From mboxrd@z Thu Jan 1 00:00:00 1970 From: Douglas Gilbert Subject: Re: [Q] In sg_io_v4 what to use as flag for "queue at_head" Date: Tue, 20 Jan 2009 14:27:55 -0500 Message-ID: <497625BB.4020609@interlog.com> References: <49746197.200@panasas.com> <4974BBC5.3080001@interlog.com> <497577C5.6080604@panasas.com> Reply-To: dgilbert@interlog.com Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from smtp.infotech.no ([82.134.31.41]:41771 "EHLO elrond2.infotech.no" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754395AbZATT2F (ORCPT ); Tue, 20 Jan 2009 14:28:05 -0500 In-Reply-To: <497577C5.6080604@panasas.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Boaz Harrosh Cc: Douglas Gilbert , FUJITA Tomonori , linux-scsi , open-osd mailing-list Boaz Harrosh wrote: > Douglas Gilbert wrote: >> or (adding "_TA_" for task attribute): >> enum { >> BSG_TA_DEFAULT = 0, // lk 2.4, 2.6 series: head of queue >> BSG_TA_HEAD_OF_Q = 0x1000, >> BSG_TA_SIMPLE, >> BSG_TA_ORDERED, >> BSG_TA_ACA, >> .... > > BSG_TA_HEAD_OF_Q I understand that's like today. What are the meaning > of the other values? Anyway I only have 2 values to implement I don't want > to add more values then I use, and have to comment NOT SUPPORTED next > to them. When used I can add them later. > > Please Note that I was asking about the at_head=0/1 of the blk_execute_rq_xxx > calls. This means that it is not transport specific at all, it is a Boolean behavior > common to all transports, governed by the request submission layer. > If task_attribute is something related to SAM-4 then surly that is not it, because > I'm looking for a flag that is independent of scsi. If later I will need that SAM-4 > thing it will be taken. > >> I would prefer using the request_attr field. >> >> Tomo, what do you think? >> >> >> Doug Gilbert > > And please, you never explained, what is "request_priority" for? > What was your original intention? Boaz, As my comment indicates "request_priority" is "task priority" in SCSI. I should have added "... in SAM-3" because the good folks at t10 changed that to "command priority" in SAM-4 (sam4r14.pdf section 8.7). [I didn't like the term "task ..." either which is one reason why I used "request ...".] So the "queue" that I'm talking about is the one on the device (target or LU, take your pick). A SCSI pass-through wants the thinnest possible layer between itself and the SCSI initiator, so in that context I view a queue in the scsi mid-level or a LLD as evil. Note also that several SCSI commands have an implicit "head of queue" attribute (e.g. INQUIRY and REPORT LUNS) within the device. Doug Gilbert