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 Received: from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 148D1C79F82 for ; Sat, 5 Sep 2026 00:34:35 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists1p.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1x2eMO-00027J-HF; Fri, 04 Sep 2026 20:34:20 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1x2eMM-00026N-7T; Fri, 04 Sep 2026 20:34:18 -0400 Received: from sea.source.kernel.org ([172.234.252.31]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1x2eMK-0007sO-OA; Fri, 04 Sep 2026 20:34:17 -0400 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) by sea.source.kernel.org (Postfix) with ESMTP id 7016242E78; Sat, 5 Sep 2026 00:34:15 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D7A491F00A3D; Sat, 5 Sep 2026 00:34:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788568455; bh=kWPyQIPT8n/OhyIiTYG454zuQPoPbaEq+jZ7dxy7hgk=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=RQdtLATRB0DkA3v8CciZkTW3b+HWdjbGrcuO7uhmdcgJa4rhwItmPP7QCzVSE4rdq nEEimtU/mbk8r27uZgjWSF9tFon3/BZbhwc468Zzrt1J8bquUvnRI/6jxOMyaUxbyL zs+WYvoJIGcTh1v8wca1U92A2n+M3wxiWYokkm+GlAG9F8oCofChM3jed2fpytgHsX NhahdYfwl4vpt02jqbj6rGBfZQEjAJPNZk2tWISgDRkxkNPMzxiEfao9XlrcH5w2Y1 D7cK7EOIk/iSC8BVBYzoJF5MffLVDvBwmy8GOP0MoRmOF4yeksBn6Wpm8JTcjUcXEY 8GTnAQL7MszCA== Message-ID: Date: Sat, 5 Sep 2026 09:34:12 +0900 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 06/12] hw/block: reject a zoned device whose write pointers are unaddressable To: Niklas Cassel , Stefan Hajnoczi , Kevin Wolf , John Snow , "Denis V. Lunev" , Hanna Reitz , "Michael S. Tsirkin" Cc: Sam Li , qemu-block@nongnu.org, qemu-devel@nongnu.org References: <20260904161801.1568841-1-cassel@kernel.org> <20260904161801.1568841-7-cassel@kernel.org> Content-Language: en-US From: Damien Le Moal Organization: Western Digital Research In-Reply-To: <20260904161801.1568841-7-cassel@kernel.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Received-SPF: pass client-ip=172.234.252.31; envelope-from=dlemoal@kernel.org; helo=sea.source.kernel.org 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, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: qemu development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 9/5/26 01:17, Niklas Cassel wrote: > The write pointers of a zoned device outlive any particular use of it, > whether the device keeps them itself or a backend records them, while the > logical block size is a property of the frontend and is chosen afresh > every time the device is attached. Nothing ties the two together. A zone > written while the device was configured with logical_block_size=512 > leaves a write pointer that is a multiple of 512, and attaching the same > device with logical_block_size=4096 makes that pointer unaddressable. > > Such a pointer is not merely misaligned. The guest addresses the device > in logical blocks, and a zone report expresses the write pointer in 512 > byte sectors, so the guest is told about a position that does not fall on > a logical block boundary. It can neither read nor write there, and the > zone can only be recovered by resetting it. The reverse direction is > harmless: a pointer laid down with a larger logical block size is still a > multiple of a smaller one. > > On a zoned null_blk device with a logical block size of 512, a 512 byte > append to a sequential zone leaves the write pointer half a logical block > into it: > > $ qemu-io --image-opts -n driver=host_device,filename=/dev/nullb0 \ > -c "zap -p 0x20000000 0x200" -c "zrp 0x20000000 1" > start: 0x100000, len 0x80000, cap 0x80000, wptr 0x100001, zcond:2 > > Attaching that disk with logical_block_size=4096 handed the guest a zone > it could not write to. > > Check at realize time that the zone size and every write pointer of a > sequential zone are multiples of the write granularity that the device is > about to report, and refuse to start otherwise. The write pointers are > already held in memory by the driver, so this costs no I/O. > > The check uses blkconf_zone_write_granularity(), the same value that a > frontend reports to its guest and validates requests against, so the > three cannot disagree. > > Signed-off-by: Niklas Cassel Looks good. Reviewed-by: Damien Le Moal -- Damien Le Moal Western Digital Research