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Fri, 16 Apr 2021 23:28:50 +0000 From: Martin Wilck To: "martin.petersen@oracle.com" CC: Hannes Reinecke , "hch@lst.de" , "dgilbert@interlog.com" , "dm-devel@redhat.com" , "linux-scsi@vger.kernel.org" , "jejb@linux.vnet.ibm.com" , "systemd-devel@lists.freedesktop.org" , "bmarzins@redhat.com" Subject: Re: RFC: one more time: SCSI device identification Thread-Topic: RFC: one more time: SCSI device identification Thread-Index: AQHXJIIevKqEvjcbJUy9Ai14uQzKmaqm92EcgBDwGwA= Date: Fri, 16 Apr 2021 23:28:50 +0000 Message-ID: <06489ea37311fe7bf73b27a41b5209ee4cca85fe.camel@suse.com> References: In-Reply-To: Accept-Language: en-US Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: user-agent: Evolution 3.38.4 authentication-results: oracle.com; dkim=none (message not signed) header.d=none;oracle.com; dmarc=none action=none header.from=suse.com; x-originating-ip: [2.202.118.173] x-ms-publictraffictype: Email x-ms-office365-filtering-correlation-id: aa1bd9c2-5edc-45a7-8919-08d9012f6438 x-ms-traffictypediagnostic: DB9PR04MB8348: x-ld-processed: f7a17af6-1c5c-4a36-aa8b-f5be247aa4ba,ExtFwd x-ms-exchange-transport-forked: True x-microsoft-antispam-prvs: x-ms-oob-tlc-oobclassifiers: OLM:10000; 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charset="iso-8859-15" Content-ID: <95D211C502429440A0E0EB11EB618115@eurprd04.prod.outlook.com> Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 X-OriginatorOrg: suse.com X-MS-Exchange-CrossTenant-AuthAs: Internal X-MS-Exchange-CrossTenant-AuthSource: DB8PR04MB6555.eurprd04.prod.outlook.com X-MS-Exchange-CrossTenant-Network-Message-Id: aa1bd9c2-5edc-45a7-8919-08d9012f6438 X-MS-Exchange-CrossTenant-originalarrivaltime: 16 Apr 2021 23:28:50.3794 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: f7a17af6-1c5c-4a36-aa8b-f5be247aa4ba X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: TCwzTV4IBEz3M59YrzaCrWbd+sxfl37BA6vzUqj2ZthehzG9Bl57hFyy5261P5LZxU0KMwIwXadze4LrvMGenA== X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB9PR04MB8348 Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org Hello Martin, Sorry for the late response, still recovering from a week out of office. On Tue, 2021-04-06 at 00:47 -0400, Martin K. Petersen wrote: >=20 > Martin, >=20 > > The kernel's preference for type 8 designators (see below) is in > > contrast with the established user space algorithms, which > > determine > > SCSI WWIDs on productive systems in practice. User space can try to > > adapt to the kernel logic, but it will necessarily be a slow and > > painful path if we want to avoid breaking user setups. >=20 > I was concerned when you changed the kernel prioritization a while > back > and I still don't think that we should tweak that code any further. Ok. > If the kernel picks one ID over another, that should be for the > kernel's > use. Letting the kernel decide which ID is best for userland is not a > good approach. Well, the kernel itself doesn't make any use of this property currently (and user space doesn't much either, afaik). > So I think my inclination would be to leave the current wwid as-is to > avoid the risk of breaking things. And then export all ID descriptors > reported in sysfs. Even though vpd83 is already exported in its > entirety, I don't have any particular concerns about the individual > values being exported separately. That makes many userland things so > much easier. And I think the kernel is in a good position to > disseminate > information reported by the hardware. >=20 > This puts the prioritization entirely in the distro/udev/scripting > domain. Taking the kernel out of the picture will make migration > easier. And it allows a user to pick their descriptor of choice > should a > device report something completely unusable in type 8. Hm, it sounds intriguing, but it has issues in its own right. For years to come, user space will have to probe whether these attribute exist, and fall back to the current ones ("wwid", "vpd_pg83") otherwise. So user space can't be simplified any time soon. Speaking for an important user space consumer of WWIDs (multipathd), I doubt that this would improve matters for us. We'd be happy if the kernel could just pick the "best" designator for us. But I understand that the kernel can't guarantee a good choice (user space can't either). What is your idea how these new sysfs attributes should be named? Just enumerate, or name them by type somehow? Thanks, Martin --=20 Dr. Martin Wilck , Tel.=A0+49 (0)911 74053 2107 SUSE Software Solutions Germany GmbH HRB 36809, AG N=FCrnberg GF: Felix Imend=F6rffer 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=-2.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,PDS_BAD_THREAD_QP_64, SPF_HELO_NONE,SPF_PASS 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 2BD06C433ED for ; Fri, 16 Apr 2021 23:29:17 +0000 (UTC) Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [216.205.24.124]) (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 9F08D610E8 for ; Fri, 16 Apr 2021 23:29:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 9F08D610E8 Authentication-Results: mail.kernel.org; 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Similar Internal Domain=false; Similar Monitored External Domain=false; Custom External Domain=false; Mimecast External Domain=false; Newly Observed Domain=false; Internal User Name=false; Custom Display Name List=false; Reply-to Address Mismatch=false; Targeted Threat Dictionary=false; Mimecast Threat Dictionary=false; Custom Threat Dictionary=false X-Scanned-By: MIMEDefang 2.78 on 10.11.54.3 X-MIME-Autoconverted: from quoted-printable to 8bit by lists01.pubmisc.prod.ext.phx2.redhat.com id 13GNT1X6016329 X-loop: dm-devel@redhat.com Cc: Hannes Reinecke , "jejb@linux.vnet.ibm.com" , "linux-scsi@vger.kernel.org" , "dm-devel@redhat.com" , "dgilbert@interlog.com" , "systemd-devel@lists.freedesktop.org" , "hch@lst.de" Subject: Re: [dm-devel] RFC: one more time: SCSI device identification X-BeenThere: dm-devel@redhat.com X-Mailman-Version: 2.1.12 Precedence: junk List-Id: device-mapper development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=dm-devel-bounces@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-ID: <95D211C502429440A0E0EB11EB618115@eurprd04.prod.outlook.com> Content-Type: text/plain; charset="iso-8859-15" Content-Transfer-Encoding: quoted-printable Hello Martin, Sorry for the late response, still recovering from a week out of office. On Tue, 2021-04-06 at 00:47 -0400, Martin K. Petersen wrote: >=20 > Martin, >=20 > > The kernel's preference for type 8 designators (see below) is in > > contrast with the established user space algorithms, which > > determine > > SCSI WWIDs on productive systems in practice. User space can try to > > adapt to the kernel logic, but it will necessarily be a slow and > > painful path if we want to avoid breaking user setups. >=20 > I was concerned when you changed the kernel prioritization a while > back > and I still don't think that we should tweak that code any further. Ok. > If the kernel picks one ID over another, that should be for the > kernel's > use. Letting the kernel decide which ID is best for userland is not a > good approach. Well, the kernel itself doesn't make any use of this property currently (and user space doesn't much either, afaik). > So I think my inclination would be to leave the current wwid as-is to > avoid the risk of breaking things. And then export all ID descriptors > reported in sysfs. Even though vpd83 is already exported in its > entirety, I don't have any particular concerns about the individual > values being exported separately. That makes many userland things so > much easier. And I think the kernel is in a good position to > disseminate > information reported by the hardware. >=20 > This puts the prioritization entirely in the distro/udev/scripting > domain. Taking the kernel out of the picture will make migration > easier. And it allows a user to pick their descriptor of choice > should a > device report something completely unusable in type 8. Hm, it sounds intriguing, but it has issues in its own right. For years to come, user space will have to probe whether these attribute exist, and fall back to the current ones ("wwid", "vpd_pg83") otherwise. So user space can't be simplified any time soon. Speaking for an important user space consumer of WWIDs (multipathd), I doubt that this would improve matters for us. We'd be happy if the kernel could just pick the "best" designator for us. But I understand that the kernel can't guarantee a good choice (user space can't either). What is your idea how these new sysfs attributes should be named? Just enumerate, or name them by type somehow? Thanks, Martin --=20 Dr. Martin Wilck , Tel.=A0+49 (0)911 74053 2107 SUSE Software Solutions Germany GmbH HRB 36809, AG N=FCrnberg GF: Felix Imend=F6rffer -- dm-devel mailing list dm-devel@redhat.com https://listman.redhat.com/mailman/listinfo/dm-devel