From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md. Date: Thu, 05 Jul 2007 21:28:17 +0900 Message-ID: <468CE3E1.3000503@gmail.com> References: <18006.38689.818186.221707@notabene.brown> <18010.12472.209452.148229@notabene.brown> <20070530093503.GA15559@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Neil Brown , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com, linux-raid@vger.kernel.org, David Chinner , Phillip Susi , Stefan Bader , Andreas Dilger To: Jens Axboe Return-path: In-Reply-To: <20070530093503.GA15559@kernel.dk> Sender: linux-raid-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Hello, Jens. Jens Axboe wrote: > On Mon, May 28 2007, Neil Brown wrote: >> I think the implementation priorities here are: >> >> 1/ implement a zero-length BIO_RW_BARRIER option. >> 2/ Use it (or otherwise) to make all dm and md modules handle >> barriers (and loop?). >> 3/ Devise and implement appropriate fall-backs with-in the block layer >> so that -EOPNOTSUP is never returned. >> 4/ Remove unneeded cruft from filesystems (and elsewhere). > > This is the start of 1/ above. It's very lightly tested, it's verified > to DTRT here at least and not crash :-) > > It gets rid of the ->issue_flush_fn() queue callback, all the driver > knowledge resides in ->prepare_flush_fn() anyways. blkdev_issue_flush() > then just reuses the empty-bio approach to queue an empty barrier, this > should work equally well for stacked and non-stacked devices. > > While this patch isn't complete yet, it's clearly the right direction to > go. Finally took a brief look. :-) I think the sequencing for zero-length barrier can be better done by pre-setting QUEUE_ORDSEQ_BAR in start_ordered() rather than short circuiting the request after it's issued. What do you think? Thanks. -- tejun