Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752286Ab3HUPxY (ORCPT ); Wed, 21 Aug 2013 11:53:24 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:44448 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751541Ab3HUPxW (ORCPT ); Wed, 21 Aug 2013 11:53:22 -0400 Date: Wed, 21 Aug 2013 08:53:14 -0700 From: Christoph Hellwig To: Roland Dreier Cc: "Nicholas A. Bellinger" , target-devel , lkml , linux-scsi , Christoph Hellwig , Hannes Reinecke , Martin Petersen , Chris Mason , James Bottomley , Nicholas Bellinger , Giridhar Malavali , Chad Dupuis Subject: Re: [PATCH 9/9] tcm_qla2xxx: Add special case for COMPARE_AND_WRITE data_direction Message-ID: <20130821155314.GA17850@infradead.org> References: <1377029280-19144-1-git-send-email-nab@daterainc.com> <1377029280-19144-10-git-send-email-nab@daterainc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1176 Lines: 21 On Wed, Aug 21, 2013 at 07:38:21AM -0700, Roland Dreier wrote: > I don't understand this. In fact the whole patch series looks quite > confused. COMPARE AND WRITE is a normal Data-Out command, with no > requirement for special bidirectional handling or anything like that. > The only slightly unusual thing is that a CAW command with a NUMBER OF > LOGICAL BLOCKS equal to N will actually transfer 2*N worth of data -- > one set of data for the compare operation and a second set to write if > the compare succeeds. But just to be clear, the transfer of those 2*N > blocks happens as a single transfer during the Data-Out phase. I think the confusion is that the implementation of COMPARE AND WRITE obviously requires a read and a write phase, and the implementation tries to mix this up with an actual bidirectional scsi command. If the core stopped keying off t_bidi_data_sg and used better flag this could be easily solved. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/