From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [RFC] relaxed barrier semantics Date: Wed, 28 Jul 2010 11:16:33 +0200 Message-ID: <20100728091633.GA10219@lst.de> References: <20100727165627.GA474@lst.de> <20100727175418.GF6820@quack.suse.cz> <20100727183546.GG7347@redhat.com> <4C4FE58C.8080403@kernel.org> <20100728082447.GA7668@lst.de> <4C4FECFE.9040509@kernel.org> <20100728085048.GA8884@lst.de> <4C4FF136.5000205@kernel.org> <20100728090025.GA9252@lst.de> <4C4FF42C.1050701@suse.de> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Christoph Hellwig , Tejun Heo , Vivek Goyal , Jan Kara , jaxboe@fusionio.com, James.Bottomley@suse.de, linux-fsdevel@vger.kernel.org, linux-scsi@vger.kernel.org, tytso@mit.edu, chris.mason@oracle.com, swhiteho@redhat.com, konishi.ryusuke@lab.ntt.co.jp To: Hannes Reinecke Return-path: Received: from verein.lst.de ([213.95.11.210]:33951 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752184Ab0G1JRB (ORCPT ); Wed, 28 Jul 2010 05:17:01 -0400 Content-Disposition: inline In-Reply-To: <4C4FF42C.1050701@suse.de> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, Jul 28, 2010 at 11:11:08AM +0200, Hannes Reinecke wrote: > My idea here is to use the 'META' request tag to emulate FUA. > >From what I've seen, the META request tag is only ever used on gfs2, > and even that is using is for tagging journal requests on write. Please don't overload META even more, it's already overloaded with at least two meanings. We do in fact already have a REQ_FUA flag, and now that I have unified the bio and request flags we can easily set it from filesystems. The problem is to emulate it properly on devices that do no actually support the FUA bit. Of which we unfortunately have a lot given that libata by default disables the FUA support even if the device supports.