Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753726AbWKHABo (ORCPT ); Tue, 7 Nov 2006 19:01:44 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753730AbWKHABn (ORCPT ); Tue, 7 Nov 2006 19:01:43 -0500 Received: from mx1.redhat.com ([66.187.233.31]:37857 "EHLO mx1.redhat.com") by vger.kernel.org with ESMTP id S1753725AbWKHABn (ORCPT ); Tue, 7 Nov 2006 19:01:43 -0500 Date: Wed, 8 Nov 2006 00:01:09 +0000 From: Alasdair G Kergon To: "Rafael J. Wysocki" Cc: Eric Sandeen , Andrew Morton , Alasdair G Kergon , linux-kernel@vger.kernel.org, dm-devel@redhat.com, Ingo Molnar , Srinivasa DS Subject: Re: [PATCH 2.6.19 5/5] fs: freeze_bdev with semaphore not mutex Message-ID: <20061108000109.GE30653@agk.surrey.redhat.com> Mail-Followup-To: "Rafael J. Wysocki" , Eric Sandeen , Andrew Morton , Alasdair G Kergon , linux-kernel@vger.kernel.org, dm-devel@redhat.com, Ingo Molnar , Srinivasa DS References: <20061107183459.GG6993@agk.surrey.redhat.com> <200611080005.50070.rjw@sisk.pl> <45511430.8030703@redhat.com> <200611080042.03563.rjw@sisk.pl> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200611080042.03563.rjw@sisk.pl> User-Agent: Mutt/1.4.1i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1336 Lines: 26 On Wed, Nov 08, 2006 at 12:42:02AM +0100, Rafael J. Wysocki wrote: > On Wednesday, 8 November 2006 00:18, Eric Sandeen wrote: > > But, how is a stampede of fs-freezers -supposed- to work? I could > > imagine something like a freezer count, and the filesystem is only > > unfrozen after everyone has thawed? Or should only one freezer be > > active at a time... which is what we have now I guess. > I think it shouldn't be possible to freeze an fs more than once. In device-mapper today, the only way to get more than one freeze on the same device is to use xfs and issue xfs_freeze before creating an lvm snapshot (or issuing the dmsetup equivalent), and at the moment we tell people not to do that any more. The device-mapper API does not permit multiple freezes of the same device. (The interesting question is actually whether the request should be cascaded in any way when devices depend on other devices.) Now if someone's introducing a new use for freeze_bdev, perhaps now's the time to revisit the semantics and allow for concurrent freeze requests. Alasdair -- agk@redhat.com - 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/