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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 594B5C2BA80 for ; Tue, 7 Apr 2020 14:45:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 300B520747 for ; Tue, 7 Apr 2020 14:45:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729225AbgDGOpJ (ORCPT ); Tue, 7 Apr 2020 10:45:09 -0400 Received: from mx2.suse.de ([195.135.220.15]:34472 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728943AbgDGOpI (ORCPT ); Tue, 7 Apr 2020 10:45:08 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx2.suse.de (Postfix) with ESMTP id 8583BAB64; Tue, 7 Apr 2020 14:45:05 +0000 (UTC) Subject: Re: [PATCH RFC v2 02/24] scsi: allocate separate queue for reserved commands To: John Garry , Christoph Hellwig Cc: axboe@kernel.dk, jejb@linux.ibm.com, martin.petersen@oracle.com, ming.lei@redhat.com, bvanassche@acm.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, virtualization@lists.linux-foundation.org, esc.storagedev@microsemi.com, chenxiang66@hisilicon.com, Hannes Reinecke References: <1583857550-12049-1-git-send-email-john.garry@huawei.com> <1583857550-12049-3-git-send-email-john.garry@huawei.com> <20200310183243.GA14549@infradead.org> <79cf4341-f2a2-dcc9-be0d-2efc6e83028a@huawei.com> <20200311062228.GA13522@infradead.org> <9c6ced82-b3f1-9724-b85e-d58827f1a4a4@huawei.com> <39bc2d82-2676-e329-5d32-8acb99b0a204@suse.de> <20ebe296-9e57-b3e3-21b3-63a09ce86036@huawei.com> From: Hannes Reinecke Message-ID: Date: Tue, 7 Apr 2020 16:45:04 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20ebe296-9e57-b3e3-21b3-63a09ce86036@huawei.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/7/20 4:35 PM, John Garry wrote: > On 07/04/2020 15:00, Hannes Reinecke wrote: >> On 4/7/20 1:54 PM, John Garry wrote: >>> On 06/04/2020 10:05, Hannes Reinecke wrote: [ .. ] >>>> This would be okay if 'this_id' would have been defined by the driver; >>>> sadly, most drivers which are affected here do set 'this_id' to -1. >>>> So we wouldn't have a nice target ID to allocate the device from, let >>>> alone the problem that we would have to emulate a complete scsi device >>>> with all required minimal command support etc. >>>> And I'm not quite sure how well that would play with the exising SCSI >>>> host template; the device we'll be allocating would have basically >>>> nothing in common with the 'normal' SCSI devices. >>>> >>>> What we could do, though, is to try it the other way round: >>>> Lift the request queue from scsi_get_host_dev() into the scsi host >>>> itself, so that scsi_get_host_dev() can use that queue, but we also >>>> would be able to use it without a SCSI device attached. >>> >>> wouldn't that limit 1x scsi device per host, not that I know if any >>> more would ever be required? But it does still seem better to use the >>> request queue in the scsi device. >>> >> My concern is this: >> >> struct scsi_device *scsi_get_host_dev(struct Scsi_Host *shost) >> { >>      [ .. ] >>      starget = scsi_alloc_target(&shost->shost_gendev, 0, >> shost->this_id); >>      [ .. ] >> >> and we have typically: >> >> drivers/scsi/hisi_sas/hisi_sas_v3_hw.c: .this_id                = -1, >> >> It's _very_ uncommon to have a negative number as the SCSI target >> device; in fact, it _is_ an unsigned int already. >> > > FWIW, the only other driver (gdth) which I see uses this API has this_id > = -1 in the scsi host template. > >> But alright, I'll give it a go; let's see what I'll end up with. > > note: If we want a fixed scsi_device per host, calling > scsi_mq_setup_tags() -> scsi_get_host_dev() will fail as shost state is > not running. Maybe we need to juggle some things there to provide a > generic solution. > It might even get worse, as during device setup things like 'slave_alloc' etc is getting called, which has a fair chance of getting confused for non-existing devices. Cf qla2xxx:qla2xx_slave_alloc() is calling starget_to_rport(), which will get us a nice oops when accessing a target which is _not_ the child of a fc remote port. And this is why I'm not utterly keen on this approach; auditing all these callbacks is _not_ fun. Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@suse.de +49 911 74053 688 SUSE Software Solutions GmbH, Maxfeldstr. 5, 90409 Nürnberg HRB 36809 (AG Nürnberg), Geschäftsführer: Felix Imendörffer