-To: <20070620055157.GC4267@in.ibm.com> References: <20070620055050.GB4267@in.ibm.com> <20070620055157.GC4267@in.ibm.com> Content-Type: text/plain Organization: Intel International BV Date: Tue, 19 Jun 2007 22:59:51 -0700 Message-Id: <1182319191.2700.9.camel@laptopd505.fenrus.org> Mime-Version: 1.0 X-Mailer: Evolution 2.10.2 (2.10.2-2.fc7) Content-Transfer-Encoding: 7bit X-SRS-Rewrite: SMTP reverse-path rewritten from by pentafluge.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1442 Lines: 44 On Wed, 2007-06-20 at 11:21 +0530, Bharata B Rao wrote: > From: Bharata B Rao > Subject: Union mount documentation. Hi, first of all I'm happy to see that people are still working on unionfs; I'd love to have functionality like this show up in Linux. I'll not claim to have any VFS knowledge whatsoever, but I was just wondering what happens in the following scenario: FS A is mounted twice, in /mnt/A and /mnt/union FS B is mounted twice, in /mnt/B and as topmost union mount on /mnt/union lets for simplicity say both filesystems are entirely empty user does on FS A: mkdir /mnt/A/somedir touch /mnt/A/somedir/somefile and then 2 things happen in parallel 1) touch /mnt/B/somefile 2) mv /mnt/union/somedir /mnt/union/somefile since the underlying FS for 2) is FS A... how will this work out locking wise? Will the VS lock the union directory only? Or will this operate only on the underlying FS? How is dcache consistency guaranteed for scenarios like this? Greetings, Arjan van de Ven -- if you want to mail me at work (you don't), use arjan (at) linux.intel.com Test the interaction between Linux and your BIOS via http://www.linuxfirmwarekit.org - 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/