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=-10.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,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 A6179C433E0 for ; Fri, 8 Jan 2021 11:03:50 +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 0AD0623977 for ; Fri, 8 Jan 2021 11:03:49 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0AD0623977 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]:37498 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kxpYa-0005xh-Ok for qemu-devel@archiver.kernel.org; Fri, 08 Jan 2021 06:03:48 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:36044) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kxpXn-0005To-Bu for qemu-devel@nongnu.org; Fri, 08 Jan 2021 06:02:59 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:58591) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kxpXi-0004QK-Kg for qemu-devel@nongnu.org; Fri, 08 Jan 2021 06:02:59 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1610103772; 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: in-reply-to:in-reply-to:references:references; bh=5s/JZx9E41odL82ibf6tqfWXXQzdQKGljqJ5J4GDEz8=; b=Rhyp4VKJVvlcI0MsHZNHiFZTwfcDRKM0CeQyYNdRHsBabf8U+S86XQb5bOhUm/+I1gm3RY zO+JEv17KSoTcKVHMEHuLwpncBlUI1G8nkRT7cCJBL4n50SWKgQwzOzfmKE0dd/qGAULQ8 GXGBErYRgXspcolaIKxdnzB2e7UZabM= 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-48-YbGPIh43P0ma8-4DVDecHg-1; Fri, 08 Jan 2021 06:02:49 -0500 X-MC-Unique: YbGPIh43P0ma8-4DVDecHg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 3362015725; Fri, 8 Jan 2021 11:02:48 +0000 (UTC) Received: from localhost (ovpn-114-98.ams2.redhat.com [10.36.114.98]) by smtp.corp.redhat.com (Postfix) with ESMTP id 62FA25B6A7; Fri, 8 Jan 2021 11:02:42 +0000 (UTC) Date: Fri, 8 Jan 2021 11:02:41 +0000 From: "Richard W.M. Jones" To: Vladimir Sementsov-Ogievskiy Subject: Re: [PATCH 4/4] block: introduce BDRV_MAX_LENGTH Message-ID: <20210108110241.GF30079@redhat.com> References: <20201203222713.13507-1-vsementsov@virtuozzo.com> <20201203222713.13507-5-vsementsov@virtuozzo.com> <20210107095817.GA2673@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=rjones@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Received-SPF: pass client-ip=63.128.21.124; envelope-from=rjones@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -29 X-Spam_score: -3.0 X-Spam_bar: --- X-Spam_report: (-3.0 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.246, 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=unavailable 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: fam@euphon.net, kwolf@redhat.com, berto@igalia.com, qemu-block@nongnu.org, 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 Fri, Jan 08, 2021 at 01:51:35PM +0300, Vladimir Sementsov-Ogievskiy wrote: > 07.01.2021 12:58, Richard W.M. Jones wrote: > >On Fri, Dec 04, 2020 at 01:27:13AM +0300, Vladimir Sementsov-Ogievskiy wrote: > >>Finally to be safe with calculations, to not calculate different > >>maximums for different nodes (depending on cluster size and > >>request_alignment), let's simply set QEMU_ALIGN_DOWN(INT64_MAX, 2^30) > >>as absolute maximum bytes length for Qemu. Actually, it's not much less > >>than INT64_MAX. > > > >>+/* > >>+ * We want allow aligning requests and disk length up to any 32bit alignment > >>+ * and don't afraid of overflow. > >>+ * To achieve it, and in the same time use some pretty number as maximum disk > >>+ * size, let's define maximum "length" (a limit for any offset/bytes request and > >>+ * for disk size) to be the greatest power of 2 less than INT64_MAX. > >>+ */ > >>+#define BDRV_MAX_ALIGNMENT (1L << 30) > >>+#define BDRV_MAX_LENGTH (QEMU_ALIGN_DOWN(INT64_MAX, BDRV_MAX_ALIGNMENT)) > > > >This change broke nbdkit tests. > > > >We test that qemu can handle a qemu NBD export of size 2^63 - 512, the > >largest size that (experimentally) we found qemu could safely handle. > >eg: > > > > https://github.com/libguestfs/nbdkit/blob/master/tests/test-memory-largest-for-qemu.sh > > > >Before this commit: > > > > $ nbdkit memory $(( 2**63 - 512 )) --run './qemu-img info "$uri"' > > image: nbd://localhost:10809 > > file format: raw > > virtual size: 8 EiB (9223372036854775296 bytes) > > disk size: unavailable > > > >After this commit: > > > > $ nbdkit memory $(( 2**63 - 512 )) --run './qemu-img info "$uri"' > > qemu-img: Could not open 'nbd://localhost:10809': Could not refresh total sector count: File too large > > > >Can I confirm that this limit is now the new official one and we > >should adjust nbdkit tests? Or was this change unintentional given > >that qemu seemed happy to handle 2^63 - 512 disks before? > > > >Note that nbdkit & libnbd support up to 2^63 - 1 bytes (we are not > >limited to whole sectors). Also the Linux kernel will let you create > >a /dev/nbdX device of size 2^63 - 1. > > > > Hi Rich! The change is intentional. > > I think the benefit of having clean limit, allowing us to align up > bytes to some alignment (which is a common operation) exceeds the > loss of 1G at the end of 2**63 range. We get simpler and safer > code. And anyway, new limit is not much worse than 2**63. That's fine, as long as we settle on this. I've updated the nbdkit tests: https://github.com/libguestfs/nbdkit/commit/c3ec8c951e39a0f921252c162c236f23c588d2bd > If at some > point we have a problem with it being too restrictive, it's than > very likely that 2**63 would be too small as well, which will > require so much work that our a bit more restrictive limit is > unlikely to increase the difficulty. The next step is definitely working on 128 bit offsets! https://rwmj.wordpress.com/2011/10/03/when-will-disk-sizes-go-beyond-64-bits/ Rich. -- Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones Read my programming and virtualization blog: http://rwmj.wordpress.com virt-df lists disk usage of guests without needing to install any software inside the virtual machine. Supports Linux and Windows. http://people.redhat.com/~rjones/virt-df/