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,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 47712C433ED for ; Thu, 22 Apr 2021 17:34:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 266E261435 for ; Thu, 22 Apr 2021 17:34:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238565AbhDVRei (ORCPT ); Thu, 22 Apr 2021 13:34:38 -0400 Received: from mail-1.ca.inter.net ([208.85.220.69]:59950 "EHLO mail-1.ca.inter.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238468AbhDVRef (ORCPT ); Thu, 22 Apr 2021 13:34:35 -0400 Received: from localhost (offload-3.ca.inter.net [208.85.220.70]) by mail-1.ca.inter.net (Postfix) with ESMTP id 283A02EA421; Thu, 22 Apr 2021 13:34:00 -0400 (EDT) Received: from mail-1.ca.inter.net ([208.85.220.69]) by localhost (offload-3.ca.inter.net [208.85.220.70]) (amavisd-new, port 10024) with ESMTP id 9DLONJYOnYVF; Thu, 22 Apr 2021 13:14:10 -0400 (EDT) Received: from [192.168.48.23] (host-45-58-219-4.dyn.295.ca [45.58.219.4]) (using TLSv1 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) (Authenticated sender: dgilbert@interlog.com) by mail-1.ca.inter.net (Postfix) with ESMTPSA id AC3EC2EA279; Thu, 22 Apr 2021 13:33:59 -0400 (EDT) Reply-To: dgilbert@interlog.com Subject: Re: [PATCH 14/42] scsi: add scsi_result_is_good() To: Bart Van Assche , Hannes Reinecke , "Martin K. Petersen" Cc: Christoph Hellwig , James Bottomley , linux-scsi@vger.kernel.org References: <20210421174749.11221-1-hare@suse.de> <20210421174749.11221-15-hare@suse.de> <51b16b13-d4e3-f0e4-718e-357d04ed958f@interlog.com> <62237423-f4f9-a426-43b5-3ff56a5dca1a@acm.org> From: Douglas Gilbert Message-ID: Date: Thu, 22 Apr 2021 13:33:59 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <62237423-f4f9-a426-43b5-3ff56a5dca1a@acm.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-CA Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.org On 2021-04-22 12:52 p.m., Bart Van Assche wrote: > On 4/22/21 8:56 AM, Douglas Gilbert wrote: >> In driver manuals Seagate often list the PRE-FETCH command as optional. As >> in: pay us some extra money and we will put it in. That suggests to me some >> big OEM likes PRE-FETCH. Where I found it supported in WDC manuals, they >> didn't support the IMMED bit which sort of defeats the purpose of it IMO. > > Since the sd driver does not submit the PRE-FETCH command, how about > moving support for CONDITION MET into the sg code and treating CONDITION > MET as an error inside the sd, sr and st drivers? I think that would > allow to simplify scsi_status_is_good(). The current definition of that > function is as follows: > > static inline int scsi_status_is_good(int status) > { > /* > * FIXME: bit0 is listed as reserved in SCSI-2, but is > * significant in SCSI-3. For now, we follow the SCSI-2 > * behaviour and ignore reserved bits. > */ > status &= 0xfe; > return ((status == SAM_STAT_GOOD) || > (status == SAM_STAT_CONDITION_MET) || > /* Next two "intermediate" statuses are obsolete in*/ > /* SAM-4 */ > (status == SAM_STAT_INTERMEDIATE) || > (status == SAM_STAT_INTERMEDIATE_CONDITION_MET) || > /* FIXME: this is obsolete in SAM-3 */ > (status == SAM_STAT_COMMAND_TERMINATED)); > } The whole stack needs to treat SAM_STAT_CONDITION_MET as a non-error. However the complex multi-layer return values are represented, reducing them to a comparison with zero, spread all over the stack just seems bad software engineering. IMO a predicate function (i.e. returning bool) is needed. I would argue that in the right circumstances, the sd driver should indeed by using PRE-FETCH. It would need help from the upper layers. It is essentially "read-ahead" in the case where the next LBA does not follow the last read LBA. A smarter read-ahead ... Doug Gilbert