Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759293AbcDAQG3 (ORCPT ); Fri, 1 Apr 2016 12:06:29 -0400 Received: from mx1.redhat.com ([209.132.183.28]:38016 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759098AbcDAQG2 (ORCPT ); Fri, 1 Apr 2016 12:06:28 -0400 From: Jeff Moyer To: Alex Bligh Cc: "linux-kernel\@vger.kernel.org" , nbd-general@lists.sourceforge.net, Eric Blake Subject: Re: Block layer - meaning of REQ_FUA on not write requests References: X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Date: Fri, 01 Apr 2016 12:06:09 -0400 In-Reply-To: (Alex Bligh's message of "Fri, 1 Apr 2016 16:27:35 +0100") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Fri, 01 Apr 2016 16:06:27 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 525 Lines: 13 Alex Bligh writes: > I am trying to clean up the documentation of the NBD protocol. NBD's > support for Force Unit Access (FUA) was modelled on the linux kernel > block layer. When I added support a few years ago, I omitted to find > out exactly what types of request it applies to. Obviously it applies > to write requests, but how about others (e.g. read)? Any request with REQ_FUA set will be treated as a flush by the block layer. As such, we do not expect reads to have this bit set. Cheers, Jeff