From patchwork Tue Feb 13 17:04:38 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kevin Wolf X-Patchwork-Id: 873011 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=nongnu.org (client-ip=2001:4830:134:3::11; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Received: from lists.gnu.org (lists.gnu.org [IPv6:2001:4830:134:3::11]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 3zgq091gKCz9t3x for ; Wed, 14 Feb 2018 04:14:33 +1100 (AEDT) Received: from localhost ([::1]:55677 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eleA3-0001cE-64 for incoming@patchwork.ozlabs.org; Tue, 13 Feb 2018 12:14:31 -0500 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52122) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ele1d-0002nc-CX for qemu-devel@nongnu.org; Tue, 13 Feb 2018 12:05:52 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ele1c-0005Fa-E1 for qemu-devel@nongnu.org; Tue, 13 Feb 2018 12:05:49 -0500 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:51168 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 1ele1U-00057z-JX; Tue, 13 Feb 2018 12:05:40 -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 3E75B7D840; Tue, 13 Feb 2018 17:05:40 +0000 (UTC) Received: from localhost.localdomain.com (ovpn-117-94.ams2.redhat.com [10.36.117.94]) by smtp.corp.redhat.com (Postfix) with ESMTP id 8F10B10075C2; Tue, 13 Feb 2018 17:05:39 +0000 (UTC) From: Kevin Wolf To: qemu-block@nongnu.org Date: Tue, 13 Feb 2018 18:04:38 +0100 Message-Id: <20180213170529.10858-5-kwolf@redhat.com> In-Reply-To: <20180213170529.10858-1-kwolf@redhat.com> References: <20180213170529.10858-1-kwolf@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]); Tue, 13 Feb 2018 17:05:40 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.2]); Tue, 13 Feb 2018 17:05:40 +0000 (UTC) for IP:'10.11.54.3' DOMAIN:'int-mx03.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'kwolf@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] [PULL 04/55] 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: kwolf@redhat.com, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" From: Fam Zheng Suggested-by: Stefan Hajnoczi Signed-off-by: Fam Zheng Reviewed-by: Stefan Hajnoczi Reviewed-by: Kashyap Chamarthy Signed-off-by: Kevin Wolf --- 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