From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 59505C4360C for ; Thu, 10 Oct 2019 12:17:48 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 307482054F for ; Thu, 10 Oct 2019 12:17:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 307482054F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:37028 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iIXO6-0001sM-P9 for qemu-devel@archiver.kernel.org; Thu, 10 Oct 2019 08:17:46 -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+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" 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, Bloc= kDriverState *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 goi= ng to be + * used for "image fleecing", i.e. it should represent a kind of sna= pshot of + * source at backup-start point in time. And target is going to be r= ead by + * somebody (for example, used as NBD export) during backup job. + * + * In this case, we need to add BDRV_REQ_SERIALISING write flag to a= void + * intersection of backup writes and third party reads from target, + * otherwise reading from target we may occasionally read already up= dated 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