Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965919AbWKHP0g (ORCPT ); Wed, 8 Nov 2006 10:26:36 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965932AbWKHP0f (ORCPT ); Wed, 8 Nov 2006 10:26:35 -0500 Received: from mx1.redhat.com ([66.187.233.31]:25540 "EHLO mx1.redhat.com") by vger.kernel.org with ESMTP id S965939AbWKHP0e (ORCPT ); Wed, 8 Nov 2006 10:26:34 -0500 Date: Wed, 8 Nov 2006 15:25:33 +0000 From: Alasdair G Kergon To: "Rafael J. Wysocki" Cc: Alasdair G Kergon , David Chinner , Eric Sandeen , Andrew Morton , 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: <20061108152533.GH30653@agk.surrey.redhat.com> Mail-Followup-To: "Rafael J. Wysocki" , Alasdair G Kergon , David Chinner , Eric Sandeen , Andrew Morton , linux-kernel@vger.kernel.org, dm-devel@redhat.com, Ingo Molnar , Srinivasa DS References: <20061107183459.GG6993@agk.surrey.redhat.com> <20061108082722.GH8394166@melbourne.sgi.com> <20061108142511.GG30653@agk.surrey.redhat.com> <200611081543.28548.rjw@sisk.pl> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200611081543.28548.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: 1711 Lines: 43 On Wed, Nov 08, 2006 at 03:43:26PM +0100, Rafael J. Wysocki wrote: > Will it be enough to cover the interactions with dm? There are cases where you *cannot* freeze the filesystem (unless you wait for userspace processes to finish what they are doing) - and only dm can tell you that. The freeze_filesystems() code ought to do it's best in any given circumstances within the constraints. So: Get the filesystem's block device. Check the full tree of devices that that block device depends upon and for any device that belongs to device-mapper check if it is suspended. If it is, skip the original device. struct mapped_device *dm_get_md(dev_t dev); int dm_suspended(struct mapped_device *md); void dm_put(struct mapped_device *md); Handling the tree is the difficult bit, but sysfs could help. [You can get the device-mapper dependencies with: struct mapped_device *dm_get_md(dev_t dev); struct dm_table *dm_get_table(struct mapped_device *md); struct list_head *dm_table_get_devices(struct dm_table *t); void dm_table_put(struct dm_table *t); void dm_put(struct mapped_device *md); ] Consider that you could have an already-frozen filesystem containing a loop device containing a device-mapper device containing a not-frozen filesystem. You won't be able to freeze that top filesystem because the I/O would queue lower down the stack. (Similar problem if the device-mapper device in the stack was suspended.) 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/