Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760233AbYBZBh2 (ORCPT ); Mon, 25 Feb 2008 20:37:28 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753155AbYBZBhU (ORCPT ); Mon, 25 Feb 2008 20:37:20 -0500 Received: from mx1.redhat.com ([66.187.233.31]:34437 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752901AbYBZBhS (ORCPT ); Mon, 25 Feb 2008 20:37:18 -0500 Date: Tue, 26 Feb 2008 01:36:56 +0000 From: Alasdair G Kergon To: Andrew Morton , Anders Henke , Jens Axboe Cc: device-mapper development , linux-kernel@vger.kernel.org Subject: Re: [dm-devel] Re: device mapper not reporting no-barrier-support? Message-ID: <20080226013656.GE1788@agk.fab.redhat.com> Mail-Followup-To: Andrew Morton , Anders Henke , Jens Axboe , device-mapper development , linux-kernel@vger.kernel.org References: <20080225132615.GA21990@1und1.de> <20080225152050.94788622.akpm@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20080225152050.94788622.akpm@linux-foundation.org> User-Agent: Mutt/1.4.1i Organization: Red Hat UK Ltd. Registered in England and Wales, number 03798903. Registered Office: Amberley Place, 107-111 Peascod Street, Windsor, Berkshire, SL4 1TE. Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1828 Lines: 51 On Mon, Feb 25, 2008 at 03:20:50PM -0800, Andrew Morton wrote: > On Mon, 25 Feb 2008 14:26:15 +0100 Anders Henke wrote: > > I'm currently stuck between Kernel LVM and DRBD, as I'm using Kernel > > 2.6.24.2 with DRBD 8.2.5 on top of an LVM2 device (LV). > > -LVM2/device mapper doesn't support write barriers That's right. > > -DRBD uses blkdev_issue_flush() to flush its metadata to disk. Which won't work if device-mapper is underneath. > > On a no-barrier-device, DRBD should receive EOPNOTSUPP, but > > it really does receive an EIO. Promptly, DRBD gives the > > error message "drbd0: local disk flush failed with status -5". > > I've posted a lengty summary of my findings to > > http://lists.linbit.com/pipermail/drbd-user/2008-February/008665.html > > ... that DRBD does catch the EOPNOTSUPP for blkdev_issue_flush and > > BIO_RW_BARRIER, but the lvm implementation of blkdev_issue_flush in > > 2.6.24.2 aparently does return EIO for blkdev_issue_flush. > I'd say it's a DM bug. The dm code is unchanged, but look at the limited endio handling in ll_rw_blk.c: static void bio_end_empty_barrier(struct bio *bio, int err) { if (err) clear_bit(BIO_UPTODATE, &bio->bi_flags); complete(bio->bi_private); } int blkdev_issue_flush(struct block_device *bdev, sector_t *error_sector) { ... wait_for_completion(&wait); if (error_sector) *error_sector = bio->bi_sector; ret = 0; if (!bio_flagged(bio, BIO_UPTODATE)) ret = -EIO; 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/