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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,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 8672CC433E0 for ; Sun, 10 Jan 2021 15:01:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 46B2F229F0 for ; Sun, 10 Jan 2021 15:01:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726418AbhAJPBb (ORCPT ); Sun, 10 Jan 2021 10:01:31 -0500 Received: from mx2.suse.de ([195.135.220.15]:50898 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726321AbhAJPBb (ORCPT ); Sun, 10 Jan 2021 10:01:31 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 54306AAF1; Sun, 10 Jan 2021 15:00:49 +0000 (UTC) Subject: Re: [PATCH 4/6] block: propagate BLKROSET on the whole device to all partitions To: Christoph Hellwig , Jens Axboe Cc: "Martin K . Petersen" , Oleksii Kurochko , Sagi Grimberg , Mike Snitzer , Ilya Dryomov , Dongsheng Yang , ceph-devel@vger.kernel.org, dm-devel@redhat.com, linux-block@vger.kernel.org, linux-nvme@lists.infradead.org References: <20210109104254.1077093-1-hch@lst.de> <20210109104254.1077093-5-hch@lst.de> From: Hannes Reinecke Message-ID: <81a37585-bf6e-9ab5-993e-e9a0881ce996@suse.de> Date: Sun, 10 Jan 2021 16:00:48 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.4.0 MIME-Version: 1.0 In-Reply-To: <20210109104254.1077093-5-hch@lst.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 1/9/21 11:42 AM, Christoph Hellwig wrote: > Change the policy so that a BLKROSET on the whole device also affects > partitions. To quote Martin K. Petersen: > > It's very common for database folks to twiddle the read-only state of > block devices and partitions. I know that our users will find it very > counter-intuitive that setting /dev/sda read-only won't prevent writes > to /dev/sda1. > > The existing behavior is inconsistent in the sense that doing: > > # blockdev --setro /dev/sda > # echo foo > /dev/sda1 > > permits writes. But: > > # blockdev --setro /dev/sda > > # echo foo > /dev/sda1 > > doesn't. > > And a subsequent: > > # blockdev --setrw /dev/sda > # echo foo > /dev/sda1 > > doesn't work either since sda1's read-only policy has been inherited > from the whole-disk device. > > You need to do: > > # blockdev --rereadpt > > after setting the whole-disk device rw to effectuate the same change on > the partitions, otherwise they are stuck being read-only indefinitely. > > However, setting the read-only policy on a partition does *not* require > the revalidate step. As a matter of fact, doing the revalidate will blow > away the policy setting you just made. > > So the user needs to take different actions depending on whether they > are trying to read-protect a whole-disk device or a partition. Despite > using the same ioctl. That is really confusing. > > I have lost count how many times our customers have had data clobbered > because of ambiguity of the existing whole-disk device policy. The > current behavior violates the principle of least surprise by letting the > user think they write protected the whole disk when they actually > didn't. > > Suggested-by: Martin K. Petersen > Signed-off-by: Christoph Hellwig > Reviewed-by: Martin K. Petersen > --- > block/genhd.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > Reviewed-by: Hannes Reinecke Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer