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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 DD19AC433FF for ; Mon, 12 Aug 2019 13:24:27 +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 B1917206C2 for ; Mon, 12 Aug 2019 13:24:27 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B1917206C2 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]:45512 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hxAJG-0002iU-UA for qemu-devel@archiver.kernel.org; Mon, 12 Aug 2019 09:24:26 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:51000) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hxAIt-0002Bg-1q for qemu-devel@nongnu.org; Mon, 12 Aug 2019 09:24:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hxAIs-00067q-4m for qemu-devel@nongnu.org; Mon, 12 Aug 2019 09:24:02 -0400 Received: from mx1.redhat.com ([209.132.183.28]:50944) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hxAIp-00065x-QP; Mon, 12 Aug 2019 09:23:59 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D22FC3CA0B; Mon, 12 Aug 2019 13:23:57 +0000 (UTC) Received: from localhost.localdomain (ovpn-116-66.ams2.redhat.com [10.36.116.66]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0246E3849; Mon, 12 Aug 2019 13:23:53 +0000 (UTC) Date: Mon, 12 Aug 2019 15:23:52 +0200 From: Kevin Wolf To: Vladimir Sementsov-Ogievskiy Message-ID: <20190812132352.GA6400@localhost.localdomain> References: <6826e3c2-bc6e-b2a2-1bf1-3ed31079f0ee@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6826e3c2-bc6e-b2a2-1bf1-3ed31079f0ee@virtuozzo.com> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Mon, 12 Aug 2019 13:23:57 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] backup bug or question 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: John Snow , qemu-devel , qemu block , Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 09.08.2019 um 15:18 hat Vladimir Sementsov-Ogievskiy geschrieben: > Hi! > > Hmm, hacking around backup I have a question: > > What prevents guest write request after job_start but before setting > write notifier? > > code path: > > qmp_drive_backup or transaction with backup > > job_start > aio_co_enter(job_co_entry) /* may only schedule execution, isn't it ? */ > > .... > > job_co_entry > job_pause_point() /* it definitely yields, isn't it bad? */ > job->driver->run() /* backup_run */ > > ---- > > backup_run() > bdrv_add_before_write_notifier() > > ... > > And what guarantees we give to the user? Is it guaranteed that write notifier is > set when qmp command returns? > > And I guess, if we start several backups in a transaction it should be guaranteed > that the set of backups is consistent and correspond to one point in time... Do the patches to switch backup to a filter node solve this automatically because that node would be inserted in backup_job_create()? Kevin