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=-2.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 3144FC10DCE for ; Thu, 12 Mar 2020 11:32:27 +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 F065720716 for ; Thu, 12 Mar 2020 11:32:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="QNWhR2by" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F065720716 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]:39644 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jCM4g-0004nZ-5A for qemu-devel@archiver.kernel.org; Thu, 12 Mar 2020 07:32:26 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:54599) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jCM3o-0003ji-JO for qemu-devel@nongnu.org; Thu, 12 Mar 2020 07:31:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jCM3n-0001YV-6J for qemu-devel@nongnu.org; Thu, 12 Mar 2020 07:31:32 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:33150 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jCM3n-0001Wy-1m for qemu-devel@nongnu.org; Thu, 12 Mar 2020 07:31:31 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1584012690; 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=cTD4u4Wu68SFCG13V+atSpPvjESIXKbysbaIuDUHkqc=; b=QNWhR2byiBGw5yWIUvHRuAQ0xksqB5FYizu44rtgN4B7l9ZIaj1gi1DXmWPmsVqCaGhgsa AnHaDkBP/o0M4eM/9pvJrBKCC42YW754yyPzN5Fo0te+c3n5EINiv4rAl8zM5ccoFd8yXJ 0U3BISPkxBL+DN+2xyCNjQWqVk50vhg= 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-124-93dpCz5xO0m_8nRJY6gymg-1; Thu, 12 Mar 2020 07:31:26 -0400 X-MC-Unique: 93dpCz5xO0m_8nRJY6gymg-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 71CAC8017CC; Thu, 12 Mar 2020 11:31:24 +0000 (UTC) Received: from [10.3.116.177] (ovpn-116-177.phx2.redhat.com [10.3.116.177]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7530F91D63; Thu, 12 Mar 2020 11:31:23 +0000 (UTC) Subject: Re: [PATCH 3/3] block: fail on open when file size is unaligned to request_alignment To: Vladimir Sementsov-Ogievskiy , Max Reitz , qemu-block@nongnu.org References: <20200130152218.7600-1-vsementsov@virtuozzo.com> <20200130152218.7600-4-vsementsov@virtuozzo.com> <4fb7d692-4009-c6a7-c765-292ac8073ae3@redhat.com> <186c8080-a45b-0756-fa4d-c38af02f3a8b@redhat.com> From: Eric Blake Organization: Red Hat, Inc. Message-ID: Date: Thu, 12 Mar 2020 06:31:22 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=WINDOWS-1252; format=flowed Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 205.139.110.61 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, den@openvz.org, qemu-devel@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 3/12/20 4:06 AM, Vladimir Sementsov-Ogievskiy wrote: >>> So the real solution would probably...=A0 Be to align the file size up = to >>> the alignment? >> >> Or to bite the bullet and finally implement byte-accurate size=20 >> everywhere (instead of our current insistence on rounding size up to=20 >> 512-byte multiples).=A0 If we have to deal with unaligned tails anyways,= =20 >> it's better to make the code universally applicable whether that=20 >> unaligned tail is to 512 or to 4k, than to have it work for 512 but to= =20 >> fail for 4k. >> >=20 > But how it helps with the problem of files unaligned to=20 > request_alignment defined by driver? In a byte-accurate world, no driver should ever report an unaligned=20 size. If the driver is capable of sub-sector sizes, it is also capable=20 of sub-sector I/O and should state as such in its request_alignment.=20 The block layer then takes care of ensuring that any access of the final=20 unaligned sector or 4k region either leaves the bytes past EOF alone, or=20 at most reads those bytes as zeroes, and maybe permits attempts to write=20 no-op zeroes to those bytes, but gracefully forbids attempts to store=20 data that would cause the file to be resized. But that's the ideal world, and it requires a lot of code auditing to=20 get there. It probably won't happen in time for the 5.0 release. --=20 Eric Blake, Principal Software Engineer Red Hat, Inc. +1-919-301-3226 Virtualization: qemu.org | libvirt.org