From nobody Tue Apr 15 21:41:15 2025 Delivered-To: importer@patchew.org Received-SPF: pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Authentication-Results: mx.zohomail.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1570709877; cv=none; d=zoho.com; s=zohoarc; b=IVaLoC8VII0gwY1SUyzGf0kx3LTawC2a2K1kAKHx1VF9Zl7GdyHC3mZQ9jPJJsplP6QmFBQC14FLvixyepfZ5u5KTkipAmkvXBjUcfk8IA4jT/iwI3Kq/ZShVBYXhQHHGa+L3qe3ZPwUbcwWy9/scMcZjkMiK0ZCR8Qe3u6u954= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zoho.com; s=zohoarc; t=1570709877; h=Content-Transfer-Encoding:Cc:Date:From:In-Reply-To:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:References:Sender:Subject:To; bh=9f+k6ksmcCALB4j7iaCyKyy1/Gdo9wseAhgk4e7fW/o=; b=O1GBJja38jLRVJNdNbyN+beBSuz74M5jj9qsd/Ze+/EHrIeOD2FeP7jgr+EMBCrFo6q/mJOy2TC+vyoOshSyb+5Cczd0fVLJRUbnKXC559FdLX4ZEkTfHpJcfycfhhT1+qiPG9SarkJYrFyvrxHicCNglQnfl5TWANhF6Y3Xf90= ARC-Authentication-Results: i=1; mx.zoho.com; spf=pass (zoho.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1570709877029729.8078518009004; Thu, 10 Oct 2019 05:17:57 -0700 (PDT) Received: from localhost ([::1]:37028 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iIXOD-0001sM-DW for importer@patchew.org; Thu, 10 Oct 2019 08:17:53 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:51737) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iIWqs-0006UQ-I7 for qemu-devel@nongnu.org; Thu, 10 Oct 2019 07:43:27 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iIWqr-00089g-G5 for qemu-devel@nongnu.org; Thu, 10 Oct 2019 07:43:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:60456) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iIWqp-00087f-5k; Thu, 10 Oct 2019 07:43:23 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6C2793066FA7; Thu, 10 Oct 2019 11:43:22 +0000 (UTC) Received: from localhost (unknown [10.36.118.5]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 1325D600C4; Thu, 10 Oct 2019 11:43:21 +0000 (UTC) From: Max Reitz To: qemu-block@nongnu.org Subject: [PULL 09/36] block/backup: improve comment about image fleecing Date: Thu, 10 Oct 2019 13:42:33 +0200 Message-Id: <20191010114300.7746-10-mreitz@redhat.com> In-Reply-To: <20191010114300.7746-1-mreitz@redhat.com> References: <20191010114300.7746-1-mreitz@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.42]); Thu, 10 Oct 2019 11:43:22 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 209.132.183.28 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Peter Maydell , qemu-devel@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" Content-Type: text/plain; charset="utf-8" From: Vladimir Sementsov-Ogievskiy Signed-off-by: Vladimir Sementsov-Ogievskiy Reviewed-by: Max Reitz Message-id: 20190920142056.12778-5-vsementsov@virtuozzo.com Signed-off-by: Max Reitz --- block/backup.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/block/backup.c b/block/backup.c index 98d7f7a905..ae28849660 100644 --- a/block/backup.c +++ b/block/backup.c @@ -747,9 +747,18 @@ BlockJob *backup_job_create(const char *job_id, BlockD= riverState *bs, job->bitmap_mode =3D bitmap_mode; =20 /* - * Set write flags: - * 1. Detect image-fleecing (and similar) schemes - * 2. Handle compression + * If source is in backing chain of target assume that target is going= to be + * used for "image fleecing", i.e. it should represent a kind of snaps= hot of + * source at backup-start point in time. And target is going to be rea= d by + * somebody (for example, used as NBD export) during backup job. + * + * In this case, we need to add BDRV_REQ_SERIALISING write flag to avo= id + * intersection of backup writes and third party reads from target, + * otherwise reading from target we may occasionally read already upda= ted by + * guest data. + * + * For more information see commit f8d59dfb40bb and test + * tests/qemu-iotests/222 */ job->write_flags =3D (bdrv_chain_contains(target, bs) ? BDRV_REQ_SERIALISING : 0) | --=20 2.21.0