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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 000C2C4360C for ; Thu, 10 Oct 2019 15:09:30 +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 C9A0A206A1 for ; Thu, 10 Oct 2019 15:09:30 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C9A0A206A1 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]:40836 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iIa4H-0000jJ-Qd for qemu-devel@archiver.kernel.org; Thu, 10 Oct 2019 11:09:29 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:58133) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iIa2W-0007LG-0L for qemu-devel@nongnu.org; Thu, 10 Oct 2019 11:07:41 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iIa2U-0007vP-NU for qemu-devel@nongnu.org; Thu, 10 Oct 2019 11:07:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:36570) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iIa2U-0007vD-F1 for qemu-devel@nongnu.org; Thu, 10 Oct 2019 11:07:38 -0400 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A82F43086E2F; Thu, 10 Oct 2019 15:07:36 +0000 (UTC) Received: from localhost.localdomain (ovpn-116-47.ams2.redhat.com [10.36.116.47]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 72F3D5D713; Thu, 10 Oct 2019 15:07:35 +0000 (UTC) Date: Thu, 10 Oct 2019 17:07:33 +0200 From: Kevin Wolf To: Markus Armbruster Subject: Re: [PATCH v2 2/2] qapi: Allow introspecting fix for savevm's cooperation with blockdev Message-ID: <20191010150733.GE7616@localhost.localdomain> References: <992ea9ca130b4fb6dbf82726aa3b1d8040c16944.1568989362.git.pkrempa@redhat.com> <87r23w2rbp.fsf@dusky.pond.sub.org> <87a7ajuzpw.fsf@dusky.pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87a7ajuzpw.fsf@dusky.pond.sub.org> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.44]); Thu, 10 Oct 2019 15:07:36 +0000 (UTC) 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: Peter Krempa , qemu-devel@nongnu.org, Michael Roth Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 02.10.2019 um 13:57 hat Markus Armbruster geschrieben: > Eric Blake writes: > > > On 10/1/19 2:34 PM, Markus Armbruster wrote: > >> Peter Krempa writes: > >> > >>> savevm was buggy as it considered all monitor owned block device nodes > >> > >> Recommend "monitor-owned block device nodes" or "block device nodes > >> owned by a monitor" > >> > >>> for snapshot. With introduction of -blockdev the common usage made all > >>> nodes including protocol nodes monitor owned and thus considered for > >>> snapshot. > >> > >> What exactly is / was the problem? > > > > > > Old way: using QMP add_device, you create a drive backend with two BDS > > (format and protocol) assigned to it; the drive backend has your given > > name, and both BDS have a generated name (beginning with '#'). The > > two BDS are not monitor-owned, rather, the drive is. > > > > New way: using QMP blockdev_add, you create the two BDS manually with > > names of your choice, then plug that blockdev into an unnamed > > blockbackend (the drive no longer needs a name, because you can get at > > everything through the BDS name). You _could_ do this in one step > > (the QAPI allows self-recursion where you can define both the format > > and protocol in one step), but it is easier to do in two steps (define > > the protocol BDS first, then define the format BDS using a "string" > > name of the protocol BDS instead of a { "driver":..., args... } object > > of the protocol layer. But by making two calls, now both BDS are > > monitor-owned. > > > > At snapshot-time, the code currently looks for all monitor-owned nodes > > when deciding what to snapshot. In the old way, this finds the named > > drive, picks up its associated top-most node, and snapshots the format > > layer. In the new way, the drive is unnamed so it is skipped, while > > there are two named BDS, but we don't want a snapshot of the protocol > > layer. > > So the problem is certain (common & sane) -blockdev use makes savevm > create additional, unwanted snapshots. Actually, the most common protocol driver is file-posix, which doesn't support snapshots, so usually the result was that savevm just fails because it can't snapshot something that it (incorrectly) thinks it should snapshot. Kevin > Your explanation should be worked into the commit message along with ... > > >>> This was fixed but clients need to be able to detect whether > >>> this fix is present. > >> > >> Fixed where? Commit hash, if possible. > > > > Pull request: > > https://lists.gnu.org/archive/html/qemu-devel/2019-09/msg04773.html > > (assuming it doesn't need a respin before landing, 8ec72832) > > ... a pointer to this fix. > > Thanks! > > [...]