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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 F2E6CC433E0 for ; Wed, 27 May 2020 15:58:46 +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 BC5BE20776 for ; Wed, 27 May 2020 15:58:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="gATX8dO8" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org BC5BE20776 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]:59908 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jdyS6-0006mI-0t for qemu-devel@archiver.kernel.org; Wed, 27 May 2020 11:58:46 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:54856) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jdyRW-0006EO-75 for qemu-devel@nongnu.org; Wed, 27 May 2020 11:58:10 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:47641) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jdyRV-0000Fr-GU for qemu-devel@nongnu.org; Wed, 27 May 2020 11:58:09 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1590595088; 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=VwTf5x6DtCC2oFz1CdZBflE9NBhTRM3YaVIXmxvJm6g=; b=gATX8dO8rDYuvCSkUMogPifp/4P0YLZAV8u+dnav8qaYI9eTzZFhogFfq3UpEdIcLF9Zti ci/nqZE+AO+ys6pwrvenFRJmHiCAUVFt7m6+18oRffpTRNeU1EGucV4gZd3iTEydFgj2wM mHryX7J8L7dzMiJWwBcwwNmyOWcxF9I= 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-9-SYMpMUzbNP2ghphNBEiJGQ-1; Wed, 27 May 2020 11:58:01 -0400 X-MC-Unique: SYMpMUzbNP2ghphNBEiJGQ-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2853B464; Wed, 27 May 2020 15:58:00 +0000 (UTC) Received: from [10.3.112.88] (ovpn-112-88.phx2.redhat.com [10.3.112.88]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7F26960C47; Wed, 27 May 2020 15:57:58 +0000 (UTC) Subject: Re: [PATCH v7 20/32] qcow2: Add subcluster support to calculate_l2_meta() To: Alberto Garcia , qemu-devel@nongnu.org References: From: Eric Blake Organization: Red Hat, Inc. Message-ID: <26daf4ff-98b0-9484-c002-53656f3e2f08@redhat.com> Date: Wed, 27 May 2020 10:57:57 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.7.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=207.211.31.81; envelope-from=eblake@redhat.com; helo=us-smtp-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/27 00:45:05 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 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_NONE=-0.0001, RCVD_IN_MSPIKE_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_PASS=-0.001, URIBL_BLOCKED=0.001 autolearn=_AUTOLEARN 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: Kevin Wolf , Derek Su , Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 5/25/20 1:08 PM, Alberto Garcia wrote: > If an image has subclusters then there are more copy-on-write > scenarios that we need to consider. Let's say we have a write request > from the middle of subcluster #3 until the end of the cluster: > > 1) If we are writing to a newly allocated cluster then we need > copy-on-write. The previous contents of subclusters #0 to #3 must > be copied to the new cluster. We can optimize this process by > skipping all leading unallocated or zero subclusters (the status of > those skipped subclusters will be reflected in the new L2 bitmap). > > 2) If we are overwriting an existing cluster: > > 2.1) If subcluster #3 is unallocated or has the all-zeroes bit set > then we need copy-on-write (on subcluster #3 only). > > 2.2) If subcluster #3 was already allocated then there is no need > for any copy-on-write. However we still need to update the L2 > bitmap to reflect possible changes in the allocation status of > subclusters #4 to #31. Because of this, this function checks > if all the overwritten subclusters are already allocated and > in this case it returns without creating a new QCowL2Meta > structure. Quite the mouthful! But the description looks correct, and the code appears to match it. > > After all these changes l2meta_cow_start() and l2meta_cow_end() > are not necessarily cluster-aligned anymore. We need to update the > calculation of old_start and old_end in handle_dependencies() to > guarantee that no two requests try to write on the same cluster. > > Signed-off-by: Alberto Garcia > --- > block/qcow2-cluster.c | 163 +++++++++++++++++++++++++++++++++--------- > 1 file changed, 131 insertions(+), 32 deletions(-) > Reviewed-by: Eric Blake -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org