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=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,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 6E7BCC433DF for ; Tue, 19 May 2020 21:14:14 +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 3626F20758 for ; Tue, 19 May 2020 21:14:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="LW5NrEZx" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3626F20758 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]:54152 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jb9Yz-0005Mc-FR for qemu-devel@archiver.kernel.org; Tue, 19 May 2020 17:14:13 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:36622) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jb9YP-0004lX-8m for qemu-devel@nongnu.org; Tue, 19 May 2020 17:13:37 -0400 Received: from us-smtp-1.mimecast.com ([205.139.110.61]:48817 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jb9YO-0003Lt-EF for qemu-devel@nongnu.org; Tue, 19 May 2020 17:13:36 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1589922815; 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=Op/MI+WEDGhRGpLa7qcmJDDcXeOtGL+P9rd2Ph1HZ34=; b=LW5NrEZxw40JC1dwOs+2jNDQ2Z6NRT3kou6NUTn+5M15TQrQwEPkTYmaUI80Hh8CJ/vnNl NhHutQ1dUKyzsduVhAE7d7WlDpIdnjA1FRx5O+QUu65gyHQUzZ4mxXZ2VJK4OChUqfU4xv dTRCqTdedwH43XRjLg0uMD1f+w61G4A= 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-462-izbndxQaOrS7t3HqxxxJtg-1; Tue, 19 May 2020 17:13:25 -0400 X-MC-Unique: izbndxQaOrS7t3HqxxxJtg-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 67D2318FE860; Tue, 19 May 2020 21:13:24 +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 ED11F101F6D8; Tue, 19 May 2020 21:13:20 +0000 (UTC) Subject: Re: [PATCH v2 5/5] iotests: add commit top->base cases to 274 To: Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org References: <20200519195501.29071-1-vsementsov@virtuozzo.com> <20200519195501.29071-6-vsementsov@virtuozzo.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: Date: Tue, 19 May 2020 16:13:20 -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: <20200519195501.29071-6-vsementsov@virtuozzo.com> Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 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=205.139.110.61; envelope-from=eblake@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/18 23:19:13 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] 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_H2=-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: kwolf@redhat.com, fam@euphon.net, qemu-devel@nongnu.org, mreitz@redhat.com, stefanha@redhat.com, den@openvz.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 5/19/20 2:55 PM, Vladimir Sementsov-Ogievskiy wrote: > These cases are fixed by previous patches around block_status and > is_allocated. > > Signed-off-by: Vladimir Sementsov-Ogievskiy > --- > tests/qemu-iotests/274 | 20 ++++++++++++ > tests/qemu-iotests/274.out | 65 ++++++++++++++++++++++++++++++++++++++ > 2 files changed, 85 insertions(+) Okay, so this test fails when applied in isolation without the rest of your series. > > diff --git a/tests/qemu-iotests/274 b/tests/qemu-iotests/274 > index 5d1bf34dff..e910455f13 100755 > --- a/tests/qemu-iotests/274 > +++ b/tests/qemu-iotests/274 > @@ -115,6 +115,26 @@ with iotests.FilePath('base') as base, \ > iotests.qemu_io_log('-c', 'read -P 1 0 %d' % size_short, mid) > iotests.qemu_io_log('-c', 'read -P 0 %d %d' % (size_short, size_diff), mid) > > + iotests.log('=== Testing qemu-img commit (top -> base) ===') > + > + create_chain() > + iotests.qemu_img_log('commit', '-b', base, top) > + iotests.img_info_log(base) > + iotests.qemu_io_log('-c', 'read -P 1 0 %d' % size_short, base) > + iotests.qemu_io_log('-c', 'read -P 0 %d %d' % (size_short, size_diff), base) So if I understand it, we are going from: base 11111111 mid ---- top -------- guest 11110000 and we want to go to: base 11110000 except that we are not properly writing the zeroes into base, because we grabbed the wrong status, ending up with: base 11111111 The status of top from 1M onwards is unallocated, and if we were to commit to just mid, Kevin's truncate fixes solve that (we now zero out the tail of mid as part of resizing it to be large enough). But you are instead skipping mid, and committing all the way to base. So we need _something_ that can tell qemu-img commit that even though the region 1m-2m is unallocated in top, we must behave as though the status of mid reports it as allocated (because when reading beyond EOF in mid, we DO read zero). Since the data is allocated not in top, but acts as though it was allocated in mid, which is above base, then the commit operation has to do something to preserve that allocation. Okay, you've convinced me we have a bug. However, I'm still not sold that patches 1 and 4 are quite the right fix. Going back to the original setup, unpatched qemu.git head reports: $ ./qemu-img map --output=json top.qcow2 [{ "start": 0, "length": 1048576, "depth": 2, "zero": false, "data": true, "offset": 327680}, { "start": 1048576, "length": 1048576, "depth": 0, "zero": true, "data": false}] I think what we really want is: [{ "start": 0, "length": 1048576, "depth": 2, "zero": false, "data": true, "offset": 327680}, { "start": 1048576, "length": 1048576, "depth": 1, "zero": true, "data": false}] because then we would be _accurately_ reporting that the zeroes that we read from 1m-2m come _because_ we read from mid (beyond EOF), which is different from our current answer that the zeroes come from top (they don't, because top deferred to mid). If we fix up qemu-img map output to correctly report zeroes beyond EOF from the correct layer, will that also fix up the bug we are seeing in qemu-img commit? -- Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org