From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Bottomley Subject: Re: [linux-usb-devel] FW: USB 2.0 external hard drive problem Date: 06 Feb 2004 10:24:25 -0500 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <1076081067.1823.5.camel@mulgrave> References: Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from stat1.steeleye.com ([65.114.3.130]:15334 "EHLO hancock.sc.steeleye.com") by vger.kernel.org with ESMTP id S265476AbUBFPYt (ORCPT ); Fri, 6 Feb 2004 10:24:49 -0500 In-Reply-To: List-Id: linux-scsi@vger.kernel.org To: Alan Stern Cc: Joerg Schilling , Matthew Dharm , magliery@csb.yale.edu, appro@fy.chalmers.se, USB development list , SCSI development list On Fri, 2004-02-06 at 09:59, Alan Stern wrote: > Who says it's wrong to retrieve sense information when there is an > underrun but not Check Condition? Can you provide a reference to a > published (or draft) document that states this? It's not wrong according to the SCSI standards, a REQUEST SENSE issued to a device with no sense data will produce a NO SENSE key. However, because of the way sense is processed in contingent allegiance conditions (suspending the I_T_L nexus until sense is cleared) it is dangerous to issue arbitrary request sense commands because you may receive sense for a different command (and prevent that command from erroring correctly). The SCSI mid-layer definitely does not expect this behaviour. A driver either does not do any sense commands at all or it only issues a REQUEST SENSE in response to a Check Condition status in order not to have the nexus halted because of a contingent allegiance condition (simulating ACA if you will). James