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=-11.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,MAILING_LIST_MULTI,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 61F72C433DB for ; Mon, 22 Mar 2021 15:14:29 +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 CDF506198B for ; Mon, 22 Mar 2021 15:14:28 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CDF506198B 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]:38582 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1lOMGB-0001EU-Th for qemu-devel@archiver.kernel.org; Mon, 22 Mar 2021 11:14:27 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:57372) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lOMEh-0008UY-AT for qemu-devel@nongnu.org; Mon, 22 Mar 2021 11:12:55 -0400 Received: from us-smtp-delivery-124.mimecast.com ([216.205.24.124]:38492) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1lOMEe-0005IP-ON for qemu-devel@nongnu.org; Mon, 22 Mar 2021 11:12:54 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1616425971; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=GD7ogjqj9wCF146CqkXH/J1L4x60zwnh8dUjYLqYjYo=; b=JgDjPqzdjWvNfndgmoRRYHcZGKG2cMg7syH7qdjYsZz73tAH98psQ29vJgQkgD/ARqvwdu OK/9XabMPIAXmJjZ85nNGKkMudi9aawrG616OzQn6vp6ZEDet9moiJCimnV3jmFaBphpan /nJsta2VNEcx9O8BcHzSh3t/aRGaRB8= 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-299--4RF6PZNNYKOxTO0TY12Mw-1; Mon, 22 Mar 2021 11:12:48 -0400 X-MC-Unique: -4RF6PZNNYKOxTO0TY12Mw-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 96BD6100A641; Mon, 22 Mar 2021 15:12:47 +0000 (UTC) Received: from merkur.fritz.box (ovpn-115-125.ams2.redhat.com [10.36.115.125]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B242619C78; Mon, 22 Mar 2021 15:12:46 +0000 (UTC) Date: Mon, 22 Mar 2021 16:12:45 +0100 From: Kevin Wolf To: Patrik =?utf-8?B?SmFub3XFoWVr?= Subject: Re: [PATCH 2/2] qapi: implementation of the block-dirty-bitmap-dump command Message-ID: References: <20210320093235.461485-1-pj@patrikjanousek.cz> <20210320093235.461485-3-pj@patrikjanousek.cz> MIME-Version: 1.0 In-Reply-To: <20210320093235.461485-3-pj@patrikjanousek.cz> X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 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=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=216.205.24.124; envelope-from=kwolf@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -27 X-Spam_score: -2.8 X-Spam_bar: -- X-Spam_report: (-2.8 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, 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=ham 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: qemu-devel@nongnu.org, lmatejka@kiv.zcu.cz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 20.03.2021 um 10:32 hat Patrik Janoušek geschrieben: > Currently, dirty bitmaps are for internal use only and there is > no support for accessing their content from third party-apps. > This patch implements new command block-dirty-bitmap-dump, which > returns content of the dirty bitmap encoded in base64. This is > very useful especially in combination with a drive that uses raw > format because third-party apps can easily use it to create > incremental or differential backup. > > Signed-off-by: Patrik Janoušek People have already pointed you to NBD to get the block dirty status (and they are right), but I think nobody has explained yet why we decided against a QMP command to return bitmaps. The problem is that disk images can be huge, and this means that dirty bitmaps describing them get pretty large, too. So your new QMP command ends up reading many megabytes from disk and sending it to the socket. While it's doing all of this I/O, QEMU is blocked and the guest may appear to be hanging until it completes. The client would also have to download the whole bitmap even if it is only interested in specific blocks. (This may or may not be relevant for you specific use case.) With the NBD export, the client can query a specific block range and its request is processed asynchronously in the background while the guest and the QMP monitor are still available. Kevin