From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Christie Subject: Re: [PATCH] block SG_IO: add SG_FLAG_Q_AT_HEAD flag Date: Wed, 11 Jun 2014 16:33:21 -0500 Message-ID: <5398CB21.3000409@cs.wisc.edu> References: <5390786E.8050601@interlog.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: Received: from sabe.cs.wisc.edu ([128.105.6.20]:39849 "EHLO sabe.cs.wisc.edu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752572AbaFKVdx (ORCPT ); Wed, 11 Jun 2014 17:33:53 -0400 In-Reply-To: <5390786E.8050601@interlog.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: dgilbert@interlog.com Cc: SCSI development list , Christoph Hellwig , James Bottomley On 06/05/2014 09:02 AM, Douglas Gilbert wrote: > After the SG_IO ioctl was copied into the block layer and > later into the bsg driver, subtle differences emerged. > > One difference is the way injected commands are queued through > the block layer (i.e. this is not SCSI device queueing nor SATA > NCQ). Summarizing: > - SG_IO on block layer device: blk_exec*(at_head=false) > - sg device SG_IO: at_head=true > - bsg device SG_IO: at_head=true > > Some time ago Boaz Harrosh introduced a sg v4 flag called > BSG_FLAG_Q_AT_TAIL to override the bsg driver default. A > recent patch titled: "sg: add SG_FLAG_Q_AT_TAIL flag" > allowed the sg driver default to be overridden. This patch > allows a SG_IO ioctl sent to a block layer device to have > its default overridden. > > ChangeLog: > - introduce SG_FLAG_Q_AT_HEAD flag in sg.h to cause > commands that are injected via a block layer > device SG_IO ioctl to set at_head=true > - make comments clearer about queueing in sg.h since the > header is used both by the sg device and block layer > device implementations of the SG_IO ioctl. > - introduce BSG_FLAG_Q_AT_HEAD in bsg.h for compatibility > (it does nothing) and update comments. > > > Signed-off-by: Douglas Gilbert Looks ok to me. Reviewed-by: Mike Christie