From patchwork Fri Feb 9 05:29:15 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fam Zheng X-Patchwork-Id: 10208249 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 78C91602D8 for ; Fri, 9 Feb 2018 05:33:20 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6959829680 for ; Fri, 9 Feb 2018 05:33:20 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 5D7EB29684; Fri, 9 Feb 2018 05:33:20 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 021D829680 for ; Fri, 9 Feb 2018 05:33:20 +0000 (UTC) Received: from localhost ([::1]:37718 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ek1JH-0007ee-51 for patchwork-qemu-devel@patchwork.kernel.org; Fri, 09 Feb 2018 00:33:19 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:57534) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ek1Fp-00058K-37 for qemu-devel@nongnu.org; Fri, 09 Feb 2018 00:29:48 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ek1Fo-00044x-56 for qemu-devel@nongnu.org; Fri, 09 Feb 2018 00:29:45 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:54728 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1ek1Fi-0003y9-TI; Fri, 09 Feb 2018 00:29:38 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.rdu2.redhat.com [10.11.54.3]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 796507D679; Fri, 9 Feb 2018 05:29:38 +0000 (UTC) Received: from lemon.usersys.redhat.com (ovpn-12-69.pek2.redhat.com [10.72.12.69]) by smtp.corp.redhat.com (Postfix) with ESMTP id DCFCC100839D; Fri, 9 Feb 2018 05:29:35 +0000 (UTC) From: Fam Zheng To: qemu-devel@nongnu.org Date: Fri, 9 Feb 2018 13:29:15 +0800 Message-Id: <20180209052915.12855-4-famz@redhat.com> In-Reply-To: <20180209052915.12855-1-famz@redhat.com> References: <20180209052915.12855-1-famz@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Fri, 09 Feb 2018 05:29:38 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Fri, 09 Feb 2018 05:29:38 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'famz@redhat.com' RCPT:'' X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 66.187.233.73 Subject: [Qemu-devel] [PATCH v7 3/3] docs: Document share-rw property more thoroughly X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , qemu-block@nongnu.org, kchamart@redhat.com, Max Reitz , stefanha@redhat.com Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP Suggested-by: Stefan Hajnoczi Signed-off-by: Fam Zheng --- docs/qemu-block-drivers.texi | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/docs/qemu-block-drivers.texi b/docs/qemu-block-drivers.texi index cd74767ed3..f1793692bb 100644 --- a/docs/qemu-block-drivers.texi +++ b/docs/qemu-block-drivers.texi @@ -845,6 +845,16 @@ QEMU transparently handles lock handover during shared storage migration. For shared virtual disk images between multiple VMs, the "share-rw" device option should be used. +By default, the guest has exclusive write access to its disk image. If the +guest can safely share the disk image with other writers the @code{-device +...,share-rw=on} parameter can be used. This is only safe if the guest is +running software, such as a cluster file system, that coordinates disk accesses +to avoid corruption. + +Note that share-rw=on only declares the guest's ability to share the disk. +Some QEMU features, such as image file formats, require exclusive write access +to the disk image and this is unaffected by the share-rw=on option. + Alternatively, locking can be fully disabled by "locking=off" block device option. In the command line, the option is usually in the form of "file.locking=off" as the protocol driver is normally placed as a "file" child