From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alasdair G Kergon Subject: Re: Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md. Date: Mon, 28 May 2007 10:43:58 +0100 Message-ID: <20070528094358.GM25091@agk.fab.redhat.com> References: <18006.38689.818186.221707@notabene.brown> <18010.12472.209452.148229@notabene.brown> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <18010.12472.209452.148229@notabene.brown> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: device-mapper development , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, Jens Axboe , David Chinner , Phillip Susi , Stefan Bader , Andreas Dilger , Tejun Heo List-Id: linux-raid.ids On Mon, May 28, 2007 at 11:30:32AM +1000, Neil Brown wrote: > 1/ A BIO_RW_BARRIER request should never fail with -EOPNOTSUP. The device-mapper position has always been that we require > a zero-length BIO_RW_BARRIER (i.e. containing no data to read or write - or emulated, possibly device-specific) before we can provide full barrier support. (Consider multiple active paths - each must see barrier.) Until every device supports barriers -EOPNOTSUP support is required. (Consider reconfiguration of stacks of devices - barrier support is a dynamic block device property that can switch between available and unavailable at any time.) Alasdair -- agk@redhat.com