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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS 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 11979C433ED for ; Wed, 19 May 2021 12:03:29 +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 7FD7E61040 for ; Wed, 19 May 2021 12:03:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7FD7E61040 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]:58402 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1ljKv9-000633-Cr for qemu-devel@archiver.kernel.org; Wed, 19 May 2021 08:03:27 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48544) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ljKsv-0002W2-F9 for qemu-devel@nongnu.org; Wed, 19 May 2021 08:01:09 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:32738) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1ljKsl-0004Ef-ED for qemu-devel@nongnu.org; Wed, 19 May 2021 08:01:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1621425657; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=pq+rG7hJdl0vY3claS72cBYfZgI/jOXZ38IOFSkTBOk=; b=XdraOE1vkUrXvie7yNU+NWL7OIs2uhbGSHnYGj3o04peAZY1Wiwr1hc5MtikMTyuNPragu fNzzcH+d/MEadNO97vRiOpS973oKiY2Am+DSScJ5LvGCpYJHjGvt7BTLIqV8r6xkVDXkfl XBBFGK2Hu63kVfW0V/k8ahlQngbfXt8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-48-KaWtLzUdPm6ajF6ZSOZotg-1; Wed, 19 May 2021 08:00:55 -0400 X-MC-Unique: KaWtLzUdPm6ajF6ZSOZotg-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 8612A101371F; Wed, 19 May 2021 12:00:54 +0000 (UTC) Received: from merkur.fritz.box (ovpn-115-58.ams2.redhat.com [10.36.115.58]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0811D5D9C0; Wed, 19 May 2021 12:00:51 +0000 (UTC) Date: Wed, 19 May 2021 14:00:50 +0200 From: Kevin Wolf To: Vladimir Sementsov-Ogievskiy Subject: Re: RFC: Qemu backup interface plans Message-ID: References: MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=kwolf@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=170.10.133.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.39, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_LOW=-0.7, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=unavailable autolearn_force=no X-Spam_action: no action 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-block@nongnu.org, "libvir-list@redhat.com" , Dmitry Mishin , Igor Sukhih , qemu-devel , Max Reitz , yur@virtuozzo.com, Nikolay Shirokovskiy , "Denis V. Lunev" , John Snow Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 19.05.2021 um 13:49 hat Vladimir Sementsov-Ogievskiy geschrieben: > 19.05.2021 14:20, Kevin Wolf wrote: > > Am 19.05.2021 um 08:11 hat Vladimir Sementsov-Ogievskiy geschrieben: > > > > > 2. Test, that we can start backup job with source = (target of > > > > > backup-top filter), so that we have "push backup with fleecing". > > > > > Make an option for backup to start without a filter, when we don't > > > > > need copy-before-write operations, to not create extra superfluous > > > > > filter. > > > > > > > > OK, so the backup job is not really a backup job, but just anything > > > > that copies data. > > > > > > Not quite. For backup without a filter we should protect source from > > > changing, by unsharing WRITE permission on it. > > > > > > I'll try to avoid adding an option. The logic should work like in > > > commit job: if there are current writers on source we create filter. > > > If there no writers, we just unshare writes and go without a filter. > > > And for this copy-before-write filter should be able to do > > > WRITE_UNCHANGED in case of fleecing. > > > > If we ever get to the point where we would make a block-copy job visible > > to the user, I wouldn't copy the restrictions from the current jobs, but > > keep it really generic to cover all cases. > > > > There is no way for the QMP command starting the job to know what the > > user is planning to do with the image in the future. Even if it's > > currently read-only, the user may want to add a writer later. > > > > I think this means that we want to always add a filter node, and then > > possibly dynamically switch between modes if being read-only provides a > > significant advantage for the job. > > Still, in push-backup-with-fleecing scheme we really don't need the > second filter, so why to insert extra thing to block graph? > > I see your point still, that user may want to add writer later. Still, > I'd be surprised if such use-cases exist now. > > What about the following: > > add some source-mode tri-state parameter for backup: > > auto: insert filter iff there are existing writers [default] > filtered: insert filter unconditionally > immutable: don't insert filter. will fail if there are existing > writers, and creating writers during block-job would be impossible Yes, that's an option, too. Kevin