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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 985CDECE587 for ; Mon, 14 Oct 2019 09:26:55 +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 6A5EE20854 for ; Mon, 14 Oct 2019 09:26:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6A5EE20854 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]:46202 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iJwcw-0003mV-Ju for qemu-devel@archiver.kernel.org; Mon, 14 Oct 2019 05:26:54 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:32933) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iJwcG-0003Jp-DH for qemu-devel@nongnu.org; Mon, 14 Oct 2019 05:26:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iJwcF-0003bj-7U for qemu-devel@nongnu.org; Mon, 14 Oct 2019 05:26:12 -0400 Received: from mx1.redhat.com ([209.132.183.28]:49635) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iJwcC-0003XO-94; Mon, 14 Oct 2019 05:26:08 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 474DD18C8913; Mon, 14 Oct 2019 09:26:06 +0000 (UTC) Received: from localhost.localdomain (unknown [10.36.118.40]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C04EB5C231; Mon, 14 Oct 2019 09:26:02 +0000 (UTC) Date: Mon, 14 Oct 2019 11:26:01 +0200 From: Kevin Wolf To: Alberto Garcia Subject: Re: [PATCH v2] block: Reject misaligned write requests with BDRV_REQ_NO_FALLBACK Message-ID: <20191014092601.GA7173@localhost.localdomain> References: <20191014081545.29694-1-berto@igalia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191014081545.29694-1-berto@igalia.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.6.2 (mx1.redhat.com [10.5.110.70]); Mon, 14 Oct 2019 09:26:06 +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: Nir Soffer , Anton Nefedov , qemu-devel@nongnu.org, qemu-block@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 14.10.2019 um 10:15 hat Alberto Garcia geschrieben: > The BDRV_REQ_NO_FALLBACK flag means that an operation should only be > performed if it can be offloaded or otherwise performed efficiently. > > However a misaligned write request requires a RMW so we should return > an error and let the caller decide how to proceed. > > This hits an assertion since commit c8bb23cbdb if the required > alignment is larger than the cluster size: > > qemu-img create -f qcow2 -o cluster_size=2k img.qcow2 4G > qemu-io -c "open -o driver=qcow2,file.align=4k blkdebug::img.qcow2" \ > -c 'write 0 512' > qemu-io: block/io.c:1127: bdrv_driver_pwritev: Assertion `!(flags & BDRV_REQ_NO_FALLBACK)' failed. > Aborted > > The reason is that when writing to an unallocated cluster we try to > skip the copy-on-write part and zeroize it using BDRV_REQ_NO_FALLBACK > instead, resulting in a write request that is too small (2KB cluster > size vs 4KB required alignment). > > Signed-off-by: Alberto Garcia Thanks, applied to the block branch. Kevin