From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1765873AbcIOM0u (ORCPT ); Thu, 15 Sep 2016 08:26:50 -0400 Received: from latin.grep.be ([46.4.76.168]:54797 "EHLO latin.grep.be" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752206AbcIOM0t (ORCPT ); Thu, 15 Sep 2016 08:26:49 -0400 Date: Thu, 15 Sep 2016 14:26:31 +0200 From: Wouter Verhelst To: Christoph Hellwig Cc: "nbd-general@lists.sourceforge.net" , linux-block@vger.kernel.org, Josef Bacik , "linux-kernel@vger.kernel.org" , Markus Pargmann , kernel-team@fb.com Subject: Re: [Nbd] [RESEND][PATCH 0/5] nbd improvements Message-ID: <20160915122631.7wus5o6qin6o7uz5@grep.be> References: <1473369130-22986-1-git-send-email-jbacik@fb.com> <20160909200203.phhvodsfs7ymukfp@grep.be> <20160915104935.ohuwgq2chsedz6fl@grep.be> <27B346AF-F144-4770-BE38-446A66E71326@alex.org.uk> <20160915112936.vb7zxe7k6rvczosg@grep.be> <20160915114005.GC23259@infradead.org> <20160915115217.GB6411@infradead.org> <20160915120159.2o5lb7rvkjndzayh@grep.be> <20160915122008.GB1155@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160915122008.GB1155@infradead.org> X-Speed: Gates' Law: Every 18 months, the speed of software halves. Organization: none User-Agent: NeoMutt/ (1.7.0) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 15, 2016 at 05:20:08AM -0700, Christoph Hellwig wrote: > On Thu, Sep 15, 2016 at 02:01:59PM +0200, Wouter Verhelst wrote: > > Yes. There was some discussion on that part, and we decided that setting > > the flag doesn't hurt, but the spec also clarifies that using it on READ > > does nothing, semantically. > > > > > > The problem is that there are clients in the wild which do set it on > > READ, so it's just a matter of "be liberal in what you accept". > > Note that FUA on READ in SCSI and NVMe does have a meaning - it > requires you to bypass any sort of cache on the target. I think it's an > wrong defintion because it mandates implementation details that aren't > observable by the initiator, but it's still the spec wording and nbd > diverges from it. That's not nessecarily a bad thing, but a caveat to > look out for. Yes. I think the kernel nbd driver should probably filter out FUA on READ. It has no meaning in the case of nbd, and whatever expectations the kernel may have cannot be provided for by nbd anyway. -- < ron> I mean, the main *practical* problem with C++, is there's like a dozen people in the world who think they really understand all of its rules, and pretty much all of them are just lying to themselves too. -- #debian-devel, OFTC, 2016-02-12