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=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,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 F2DD3C433C1 for ; Fri, 26 Mar 2021 08:01:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B8D0761A3F for ; Fri, 26 Mar 2021 08:01:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229528AbhCZIAj (ORCPT ); Fri, 26 Mar 2021 04:00:39 -0400 Received: from mx2.suse.de ([195.135.220.15]:38634 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229573AbhCZIAP (ORCPT ); Fri, 26 Mar 2021 04:00:15 -0400 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 6B349ADEF; Fri, 26 Mar 2021 08:00:13 +0000 (UTC) Subject: Re: [PATCH -next 1/5] block: add disk sequence number To: Matteo Croce , Matthew Wilcox Cc: linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Lennart Poettering , Luca Boccassi , Jens Axboe , Alexander Viro , Damien Le Moal , Tejun Heo , =?UTF-8?Q?Javier_Gonz=c3=a1lez?= , Niklas Cassel , Johannes Thumshirn References: <20210315200242.67355-1-mcroce@linux.microsoft.com> <20210315200242.67355-2-mcroce@linux.microsoft.com> <20210315201824.GB2577561@casper.infradead.org> <20210315210452.GC2577561@casper.infradead.org> From: Hannes Reinecke Message-ID: Date: Fri, 26 Mar 2021 09:00:12 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: 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 3/25/21 6:29 PM, Matteo Croce wrote: > On Mon, Mar 15, 2021 at 10:05 PM Matthew Wilcox wrote: >> >> On Mon, Mar 15, 2021 at 08:18:24PM +0000, Matthew Wilcox wrote: >>> On Mon, Mar 15, 2021 at 09:02:38PM +0100, Matteo Croce wrote: >>>> From: Matteo Croce >>>> >>>> Add a sequence number to the disk devices. This number is put in the >>>> uevent so userspace can correlate events when a driver reuses a device, >>>> like the loop one. >>> >>> Should this be documented as monotonically increasing? I think this >>> is actually a media identifier. Consider (if you will) a floppy disc. >>> Back when such things were common, it was possible with personal computers >>> of the era to have multiple floppy discs "in play" and be prompted to >>> insert them as needed. So shouldn't it be possible to support something >>> similar here -- you're really removing the media from the loop device. >>> With a monotonically increasing number, you're always destroying the >>> media when you remove it, but in principle, it should be possible to >>> reinsert the same media and have the same media identifier number. >> >> So ... a lot of devices have UUIDs or similar. eg: >> >> $ cat /sys/block/nvme0n1/uuid >> e8238fa6-bf53-0001-001b-448b49cec94f >> >> https://linux.die.net/man/8/scsi_id (for scsi) >> > > Hi, > > I don't have uuid anywhere: > > matteo@saturno:~$ ll /dev/sd? > brw-rw---- 1 root disk 8, 0 feb 16 13:24 /dev/sda > brw-rw---- 1 root disk 8, 16 feb 16 13:24 /dev/sdb > brw-rw---- 1 root disk 8, 32 feb 16 13:24 /dev/sdc > brw-rw---- 1 root disk 8, 48 feb 16 13:24 /dev/sdd > brw-rw---- 1 root disk 8, 64 mar 4 06:26 /dev/sde > brw-rw---- 1 root disk 8, 80 feb 16 13:24 /dev/sdf > matteo@saturno:~$ ll /sys/block/*/uuid > ls: cannot access '/sys/block/*/uuid': No such file or directory > > mcroce@t490s:~$ ll /dev/nvme0n1 > brw-rw----. 1 root disk 259, 0 25 mar 14.22 /dev/nvme0n1 > mcroce@t490s:~$ ll /sys/block/*/uuid > ls: cannot access '/sys/block/*/uuid': No such file or directory > > I find it only on a mdraid array: > > $ cat /sys/devices/virtual/block/md127/md/uuid > 26117338-4f54-f14e-b5d4-93feb7fe825d > > I'm using a vanilla 5.11 kernel. > The 'uuid' is optional for NVMe devices, and indeed not even present for other device types. Use the 'wwid' attribute, which contains a unique identifier for all nvme devices: # cat /sys/block/nvme*/wwid nvme.8086-4356504436343735303034323430304e474e-564f303430304b45464a42-00000001 nvme.8086-4356504436343735303034363430304e474e-564f303430304b45464a42-00000001 uuid.3c6500ee-a775-4c89-b223-e9551f5a9f7a and for SCSI the wwid is part of the SCSI device: # cat /sys/block/sd*/device/wwid naa.600508b1001ce2e648a35b6ec14a3996 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